Forecast Discussions mentioning "ACARS", "MDCRS", "AIRCRAFT", "TAMDAR", or "AMDAR" received at FSL on 08/11/07

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NWS LOS ANGELES/OXNARD CA
209 PM PDT THU AUG 9 2007 .SHORT TERM...(FRI-SUN) VERY MINOR DAY TO DAY CHANGE EXPECTED OVER THIS PERIOD OTHER THAN A SLIGHT WARMUP...BRINGING TEMPS TO JUST ABOVE NORMAL. THE LARGE HIGH PRESSURE SYSTEM OVER THE SOUTHERN PLAINS SLOWLY BUILDS WESTWARD TO HELP INCREASE OUR HEIGHTS A BIT BY SUNDAY. WE`LL SEE LITTLE CHANGE IN OUR ONSHORE GRADIENTS...IF NOT SOME SLIGHT WEAKENING...THUS WEAKENING THE EFFECTS OF THE MARINE LAYER. OVERNIGHT COASTAL STRATUS AND FOG SHOULD BEHAVE MUCH THE SAME THROUGH THE PERIOD...FAVORING COASTAL AREAS NORTH OF POINT CONCEPTION AND NEARER THE BEACHES ALONG THE LOS ANGELES COUNTY COAST AS A RESULT OF AT LEAST WEAK EDDIES WHICH SHOULD FORM EACH NIGHT. BUT AT THIS POINT EXPECT CLOUDS AND FOG TO BE LIMITED TO THESE AREAS THROUGH SUNDAY. SUNDOWNER WINDS IN SBA MOUNTAINS MENTIONED IN PREVIOUS DISCUSSION CAN BE MORE CHARACTERIZED AS AN OFFSHORE EVENT. NOT EXPECTING ANYTHING TOO STRONG BUT STILL SOME LOCAL GUSTY WINDS FRIDAY NIGHT AND SATURDAY NIGHT THROUGH AND BELOW CANYONS AND PASSES. GRADIENT IS STRONGEST SATURDAY NIGHT. .LONG TERM...(MON-THU) HAVE HAD TO DEAL WITH SOME WAFFLING IN THE MODELS ON THE NORTHERN EXTENT OF THE MONSOON MOISTURE THAT COULD PEAK AROUND THE MIDDLE TO END OF NEXT WEEK. AS HAS BEEN THE CASE SO FAR THIS SUMMER...WE ARE JUST ON THE EDGE OF ANY DECENT MONSOON MOISTURE IN MIDDLE OF THE BATTLE OF THE ONSHORE SOUTHWESTERLY FLOW AND THE MORE MOIST SOUTHEASTERLY FLOW. 12Z GFS IS IN FACT TRENDING WETTER VERSUS THE 06Z RUN...AND SHOWING A PRETTY GOOD SOUTHEAST FETCH THROUGH AN 850-300 MB LAYER. THE GFS PUTS THE 1 INCH PRECIPITABLE WATER LINE AS FAR NORTH AS AROUND THE VTU-LA COUNTY LINE BY MIDDAY MONDAY AND KEEPS IT THERE THROUGH THE REST OF THE WEEK. AGAIN...DOESN`T TAKE MUCH CHANGE IN THE FLOW TO DIRECT THE MOISTURE OFF TO OUR EAST SO STILL A LOT OF UNCERTAINTY IN THE FORECAST. IF THE 12Z GFS VERIFIES WE`D SEE A DECENT CHANCE OF THUNDER...ESPECIALLY IN THE SOUTH...BY WEDNESDAY AND THURSDAY WHEN THE REAL GOOD LOW LEVEL MOISTURE COULD BE IN PLACE. ON THE OTHER HAND...BOTH THE GFS ENSEMBLES AND THE ECMWF ARE DEEPER WITH THE UPPER TROUGH OVER THE PAC NW...WHICH WOULD FAVOR MORE SOUTHWESTERLY AND DRIER FLOW OVER THE AREA...AND KEEPING MONSOON MOISTURE WELL ENOUGH TO OUR EAST. GIVEN THIS UNCERTAINTY HAVE DECIDED TO CONTINUE WITH A SUNNY AND DRY FORECAST THROUGH THE PERIOD...WITH A BROADER EXTENDING MARINE LAYER BY MONDAY AND HANGING AROUND THROUGH THURSDAY. CAN GRADUALLY INTRODUCE ACTIVITY IF WE SEE MORE STABILITY AND CERTAINTY IN THE MODELS. && .AVIATION... 09/2115Z LATEST AMDAR SOUNDINGS INDICATE MARINE INVERSION AROUND 1200 FEET THIS AFTERNOON ACROSS THE LAX BASIN. SATELLITE SHOWS CLEAR SKIES ACROSS THE ENTIRE AREA. OVERALL...FORECAST THINKING FOR THE 00Z TAF PACKAGE HAS NOT CHANGED FROM THE PREVIOUS TAF PACKAGE. VFR CONDS WILL CONTINUE AT ALL AIRFIELDS THROUGH THIS EVENING. OVERNIGHT... EXPECT STRATUS CLOUDS TO REFORM WITH CONTINUED ONSHORE FLOW AND WEAK EDDY. HOWEVER...WITH CURRENT DEPTH...STRATUS SHOULD REMAIN CONFINED TO ONLY THE COASTAL TAFS OVERNIGHT. KLAX...VFR CONDS THROUGH THE EVENING WITH A 10-12 KNOT SEA BREEZE WHICH SHOULD END AROUND 06Z. EXPECT STRATUS TO RETURN TO THE AIRFIELD AROUND 09Z WITH IFR CIGS AND VFR VSBYS. OVERALL...MODERATE TO HIGH CONFIDENCE IN STRATUS FORMATION OVERNIGHT TONGIHT. KBUR...VFR CONDS THROUGH THE ENTIRE PERIOD WITH HIGH CONFIDENCE. $$ .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXCWFLOX). && $$ PUBLIC...JACKSON AVIATION...THOMPSON
AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
128 PM PDT THU AUG 9 2007 .SYNOPSIS... THE MARINE LAYER AND ONSHORE FLOW WILL CAUSE COASTAL LOW CLOUDS AND FOG IN THE NIGHTS AND MORNINGS...EXTENDING LOCALLY INLAND THROUGH THE WEEKEND. OTHERWISE...DRY SOUTHWEST FLOW ALOFT WILL KEEP THE WEATHER FAIR THROUGH FRIDAY. HIGH PRESSURE OVER THE CENTRAL AND SOUTH CENTRAL STATES WILL EXPAND WESTWARD BRINGING A WARMING TREND FOR THE WEEKEND THROUGH EARLY NEXT WEEK. THIS WILL ALSO BRING A RETURN OF MONSOONAL MOISTURE WITH A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS IN THE MOUNTAINS AND DESERTS. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (TONIGHT THROUGH SUNDAY)... LOW CLOUDS CLEARED RAPIDLY TO THE COAST BY 11AM THIS MORNING IN MOST AREAS. EXPECT MARINE LAYER TO BE MORE SHALLOW AT NIGHT AND NOT PENETRATE INLAND QUITE AS FAR AS HIGH PRESSURE BEGINS TO BUILD WESTWARD OVER THE AREA. ALSO BECAUSE OF BUILDING HIGH PRESSURE EXPECT MARINE LAYER TO BURN OFF SOONER MORNINGS THROUGH THE WEEKEND. NAM COMPUTER MODEL SHOWS SOME MID LEVEL MOISTURE MOVING IN FRIDAY AFTERNOON. WHEREAS GFS HOLDS IT OFF UNTIL SATURDAY. LOOKING AT WATER VAPOR LOOK BELIEVE SLOWER GFS MORE ON TRACK. THIS WILL BRING AN INCREASING CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS OVER THE MOUNTAINS AND DESERT THIS WEEKEND. ALSO WITH BUILDING HIGH PRESSURE TEMPERATURES WILL BEGIN TO RISE...ESPECIALLY INLAND AREAS OVER THE WEEKEND AND INTO EARLY NEXT WEEK. && .LONG TERM (MONDAY THROUGH THURSDAY)... HIGH PRESSURE WILL CONTINUE TO BUILD WITH WARMING CONTINUING INTO TUESDAY WITH TEMPERATURES RISING TO SLIGHTLY ABOVE SEASONAL LEVELS. THE INFLUX OF MONSOONAL MOISTURE WILL CONTINUE THE SLIGHT CHANCE OF AFTERNOON AND EARLY EVENING THUNDERSTORMS. THE GFS SHOWS HIGHEST PRECIPITABLE WATER MONDAY AND ESPECIALLY TUESDAY. FOR THE LATTER HALF OF NEXT WEEK...A LOW PRESSURE TROUGH OVER THE EASTERN PACIFIC WILL BEGIN TO MOVE INLAND ALONG THE WEST COAST. THIS WILL BRING SLOW COOLING...A DEEPER MARINE LAYER AND DRIER SOUTHWEST FLOW ALOFT...ENDING THE THUNDERSTORM THREAT. && .092015Z...ACARS SOUNDINGS SHOW THAT THE MARINE INVERSION HAS SHRUNK TO ABOUT 1800 FEET. EXPECT THE INVERSION TO LOWER FURTHER OVERNIGHT TO ABOUT 1400 FEET. STRATUS WILL RETURN TONIGHT WITH ONSET GENERALLY IN THE 04Z-06Z RANGE IN COASTAL SAN DIEGO COUNTY AND 08Z-10Z RANGE IN COASTAL ORANGE COUNTY...EXCEPT FOR LOCAL BROKEN CONDITIONS LATE THIS AFTERNOON MAINLY IN COASTAL SAN DIEGO COUNTY. WITH SOME LOWERING OF THE INVERSION HEIGHT...BASES WILL BE IN THE 1200-1500 FT RANGE MSL. LOCAL 3-5 MILE VIS WILL OCCUR IN THE VALLEYS WITH SOME TERRAIN OBSCURED FRI MORNING. ABOVE THE INVERSION...UNLIMITED CIGS AND VFR VSBYS WILL OCCUR THROUGH FRIDAY. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...CLARK AVIATION/MARINE...MAXWELL NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
915 AM PDT THU AUG 9 2007 .SYNOPSIS... THE MARINE LAYER AND ONSHORE FLOW WILL CAUSE COASTAL LOW CLOUDS AND FOG IN THE NIGHTS AND MORNINGS...EXTENDING LOCALLY INLAND. OTHERWISE...DRY SOUTHWEST FLOW ALOFT WILL KEEP THE WEATHER FAIR THROUGH FRIDAY. HIGH PRESSURE OVER THE CENTRAL AND SOUTH CENTRAL STATES WILL EXPAND WESTWARD BRINGING A WARMING TREND FOR THE WEEKEND THROUGH EARLY NEXT WEEK. THIS WILL ALSO BRING A RETURN OF MONSOONAL MOISTURE WITH A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS IN THE MOUNTAINS AND DESERTS. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (TODAY THROUGH SATURDAY)... NKX SOUNDING AND AIRCRAFT REPORTS INDICATE TOP OF THE MARINE LAYER ABOUT 2300 FEET THIS MORNING. VISIBLE SATELLITE IMAGERY SHOWS MARINE LAYER TO WESTERN MOUNTAIN SLOPES. EXPECT CLOUDS TO CLEAR TO NEAR THE BEACHES BY MID OR LATE MORNING. HIGH PRESSURE OVER THE CENTRAL AND SOUTH CENTRAL STATES WILL EXPAND WESTWARD THROUGH THE WEEKEND...TREND WILL BE FOR A DECREASING MARINE LAYER DEPTH WITH STRATUS SPREADING INLAND SLOWER AT NIGHT AND NOT AS FAR INLAND...AND ALSO CLEARING FASTER EACH MORNING. BUILDING HIGH PRESSURE WILL BRING WARMING TO NEAR SEASONAL LEVELS BY SATURDAY. SOUTH FLOW ALOFT FOR SATURDAY WILL BRING A RETURN OF MID LEVEL MONSOONAL MOISTURE WITH A SLIGHT CHANCE OF AFTERNOON AND EARLY EVENING THUNDERSTORMS IN THE MOUNTAINS. && .LONG TERM (SUNDAY THROUGH WEDNESDAY)... AS HIGH PRESSURE CONTINUES TO BUILD WARMING WILL CONTINUE INTO TUESDAY WITH TEMPERATURES RISING TO SLIGHTLY ABOVE SEASONAL LEVELS. THE INFLUX OF MONSOONAL MOISTURE WILL CONTINUE THE SLIGHT CHANCE OF AFTERNOON AND EARLY EVENING THUNDERSTORMS. THE GFS SHOWS HIGHEST PRECIPITABLE WATER MONDAY AND TUESDAY...THOUGH THE INFLUX FOR MONDAY AND TUESDAY MAY BE A LITTLE OVERDONE. FOR THE LATTER HALF OF NEXT WEEK...A LOW PRESSURE TROUGH OVER THE EASTERN PACIFIC WILL BEGIN TO MOVE INLAND ALONG THE WEST COAST. THIS WILL BRING SLOW COOLING...A DEEPER MARINE LAYER AND DRIER SOUTHWEST FLOW ALOFT. && .AVIATION... 091600Z...WEAK SHORT WAVE DEEPENED THE MARINE LAYER TO AROUND 2300 FEET. STRATUS...WITH BASES OF AROUND 1700 FEET WITH TOPS TO 2500 FEET WILL MOSTLY DISSIPATE BY 18Z NEAR THE COAST. STRATUS WILL RETURN TONIGHT WITH ONSET GENERALLY IN THE 04Z-06Z RANGE IN COASTAL SAN DIEGO COUNTY AND 08Z-10Z RANGE IN COASTAL ORANGE COUNTY...EXCEPT FOR LOCAL BROKEN CONDITIONS LATE THIS AFTERNOON. WITH SOME LOWERING OF THE INVERSION HEIGHT...BASES WILL BE IN THE 1200-1500 FT RANGE MSL. LOCAL 3-5 MILE VIS WILL OCCUR IN THE VALLEYS WITH SOME TERRAIN OBSCURRED...BOTH THIS MORNING AND FRI MORNING. ABOVE THE INVERSION...UNLIMITED CIGS AND VFR VSBYS WILL OCCUR THROUGH FRIDAY. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...CLARK AVIATION/MARINE...MAXWELL NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
325 AM PDT THU AUG 9 2007 .SYNOPSIS... THE MARINE LAYER AND ONSHORE FLOW WILL CAUSE COASTAL LOW CLOUDS AND FOG IN THE NIGHTS AND MORNINGS...EXTENDING LOCALLY INLAND. OTHERWISE...DRY SOUTHWEST FLOW ALOFT WILL KEEP THE WEATHER FAIR THROUGH FRIDAY. HIGH PRESSURE OVER THE CENTRAL AND SOUTH CENTRAL STATES WILL EXPAND WESTWARD BRING A WARMING TREND FOR THE WEEKEND THROUGH EARLY NEXT WEEK. THIS WILL ALSO BRING A RETURN OF MONSOONAL MOISTURE WITH A SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS IN THE MOUNTAINS AND DESERTS. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (TODAY THROUGH SATURDAY)... ACARS SOUNDINGS FROM SAN SHOW A DECREASE IN THE MARINE LAYER DEPTH TO AROUND 1900 FEET WITH ACARS SOUNDINGS IN THE LOS ANGELES AREA SHOWING A DECREASE TO AROUND 1200 FEET. SATELLITE IMAGERY SHOWS INLAND EXTEND CONSISTENT WITH THIS DEPTH WITH STRATUS EXTENDING WELL INLAND INTO THE SAN DIEGO COUNTY VALLEYS WITH STRATUS ONLY SPREADING SLOWLY INLAND INTO ORANGE COUNTY. AS HIGH PRESSURE OVER THE CENTRAL AND SOUTH CENTRAL STATES EXPANDS WESTWARD THROUGH THE WEEKEND...TREND WILL BE FOR A DECREASING MARINE LAYER DEPTH WITH STRATUS SPREADING INLAND SLOWER AT NIGHT...NOT AS FAR INLAND...AND CLEARING FASTER EACH MORNING. BUILDING HIGH PRESSURE WILL BRING WARMING TO NEAR SEASONAL LEVELS BY SATURDAY. SOUTH FLOW ALOFT FOR SATURDAY WILL BRING A RETURN OF MID LEVEL MONSOONAL MOISTURE WITH A SLIGHT CHANCE OF AFTERNOON AND EARLY EVENING THUNDERSTORMS IN THE MOUNTAINS. && .LONG TERM (SUNDAY THROUGH WEDNESDAY)... WARMING WILL CONTINUE INTO TUESDAY WITH TEMPERATURES RISING TO SLIGHTLY ABOVE SEASONAL LEVELS. THE INFLUX OF MONSOONAL MOISTURE WILL CONTINUE THE SLIGHT CHANCE OF AFTERNOON AND EARLY EVENING THUNDERSTORMS. GFS SHOWS HIGHEST PW`S MONDAY AND TUESDAY...THOUGH THE INFLUX FOR MONDAY AND TUESDAY LOOKS A LITTLE OVERDONE. FOR THE LATTER HALF OF NEXT WEEK...LOW PRESSURE OVER THE EASTERN PACIFIC WILL BEGIN TO MOVE INLAND ALONG THE WEST COAST. THIS WILL BRING SLOW COOLING AND DRIER SOUTHWEST FLOW ALOFT. && .AVIATION... 091015Z...A WEAK SHORT WAVE TROUGH MOVING BY TO THE NORTH WILL INCREASE THE MARINE LAYER EARLY THIS MORNING TO ABOUT 2300 FT. THEN...HIGH PRESSURE ALOFT WILL MOVE OVER THIS AFTERNOON...LOWERING THE MARINE LAYER TO ABOUT 1700 FT. BASES THIS MORNING ABOUT 1800 FT MSL...LOWERING TO ABOUT 1400 FT TONIGHT AND FRIDAY MORNING. VSBY ABOVE 7SM WITH SOME 3-5SM MAINLY NEAR THE FOOTHILLS THIS MORNING. AREAS OF VSBY 3-5SM LATE TONIGHT AND FRIDAY MORNING. STRATUS WILL CLEAR ABOUT 16-17Z THIS MORNING AND EARLIER FRIDAY MORNING. STRATUS RETURNING LATE TONIGHT ABOUT 5Z NEAR THE COAST AND 10Z INLAND. WINDS ALOFT MOSTLY LIGHT SOUTHWEST THROUGH FRIDAY MORNING...THEN LIGHT SOUTHEAST TO SOUTH FRIDAY AFTERNOON. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...MARTIN AVIATION/MARINE...WHITLOW NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
323 PM CDT THU AUG 9 2007 .DISCUSSION FOR AFTERNOON GRIDS/ZONES... 323 PM CDT LAST SHOT AT RAIN THIS AFTERNOON/EARLY EVENING AFTER A WEEK OF UNSETTLED WEATHER. ISOLATED SHOWERS HAVE DEVELOPED OUT AHEAD OF AN INVERTED TROF EXTENDING NORTHWESTWARD FROM A SFC LOW IN NW OHIO. THE BEST CHANCES FOR ANY OF THESE SHOWERS GAINING ANY VERTICAL MOMENTUM IS IN NW INDIANA WHERE SPC MESOANALYSIS SHOW ABOUT 1500-2500 J/KG OF SFC BASED CAPE. STILL...ACARS SOUNDINGS ARE SHOWING A FAIRLY STRAIGHT UP AND DOWN PROFILE AND ARE MAINLY STABLE. EXTENSIVE LOW TO MID LEVEL CLOUD COVER HAS ALSO INHIBITED ANY FURTHER STORM GROWTH AS WELL...SO WHILE SOME STORM DEVELOPMENT IS POSSIBLE...AM NOT EXPECTING ANYTHING SEVERE...WHICH NOW COINCIDES WITH SPC PULLING BACK THE DAY ONE SLIGHT RISK AREA. THE OUTLOOK PAST TONIGHT IS FOR A FAIRLY QUIET WEATHER PATTERN THROUGH SUNDAY AS AN UPPER LEVEL RIDGE ACROSS THE SOUTHEASTERN US PROPAGATES NORTHWESTWARD INTO THE CENTRAL PLAINS. WHILE TEMPERATURES WILL REMAIN ABOVE WHAT IS TYPICAL FOR THIS TIME OF YEAR...IT WILL AT LEAST FEEL A BIT MORE COMFORTABLE AS DEW POINTS SHOULD DROP INTO THE LOW 60S BY SATURDAY MORNING AS AN ELONGATED SFC RIDGE EXTENDS FROM SOUTHERN CANADA DOWN ALONG THE MISSISSIPPI RIVER FRIDAY THROUGH SATURDAY. THIS RIDGE WILL EVENTUALLY TRANSITION EASTWARD AS A SHORTWAVE TROF UP NEAR THE HUDSON BAY SPINS UP A SFC LOW IN ONTARIO AND DROPS A COLD FRONT INTO THE REGION. THIS WILL BRING THE NEXT CHANCE FOR PRECIP ACROSS NORTHERN IL/IN. THE MODELS ARE SHOWING ON AVERAGE ABOUT 2000 J/KG OF CAPE OUT AHEAD OF THE FRONT...BUT WITH STRONG WAA TAKING PLACE...THERE WILL LIKELY BE A FAIRLY SUBSTANTIAL CAP IN PLACE TO LIMIT ANY DEVELOPMENT. THE LLJ ISNT ALL THAT IMPRESSIVE EITHER AND IS SOMEWHAT CUTOFF FROM THE GULF...SO AM NOT REALLY EXPECTING A WIDESPREAD RAIN EVENT AT THE MOMENT. NOT A WHOLE LOT OF SHEAR IN PLACE EITHER...SO WILL PROBABLY JUST HAVE YOUR TYPICAL RUN-OF-THE-MILL CONVECTIVE STORMS THAT ARE FAIRLY BRIEF. SUNDAY WILL END UP BEING THE HOTTEST DAY OF THE FORECAST PERIOD WITH HIGHS REACHING THE LOW TO MID 90S...BUT WITH DEW POINTS IN THE MID 60S...AM NOT EXPECTING TO NEED ANY HEAT ADVISORY HEADLINES WITH THE HEAT INDEX STAYING AT OR BELOW 100. A SECOND COLD FRONT WILL DROP DOWN ON WEDNESDAY/THURSDAY WHICH COULD ACTUALLY BRING SOME COLDER AIR DOWN WITH IT FROM CANADA INTO THE GREAT LAKES REGION. THE GFS IS SHOWING H85 TEMPS LESS THAN 10C BY THURSDAY BEHIND THIS FRONT. WHETHER OR NOT THIS AIR ACTUALLY MAKES IT DOWN TO US AND TRANSLATES TO THE SFC IS ANOTHER QUESTION. HAVE STARTED TRENDING DOWNWARD WITH HIGH TEMPS ON DAY 7...BUT WILL HOLD OFF FOR THE TIME BEING ON DROPPING THEM TOO MUCH. HALBACH && .AVIATION... 143 PM CDT MESOANALYSIS SHOWS FOUR SURFACE TROUGHS BETWEEN THE MISSISSIPPI BORDER AND EASTERN INDIANA. THE TWO THAT ARE WEST OF NORTHERN ILLINOIS WILL BRING A WIND SHIFT THIS EVENING. THE FIRST TROUGH AT 16 UTC LIES FROM GREEN BAY TO ROCKFORD. THE ANOTHER TROUGH LIES ALONG THE MISSISSIPPI RIVER. STREAMLINES ON THE 17 UTC SURFACE MAPS SHOW SOUTHWEST WIND OVER ALL THE TAF LOCATIONS. THE ACARS SOUNDING AT ORD AT 1632 UTC SHOW SOUTHWEST WIND UP TO 925 MB THEN WEST ABOVE 925 MB. WILL FORECAST SOME MVFR CEILINGS LATER THIS AFTERNOON. THE NEPHANALYSIS SHOWS MVFR CEILINGS ACROSS NORTHWEST ILLINOIS AT 17 UTC. THESE ARE PROBABLY STRATOCUMULUS AND CUMULUS CLOUDS. WILL FORECAST CLEARING THIS EVENING. THE WIND SHIFT WITH THE TROUGH OVER THE MISSISSIPPI RIVER IS EXPECTED TO OCCUR AFTER 00 UTC...WHEN THE TROUGH MOVES EAST. WE EXPECT THE WIND TO BECOME LIGHT TONIGHT AS A NOCTURNAL INVERSION DEVELOPS. THERE IS A LOT OF MOISTURE IN THE ATMOSPHERIC LAYER. THE FORECAST SOUNDINGS FROM THE WRF AT NMC AND OUR LOCALLY RUN WRF SHOW DEW POINT SPREAD TO BE BELOW 5 DEGREES BELOW 600 FEET. THERE IS A LOT OF MOISTURE FROM ALL THE PAST RAIN. WILL FORECAST SOME LIGHT FOG LATE TONIGHT. && .MARINE DISCUSSION... 225 PM CDT A WEAK LOW ALONG THE MISSISSIPPI RIVER EXTENDS INTO INDIANA. THIS WILL BRING SOME LIGHT WIND OVER LAKE MICHIGAN. WILL FORECAST WIND AROUND 5 TO 15 KNOTS THROUGH SATURDAY. USING THE GFS MODEL...WILL FORECAST THE LOW TO MOVE INTO NORTHERN PENNSYLVANIA AND A HIGH OVER MISSOURI AND IOWA BY FRIDAY MORNING. WE EXPECT THE WIND WILL BE FROM THE SOUTH FRIDAY. BY SATURDAY THE WIND WILL BECOME LIGHT AS A HIGH MOVES OVER THE GREAT LAKES. AS A LOW MOVES INTO NORTHERN QUEBEC A FRONT WILL APPROACH THE LAKE MICHIGAN ON SUNDAY. WE EXPECT WAVES TO BE IN THE 1 TO 4 FOOT RANGE THROUGH SUNDAY AT THIS TIME. && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1343 PM CDT THU AUG 9 2007 .DISCUSSION FOR MORNING GRIDS/ZONES... 345 AM CDT MAIN FORECAST CONCERNS WILL CONTINUE TO BE ON PRECIP POTENTIAL THROUGH THIS AFTERNOON. CONVECTION HAS INCREASED IN INTENSITY SOUTH OF INTERSTATE 80 OVER THE PAST FEW HOURS...AND RADAR IMAGERY SUGGESTING THE BACK EDGE OF YET ANOTHER MESOSCALE CONVECTIVE VORTEX TRACKING THROUGH NORTHWEST ILLINOIS AT THIS TIME. INCREASING LOW LEVEL SOUTHWESTERLY FLOW AHEAD OF THIS FEATURE IS RESULTING IN NEW SHOWER DEVELOPMENT INTO NORTHWEST INDIANA. PRECIP HAS BEEN MORE STRATIFORM IN NATURE ACROSS FAR NORTHERN ILLINOIS. SPC MESOSCALE ANALYSIS GRAPHICS INDICATING AROUND 2000 J/KG OF MUCAPE THIS MORNING WITH 0 TO 6 KM DEEP LAYER SHEAR MAGNITUDES ON THE ORDER OF 30-40 KNOTS. OLD SFC FRONTAL BOUNDARY WHICH PASSED THROUGH NORTHERN ILLINOIS DID MAKE IT FARTHER SOUTH THAN EXPECTED AND HAS SLOWLY BEGUN TO CREEP NORTHWARD OVERNIGHT...MAKING IT AS FAR NORTH AS FAR SOUTHERN PORTIONS OF THE CWA OVERNIGHT. THIS RESULTED IN DECREASE POTENTIAL OF HEAVY RAINS ACROSS FAR NORTHERN ILLINOIS. BASED ON CURRENT CONVECTIVE/RADAR TRENDS...WILL BE CANCELLING FLASH FLOOD WATCH FOR NORTHERN HALF OF THE CWA WHICH WAS IN EFFECT UNTIL 15Z THIS MORNING. WEAK SURFACE PRESSURE FALLS ARE NOTED AT 08Z ACROSS CENTRAL/NORTHERN ILLINOIS LIKELY IN RESPONSE NORTHERN STREAM SHORT WAVE TRACKING ACROSS MINNESOTA. CURRENT MASS FIELDS SUGGEST MODELS A BIT TOO FAR NORTH WITH THE SFC LOW BUT GIVEN APPROACH OF THIS NORTHERN STREAM SHORT WAVE...MAY SEE SFC LOW REORIENT A BIT NORTHWARD OF ITS CURRENT LOCATION. AS THE NORTHERN STREAM SHORT WAVE SHIFTS EASTWARD TODAY...SFC LOW AND ATTENDANT COLD FRONT WILL TRACK THROUGH THE AREA. BEST CHANCE OF AFTERNOON SEVERE THREAT APPEARS TO BE ACROSS EXTREME SOUTHEAST PORTIONS OF THE CWA IN CLOSER PROXIMITY TO FRONT/WIND SHIFT. CONDITIONS SHOULD REMAIN RELATIVELY UNSTABLE FOR A TIME BEHIND THE FRONT...BUT THE BULK OF THE MID/UPPER LEVEL FORCING SHOULD BE AFFECTING MAINLY THE FAR SOUTHEAST BY THIS AFTERNOON. CONVECTIVELY ENHANCED VORT MAX ACROSS NORTHERN MISSOURI WILL LIKELY BE THE FEATURE TO MONITOR FOR THIS AFTERNOON. WILL SHOW DECREASING TREND TO PRECIP LATER THIS MORNING...WITH AFTERNOON CHANCE POPS MAXIMIZED ACROSS FAR EASTERN PORTIONS OF THE AREA...AND MAINLY INTO NORTHWEST INDIANA. SPC HAS ADJUSTED SLIGHT RISK SLIGHTLY SOUTHWARD FROM PREVIOUS OUTLOOK AND CURRENT TRENDS SEEM TO SUPPORT THIS. MAIN THREAT SEVERE THREAT THIS AFTERNOON WOULD BE FOR DAMAGING WINDS AND POTENTIAL FOR ANY STORMS TO PRODUCE VERY HEAVY RAINFALL WITH DEW PTS LIKELY TO REMAIN POOLED IN THE LOW TO MID 70S NEAR THE FRONTAL BOUNDARY ACROSS THE SOUTHEAST. SFC RIDGE AXIS WILL BUILD INTO THE AREA TONIGHT INTO FRIDAY BRINGING A RETURN OF SOME QUIET WEATHER. DID NOT INCLUDE IN THIS FORECAST...BUT THERE DOES SEEM SOME POTENTIAL FOR SOME FOG TO DEVELOP TONIGHT GIVEN DECOUPLING THIS EVENING...CLEARING SKIES...AND SFC DEW PTS IN THE 60S. OTHERWISE...HAVE NOT MADE MANY CHANGES THROUGH THE REMAINDER OF THE FORECAST. FRIDAY WILL FEEL A BIT MORE COMFORTABLE WITH LOWER HUMIDITIES...AND SOME SLIGHTLY COOLER CONDITIONS NEAR THE LAKE WITH CONDITIONS SEEMING FAVORABLE FOR LAKE BREEZE DEVELOPMENT IN THE AFTERNOON. MAIN STORY LATE THIS WEEKEND INTO NEXT WEEK MAY TURN TO THE HEAT ONCE AGAIN. SATURDAY LOOKS TO BE A TRANSITION DAY AS LOW LEVEL RIDGE AXIS BEGINS TO SHIFT EASTWARD...AND AS SFC TROUGH REFOCUSES ACROSS THE NORTHERN PLAINS. 00Z GFS INDICATES 850 HPA TEMPS INCREASING BACK INTO +22 TO +25 DEG C RANGE SUNDAY AFTERNOON AS ANOTHER SHORT WAVE ACROSS SOUTHERN CANADA DAMPENS THE UPPER RIDGE AND TAKES A FRONT SOUTHWARD INTO NORTHERN ILLINOIS DURING THE AFTERNOON. MAGNITUDE OF LOW LEVEL MOISTURE AND DEGREE OF CONVECTIVE INHIBITION WILL BE THE MAIN ISSUES TO RESOLVE FOR PRECIP CHANCES SUNDAY. WILL HOLD OFF AN SUNDAY AFTERNOON MENTION AT THIS TIME AND KEEP POPS CONFINED TO SUNDAY NIGHT. MARSILI && .AVIATION... 1343 CDT MESOANALYSIS SHOWS FOUR SURFACE TROUGHS BETWEEN THE MISSISSIPPI BORDER AND EASTERN INDIANA. THE TWO THAT ARE WEST OF NORTHERN ILLINOIS WILL BRING A WIND SHIFT THIS EVENING. THE FIRST TROUGH AT 16 UTC LIES FROM GREEN BAY TO ROCKFORD. THE ANOTHER TROUGH LIES ALONG THE MISSISSIPPI RIVER. STREAMLINES ON THE 17 UTC SURFACE MAPS SHOW SOUTHWEST WIND OVER ALL THE TAF LOCATIONS. THE ACARS SOUNDING AT ORD AT 1632 UTC SHOW SOUTHWEST WIND UP TO 925 MB THEN WEST ABOVE 925 MB. WILL FORECAST SOME MVFR CEILINGS LATER THIS AFTERNOON. THE NEPHANALYSIS SHOWS MVFR CEILINGS ACROSS NORTHWEST ILLINOIS AT 17 UTC. THESE ARE PROBABLY STRATOCUMULUS AND CUMULUS CLOUDS. WILL FORECAST CLEARING THIS EVENING. THE WIND SHIFT WITH THE TROUGH OVER THE MISSISSIPPI RIVER IS EXPECTED TO OCCUR AFTER 00 UTC...WHEN THE TROUGH MOVES EAST. WE EXPECT THE WIND TO BECOME LIGHT TONIGHT AS A NOCTURNAL INVERSION DEVELOPS. THERE IS A LOT OF MOISTURE IN THE ATMOSPHERIC LAYER. THE FORECAST SOUNDINGS FROM THE WRF AT NMC AND OUR LOCALLY RUN WRF SHOW DEW POINT SPREAD TO BE BELOW 5 DEGREES BELOW 600 FEET. THERE IS A LOT OF MOISTURE FROM ALL THE PAST RAIN. WILL FORECAST SOME LIGHT FOG LATE TONIGHT. && .MARINE DISCUSSION... 225 PM CDT A WEAK LOW ALONG THE MISSISSIPPI RIVER EXTENDS INTO INDIANA. THIS WILL BRING SOME LIGHT WIND OVER LAKE MICHIGAN. WILL FORECAST WIND AROUND 5 TO 15 KNOTS THROUGH SATURDAY. USING THE GFS MODEL...WILL FORECAST THE LOW TO MOVE INTO NORTHERN PENNSYLVANIA AND A HIGH OVER MISSOURI AND IOWA BY FRIDAY MORNING. WE EXPECT THE WIND WILL BE FROM THE SOUTH FRIDAY. BY SATURDAY THE WIND WILL BECOME LIGHT AS A HIGH MOVES OVER THE GREAT LAKES. AS A LOW MOVES INTO NORTHERN QUEBEC A FRONT WILL APPROACH THE LAKE MICHIGAN ON SUNDAY. WE EXPECT WAVES TO BE IN THE 1 TO 4 FOOT RANGE THROUGH SUNDAY AT THIS TIME. && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
727 AM EDT THU AUG 9 2007 UPDATED FOR 12Z TAF ISSUANCE .SYNOPSIS... 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW PERSISTENT UPR RDG OVER THE GRT LKS BTWN TROFFING IN NEW ENGLAND AND MORE ZONAL FLOW FM THE PAC NW INTO THE NRN PLAINS. SFC HI PRES CENTERED JUST E OF LK SUP EARLY THIS MRNG...AND MOST RECENT TAMDAR SDNGS/00Z GRB RAOB SHOW A DRY/STABLE AIRMASS IN PLACE OVER THE UPR GRT LKS. SKIES ARE MOCLR OVER THE E CLOSER TO THE HI CENTER...BUT HI CLDS ARE MOVING INTO THE WRN ZNS IN ADVANCE OF SHRWTV OVER ND MOVING E THRU MORE ZONAL FLOW TO THE W. SOME SHRA/ISOLD MOVING INTO WRN MN ALG SFC TROF AHD OF THIS SYS...BUT COVG APPEARS TO BE BREAKING UP AS PCPN MOVES INTO DRY AIRMASS IN PLACE ACRS THE UPR GRT LKS AND EXTENDING AS FAR W AS INL/MPX. 00Z RAOBS IN THOSE LOCATIONS SHOW VERY DRY AIR LINGERING BTWN H85-7 EVEN THAT FAR W FM SFC HI. SHARP GRADIENT OF LLVL MSTR DOES APPEAR JUST S OF MPX (SFC DWPT ARND 57 JUST N OF MPX BUT 70 TO THE S). MORE WDSPRD CONVECTION PRESENT OVER IA/IL ON PERSISTENT BNDRY TO THE N OF STEAMY AIRMASS ACRS THE SCNTRL CONUS. MAIN FCST CONCERNS THIS PACKAGE ARE PCPN CHCS TODAY INTO THIS EVNG. FOR TDAY...SHRTWV OVER THE NRN PLAINS FCST TO DEFLECT ARND UPR RDG IN PLACE AND MORE ENEWD THIS MRNG...BRUSHING THE NW COUNTIES WITH SOME DVPA/H7-3 QVECTOR CNVGC. CONSIDERING VERY DRY AIR AT H85 UPSTREAM...TEMPTED TO CONCLUDE 00Z NAM IS TOO AGGRESSIVE WITH MSTR RETURN INTO THE WRN ZNS THIS MRNG IN SW FLOW AHEAD OF SHRTWV. BUT SHARP GRADIENT OF MSTR TO THE S IS CAUSE FOR CONCERN. GFS ALSO SHOWS THE SW FLOW...BUT IS NOT AS AGGRESSIVE WITH INCRSG LLVL DWPTS AS THE NAM (GFS FCST SDNG FOR IWD AT 12Z INDICATES CONVECTIVE TEMP ARND 80). BOTH MODELS SHOW A MID LVL CAP/DRY LYR CENTERED ARND H7...BUT WL MAINTAIN ISOLD -SHRA TO ACCOUNT FOR MSTR RETURN AND POTENTIAL FOR SOME SPRINKLES MOVING THRU MN TO SURVIVE INTO THE WRN CWA THIS MRNG WITH DPVA BEGINNING TO ERODE CAP. BETTER CHC FOR PCPN SEEMS TO BE OVER THE W HALF THIS AFTN...WHEN DIURNAL HTG HELPS BOOST TEMPS TO THE CONVECTIVE TEMP LOWERED WITH SOME LLVL MSTR INFLUX AS TRAILING SHRTWV LOBE/ASSOCIATED DPVA AND H85-3 QVECTOR CNVGC WEAKENS MID LVL CAP. ENHANCED LLVL CNVGC WITH ARRIVAL OF WEAK SFC TROF/LK BREEZE CNVGC MIGHT ALSO HELP SHRA CHCS. MODIFIED GFS FCST SDNG FOR MIXED SFC T/TD 81/61 YIELDS LOWEST 100MB MLCAPE OF 875 J/KG WITH NO CIN OVER THE INTERIOR WCNTRL. BUMPED UP POPS TO 30 IN THIS AREA...WHERE RUC13 GENERATES A BIT MORE CNVCTN LATE IN THE DAY. APPEARS AS THOUGH THE E WL REMAIN DRY CLOSER TO HI PRES/DRIER AIR AND WHERE GFS SHOWS STRONGER CAP PERSISTING THRU THE DAY. HOWEVER... EVEN GFS SHOWS SOME LLVL MSTR RETURN THERE IN THE DAY WITH SFC TD RISING TO ARND 60... HELPING TO MITIGATE DROP IN RH. TNGT...GFS/NAM HINT AT ANOTHER WEAK SHRTWV/AXIS OF MSTR DROPPING INTO THE UPR GRT LKS AND BRUSHING THE NRN TIER WITH BAND OF HIER RH. THE NAM IS A BIT FASTER WITH THIS FEATURE...BUT WL TREND TOWARD THE GFS/CNDN IDEA OF PATCH OF HIER MSTR MOVING OVER THE KEWEENAW/NCNTRL LK SUP AT 06Z AND THEN INTO ERN LK SUP/ERN ZNS TOWARD 12Z. THE CNDN MODEL DOES GENERATE SOME PCPN OVER LK SUP AND THE KEWEENAW...BUT TIME OF DAY WOULD SUG THIS SHRTWV PASSAGE WL BE DRY. ELECTED TO ADD LO CHC POPS ONLY OVER LK SUP CLOSER TO SHRTWV TRACK/DEEPER MSTR... ESPECIALLY SINCE GFS MOS POPS FOR CMX/ERY ONLY IN THE 10-15 RANGE. RAISED GOING LO TEMPS FCST A COUPLE OF DEGREES TO ACCOUNT FOR HIER PWAT FCST OVER THE AREA...UP TO ARND 1.33 INCHES. EXPECT THE LOWEST TEMPS OVER THE FAR W INTERIOR FARTHEST FM SHRTWV TRACK/DEEPER MSTR/ HIER PWAT. FRI PROMISES TO BE A MOSUNNY AND WARMER DAY WITH SHRTWV RDGING/SFC HI PRES RDG BLDG INTO THE UPR LKS. BOTH UKMET/GFS SHOW H85 TEMPS REACHING 20C OVER THE W IN BY 00Z SAT. MIXING TO H8-75 ON GFS FCST SDNGS YIELDS HI TEMPS INTO THE UPR 80S AWAY FM LK MODERATION... WHICH WL BE GREATEST DOWNWIND OF LK SUP WITH LLVL NNW FLOW. DIURNAL CU WL PROBABLY BE RESTRICTED TO THE ERN ZNS WHERE H85 TEMPS LOOK TO BE A BIT LOWER. GFS FCST SDNGS SUG DWPTS WL MIX AS LO AS THE MID 50S IN THE AFTN OVER THE INTERIOR W...RESULTING IN MIN RH AS LO AS 35 PERCENT OR SO IN THAT AREA. FRI NGT WL START ON THE TRANQUIL SIDE WITH HI PRES RDG STILL ARND... BUT RETURN SW FLOW LATE IN THE NGT WL DVLP OVER THE W. GFS/UKMET/NAM GENERATE SOME PCPN IN THIS AREA...BUT LLJ AXIS REMAINS FOCUSED TO THE W THRU 12Z. WITH ANTECEDENT RELATIVELY DRY AIRMASS...MAINTAINED DRY FCST...ESPECIALLY SINCE UKMET SHOWS VERY LO H85 DWPTS HANGING IN OVER NRN WI THRU 12Z. EXPECT THE LOWEST TEMPS OVER THE INTERIOR E...CLOSER TO DEPARTING DRIER AIRMASS/FLATTER PRES GRADIENT ASSOCIATED WITH DEPARTING HI. 00Z UKMET/GFS/CNDN MODELS HAVE TRENDED FASTER IN PUSHING COMMA TAIL FEATURE OF SHRTWV RIDING TO THE NW THRU THE FA ON SAT...SHOWING A VEERING H85 FLOW ADVECTING HIER H85 DWPTS INTO THE FA (UKMET UP TO 14C...GFS UP TO 16C). GFS APPEARS TO SUFFER CONVECTIVE FEEDBACK... BUT UKMET/CNDN FCSTS WARRANT A CHC POP SPREADING ACRS THE ENTIRE FA BY THE END OF THE DAY. THIS STRONGER SW FLOW APPEARS TO BE SUFFICIENT TO ADVECT HIER MSTR TO THE NE OF PERSISTENT BNDRY THAT HAS BEEN STUCK TO THE S FOR QUITE AWHILE. SO...SAT LOOKS TO BE A MORE HUMID DAY WITH INCRS IN LLVL MSTR. ALTHOUGH UKMET SHOWS H85 TEMPS INCRSG TO 22C W-19C E... SUSPECT CLD COVER ACCOMPANYING MSTR RETURN WL KEEP TEMPS FROM SOARING TOO FAR. RAISED MIN TEMPS AND INCLUDED A 30 POP SAT NGT ACRS THE ENTIRE FA WITH EXPECTATION THAT COLD FNT WL BE REACHING THE CNTRL ZNS ARND 12Z SUN. COORDINATED WITH APX/GRB. && .AVIATION (FOR THE 12Z TAF ISSUANCE)... SURFACE AND UPPER LEVEL TROUGHS OVER MN ARE HELPING IN GENERATING A LINE OF SHOWERS AND EMBEDDED TSRA FROM INL SE TO LA CROSSE AS OF 1120Z. MOST MODELS SEEM TO WANT TO KEEP THE NORTHERN PORTION OF THE LINE GOING...THOUGH IT APPEARS IT WILL PROGRESS SLOWLY EASTWARD. HAVE INTRODUCED A PROB30 FOR CMX BTWN 21-24Z TO ACCOUNT FOR THIS. AS FOR SAW...TSRA ARE A LITTLE MORE UNCERTAIN AS HEATING...MOISTURE AND LAKE BREEZES WILL LIKELY BE REQUIRED TO INITIATE CONVECTION. TO GET ALL THREE JUXTAPOSED TODAY MIGHT BE PROBLEMATIC...AT LEAST AT SAW...AND THEREFORE HAVE LEFT OUT ANY MENTION OF A TEMPO OR PROB30. AFTER THE PASSAGE OF THE TROUGHS...THERE ARE INDICATIONS OF A LOW CLOUD DECK POSSIBLY DEVELOPING (AFTER 06Z). GIVEN THAT THERE ARE NO LOW CLOUDS PRESENT AT THE MOMENT BEHIND THE TROUGH...IN FACT THE SKIES ARE CLEAR...HAVE DECLINED NOT TO INCLUDE ANY CEILING LOWER THAN VFR. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)... WINDS ARE EXPECTED TO REMAIN BELOW 20 KT THROUGH MON. HOWEVER... WINDS MAY COME CLOSE TO 20 KT ON EASTERN LAKE SUPERIOR ON SAT NIGHT AND SUN AFTERNOON INTO SUN NIGHT. THE REASON IS DUE TO A COLD FRONT CROSSING LAKE SUPERIOR...WITH SOUTHERLY WINDS AHEAD OF THE FRONT SAT NIGHT AND NORTHWESTERLY WINDS BEHIND THE FRONT SUN AFTERNOON INTO SUN NIGHT. && .MQT WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...KC MARINE/AVIATION...AJ
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
425 AM EDT THU AUG 9 2007 .SYNOPSIS... 00Z RAOBS/LATEST WV IMAGERY AND RUC ANALYSIS SHOW PERSISTENT UPR RDG OVER THE GRT LKS BTWN TROFFING IN NEW ENGLAND AND MORE ZONAL FLOW FM THE PAC NW INTO THE NRN PLAINS. SFC HI PRES CENTERED JUST E OF LK SUP EARLY THIS MRNG...AND MOST RECENT TAMDAR SDNGS/00Z GRB RAOB SHOW A DRY/STABLE AIRMASS IN PLACE OVER THE UPR GRT LKS. SKIES ARE MOCLR OVER THE E CLOSER TO THE HI CENTER...BUT HI CLDS ARE MOVING INTO THE WRN ZNS IN ADVANCE OF SHRWTV OVER ND MOVING E THRU MORE ZONAL FLOW TO THE W. SOME SHRA/ISOLD MOVING INTO WRN MN ALG SFC TROF AHD OF THIS SYS...BUT COVG APPEARS TO BE BREAKING UP AS PCPN MOVES INTO DRY AIRMASS IN PLACE ACRS THE UPR GRT LKS AND EXTENDING AS FAR W AS INL/MPX. 00Z RAOBS IN THOSE LOCATIONS SHOW VERY DRY AIR LINGERING BTWN H85-7 EVEN THAT FAR W FM SFC HI. SHARP GRADIENT OF LLVL MSTR DOES APPEAR JUST S OF MPX (SFC DWPT ARND 57 JUST N OF MPX BUT 70 TO THE S). MORE WDSPRD CONVECTION PRESENT OVER IA/IL ON PERSISTENT BNDRY TO THE N OF STEAMY AIRMASS ACRS THE SCNTRL CONUS. MAIN FCST CONCERNS THIS PACKAGE ARE PCPN CHCS TODAY INTO THIS EVNG. FOR TDAY...SHRTWV OVER THE NRN PLAINS FCST TO DEFLECT ARND UPR RDG IN PLACE AND MORE ENEWD THIS MRNG...BRUSHING THE NW COUNTIES WITH SOME DVPA/H7-3 QVECTOR CNVGC. CONSIDERING VERY DRY AIR AT H85 UPSTREAM...TEMPTED TO CONCLUDE 00Z NAM IS TOO AGGRESSIVE WITH MSTR RETURN INTO THE WRN ZNS THIS MRNG IN SW FLOW AHEAD OF SHRTWV. BUT SHARP GRADIENT OF MSTR TO THE S IS CAUSE FOR CONCERN. GFS ALSO SHOWS THE SW FLOW...BUT IS NOT AS AGGRESSIVE WITH INCRSG LLVL DWPTS AS THE NAM (GFS FCST SDNG FOR IWD AT 12Z INDICATES CONVECTIVE TEMP ARND 80). BOTH MODELS SHOW A MID LVL CAP/DRY LYR CENTERED ARND H7...BUT WL MAINTAIN ISOLD -SHRA TO ACCOUNT FOR MSTR RETURN AND POTENTIAL FOR SOME SPRINKLES MOVING THRU MN TO SURVIVE INTO THE WRN CWA THIS MRNG WITH DPVA BEGINNING TO ERODE CAP. BETTER CHC FOR PCPN SEEMS TO BE OVER THE W HALF THIS AFTN...WHEN DIURNAL HTG HELPS BOOST TEMPS TO THE CONVECTIVE TEMP LOWERED WITH SOME LLVL MSTR INFLUX AS TRAILING SHRTWV LOBE/ASSOCIATED DPVA AND H85-3 QVECTOR CNVGC WEAKENS MID LVL CAP. ENHANCED LLVL CNVGC WITH ARRIVAL OF WEAK SFC TROF/LK BREEZE CNVGC MIGHT ALSO HELP SHRA CHCS. MODIFIED GFS FCST SDNG FOR MIXED SFC T/TD 81/61 YIELDS LOWEST 100MB MLCAPE OF 875 J/KG WITH NO CIN OVER THE INTERIOR WCNTRL. BUMPED UP POPS TO 30 IN THIS AREA...WHERE RUC13 GENERATES A BIT MORE CNVCTN LATE IN THE DAY. APPEARS AS THOUGH THE E WL REMAIN DRY CLOSER TO HI PRES/DRIER AIR AND WHERE GFS SHOWS STRONGER CAP PERSISTING THRU THE DAY. HOWEVER... EVEN GFS SHOWS SOME LLVL MSTR RETURN THERE IN THE DAY WITH SFC TD RISING TO ARND 60... HELPING TO MITIGATE DROP IN RH. TNGT...GFS/NAM HINT AT ANOTHER WEAK SHRTWV/AXIS OF MSTR DROPPING INTO THE UPR GRT LKS AND BRUSHING THE NRN TIER WITH BAND OF HIER RH. THE NAM IS A BIT FASTER WITH THIS FEATURE...BUT WL TREND TOWARD THE GFS/CNDN IDEA OF PATCH OF HIER MSTR MOVING OVER THE KEWEENAW/NCNTRL LK SUP AT 06Z AND THEN INTO ERN LK SUP/ERN ZNS TOWARD 12Z. THE CNDN MODEL DOES GENERATE SOME PCPN OVER LK SUP AND THE KEWEENAW...BUT TIME OF DAY WOULD SUG THIS SHRTWV PASSAGE WL BE DRY. ELECTED TO ADD LO CHC POPS ONLY OVER LK SUP CLOSER TO SHRTWV TRACK/DEEPER MSTR... ESPECIALLY SINCE GFS MOS POPS FOR CMX/ERY ONLY IN THE 10-15 RANGE. RAISED GOING LO TEMPS FCST A COUPLE OF DEGREES TO ACCOUNT FOR HIER PWAT FCST OVER THE AREA...UP TO ARND 1.33 INCHES. EXPECT THE LOWEST TEMPS OVER THE FAR W INTERIOR FARTHEST FM SHRTWV TRACK/DEEPER MSTR/ HIER PWAT. FRI PROMISES TO BE A MOSUNNY AND WARMER DAY WITH SHRTWV RDGING/SFC HI PRES RDG BLDG INTO THE UPR LKS. BOTH UKMET/GFS SHOW H85 TEMPS REACHING 20C OVER THE W IN BY 00Z SAT. MIXING TO H8-75 ON GFS FCST SDNGS YIELDS HI TEMPS INTO THE UPR 80S AWAY FM LK MODERATION... WHICH WL BE GREATEST DOWNWIND OF LK SUP WITH LLVL NNW FLOW. DIURNAL CU WL PROBABLY BE RESTRICTED TO THE ERN ZNS WHERE H85 TEMPS LOOK TO BE A BIT LOWER. GFS FCST SDNGS SUG DWPTS WL MIX AS LO AS THE MID 50S IN THE AFTN OVER THE INTERIOR W...RESULTING IN MIN RH AS LO AS 35 PERCENT OR SO IN THAT AREA. FRI NGT WL START ON THE TRANQUIL SIDE WITH HI PRES RDG STILL ARND... BUT RETURN SW FLOW LATE IN THE NGT WL DVLP OVER THE W. GFS/UKMET/NAM GENERATE SOME PCPN IN THIS AREA...BUT LLJ AXIS REMAINS FOCUSED TO THE W THRU 12Z. WITH ANTECEDENT RELATIVELY DRY AIRMASS...MAINTAINED DRY FCST...ESPECIALLY SINCE UKMET SHOWS VERY LO H85 DWPTS HANGING IN OVER NRN WI THRU 12Z. EXPECT THE LOWEST TEMPS OVER THE INTERIOR E...CLOSER TO DEPARTING DRIER AIRMASS/FLATTER PRES GRADIENT ASSOCIATED WITH DEPARTING HI. 00Z UKMET/GFS/CNDN MODELS HAVE TRENDED FASTER IN PUSHING COMMA TAIL FEATURE OF SHRTWV RIDING TO THE NW THRU THE FA ON SAT...SHOWING A VEERING H85 FLOW ADVECTING HIER H85 DWPTS INTO THE FA (UKMET UP TO 14C...GFS UP TO 16C). GFS APPEARS TO SUFFER CONVECTIVE FEEDBACK... BUT UKMET/CNDN FCSTS WARRANT A CHC POP SPREADING ACRS THE ENTIRE FA BY THE END OF THE DAY. THIS STRONGER SW FLOW APPEARS TO BE SUFFICIENT TO ADVECT HIER MSTR TO THE NE OF PERSISTENT BNDRY THAT HAS BEEN STUCK TO THE S FOR QUITE AWHILE. SO...SAT LOOKS TO BE A MORE HUMID DAY WITH INCRS IN LLVL MSTR. ALTHOUGH UKMET SHOWS H85 TEMPS INCRSG TO 22C W-19C E... SUSPECT CLD COVER ACCOMPANYING MSTR RETURN WL KEEP TEMPS FROM SOARING TOO FAR. RAISED MIN TEMPS AND INCLUDED A 30 POP SAT NGT ACRS THE ENTIRE FA WITH EXPECTATION THAT COLD FNT WL BE REACHING THE CNTRL ZNS ARND 12Z SUN. COORDINATED WITH APX/GRB. && .AVIATION (FOR THE 06Z TAF ISSUANCE)... VFR CONDITIONS LOOK TO PREVAIL THROUGH THE TAF PERIOD. HIGH CLOUDS SPREADING NORTH FROM THUNDERSTORMS IN IOWA IS HELPING TO KEEP TEMPERATURES FROM REACHING THE DEWPOINTS AT BOTH SITES. GIVEN THAT THE HIGH CLOUDS SHOULD PERSIST FOR A FEW MORE HOURS...PERHAPS LONGER...TEMPERATURES WILL STAY ABOVE THE DEWPOINTS. SINCE LITTLE RAIN HAS FALLEN AT EITHER SITE...HAVE DECIDED TO REMOVE GROUND FOG POSSIBILITIES. RAIN CHANCES FOR TODAY ARE SLIM AT THE TAF SITES...20 PERCENT OR LESS...AND WILL LIKELY DEPEND ON THE AMOUNT OF HEATING WE CAN GET. THEREFORE NO INTRODUCTION OF PROB30 IS PLANNED. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)... WINDS ARE EXPECTED TO REMAIN BELOW 20 KT THROUGH MON. HOWEVER... WINDS MAY COME CLOSE TO 20 KT ON EASTERN LAKE SUPERIOR ON SAT NIGHT AND SUN AFTERNOON INTO SUN NIGHT. THE REASON IS DUE TO A COLD FRONT CROSSING LAKE SUPERIOR...WITH SOUTHERLY WINDS AHEAD OF THE FRONT SAT NIGHT AND NORTHWESTERLY WINDS BEHIND THE FRONT SUN AFTERNOON INTO SUN NIGHT. && .MQT WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...KC MARINE/AVIATION...AJ
AREA FORECAST DISCUSSION
NWS GAYLORD MI
125 AM EDT THU AUG 9 2007 .AVIATION...THIN MOIST LAYER AROUND 4KFT COULD STILL POSSIBLE TURN INTO SOME SCATTERED DECK OVERNIGHT WITH CONTINUED CLEAR SKIES/LIGHT WINDS AND GOOD RADIATIONAL COOLING. OTHERWISE...ONLY AN INCREASE IN HIGH LEVEL CLOUDS EXPECTED OVERNIGHT...ESPECIALLY TVC WHERE THUNDERSTORMS WELL TO THE SOUTH WILL BLOW CONVECTIVE CLOUD DEBRIS INTO THIS AREA. NO PRECIP EXPECTED TONIGHT...AS MAIN MOISTURE AND INSTABILITY AXIS WELL TO OUR SOUTH...AND SEE NO REASON FOR IT TO MAKE IT UP THIS WAY OVERNIGHT. ALL THE ACTION SHOULD REMAIN ACROSS SRN WI/NRN IL/SRN LOWER AND NRN INDY. MAYBE A FEW MID LEVEL ECHOES ON RADAR IN THE MORNING TOMORROW...BUT STILL THINK PRECIP WILL REMAIN SOUTH OF ALL TAF SITE...ESPECIALLY PLN/APN. SFC FRONT EXPECTED TO NEAR NW LAKE MICHIGAN BY 06Z...BUT ONLY VERY SMALL CHANCES FOR RAIN WITH THIS FEATURE...PLUS IT IS AFTER THIS TAF PERIOD. WILL KEEP VFR CONDITIONS IN TAFS OVER THE NEXT 24HRS. SMD && .UPDATE...SFC/RUC/SATELLITE/RADAR AND UPPER AIR ANALYSIS SHOWING MID LEVEL RIDGING OVERHEAD AND PLENTIFUL DRY AIR IN PLACE THROUGHOUT THE COLUMN. LOCAL TAMDAR SOUNDINGS SHOW A THIN LAYER OF HIGHER RH BETWEEN 870-820MB (WHERE STRATO CU HAD A HARD TIME MIXING OUT TODAY). THE CLEAR SKIES START TO THE NIGHT MAY ALLOW FOR ENOUGH RADIATIONAL COOLING AT THE TOP OF THIS MOIST LAYER TO ALLOW FOR REDEVELOPMENT OF A 3-3.5KFT DECK OF LOWER CLOUDS...BUT AM NOT TOTALLY SOLD ON THIS IDEA. OTHER CLOUDS ARE IN THE PICTURE TOO. HIGHER LEVEL CLOUDS ALREADY SNEAKING IN ACROSS SRN COUNTIES OF NRN LOWER. PATTERN SHOWS MID LEVEL SHORTWAVE TROUGH WORKING ESE THROUGH THE DAKOTAS AND THIS FEATURE WILL CONTINUE THIS ESE TRACK THROUGH THE NIGHT. SFC FRONT STILL WELL SOUTH OF THE REGION WITH HIGHEST THETA-E AXIS ACROSS NRN IL/INDY WHILE H8 LLJ OF 30-35KTS POINTING INTO IOWA...WHERE RAINFALL HAS BEEN TREMENDOUS LATELY. ALSO...MCV ACROSS SRN LAKE MICHIGAN WORKING EASTWARD AND SUPPORTING SCATTERED SHOWERS/STORM ACTIVITY ACROSS FAR SRN LOWER. ALL-IN-ALL...THE BIG QUESTION THAT SURROUNDS NRN MICHIGAN TONIGHT IS HOW FAR NORTH WILL THE THETA-E/HIGH MOISTURE CONTENT AIR GET? MODELS DIFFER ON THEIR SOLUTIONS SO OBSERVATIONAL DATA WILL BE THE MAIN DRIVING FORCE FOR THE TONIGHT UPDATE...WITH A FEW MODEL POSITIVES THROWN IN. AIR MASS IS EXTREMELY DRY AND IT WILL TAKE QUITE THE INCREASE IN SRLY FLOW TO BRING ANY APPRECIABLE MOISTURE UP INTO NRN MICHIGAN (OUTSIDE OF HIGH LEVEL CLOUDS). NONE OF THE MODELS SHOW AN INCREASE LARGE ENOUGH TO BRING DEEPER MOISTURE INTO THE REGION...AS SRLY WIND FORECASTS ARE ALL MINIMAL (ACTUALLY H8 WINDS RATHER LIGHT TONIGHT). MCV`S ACROSS IOWA WILL TRACK ALONG THE FRONTAL ZONE...WHILE THE ESE DIVING NRN STREAM WAVE WILL NOT DEVELOP A STRONG ENOUGH SFC LOW TO BRING THE BOUNDARY NORTHWARD. PLUS...CURRENT MCS IN IOWA IS ALREADY DIVING SE AND INTO NRN MO...AND THIS MAY KEEP H8 LLJ EVEN FURTHER SOUTH FOR THE NIGHT. ADDITIONAL MCS DEVELOPMENT IS POSSIBLE LATER TONIGHT...AS INITIAL MCS COULD DIMINISH AS IT WILL BE DIVING OFF THE MAIN MOISTURE/INSTABILITY AXIS. EVEN IF THERE IS ADDITIONAL DEVELOPMENT LATER TONIGHT...THE BOUNDARY DOES NOT LOOK TO GO NORTH. SO...CHANCES FOR RAIN LOOK MINIMAL AT BEST TONIGHT. MAYBE SOME LIGHT RETURNS IN THE MID LEVELS LATE TONIGHT...BUT THAT IS ALL I SEE...AND NOTHING WORTHY OF THROWING INTO THE FORECAST. WILL KEEP THINGS PRECIP-FREE FOR THE BALANCE OF THE NIGHT. GOING INTO TOMORROW...MORE OF THE SAME. MAYBE THE NRN END OF THE CONVECTIVE DEBRIS PASSING BY ACROSS OUR SRN CWA...WHILE NRN STREAM WAVE WORKS IN ACROSS EASTERN UPPER/STRAITS REGION. ACTUALLY...I COULD SEE SOME LIGHT RAIN SHOWERS (NO THUNDER) COMING IN WITH IT`S ASSOCIATED SFC TROUGH. AM NOT UPDATING THIS FORECAST ATTM...BUT A SMALL POP COULD BE WARRANTED THURSDAY NIGHT ACROSS OUR NRN CWA. DID BUMP MIN TEMPS UP TONIGHT ACROSS NRN LOWER...AND MAINLY THE SRN COUNTIES DUE TO CLOUDS. SMD && .DISCUSSION...SFC HIGH PRESSURE AND SHORT WAVE RIDGING NOW ESTABLISHED ACROSS THE STATE. EARLIER BKN STCU DECK ACROSS THE NRN COUNTIES HAS ALL BUT MIXED OUT THIS AFTERNOON LEAVING SOME CIRRUS DRIFTING THROUGH THE REGION. SFC FRONT THAT DROPPED THROUGH NRN MICHIGAN TUESDAY NOW SITTING ALONG THE SRN MICHIGAN BORDER... WESTWARD TO LOW PRESSURE OVER SOUTH DAKOTA WITH CONVECTION STILL ONGOING IN THE VCNTY OF THE FRONT OVER IOWA. MEANWHILE...WEAK NRN STREAM SHORT WAVE AND ASSOCIATED COLD FRONT MOVING THROUGH THE DAKOTAS WITH ADDITIONAL PRECIP OCCURING NEAR THE NORTH DAKOTA/ CANADIAN BORDER. MAIN FORECAST ISSUES OVER THE NEXT 24 HOURS ONCE AGAIN REVOLVE PRECIP POTENTIAL AS ADDITIONAL CONVECTION CONTINUES TO DEVELOP UPSTREAM. AS HAS BEEN THE CASE OVER THE LAST SEVERAL DAYS...SHORT TERM MODELS CONTINUE TO HAVE PROBLEMS AND DISAGREEMENTS WITH THE SPECIFICS. GFS CONTINUES TO BE MOST AGGRESSIVE...DRAGGING WHAT APPEARS TO BE CONVECTIVELY INDUCED MID LEVEL WAVE AND CLOSED LOW LEVEL CIRCULATION UP ACROSS NRN LOWER MICHIGAN LATE TONIGHT THROUGH THURSDAY...PAINTING A FAIRLY WET PICTURE. HOWEVER...CONVECTIVE FEEDBACK ISSUES APPEAR TO BE PLAYING A BIG ROLE IN THIS MODEL SOLUTION (I.E. BIG GRID SCALE PRECIP BULLSEYE AND LOW LEVEL CIRCULATION SPIN-UP). AND GIVEN THE LOCATION OF THE FRONT/MOISTURE AND INSTABILITY GRADIENT WELL OFF TO THE SOUTH...SEEMS MORE LIKELY THAT BULK OF CONVECTION WILL TRACK THROUGH THE SRN PART OF THE STATE OVER THE NEXT 24 HOURS...MORE ALONG THE LINES OF THE NAM-WRF IDEA. THUS PLAN IS TO MAINTAIN RAIN CHANCES JUST ACROSS THE SOUTHERN HALF OF THE CWA (SOUTH OF M-72) FOR TOMORROW...HIGHEST POPS ALONG THE M-55 CORRIDOR. ALSO...WILL NOT GET SPECIFIC WITH TIMING GIVEN THE UNCERTAINTIES. OTHERWISE...MAINLY CLEAR SKIES ANTICIPATED FOR THE CWA TONIGHT WITH SOME THICKER CI/CS DRIFTING THROUGH AT TIMES AND LOW TEMPERATURES IN THE 50S. INCREASING CLOUD COVER FOR THURSDAY ESPECIALLY ACROSS THE SOUTHERN COUNTIES WITH WHATEVER CONVECTION GETS IN HERE. ADAM THURSDAY NIGHT INTO SATURDAY...MORE DRY WEATHER IN THE WORKS THROUGH THIS PERIOD AS LONGWAVE RIDGING EXTENDS FROM THE SOUTHERN PLAINS THROUGH THE WESTERN GREAT LAKES. AT THE SURFACE...HIGH PRESSURE PROGGED TO SLIP ACROSS JAMES BAY...WHICH SHOULD DRIVE A RELATIVELY DRY (DEWPOINTS IN THE 50S) AIRMASS ACROSS NORTHERN MICHIGAN FRIDAY AFTERNOON INTO SATURDAY. VERY LITTLE SUPPORT FOR ANY PRECIPITATION DESPITE EXPECTED LAKE BREEZES (950-900MB WINDS ONLY 10 KNOTS OR SO)...AS MODIFIED SOUNDINGS WITH TEMPS IN THE LOW/MID 80S FAIL TO PRODUCE NOTABLE INSTABILITY IN THE PRESENCE OF DECREASED BOUNDARY LAYER MOISTURE. GFS REMAINS AN OUTLIER IN DRIVING AN MCS ACROSS THE REGION ON SATURDAY...AND APPEARS UNREASONABLE GIVEN AXIS OF LOW THETA-E AIR RIDGED ACROSS THE REGION. TEMPS LOOK RATHER SEASONABLE FOR MID AUGUST PER H85 TEMPS IN THE 14-17C RANGE...MAINLY IN THE LOWER TO MIDDLE 80S...WITH LOWS IN THE UPPER 50S/LOW 60S. LATER PERIODS (SATURDAY NIGHT THROUGH WEDNESDAY)...ANOTHER PERIOD OF MAINLY DRY AND SEASONABLE WEATHER APPEARS ON TAP THROUGH THE EXTENDED PORTION OF THE FORECAST. OVERALL PATTERN LOOKS TO UNDERGO RETROGRESSION WITH MID LEVEL RIDGE INITIALLY OVER THE DEEP SOUTH SHIFTING BACK TOWARD ITS CLIMATOLOGICALLY-FAVORED LOCATION OVER THE INTERMOUNTAIN WEST/HIGH PLAINS AS TROUGHING SHARPENS OVER ALONG THE PACIFIC COAST IN RESPONSE TO DEEP RIDGING DEVELOPING ACROSS ALASKA. THIS WILL EFFECTIVELY PLACE NORTHERN MICHIGAN ONCE AGAIN IN DRY NORTHWEST FLOW ALOFT...WITH LITTLE IN THE WAY OF PRECIPITATION CHANCES FORESEEN. THE LONE EXCEPTION CONTINUES TO BE ON SUNDAY...WITH MEDIUM RANGE GUIDANCE CONTINUING TO PROG A WEAK FRONTAL PASSAGE THROUGH THE AFTERNOON HOURS AS A WEAK WAVE DROPS THROUGH THE FLOW. HOWEVER...BEST FORCING ONCE AGAIN RESIDES NORTH OF THE REGION...AND AVAILABLE MOISTURE ALSO IN QUESTION OWING TO ONGOING LOW LEVEL RIDGING IN ADVANCE OF THE SYSTEM. HENCE...CHANCES ARE QUITE SMALL FOR ANY SIGNIFICANT RAINFALL...BUT GIVEN CONSISTENCY WITH ENSEMBLE MODEL GUIDANCE QPF...PREFER TO KEEP A SMALL CHANCE INTACT. OTHERWISE...IT APPEARS LOW LEVEL RIDGING WILL SLIDE ACROSS THE REGION IN THE WAKE OF THIS SYSTEM...BRINGING A SHOT OF SLIGHTLY COOLER...AND MUCH DRIER AIR THROUGH THE FIRST HALF OF NEXT WEEK. TEMPERATURES WILL BE WARMEST ON SUNDAY IN ADVANCE OF THE FRONT...WITH H85 NUMBERS AROUND 18-19C PER GFS ENSEMBLE MEAN SUPPORTING HIGHS IN THE MID TO PERHAPS UPPER 80S...COOLING BACK TO THE UPPER 70S/LOW 80S MONDAY THROUGH WEDNESDAY TIMEFRAME AS UPPER FLOW AMPLIFIES WITH TROUGHING DEVELOPING INTO THE NORTHEAST...AND H85 TEMPS DIPPING TO 14-15C. THE ONE CAVEAT TO THE WHOLE EXTENDED PORTION OF THE FORECAST WILL BE A VERY SMALL POTENTIAL FOR DEVIATIONS FROM THE EXPECTED DRY WEATHER WITH ANY WEAK WAVES RIDING THROUGH THE FLOW. OVERALL PATTERN APPEARS FAVORABLE FOR UPSTREAM MCS DEVELOPMENT OVER THE NORTHERN PLAINS NEAR THE TOP OF THE RIDGE...THOUGH CERTAINLY TIMING OF SUCH FEATURES IS ALL BUT IMPOSSIBLE TO NAIL DOWN AT THIS POINT. HOWEVER...GIVEN EXPECTED INFLUX OF DRIER AIRMASS ACROSS THE CWA...THEREBY FORCING THETA-E RIDGE TO BUILD WEST OF THE LAKES...WOULD THINK ANYTHING MCS-WISE THAT GET GOING TO THE WEST WOULD LIKELY RIDE THIS MOISTURE GRADIENT AND PRESENT NO PROBLEMS FOR THE NORTHERN LAKES. THAT SAID...CERTAINLY SOMETHING TO BE WATCHED THROUGH THE WEEKEND AS ANY ADDITIONAL RAIN CHANCES WOULD BE WELCOMED AT THIS POINT. LAWRENCE && .APX WATCHES/WARNINGS/ADVISORIES...NONE. && $$
AREA FORECAST DISCUSSION
NWS DETROIT/PONTIAC MI
100 AM EDT THU AUG 9 2007 .AVIATION... A CLUSTER OF STORMS IN THE DETROIT AREA AT PRESS TIME WILL LIKELY BE JOINED BY A FEW MORE STORMS DURING THE EARLY MORNING HOURS. THIS WILL BE PART OF INCREASING COVERAGE OF SHOWERS AND THUNDERSTORMS THAT WILL BRING VFR CONDITIONS DOWN TO MVFR AROUND SUNRISE, AND THEN TO AT LEAST PATCHES OF IFR AFTER ABOUT 14Z. THIS IS WHEN WE CAN EXPECT THE REMNANTS OF YET ANOTHER CONVECTIVE COMPLEX TO ARRIVE IN SE MICHIGAN, POSSIBLY SIMILAR TO THAT WHICH OCCURRED ON TUESDAY. THIS SYSTEM WILL BRING WIDESPREAD MVFR CONDITIONS WITH PATCHES OF IFR VISIBILITY AND/OR CEILING WITH PATCHES OF HEAVY RAINFALL. EXPECT THIS PATTERN TO EXIT SE MICHIGAN BY MID TO LATE AFTERNOON. CONDITIONS WILL IMPROVE FURTHER THIS EVENING AS HIGH PRESSURE BEGINS BUILDING INTO THE AREA ON LIGHT NORTH WINDS. && .PREV DISCUSSION...ISSUED 1007 PM EDT WED AUG 8 2007 UPDATE... THE MCV ABOUT OVER THE SOUTH END OF LAKE MICHIGAN AT PRESS TIME WILL CONTINUE TO AFFECT THE WEATHER IN SE MICHIGAN TONIGHT. THIS SYSTEM WILL SUPPORT AT LEAST A MODEST INCREASE IN SHOWER COVERAGE, ALONG WITH SCATTERED THUNDERSTORM ACTIVITY. THERE MAY BE A LULL AS SURFACE-BASED CONVECTION WEAKENS BUT THIS WILL BE REPLACED BY THE ELEVATED VARIETY AS THE MCV STARTS TO MOVE SOME LOW LEVEL MOISTURE BACK NORTHWARD. OUR GOING FORECAST HAS THIS HANDLED WELL WITH FUTURE ADJUSTMENTS POSSIBLE TO RAISE POPS FARTHER NORTH LATER THIS EVENING. SEVERE WEATHER POTENTIAL WILL BE LIMITED BY MODEST MID LEVEL LAPSE RATES BUT HEAVY RAINFALL IS STILL POSSIBLE WITH 1.6 INCH PW REPORTED BY THE 00Z DTX SOUNDING. FARTHER WEST, THERE IS ANOTHER LARGE CONVECTIVE SYSTEM DEVELOPING OVER IOWA AGAIN THIS EVENING. GENERAL SURFACE PRESSURE FALLS ASSOCIATED WITH THE UPPER WAVE MOVING THROUGH THE NORTHERN PLAINS IS HELPING WITH THIS DEVELOPMENT, THE REMANTS OF WHICH ARE EXPECTED TO ARRIVE IN SE MICHIGAN AFTER SUNRISE THURSDAY MORNING. THERE IS SOME POTENTIAL FOR THIS SYSTEM TO STAY ORGANIZED AS IT REACHES OUR AREA AS BACKGROUND LOW PRESSURE WILL BE SUPPORTED BY THE UPPER WAVE OVER THE NORTHERN PLAINS AS IT MOVES INTO THE NORTHERN GREAT LAKES. THE SURFACE LOW MAY NOT END UP AS DEEP BUT THE PACE OF THE SYSTEM SHOULD BE CLOSE TO THAT SHOWN BY THE GFS. THIS LOW PRESSURE SYSTEM WILL ALSO SUPPORT STRONG LOW TO MID LEVEL THETA-E ADVECTION OUT AHEAD OF THE MCS AS IT MOVES THROUGH LOWER MICHIGAN, SO SOME NEW DEVELOPMENT IS ALSO POSSIBLE TO THE EAST OF THE MCS OVERNIGHT RESULTING IN EFFECTIVE TIMING MORE LIKE THE FASTER GFS. LIKELY POPS IN OUR GOING FORECAST FOR THURSDAY ALSO HAS THIS HANDLED WELL. PREV DISCUSSION...ISSUED 422 PM EDT WED AUG 8 2007 SHORT TERM...TONIGHT FORECAST CONCERNS FOR THIS EVENING AND TONIGHT REVOLVE AROUND THUNDERSTORM POTENTIAL AND EVOLUTION AS LOW LEVEL FRONTAL BOUNDARY REMAINS IN PLACE OVER THE UPPER OHIO VALLEY. SOUTHERN LOWER MICHIGAN REMAINS SANDWICHED BETWEEN A DRY AIRMASS WITH DEWPOINTS IN THE UPPER 50S TO OUR NORTH AND A VERY MOIST AIRMASS WITH DEWPOINTS IN THE LOW 70S TO OUR SOUTH. AN MCV CAN BE SEEN ON SATELLITE IMAGERY MOVING EAST ACROSS NORTHERN ILLINOIS AND IS MOVING INTO AN ATMOSPHERE WITH MIXED LAYER CAPES OVER 2000 J/KG. THE CAP HAS BEEN ERODING ALL DAY WITH THE LATEST TAMDAR SOUNDING OUT OF DTW SHOWING THAT IT IS ALMOST GONE. SURFACE FLOW IS RATHER WEAK ALONG THE STALLED OUT BOUNDARY AND ANY POCKETS OF WEAK CONVERGENCE COULD ACT TO TRIGGER SHOWERS THIS EVENING. WILL EXPECT TO SEE THUNDERSTORMS FILL IN ACROSS NORTHERN INDIANA WITH A FEW SCATTERED THUNDERSTORMS POSSIBLE ACROSS OUR SOUTHERN TWO TIERS OF COUNTIES. FURTHER NORTH...INSTABILITY IS LIMITED AND WILL HAVE TO WAIT FOR MOISTURE TO START PUSHING BACK NORTH OVERNIGHT TO SEE ANY RAIN. AS SHORTWAVE ENERGY OVER THE PLAINS PROGRESSES EASTWARD TONIGHT...THE MCV WILL TRACK EAST ACROSS EXTREME SOUTHERN LOWER MICHIGAN AHEAD OF A SURFACE TROUGH NOSING INTO IOWA/ILLINOIS. THE LOW LEVEL THETA-E RIDGE WILL START TO PUSH BACK NORTH AND WILL EXPECT SHOWERS AND SCATTERED THUNDERSTORMS TO INCREASE SOUTH OF I-69. ELEVATED INSTABILITY IS NOT IMPRESSIVE TONIGHT WITH WARM MID LEVELS...BUT PRECIPITABLE WATER VALUES WILL APPROACH 2 INCHES AND 850MB DEWPOINTS ARE AROUND 17C. WITH MID LEVEL FLOW SET UP PARALLEL TO THIS BOUNDARY WE MAY SEE SOME TRAINING OF STORMS OVERNIGHT AND WILL HAVE TO MONITOR FOR HEAVY RAIN. ONE LIMITING FACTOR IS THAT THE LOW LEVEL JET WILL BE FOCUSED FURTHER TO THE WEST ACROSS IOWA/ILLINOIS NEAR THE SURFACE TROUGH AND WILL EXPECT THE MORE ROBUST CONVECTION TO DEVELOP IN THIS AREA. HAVE GONE A FEW DEGREES ABOVE GUIDANCE MINS FOR TONIGHT...ESPECIALLY ACROSS OUR SOUTHERN COUNTIES WHERE DEWPOINTS ARE NOT EXPECTED TO FALL MUCH OVERNIGHT. LONG TERM...THURSDAY THROUGH NEXT WEDNESDAY THROUGH SATURDAY... MODELS VARY IN DETAILS AT 500 MB...BUT MODELS ARE IN AGREEMENT SHOWING QUITE VIGOROUS VORTICITY EXITING THE NORTHERN PLAINS AND PASSING THROUGH THE GREAT LAKES REGION THURSDAY INTO THURSDAY NIGHT. AT THE SURFACE...A QUASISTATIONARY FRONT IN CLOSE PROXIMITY TO THE SOUTHERN BORDER WITH WAVE MOVING EASTWARD ALONG IT...FOLLOWED BY HIGH PRESSURE BUILDING IN FOR FRIDAY. 850 TO 500 MB MOISTURE EXPECTED TO MAXIMIZE THURSDAY...WANE THURSDAY NIGHT...THEN BE OVERALL LEAN THROUGH SATURDAY. LOWER AS AT 925 MB...MOISTURE QUITE GOOD THURSDAY INTO THURSDAY NIGHT THANKS TO LOCATION ALONG AND NORTH OF TRACK OF SURFACE LOW...THEN LESSENING BY FRIDAY. PRECIPITABLE WATER IN THE NEIGHBORHOOD OF 2 INCHES THURSDAY...SO WILL HAVE TO CONTINUE TO WATCH FOR LOCALLY HEAVY RAIN PRODUCING THUNDERSTORMS WITH FLOODING NOT OUT OF THE QUESTION. LOW TO MID LEVEL OMEGA FIELDS SHOW QUITE VIGOROUS ASCENT AT TIMES THURSDAY INTO THURSDAY EVENING...THOUGH PROBABLY THE NAM BULLSEYE OF 10 TO 15 UBAR/SEC IS OVERDONE. 850 TO 500 MB QVECTOR CONVERGENCE SEEN AS SLIGHT THURSDAY INTO THURSDAY EVENING...THEN DIVERGENCE/IMPLIED DESCENT THROUGH SATURDAY. LOW LEVEL WIND CONVERGENCE FAIRLY ROBUST ON THURSDAY TOO...THOUGH MODELS VARY CONSIDERABLY IN DETAILS. ALSO A BIT OF 250 MB DIVERGENCE SEEN THURSDAY. GIVEN TRACK OF WEAK SURFACE LOW ALONG/NEAR THE OHIO BORDER THURSDAY...INSTABILITY AND THUS POTENTIAL FOR SEVERE WEATHER WILL BE MAXIMIZED IN SOUTHERN COUNTIES OF SOUTHEAST MI. LOW TO MID LEVEL LAPSE RATES ARE EXPECTED TO BE STEEPER SOUTH OF THE BORDER...BUT ZERO TO 6 KM BULK SHEAR TO NEAR 40 KNOTS THURSDAY INTO THURSDAY NIGHT WILL BE SUFFICIENT TO ENHANCE THE SEVERE POTENTIAL. AFTER SATURDAY... BROAD 500 MB PLAINS RIDGE TO PERSIST AS PER GOOD MODEL CONSENSUS. THIS WITH A TREND TOWARD RISING HEIGHTS WITH RIDGE AND ASSOCIATED WEAKENING OF THE WESTERLIES OVER THE NORTHERN TIER OF STATES ATOP THE RIDGE LATE WEEKEND INTO MID WEEK. AT THE SURFACE...THERE IS DECENT MODEL AGREEMENT INCLUDING GFS ENSEMBLE MEAN IN DEPICTING A COLD FRONT PASSING THROUGH ABOUT SUNDAY...THEN HIGH PRESSURE TO AGAIN ESTABLISH ITSELF. THIS RIDGE CENTERED TO THE WEST AT LEAST SHOULD KEEP EXCESSIVE HEAT AT BAY THROUGH THE PERIOD. WILL RETAIN CURRENT SLIGHT MENTION FOR SHOWERS/THUNDERSTORMS SUNDAY...WITH THIS IDEA SUPPORTED BY OVERNIGHT DGEX AS WELL. MARINE... A SMALL CHANCE OF THUNDERSTORMS WILL PERSIST TONIGHT...WITH BETTER CHANCES THURSDAY AND THURSDAY EVENING AS A WEAK LOW CENTER SKIRTS THE SOUTHERN GREAT LAKES REGION. WINDS WILL TURN TO EASTERLY OVERNIGHT THEN GRADUALLY TURN TO NORTHERLY THURSDAY NIGHT BEHIND THE WEAK LOW. WIND GUSTS WILL STAY BELOW 20 KNOTS THROUGH THURSDAY NIGHT AND WAVES WILL BE MOSTLY 2 FEET OR LESS. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LAKE HURON...NONE. LAKE ST CLAIR...NONE. MI WATERS OF LAKE ERIE...NONE. && $$ AVIATION.....BT UPDATE.......BT SHORT TERM...KAHL LONG TERM....DWD MARINE.......KAHL YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
AREA FORECAST DISCUSSION
NWS GRAND RAPIDS MI
426 AM EDT SAT AUG 11 2007 LATEST UPDATE...ALL BUT AVIATION... .SYNOPSIS...(426 AM SAT AUG 11 2007) HIGH PRESSURE OVER THE CENTRAL GREAT LAKES WILL DRIFT EAST OF THE AREA TODAY. THIS WILL ALLOW A COLD FRONT THAT WAS OVER MINNESOTA TO MOVE TOWARD MICHIGAN LATE TONIGHT AND SUNDAY. THE FRONT WILL BRING A CHANCE FOR SCATTERED SHOWERS AND THUNDERSTORMS TO THE REGION. THE BEST CHANCE OF RAIN WILL OCCUR ACROSS CENTRAL LOWER MICHIGAN WITH LESSER CHANCES ACROSS SOUTHERN LOWER MICHIGAN. THE FRONT WILL BE EAST THE AREA BY EARLY SUNDAY EVENING...WITH HIGH PRESSURE FILLING BACK IN BY MONDAY. LESS HUMID AIR WILL MOVE INTO THE AREA ON MONDAY. && .SHORT TERM... (426 AM EDT SAT AUG 9 2007) MAIN CHALLENGE WITH THIS PACKAGE WAS TIMING A COLD FRONT THROUGH THE AREA ON SUNDAY. 00Z MODEL RUNS INDICATE A BIT FASTER MOVING FRONT AND THIS MAKES SENSE GIVEN THE WEAK UPPER RIDGE THAT WAS OVER THE GREAT LAKES THIS MORNING. THIS RIDGE SHOULD FLATTEN BY THIS EVENING AND ALLOW A PROGRESSIVE FLOW. ALSO...SATELLITE AND RADAR TRENDS SHOW STORMS HAVE ADVANCED ACROSS MUCH OF MN THIS MORNING...WELL AHEAD OF THE SURFACE FRONT THAT STILL LIES ACROSS EASTERN ND. THE WEAK UPPER RIDGE WILL HOLD BACK ANY PCPN FOR TODAY...ALTHOUGH THE CLOUD COVER SHOULD BEGIN TO THICKEN OVER THE NW CWA...NEAR LDM...BY LATE AFTERNOON. BY TONIGHT WILL BEGIN POPS IN THE NORTHERN HALF OF THE CWA THIS EVENING. THIS WILL LARGELY BE DRIVEN BY THE PRE-FRONTAL VORT MAX THAT WAS OVER EASTERN MN THIS MORNING. THIS FEATURE ALSO COINCIDES WITH THE LEFT EXIT REGION OF THE UPPER JET THAT MOVES INTO THE AREA TOWARD...OR JUST AFTER MIDNIGHT. THE BEST DYNAMICS REMAIN NORTH OF THE REGION...SKIMMING ACROSS CENTRAL LOWER MICHIGAN. WILL HAVE THE HIGHEST CHANCE POPS NORTH OF A MKG-MOP LINE...AND JUST SLIGHT CHANCE POPS SOUTH TO I96. THE SURFACE FRONT COMES ACROSS THE CWA THROUGH THE DAY SUNDAY. FAVORABLE INSTABILITY WITH CAPE VALUES AROUND 2500 J/KG DEVELOP AHEAD OF THE FRONT ACROSS THE SERN CWA. THE TIMING OF THE FRONT WILL LARGELY DEPEND ON WHETHER SEVERE STORMS DEVELOP OVER THE GRR COUNTY WARNING AREA. IT WOULD APPEAR THE BETTER CHANCE OF SEVERE WEATHER WILL BE EAST AND SOUTHEAST OF THE AREA BY MID/LATE AFTERNOON IF THE PACE OF THE FRONT IS SUSTAINED. CANADIAN HIGH PRESSURE FILLS IN BEHIND THE DEPARTING FRONT SUNDAY NIGHT AND MONDAY. DEWPOINTS WILL FALL THROUGH THE 60S AND 50S...MAKING FOR A COMFORTABLE SUMMER DAY ON MONDAY. && .LONG TERM...(426 AM EDT SAT AUG 11 2007) OVERALL I CHANGED LITTLE IN THE PERIOD FROM MONDAY NIGHT THROUGH FRIDAY. IT DOES NOT LOOK GOOD FOR SIGNIFICANT RAINFALL THROUGH THIS PERIOD ANYWHERE IN OUR CWA AS NORTHWEST UPPER LEVEL FLOW CONTINUES TO RULE THE WESTERN GREAT LAKES. A SIGNIFICANT COOLING TREND SEEMS IN THE WORKS FOR THE MIDDLE AND END OF NEXT WEEK. THAT IS THE RESULT OF TWO LARGE UPPER LOWS IN THE CANADIAN SUBARCTIC CONSOLATION NEAR LABRADOR NEXT WEEK. && .AVIATION...(157 AM EDT SAT AUG 11 2007) A TAMDAR SOUNDING FROM GRR AT 0330Z SHOWS WINDS ARE 20 KNOTS AT 1600 FT ABOVE THE GROUND. THAT IS MORE THAN ENOUGH TO KEEP THE BOUNDARY LAYER AIR MIXED ENOUGH TO SIGNIFICANTLY REDUCE THE RISK OF ANY SIGNIFICANT FOG OVERNIGHT. BEYOND THAT THE VERY DRY AIR IN PLACE WILL ASSURE US VFR SKIES AND VISIBILITIES THROUGH 06Z SUNDAY. && .MARINE... (426 AM EDT SAT AUG 11 2007) SOUTHWEST TO SOUTH WINDS WILL PICK UP THROUGH TODAY AND TONIGHT AS THE COLD FRONT APPROACHES. THE COLD FRONT WILL PASS THE NEARSHORE WATERS AROUND MID DAY ON SUNDAY...REDUCING PCPN CHANCES INTO THE AFTERNOON AND ALSO SHIFTING THE WINDS TO NORTHERLY. WAVES SHOULD KICK UP TO 2 TO 4 FEET AS FRONT COMES THROUGH. WATER TEMPS SHOULD FALL SUNDAY NIGHT INTO MONDAY AS NORTHEAST WINDS DEVELOP WITH THE APPROACHING HIGH PRESSURE AND UPWELLING OCCURS. && .HYDROLOGY... (426 AM EDT SAT AUG 11 2007) NO HYDRO ISSUES EXPECTED THROUGH THE WEEKEND WITH A LACK OF WIDESPREAD RAINFALL EXPECTED AND RIVER AND STREAM LEVELS CURRENTLY NORMAL TO BELOW NORMAL. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ SYNOPSIS: JK SHORT TERM: JK LONG TERM: WDM AVIATION: WDM MARINE: JK HYDROLOGY: NJJ/JK
AREA FORECAST DISCUSSION
NWS GRAND RAPIDS MI
157 AM EDT SAT AUG 11 2007 LATEST UPDATE...AVIATION... .SYNOPSIS... (405 PM FRI AUG 10 2007) HIGH PRESSURE EXTENDING FROM HUDSON BAY DOWN SOUTH TO TEXAS WILL REMAIN IN CONTROL OF THE WEATHER FOR SOUTHWEST LOWER MICHIGAN THROUGH THE DAY ON SATURDAY. THIS AREA OF HIGH PRESSURE WILL BRING A GOOD DEAL OF SUNSHINE TO THE AREA ALONG WITH WARM TEMPERATURES. A COLD FRONT WILL APPROACH THE AREA LATE SATURDAY NIGHT...AND PASS THROUGH THE AREA DURING THE DAY ON SUNDAY. A FEW SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WITH THIS FEATURE...HOWEVER WIDESPREAD RAINFALL IS NOT EXPECTED. && .SHORT TERM... (405 PM EDT FRI AUG 9 2007) SATELLITE IMAGERY THIS AFTERNOON SHOWS STILL A FAIR AMOUNT OF CU OVER MOST INLAND AREAS...WITH MOSTLY SUNNY SKIES CLOSER TO THE LAKESHORE. THIS CU IS GRADUALLY MIXING OUT AS DRIER AIR IS MIXING DOWN FROM ALOFT AND AS SLIGHTLY DRIER AIR IS ADVECTING IN FROM THE NORTH. THIS DRIER AIR ALONG WITH A 10-15 KNOT BREEZE JUST ABOVE THE SFC SHOULD KEEP FOG TO A MINIMUM ACROSS THE AREA TONIGHT. WOULD EXPECT A BIT OF 3-5SM TYPE FOG TONIGHT...NOT SIGNIFICANT ENOUGH TO MENTION IN THE FCST. SKIES SHOULD REMAIN MOSTLY CLEAR AFTER THE CU DISSIPATES. SKIES WILL REMAIN MOSTLY SUNNY THROUGH MOST OF THE DAY ON SAT AS RIDGING REMAINS IN CONTROL...AND THERE IS A BIT LESS MOISTURE TO WORK WITH AS FAR AS CU POTENTIAL IS CONCERNED. SOME HIGH CLOUDS ARE EXPECTED TO MOVE IN DURING THE AFTERNOON FROM THE NW...OUT AHEAD OF THE COLD FRONT AS MID LEVEL THETA E INCREASES. TEMPS ON SAT SHOULD BE A BIT WARMER AS H850 TEMPS WARM A COUPLE OF DEGREES C. OUT TO OUR WEST...AN MCS IS EXPECTED TO FIRE SAT EVENING AS A 35 KT LLJ OUT AHEAD OF A SRN STREAM SFC WAVE ON THE COLD FRONT. IN ADDITION...THE RRQ OF A NRN STREAM JET AND THE LFQ OF A SRN STREAM JET COUPLE TO ASSIST WITH CONVECTION. THE LLJ WEAKENS AND THE UPPER LEVEL JETS DECOUPLE BEFORE MOVING FURTHER EAST INTO THE AREA. DEEP LAYER THICKNESSES WOULD BRING THE REMNANTS OF THE MCS INTO THE AREA LATE SAT NIGHT. MODEL CONSENSUS EXCEPT THE NAM BRINGS A LITTLE QPF INTO THE AREA. WE HAVE ADDED A LOW CHC POP TO THE CWFA TO ACCOUNT FOR THIS...HIGHEST OVER THE NW. THE COLD FRONT IS EXPECTED TO EXTEND FROM HUDSON BAY...TO KMQT...TO ERN CO AT 12Z SUN. THE FRONT WILL THEN MOVE THROUGH THE CWFA DURING THE DAY ON SUN...AND SHOULD BE EXITING THE SE CORNER OF THE CWFA AT 00Z MON. THE BEST UPPER DYNAMICS AND SFC LOW WILL BE PASSING WELL NORTH OF THE AREA. THE SRN STREAM WAVE IS EXPECTED TO BYPASS THE AREA TO THE SW. THIS LEAVES A WEAKENING FRONT MOVING THROUGH. WE DO EXPECT THAT THERE WILL BE A FEW SHOWERS AND STORMS DEVELOP ALONG THE FRONT AS CAPES ARE EXPECTED TO REACH INTO THE 2000-2500 J/KG AND SFC BASED LI/S WILL FALL BELOW -5C. ANY STORMS THAT DO DEVELOP WILL HAVE THE POTENTIAL FOR BECOMING ORGANIZED AND SEVERE WITH DEEP LAYER SHEAR VALUES OF 30-40 KTS EXPECTED. WIDESPREAD RAIN IS NOT EXPECTED HOWEVER...AND WE HAVE CONTINUED WITH A 30 POP FOR SUN. PCPN SHOULD END PRIOR TO SUN EVENING WITH THE FRONT EXITING BY THIS TIME. && .LONG TERM...(405 PM EDT FRI AUG 10 2007) THE MID RANGE MODELS HAVE GOOD CONTINUITY AND AGREEMENT ON THE SYNOPTIC SCALE. THE MAIN FORECAST CHALLENGE IS THE TIMING OF FEATURES OVER TOPPING THE RIDGE ALOFT OVER THE MIDWEST AND WEST. ALSO TO BE DETERMINED IS THE MOISTURE AVAILABLE. WITH THE GOOD CONTINUITY OF THE MODELS... THE ONLY CHANGES MADE TO THE GRIDS WERE MADE TO IMPROVE AGREEMENT WITH OTHER OFFICES. && .AVIATION...(157 AM EDT SAT AUG 11 2007) A TAMDAR SOUNDING FROM GRR AT 0330Z SHOWS WINDS ARE 20 KNOTS AT 1600 FT ABOVE THE GROUND. THAT IS MORE THAN ENOUGH TO KEEP THE BOUNDARY LAYER AIR MIXED ENOUGH TO SIGNIFICANTLY REDUCE THE RISK OF ANY SIGNIFICANT FOG OVERNIGHT. BEYOND THAT THE VERY DRY AIR IN PLACE WILL ASSURE US VFR SKIES AND VISIBILITIES THROUGH 06Z SUNDAY. && .MARINE... (405 PM EDT FRI AUG 10 2007) NORTHWEST LAKE BREEZES THIS AFTERNOON WILL BECOME AN EAST TO SOUTHEAST WIND OVERNIGHT AS THE SFC HIGH BEGINS TO SLIP NORTHEAST OF THE AREA. SOME 2 FOOT WAVES POSSIBLE LATE THIS AFTERNOON/EARLY THIS EVENING WILL DIMINISH TONIGHT. WAVES SHOULD GENERALLY REMAIN UNDER A FOOT UNTIL SUN WHEN THE WINDS WILL PICK UP A BIT NEAR THE FRONT. && .HYDROLOGY... (405 PM EDT FRI AUG 10 2007) NO HYDRO ISSUES EXPECTED THROUGH THE WEEKEND WITH A LACK OF WIDESPREAD RAINFALL EXPECTED AND RIVER AND STREAM LEVELS CURRENTLY NORMAL TO BELOW NORMAL. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ SYNOPSIS: NJJ SHORT TERM: NJJ LONG TERM: IOD AVIATION: WDM MARINE: NJJ HYDROLOGY: NJJ
AREA FORECAST DISCUSSION...UPDATED
NWS MARQUETTE MI
1120 AM EDT SAT AUG 11 2007 .UPDATE... COMMA HEAD PORTION OF AN MCV...ORIGINATING FROM THE MCS OVER MN EARLIER THIS MORNING...SUPPORTED AN AREA OF SHOWERS OVER W UPR MI. MUCAPE VALUES INTO THE 1000-1500 J/KG RANGE COULD ALSO SUPPORT AN ISOLD TSRA EVEN THOUGH NO CLOUD TO GROUND LIGHTNING WAS NOTED WITH THIS FEATURE THROUGH 15Z. OTHERWISE...CONVECTIVE DEBREIS MID/HIGH CLOUDS COVERED MUCH OF WEST/CNTRL UPPER MI. ALTHOUGH UPSTREAM SFC PATTERN WAS COMPLICATED BY NUMEROUS OUTFLOW BOUNDAIRES...MAIN COLD FRONT WAS MOVING THROUGH NW MN AT 15Z AND SHOULD MOVE INTO NW BY 00Z. EXPECT THE SHRA FROM THE MCV TO SLOWLY WEAKEN OR DISSIPATE IN THE EARLY AFTERNOON. THE LEFTOVER CLOUDS SHOULD HOLD DOWN SFC HEATING AND TEMP RECOVERY KEEPING MAX READINGS MAINLY IN THE LOWER TO MID 80S. KMPX/KINLD AND AREA TAMDAR SNDGS SUGGEST CAPPING SHOULD PREVAIL ENOUGH TO PREVENT SFC BASED CONVECTION UNTIL THE FRONT AND ASSOCIATE LOW LVL CONV FROM MN MOVES INTO THE AREA. SO...SOME SCT SHRA/TSRA MAY DEVELP AND MOVE INTO W UPPER MI LATE THIIS AFTERNOON AS THE FRONT APPROACHES. DISCUSSION...ISSUED 535 AM EDT SAT AUG 11 2007 CONCERNS FOCUS ON THUNDERSTORMS CHCS TODAY AND TONIGHT AND POTENTIAL FOR SVR. LINEAR MCS MOVING FROM MN INTO WRN WI AS NOTED ON SATELLITE IMAGERY AND RADAR LOOPS SUPPORTED BY LIFT/MOISTURE AT NOSE OF 40 KT LOW-LVL JET. LATEST RUC MODEL INDICATES DIFFLUENT THCKNS SHOULD CONTINUE TO PUSH MCS AWAY FROM UPR MI AS IT WEAKENS IN MORE STABLE ENVIRONMENT OVER WI. TODAY...GFS SNDGS SHOW GENERALLY A CAPPED ATMOSPHERE OVER UPR MI AHEAD OF INCOMING COLD FRONT OVER THE PLAINS. CLOUDS FROM MCS OVER WI COULD ALSO ENHANCE CAPPED ENVIRONMENT. MODEL SNDGS SUGGEST WE MAY HAVE TO WAIT UNTIL LATE AFTERNOON AS INSTABILITY BUILDS AND THE COLD FRONT DRAWS NEAR BEFORE CONVECTION FIRES OVER THE WRN HALF COUNTIES. KEPT IN CHC POPS FOR THE WEST HALF AS THE 850 MB THETA-E RDG NOSES INTO THE AREA AND MLCAPES INCREASE TO 1000-1500 J/KG PER GFS. TONIGHT...EXPECT CAP TO ERODE BY LATE AFTERNOON AND EVENING WITH HEIGHT FALLS FROM APPROACHING SHORTWAVE AND INCREASING INSTABILITY (MLCAPE VALUES 1000-1500 J/KG). THIS SHOULD ALLOW CONVECTION TO SPREAD INTO UPPER MI. 40-50 KT FCST MID LEVEL WINDS WOULD SUPPORT SHEAR VALUES SUFFICIENT FOR SUPERCELLS. 06Z NAM AND RUC13 HINT THAT CONVECTION COULD EVOLVE INTO A LINEAR MCS AS IT MOVES THROUGH UPPER MI WITH DAMAGING WINDS AND SOME LARGE HAIL AS THE MAIN HAZARDS PER SPC DAY1 OUTLOOK. GIVEN PROGRESSIVE NATURE OF THE CONVECTION...DO NOT EXPECT VERY HIGH PRECIP AMOUNTS FROM CONVECTION. BUMPED UP POPS TO LIKELY OVER WRN HALF COUNTIES WHERE MODELS FCST THE BEST INSTABILITY AND UPR DIV TO BE. KEPT HIGH CHC POPS IN FOR ERN COUNTIES. SUN AND MON...MODELS TRENDING FASTER WITH DEPARTURE OF COLD FRONT SO DROPPED POPS FOR ERN COUNTIES ON SUN AND WENT WITH A DRY FCST. CAA AND STRONG DRYING TAKES OVER WITH ENHANCED MIXING RESULTING IN GUSTY NW WINDS TO 25 MPH. MIXING OF DRIER AIR TO THE SFC WILL RESULT IN DEWPOINTS IN THE 40S ON SUN AND RH VALUES IN THE 30 TO 40 PERCENT RANGE. HIGH PRES WILL DOMINATE FROM SUN NIGHT INTO MON WITH DRY WEATHER IN STORE. THE GRADIENT SHOULD REMAIN WEAK ENOUGH MON FOR LAKE BREEZE DEVELOPMENT. MON NIGHT AND TUE...MODELS STILL CONSISTENT WITH BRINGING IN NEXT SIGNIFICANT SHORTWAVE AND SFC FRONT THROUGH THE AREA BY TUE MORNING. WILL KEEP GOING FCST CHC POPS MON NIGHT AHEAD OF THIS SYSTEM. LIMITED MOISTURE RECOVERY MAY HINDER CHC OF SIGNIFICANT RAINFALL. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)...WINDS ARE EXPECTED TO GENERALLY REMAIN BELOW 20 KT THROUGH THE DAY...HOWEVER A FEW GUSTS TO AROUND 25 KT ARE EXPECTED OVER EASTERN LAKE SUPERIOR FOR A SHORT TIME AROUND MIDNIGHT TONIGHT WITH THE PASSAGE OF THE COLD FRONT. SUNDAY AFTERNOON...A FEW GUSTS TO AROUND 25 KT AGAIN POSSIBLE OVER EASTERN LAKE SUPERIOR UNTIL HIGH PRESSURE ESTABLISHES ITSELF OVER THE REGION SUNDAY EVENING....THUS WAVES SHOULD GET UP TO 4 TO 6 FT FOR A SHORT PERIOD SUN NIGHT IN THIS AREA. && .AVIATION (FOR THE 12Z TAF ISSUANCE)... MAIN CONCERNS ASSOCIATED WITH TIMING/IMPACTS OF CONVECTIVE ACTIVITY. WHILE MCS CONTINUES TO MOVE SE ACROSS THE MISSISSIPPI VALLEY...BEST CHANCES FOR CONVECTION REMAIN WITH APPROACH/PASSAGE OF COLD FRONT WHICH IS TRIGGERING THUNDERSTORMS ALONG THE RED RIVER VALLEY OF THE NORTH AT THIS TIME. AS THE FRONT MOVED INTO OUR REGION...THERE IS SOME CONCERN THAT IF STRONGER STORMS DEVELOP AS EXPECTED... THEY COULD PRODUCE MVFR CEILINGS AND VISIBILITIES FOR A TIME AT KCMX AND KSAW. IN ADDITION...IF WINDS GO LIGHT ENOUGH OVERNIGHT AFTER THE FRONTAL PASSAGE...THERE IS A POTENTIAL FOR FOG DEVELOPMENT. AT THIS TIME...DO NOT EXPECT WINDS TO SLACKEN ENOUGH TO ALLOW VISIBILITIES TO GO BELOW MVFR. && .MQT WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...VOSS AVIATION/MARINE...RJT
AREA FORECAST DISCUSSION...UPDATED
NWS DULUTH MN
1052 AM CDT SAT AUG 11 2007 .UPDATE...S/W TROF AXIS AND ASSOCIATED UPPER SPEED MAX AND SFC LOW CONTINUE TO TRANSLATE EASTWARD ACROSS THE DAKOTAS LATE THIS MORNING..WITH BEST AXIS OF LARGE SCALE FORCING FOR ASCENT APPARENTLY OVER THE ERN DAKOTAS AND WRN MN ATTM. HOWEVER..EFFECTS OF OVERNIGHT/MORNING CONVECTION AND RESIDUAL BOUNDARIES AND CLOUDS WILL MAKE FOR AN EXCEPTIONALLY COMPLICATED FORECAST FOR THE REST OF TODAY AND THIS EVENING...ESPECIALLY WITH RESPECT TO SEVERE POTENTIAL AND SURFACE-BASED STORMS IN THE DULUTH CWA. INTENSE OVERNIGHT MCS THAT AFFECTED THE I-94 CORRIDOR AND THE TWIN CITIES HAS LAID OUT AN OUTFLOW BOUNDARY THAT CURRENTLY EXTENDS FROM ECENT IOWA..NWWD TO NEAR ALBERT LEA AND MANKATO IN SRN MN..WITH A SECONDARY OUTFLOW BOUNDARY OVER WCENT/SW MN STILL PUSHING SWD..AS EVIDENCED BY STABLE ROLL CLOUD PER VIZ SAT FROM NEAR ST CLOUD TO REDWOOD FALLS. THE INITIAL BOUNDARY FROM THE OVERNIGHT STORMS APPEARS TO BE RATHER DEEP PER LATEST TAMDAR SOUNDINGS IN THE MSP AREA..AND APPARENT STEEP ISENTROPIC UPGLIDE ALONG THIS SURFACE LEADING TO NEW CONVECTIVE INITIATION TO THE SOUTH OF MSP RECENTLY. THE MAIN QUESTION OF THE DAY FOR THE DULUTH CWA IS HOW FAR NORTH WILL THESE BOUNDARIES RETREAT THIS AFTERNOON WITH AID FROM HEATING..AND ALSO FROM WARM ADVECTION AHEAD OF THE APPROACHING WAVE/FRONT. THE BEST BOUNDARY LAYER MOISTURE AND LLJ AXIS IS FORECASTED TO LIE FROM SCENT MN NEWD INTO NW WISCONSIN BY THE 21-03Z TIME FRAME..AND THIS APPEARS TO BE WHERE THE BEST COMBINATION OF CAPE /AOA 2500 J/KG/ DEEP LAYER WIND SHEAR /AOA 45 KTS/ AND LOW LEVEL MASS CONVERGENCE WILL BE LOCATED. IF THE RESIDUAL OUTFLOW BOUNDARY ACROSS SRN MN CAN MIX OUT AND RETREAT NWD AS A WARM FRONT..THE CHANCES FOR SFC BASED STORMS..INCLUDING SUPERCELLS..WILL INCREASE ACROSS THE SRN PART OF THE DLH CWA..PRIMAILY AREAS FROM PINE/CARLTON COUNTIES EWD ACROSS NW WISCONSIN. IF NOT..THE BEST SVR WX THREAT IS LIKELY TO REMAIN JUST SOUTH OF THE DLH CWA INTHE CAPE GRADIENT REGION ALONG THE I94 CORRIDOR. CONVERGENCE ALONG THE FRONT FROM THE BRAINERD LAKES AREA NWD TO VOYAGEURS NATIONAL PARK MAY ALSO BE SUFFICIENT FOR SOME SEVERE STORMS TO INITIATE AND MOVE EASTWARD INTO THE MN ARROWHEAD..WRN LAKE SUPERIOR AND THE TWIN PORTS AREA. UPDATES TO REFLECT ABOVE THINKING IN THE GRIDS AND ASSOCIATED TEXT PRODUCTS ARE ALREADY AVAILABLE..AND WE WILL UPDATE THE HWO IN THE NEXT COUPLE HOURS TO TRY AND REFINE THE THREAT AREAS AND TIMING. MILLER && .AVIATION...MVFR CEILINGS AND VISIBILITIES EXPECTED WITH SCATTERED THUNDERSTORMS THIS AFTERNOON AND EVENING..ESPECIALLY DLH AND HYR. LOW LEVEL JET WILL STRENGTHEN OVER NW WISCONSIN THIS AFTERNOON.. AND MAY RESULT IN MARGINAL LLWS CONDITIONS BY 00Z AND BEYOND. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. LS...NONE. && .PREV DISCUSSION... /ISSUED 308 AM CDT SAT AUG 11 2007/ DISCUSSION... VIGOROUS S/WV MAKING ITS WAY ACRS CWA ATTM AS SFC SYSTEM MOVES E ACRS CENTRAL PLAINS. STRONGEST STORMS JUST S OF OUR CWA NEAR GREATEST INSTABILITY IN AREA WHERE LOLVL JET IS RISING OVR WFNTL BNDRY. SEE SWODY1 FOR DETAILS. MODELS IN GOOD AGMT IN MOVG SYSTEM THRU OUR CWA BY LATE SAT. SUN SHUD BE FAIRLY QUIET AS SFC HIGH SLIDES ACRS THE REGION...WITH POPS INCREASING AGN ON MON AS LOLVL FLOW BECMS SLY ON BACK SIDE OF HIGH AND UPR RIDGE IS FLATTENS OUT BY S/WV MOVG ACRS SRN CN. CONVECTIVE ACTIVITY WILL DEPEND LARGELY ON AMT OF RETURN MSTR AND STRENGTH OF CAP...BUT SLGT OR LOW CHC POPS LOOK RSNBL FOR NOW. AVIATION... VFR CONDITIONS THROUGH THE PERIOD. HOWEVER...SCT THUNDERSTORMS EXPECTED THROUGHOUT THE DAY WITH GUSTY WINDS...MVFR CEILINGS AND VISIBILITIES ACCOMPANYING THE STRONGER STORMS. LLWS EARLY THIS MORNING IN VCNTY OF KDLH WS020/19040KT THROUGH 12Z. && POINT TEMPS/POPS... DLH 82 59 77 51 / 50 40 10 0 INL 82 55 74 52 / 50 10 10 0 BRD 85 60 80 57 / 60 20 10 0 HYR 85 61 84 44 / 40 60 10 0 ASX 83 61 79 47 / 40 60 10 0 && $$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
335 PM CDT SAT AUG 11 2007 .DISCUSSION REGARDING AFTERNOON GRIDS/FCST... 335 PM CDT MAIN FCST CONCERNS THIS PERIOD ARE TRACKING OF EXPECTED MCS TO PASS MAINLY TO THE NORTH OF IL OVERNIGHT TNGT AND NEXT MCS EXPECTED TO DVLP ACROSS THE PLAINS AND PUSH INTO THE WESTERN GREAT LAKES MONDAY NIGHT INTO EARLY TUESDAY. 19Z SURFACE ANALYSIS SHOWING SPRAWLING HIGH PRES FROM LAKE HURON ACROSS LAKE ERIE INTO THE OHIO VALLEY. AS THIS AREA OF HIGH PRESSURE CONTINUES TO SLOWLY DRIFT EAST... BROAD SCALE SUBSIDENCE WITH THIS FEATURE HELPING TO MAINTAIN MAINLY CLEAR SKIES THIS EVENING DESPITE THIN CI CONVECTIVE DEBRIS MOVING OVER THE AREA. RETURN SOUTHERLY FLOW INCREASING RAPIDLY ACROSS NRN IL LATE THIS AFTERNOON AS SFC PRESSURE GRADIENT TIGHTENS IN THE WAKE OF DEPARTING SFC HIGH WITH RFD GUSTING TO 22 MPH AT 19Z. SFC DEW POINTS HAVE MIXED OUT LOWERING TO A SOMEWHAT MORE COMFORTABLE 62 TO 65 DEG F RANGE PER 20Z OBS... HOWEVER WITH SOUTHERLY FLOW INCREASING... AND DEW POINTS AROUND 70 ACROSS CENTRAL IL... EXPECT HIGHER DEW POINT AIR TO RETURN THIS EVENING. THIS WILL LIMIT FALL OF TEMPS OVERNIGHT AND HAVE GONE SLIGHTLY ABOVE GUIDANCE ON MINS. MAIN FORCING FOR CONVECTIVE DEVELOPMENT APPEARS TO BE WELL NORTH OF IL TNGT CLOSER TO FAST MOVING UPPER LEVEL SHORT WAVE TROUGH PROGGED TO PUSH INTO THE NORTHERN GREAT LAKES. AREA OF LOW LVL WARM AIR ADVECTION AND ISENTROPIC LIFT PER 310K THETA SURFACE PROGS BULLSEYED TO OUR NORTH CLOSER TO TRACK OF H850 LOW/TROUGH. MAY SEE BKN LINE OF CONVECTION DEVELOP FARTHER SOUTH ALONG WEAK SFC COLD FRONT EXTENDING TO THE SOUTHWEST OF THE PARENT LOW HOWEVER. THE SOUTHERN EXTENT OF SUCH A POSSIBLE LINE MAY BRUSH THE FAR NORTHERN SECTIONS OF IL LATE TNGT AFTER MIDNIGHT. WEAK COLD FRONT SAGS SOUTH INTO FAR NRN IL BY 12Z SUN AND THEN REACHES CLOSE TO I-80 BY 18Z. EXPECT BREAK IN PRECIPITATION CHANCES GIVEN MINIMAL LOW LEVEL CONVERGENCE ALONG THE BOUNDARY AND LACK OF ANY REAL UPPER LEVEL SUPPORT WITH FROPA DURING THE MORNING ON SUN. AS INSTABILITY INCREASES DURING THE AFTERNOON WOULD EXPECT TO SEE ISOLATED TO SCATTERED TSTMS DEVELOP ALONG THE BOUNDARY AS IT CONTINUES TO SAG SOUTH OF I-80 AND EXITS THE CWFA BY EVENING. 1024 MB SFC HIGH BUILDS INTO THE WESTERN GREAT LAKES BY 12Z MON WITH A MODEST NORTHEASTERLY FLOW ACROSS THE AREA. WITH INCREASING DRYING IN THE LOW LEVELS AND SUBSIDENCE ALOFT WILL EXPECT SKIES TO GENERALLY CLEAR SUN NIGHT. MONDAY LOOKS SOMEWHAT LIKE A REPEAT OF TODAY (SATURDAY) WITH A WEAK NE FLOW AND MODEST LAKE BREEZES. H850 TEMPS SIMILAR RANGING FROM 18-21 DEG C SO EXPECT MAXES TO REACH UPPER 80S ON MON. MORE INTERESTING SCENARIO DEVELOPING FOR MONDAY NIGHT AS SFC HIGH PRESSURE RIDGE DEPARTS FOR THE EASTERN GREAT LAKES. NEXT IN A SERIES OF UPPER LEVEL IMPULSES SLIDES ESE IN NW FLOW ALOFT ACROSS THE PLAINS INTO THE WESTERN GREAT LAKES. 45 KT LOW LVL JET PROGGED FOR MONDAY NIGHT OVER THE PLAINS COMBINED WITH FAVORABLE UPPER DYNAMICS SHOULD ENABLE MCS TO DEVELOP AND THEN TRACK ESE INTO NRN IL LATE MONDAY NIGHT/EARLY TUESDAY. WITH THIS FEATURE TRACKING QUITE A BIT FARTHER SOUTH THEN THE FIRST... JUST ABOUT ALL AREAS ALONG AND NORTH OF I-80 STAND A GOOD CHANCE FOR PCPN WITH DIMINISHING CHANGES AS ONE GOES SOUTH OF I-80. YET ANOTHER CHANCE FOR PRECIPITATION WILL COME WED AS THE WEAK SURFACE COLD FRONT ASSOCIATED WITH EARLY TUESDAYS MCS DROPS SOUTH OF THE FORECAST AREA AND STALLS SOUTH OF I-80. WITH YET ANOTHER UPR LVL SHORT WAVE GLIDING ACROSS VIA THE WNW FLOW ALOFT MAY BE SETTING UP A GOOD SCENARIO FOR OVERRUNNING ELEVATED CONVECTION FOR WED AND WED NIGHT. WITH THIS HAVE MAINTAINED CHC POPS THIS PERIOD., BOUNDARY PROGGED TO SAG FURTHER SOUTH THURSDAY. WITH THIS THOUGHT HAVE LEFT POPS OUT FOR NOW... HOWEVER A MORE NORTHERLY PRESENCE WOULD RESULT IN A CONTINUED CHC OF RAIN ACROSS NRN IL AND THIS WILL HAVE TO BE WATCHED CLOSELY. ED F && .AVIATION... 1235 PM A WEAK LAKE BREEZE SEEMS TO BE OCCURRING AS THE WIND AT ORD IS FROM THE EAST. THE ACARS SOUNDING SHOWS A SOUTHEAST WIND UP TO 5450 FT AT ORD AT 1622 UTC. HIGH PRESSURE OVER MICHIGAN WILL PROVIDE A SOUTHEAST WIND IN NORTHWEST INDIANA AND NORTHEAST ILLINOIS THIS AFTERNOON AND EVENING. AS THE FRONT APPROACHES NORTHWEST ILLINOIS TONIGHT SOME SHOWERS AND THUNDERSTORMS MAY DEVELOP AFTER 06 UTC IN FAR NORTHERN ILLINOIS. SOME OF THESE THUNDERSTORMS MAY APPROACH ROCKFORD BUT WE FEEL THEY MAY REMAIN NORTH OF THE CITY. THUNDER MAY BE HEARD AT THE AIRPORT. THE FRONT WILL PASS THROUGH ROCKFORD AROUND 1400 UTC AND THROUGH ORD AROUND 16 TO 17 UTC. WE WILL FORECAST A WIND SHIFT TO 300 TO 310 DEGREES WITH A WIND SPEED OF 10 TO 13 KNOTS. THERE MAY BE SOME FOG IN THE MORNING BUT IT WILL BE GROUND FOG. THE FOG WILL BE DISSIPATED BY 8 AM CDT ACROSS MOST AREAS. WE USED THE GFS AND LOCALLY RUN WRF MODEL FOR TIMING OF THE FRONT AND WIND DIRECTION FORECAST. && .MARINE DISCUSSION... 300 PM CDT WE EXPECT THE WIND SPEED TO INCREASE LATER TONIGHT. THE LOW IN CANADA WILL DEEPEN AND INCREASE THE PRESSURE GRADIENT BETWEEN IT AND THE HIGH OVER LAKE EIRE. THE COLD FRONT WILL BRING A WIND SHIFT ACROSS THE LAKE BY SUNDAY AFTERNOON. A HIGH WILL MOVE INTO LAKE MICHIGAN AND WE EXPECT THE WIND TO DECREASE FOR MONDAY THROUGH TUESDAY. TUESDAY NIGHT ANOTHER LOW WILL HAVE MOVED A COLD FRONT THROUGH LAKE MICHIGAN AND ANOTHER HIGH OVER CANADA WILL SPREAD INTO THE GREAT LAKES BY WEDNESDAY MORNING. WE USED THE GFS MODEL AND LOCALLY RUN WRF MODEL FOR THE WIND FORECAST. && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
255 PM CDT SAT AUG 11 2007 .DISCUSSION REGARDING MORNING ZONES/GRIDS... 355 AM CDT ERLY MORNING SFC ANALYSIS SHOWS HIGH PRES OVR UPR GRTLKS RGN AS EXPECTED. LARGE SCALE SUBSIDENCE ASSD WITH THIS FEATURE WILL KEEP SKIES GENLY CLR TDY. IN ADDN...RATHER SHARP AMPLITUDE TO MID LVL RIDGE THAT HAS SHIFTED EWD OVR WRN GRTLKS HAS BEEN ACTING AS A BLOCK TO MOST CONVECTIVE DEBRIS FROM STORMS OVR PLAINS...HOWEVER...INTENSE BOWING CLUSTER OVR MN ATTM MAY SPREAD SOME HIGH CLOUDS ACROSS AREA THIS MORNING. NONETHELESS...WILL KEEP CHARACTER OF THE DAY MOSTLY SUNNY. TEMPS TO RESPOND WELL TO SUNSHINE AND MOST AREAS SHOULD SEE MERCURY CLIMB TO AT OR JUST ABV 90. EXCEPTION WILL BE EXTRM NERN IL DUE TO ELY-SELY WIND OFF LK. WIL GO A DEGREE OR TWO ABV GUID FOR LOWS TNGT AS WELL. SFC FLOW TO VEER INTO SW AHD OF APCHG COLD FRONT AND CLOUD COVG ALSO EXPECTED TO INCRS. IN ADDITION...SFC OBS SHOW THAT DEW POINTS HAVE CREPT UP TO NR 70 AGN...AND WITH FETCH TO BCM MORE SLY HEADING INTO TNGT...DON`T EXPECT THESE TO LWR ANY. AS FAR AS PCPN IS CONCERNED...FRONT APCHG FROM NW COULD PROVIDE FOR SOME CONVECTION LATER TNGT INTO SUNDAY. HOWEVER...SHORT WAVE NOW OVR SRN SASK...ERN MT IS FCST TO BE EAST OF AREA BY 12Z SUN...AND WITH LOSS OFF INSTABILITY OVERNIGHT...SEE LTL REASON TO HAVE PCPN IN FCST XCP PERHAPS FOR NRN TIER OF CTYS TNGT AS THIS BETTER UPR LVL SUPPORT AND FORCING FOR STORMS PASSES TO N...ACROSS UPR GRTLKS...POSSIBLY CLIPPING AREA NR WI STA LN. ON SUNDAY...EXPECTED FRONTAL TIMING IS POOR FOR MOST OF FA...BUT WITH THIS BOUNDARY MOVG THRU SRN/SERN PORTION OF AREA DURG MID AFTN ...INSTABILITY MAY BE SUFFICIENT BY THAT TIME TO POP SOME ISOLD-SCT TSTMS. HIGH PRES ONCE AGAIN BUILDS ACROSS UPR GRTLKS IN WAKE OF DEPARTING SHRT WAVE SUN NGT-MON SO WILL GO WITH CLRG SUN NGT. WITH HIGH PRES RIDGE SETTLING SWD ACROSS WRN GRTLKS...EXPECT CONDS SUN NGT-MON MRNG TO BE SIMILAR TO TDY. LOOKS GOOD AT THIS POINT FOR VIEWING PERSIEDS SUN NGT. NOT A WHOLE LOT OF CHG TO GOING FCST THRU NXT WEEK...ALTHOUGH GFS IS WAVERING ON DEGREE OF COOLING FCST LATE IN PERIOD. HUGE SPRAWLING UPR HI OVR MID CONUS TO RMN IN PLACE WITH SMALL IMPULSES RIDING ALG ITS PERIPHERY...FROM THE NRN PLAINS ESEWD ACROSS GRTLKS RGN. THIS SCENARIO SUPPORTS FCST OF RECURRING WAVE PASSAGES WITH ABOUT A 36-48 HR PERIODICITY. RIGHT NOW...EXPECT MONDAY TO BE SIMILAR TO TDY AS ANOTHER SFC RIDGE DROPS SEWD ACROSS MIDWEST...THEN WAA PATN STRENGTHENS AHD OF ANOTHER SHRT WAVE/FRONTAL PASSAGE TUES MRNG /...DITTO SUNDAY.../ BEST LLVL FORCING ONCE AGAIN SLATED FOR UPR MIDWEST SO WILL KEEP PCPN MENTION OUT OF FA FOR NOW. WX COULD TURN WETTER HERE MIDWEEK AS GFS SUGGESTS OVERRUNNING/ELEVATED CONVECTION SET UP AS TUESDAY`S FRONT STALL OUT S OF AREA AND YET ANOTHER SHRT WAVE RIPPLES SEWD THROUGH UPR MS VLY. BASED ON THIS...WILL MAINTAIN CHC POPS WED-WED NGT. MERZLOCK && .AVIATION... 1235 PM A WEAK LAKE BREEZE SEEMS TO BE OCCURRING AS THE WIND AT ORD IS FROM THE EAST. THE ACARS SOUNDING SHOWS A SOUTHEAST WIND UP TO 5450 FT AT ORD AT 1622 UTC. HIGH PRESSURE OVER MICHIGAN WILL PROVIDE A SOUTHEAST WIND IN NORTHWEST INDIANA AND NORTHEAST ILLINOIS THIS AFTERNOON AND EVENING. AS THE FRONT APPROACHES NORTHWEST ILLINOIS TONIGHT SOME SHOWERS AND THUNDERSTORMS MAY DEVELOP AFTER 06 UTC IN FAR NORTHERN ILLINOIS. SOME OF THESE THUNDERSTORMS MAY APPROACH ROCKFORD BUT WE FEEL THEY MAY REMAIN NORTH OF THE CITY. THUNDER MAY BE HEARD AT THE AIRPORT. THE FRONT WILL PASS THROUGH ROCKFORD AROUND 1400 UTC AND THROUGH ORD AROUND 16 TO 17 UTC. WE WILL FORECAST A WIND SHIFT TO 300 TO 310 DEGREES WITH A WIND SPEED OF 10 TO 13 KNOTS. THERE MAY BE SOME FOG IN THE MORNING BUT IT WILL BE GROUND FOG. THE FOG WILL BE DISSIPATED BY 8 AM CDT ACROSS MOST AREAS. WE USED THE GFS AND LOCALLY RUN WRF MODEL FOR TIMING OF THE FRONT AND WIND DIRECTION FORECAST. && .MARINE DISCUSSION... 300 PM CDT WE EXPECT THE WIND SPEED TO INCREASE LATER TONIGHT. THE LOW IN CANADA WILL DEEPEN AND INCREASE THE PRESSURE GRADIENT BETWEEN IT AND THE HIGH OVER LAKE EIRE. THE COLD FRONT WILL BRING A WIND SHIFT ACROSS THE LAKE BY SUNDAY AFTERNOON. A HIGH WILL MOVE INTO LAKE MICHIGAN AND WE EXPECT THE WIND TO DECREASE FOR MONDAY THROUGH TUESDAY. TUESDAY NIGHT ANOTHER LOW WILL HAVE MOVED A COLD FRONT THROUGH LAKE MICHIGAN AND ANOTHER HIGH OVER CANADA WILL SPREAD INTO THE GREAT LAKES BY WEDNESDAY MORNING. WE USED THE GFS MODEL AND LOCALLY RUN WRF MODEL FOR THE WIND FORECAST. && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1235 PM CDT SAT AUG 11 2007 .DISCUSSION REGARDING MORNING ZONES/GRIDS... 355 AM CDT ERLY MORNING SFC ANALYSIS SHOWS HIGH PRES OVR UPR GRTLKS RGN AS EXPECTED. LARGE SCALE SUBSIDENCE ASSD WITH THIS FEATURE WILL KEEP SKIES GENLY CLR TDY. IN ADDN...RATHER SHARP AMPLITUDE TO MID LVL RIDGE THAT HAS SHIFTED EWD OVR WRN GRTLKS HAS BEEN ACTING AS A BLOCK TO MOST CONVECTIVE DEBRIS FROM STORMS OVR PLAINS...HOWEVER...INTENSE BOWING CLUSTER OVR MN ATTM MAY SPREAD SOME HIGH CLOUDS ACROSS AREA THIS MORNING. NONETHELESS...WILL KEEP CHARACTER OF THE DAY MOSTLY SUNNY. TEMPS TO RESPOND WELL TO SUNSHINE AND MOST AREAS SHOULD SEE MERCURY CLIMB TO AT OR JUST ABV 90. EXCEPTION WILL BE EXTRM NERN IL DUE TO ELY-SELY WIND OFF LK. WIL GO A DEGREE OR TWO ABV GUID FOR LOWS TNGT AS WELL. SFC FLOW TO VEER INTO SW AHD OF APCHG COLD FRONT AND CLOUD COVG ALSO EXPECTED TO INCRS. IN ADDITION...SFC OBS SHOW THAT DEW POINTS HAVE CREPT UP TO NR 70 AGN...AND WITH FETCH TO BCM MORE SLY HEADING INTO TNGT...DON`T EXPECT THESE TO LWR ANY. AS FAR AS PCPN IS CONCERNED...FRONT APCHG FROM NW COULD PROVIDE FOR SOME CONVECTION LATER TNGT INTO SUNDAY. HOWEVER...SHORT WAVE NOW OVR SRN SASK...ERN MT IS FCST TO BE EAST OF AREA BY 12Z SUN...AND WITH LOSS OFF INSTABILITY OVERNIGHT...SEE LTL REASON TO HAVE PCPN IN FCST XCP PERHAPS FOR NRN TIER OF CTYS TNGT AS THIS BETTER UPR LVL SUPPORT AND FORCING FOR STORMS PASSES TO N...ACROSS UPR GRTLKS...POSSIBLY CLIPPING AREA NR WI STA LN. ON SUNDAY...EXPECTED FRONTAL TIMING IS POOR FOR MOST OF FA...BUT WITH THIS BOUNDARY MOVG THRU SRN/SERN PORTION OF AREA DURG MID AFTN ...INSTABILITY MAY BE SUFFICIENT BY THAT TIME TO POP SOME ISOLD-SCT TSTMS. HIGH PRES ONCE AGAIN BUILDS ACROSS UPR GRTLKS IN WAKE OF DEPARTING SHRT WAVE SUN NGT-MON SO WILL GO WITH CLRG SUN NGT. WITH HIGH PRES RIDGE SETTLING SWD ACROSS WRN GRTLKS...EXPECT CONDS SUN NGT-MON MRNG TO BE SIMILAR TO TDY. LOOKS GOOD AT THIS POINT FOR VIEWING PERSIEDS SUN NGT. NOT A WHOLE LOT OF CHG TO GOING FCST THRU NXT WEEK...ALTHOUGH GFS IS WAVERING ON DEGREE OF COOLING FCST LATE IN PERIOD. HUGE SPRAWLING UPR HI OVR MID CONUS TO RMN IN PLACE WITH SMALL IMPULSES RIDING ALG ITS PERIPHERY...FROM THE NRN PLAINS ESEWD ACROSS GRTLKS RGN. THIS SCENARIO SUPPORTS FCST OF RECURRING WAVE PASSAGES WITH ABOUT A 36-48 HR PERIODICITY. RIGHT NOW...EXPECT MONDAY TO BE SIMILAR TO TDY AS ANOTHER SFC RIDGE DROPS SEWD ACROSS MIDWEST...THEN WAA PATN STRENGTHENS AHD OF ANOTHER SHRT WAVE/FRONTAL PASSAGE TUES MRNG /...DITTO SUNDAY.../ BEST LLVL FORCING ONCE AGAIN SLATED FOR UPR MIDWEST SO WILL KEEP PCPN MENTION OUT OF FA FOR NOW. WX COULD TURN WETTER HERE MIDWEEK AS GFS SUGGESTS OVERRUNNING/ELEVATED CONVECTION SET UP AS TUESDAY`S FRONT STALL OUT S OF AREA AND YET ANOTHER SHRT WAVE RIPPLES SEWD THROUGH UPR MS VLY. BASED ON THIS...WILL MAINTAIN CHC POPS WED-WED NGT. MERZLOCK && .AVIATION... 1235 PM A WEAK LAKE BREEZE SEEMS TO BE OCCURRING AS THE WIND AT ORD IS FROM THE EAST. THE ACARS SOUNDING SHOWS A SOUTHEAST WIND UP TO 5450 FT AT ORD AT 1622 UTC. HIGH PRESSURE OVER MICHIGAN WILL PROVIDE A SOUTHEAST WIND IN NORTHWEST INDIANA AND NORTHEAST ILLINOIS THIS AFTERNOON AND EVENING. AS THE FRONT APPROACHES NORTHWEST ILLINOIS TONIGHT SOME SHOWERS AND THUNDERSTORMS MAY DEVELOP AFTER 06 UTC IN FAR NORTHERN ILLINOIS. SOME OF THESE THUNDERSTORMS MAY APPROACH ROCKFORD BUT WE FEEL THEY MAY REMAIN NORTH OF THE CITY. THUNDER MAY BE HEARD AT THE AIRPORT. THE FRONT WILL PASS THROUGH ROCKFORD AROUND 1400 UTC AND THROUGH ORD AROUND 16 TO 17 UTC. WE WILL FORECAST A WIND SHIFT TO 300 TO 310 DEGREES WITH A WIND SPEED OF 10 TO 13 KNOTS. THERE MAY BE SOME FOG IN THE MORNING BUT IT WILL BE GROUND FOG. THE FOG WILL BE DISSIPATED BY 8 AM CDT ACROSS MOST AREAS. WE USED THE GFS AND LOCALLY RUN WRF MODEL FOR TIMING OF THE FRONT AND WIND DIRECTION FORECAST. && .MARINE DISCUSSION... 300 AM CDT THE HIGH PRESSURE THAT BROUGHT CALM WINDS/WAVES TO LAKE MICHIGAN WILL CONTINUE TO SLOWLY SETTLE SOUTHEAST OVER THE EASTERN GREAT LAKES TODAY...WHILE LOW PRESSURE DEVELOPS IN SOUTHERN MANITOBA. THE LOW WILL TRACK NORTHEAST TOWARD HUDSON BAY BY SUNDAY MORNING. AS THIS HAPPENS...PRESSURE GRADIENTS ACROSS THE LAKE WILL STRENGTHEN AND WINDS WILL BEGIN TO INCREASE. AS THE LOW TRACKS NORTHEASTWARD...A COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN ON SUNDAY...TURNING WINDS NORTHERLY AND INCREASING TO AROUND 20KT. ANOTHER HIGH PRESSURE AREA WILL BUILD IN BEHIND THE FRONT OVER THE NORTHERN PLAINS SUNDAY AND THE UPPER GREAT LAKES SUNDAY NIGHT. A LOW WILL MOVE OUT OF THE CANADIAN ROCKIES MONDAY MORNING AND TRACK EAST ACROSS ONTARIO ON MONDAY NIGHT AND TUESDAY WITH AN ASSOCIATED COLD FRONT MOVING THROUGH THE WESTERN GREAT LAKES REGION TUESDAY. KREIN && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
AREA FORECAST DISCUSSION...UPDATED
NWS MARQUETTE MI
200 PM EDT SAT AUG 11 2007 .UPDATE...ISSUED 1120 AM EDT SAT AUG 11 2007 COMMA HEAD PORTION OF AN MCV...ORIGINATING FROM THE MCS OVER MN EARLIER THIS MORNING...SUPPORTED AN AREA OF SHOWERS OVER W UPR MI. MUCAPE VALUES INTO THE 1000-1500 J/KG RANGE COULD ALSO SUPPORT AN ISOLD TSRA EVEN THOUGH NO CLOUD TO GROUND LIGHTNING WAS NOTED WITH THIS FEATURE THROUGH 15Z. OTHERWISE...CONVECTIVE DEBRIS MID/HIGH CLOUDS COVERED MUCH OF WEST/CNTRL UPPER MI. ALTHOUGH UPSTREAM SFC PATTERN WAS COMPLICATED BY NUMEROUS OUTFLOW BOUNDARIES...MAIN COLD FRONT WAS MOVING THROUGH NW MN AT 15Z AND SHOULD MOVE INTO NW BY 00Z. EXPECT THE SHRA FROM THE MCV TO SLOWLY WEAKEN OR DISSIPATE IN THE EARLY AFTERNOON. THE LEFTOVER CLOUDS SHOULD HOLD DOWN SFC HEATING AND TEMP RECOVERY KEEPING MAX READINGS MAINLY IN THE LOWER TO MID 80S. KMPX/KINL AND AREA TAMDAR SNDGS SUGGEST CAPPING SHOULD PREVAIL ENOUGH TO PREVENT SFC BASED CONVECTION UNTIL THE FRONT AND ASSOCIATE LOW LVL CONV FROM MN MOVES INTO THE AREA. SO...SOME SCT SHRA/TSRA MAY DEVELOP AND MOVE INTO W UPPER MI LATE THIS AFTERNOON AS THE FRONT APPROACHES. DISCUSSION...ISSUED 535 AM EDT SAT AUG 11 2007 CONCERNS FOCUS ON THUNDERSTORMS CHCS TODAY AND TONIGHT AND POTENTIAL FOR SVR. LINEAR MCS MOVING FROM MN INTO WRN WI AS NOTED ON SATELLITE IMAGERY AND RADAR LOOPS SUPPORTED BY LIFT/MOISTURE AT NOSE OF 40 KT LOW-LVL JET. LATEST RUC MODEL INDICATES DIFFLUENT THCKNS SHOULD CONTINUE TO PUSH MCS AWAY FROM UPR MI AS IT WEAKENS IN MORE STABLE ENVIRONMENT OVER WI. TODAY...GFS SNDGS SHOW GENERALLY A CAPPED ATMOSPHERE OVER UPR MI AHEAD OF INCOMING COLD FRONT OVER THE PLAINS. CLOUDS FROM MCS OVER WI COULD ALSO ENHANCE CAPPED ENVIRONMENT. MODEL SNDGS SUGGEST WE MAY HAVE TO WAIT UNTIL LATE AFTERNOON AS INSTABILITY BUILDS AND THE COLD FRONT DRAWS NEAR BEFORE CONVECTION FIRES OVER THE WRN HALF COUNTIES. KEPT IN CHC POPS FOR THE WEST HALF AS THE 850 MB THETA-E RDG NOSES INTO THE AREA AND MLCAPES INCREASE TO 1000-1500 J/KG PER GFS. TONIGHT...EXPECT CAP TO ERODE BY LATE AFTERNOON AND EVENING WITH HEIGHT FALLS FROM APPROACHING SHORTWAVE AND INCREASING INSTABILITY (MLCAPE VALUES 1000-1500 J/KG). THIS SHOULD ALLOW CONVECTION TO SPREAD INTO UPPER MI. 40-50 KT FCST MID LEVEL WINDS WOULD SUPPORT SHEAR VALUES SUFFICIENT FOR SUPERCELLS. 06Z NAM AND RUC13 HINT THAT CONVECTION COULD EVOLVE INTO A LINEAR MCS AS IT MOVES THROUGH UPPER MI WITH DAMAGING WINDS AND SOME LARGE HAIL AS THE MAIN HAZARDS PER SPC DAY1 OUTLOOK. GIVEN PROGRESSIVE NATURE OF THE CONVECTION...DO NOT EXPECT VERY HIGH PRECIP AMOUNTS FROM CONVECTION. BUMPED UP POPS TO LIKELY OVER WRN HALF COUNTIES WHERE MODELS FCST THE BEST INSTABILITY AND UPR DIV TO BE. KEPT HIGH CHC POPS IN FOR ERN COUNTIES. SUN AND MON...MODELS TRENDING FASTER WITH DEPARTURE OF COLD FRONT SO DROPPED POPS FOR ERN COUNTIES ON SUN AND WENT WITH A DRY FCST. CAA AND STRONG DRYING TAKES OVER WITH ENHANCED MIXING RESULTING IN GUSTY NW WINDS TO 25 MPH. MIXING OF DRIER AIR TO THE SFC WILL RESULT IN DEWPOINTS IN THE 40S ON SUN AND RH VALUES IN THE 30 TO 40 PERCENT RANGE. HIGH PRES WILL DOMINATE FROM SUN NIGHT INTO MON WITH DRY WEATHER IN STORE. THE GRADIENT SHOULD REMAIN WEAK ENOUGH MON FOR LAKE BREEZE DEVELOPMENT. MON NIGHT AND TUE...MODELS STILL CONSISTENT WITH BRINGING IN NEXT SIGNIFICANT SHORTWAVE AND SFC FRONT THROUGH THE AREA BY TUE MORNING. WILL KEEP GOING FCST CHC POPS MON NIGHT AHEAD OF THIS SYSTEM. LIMITED MOISTURE RECOVERY MAY HINDER CHC OF SIGNIFICANT RAINFALL. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)...WINDS ARE EXPECTED TO GENERALLY REMAIN BELOW 20 KT THROUGH THE DAY...HOWEVER A FEW GUSTS TO AROUND 25 KT ARE EXPECTED OVER EASTERN LAKE SUPERIOR FOR A SHORT TIME AROUND MIDNIGHT TONIGHT WITH THE PASSAGE OF THE COLD FRONT. SUNDAY AFTERNOON...A FEW GUSTS TO AROUND 25 KT AGAIN POSSIBLE OVER EASTERN LAKE SUPERIOR UNTIL HIGH PRESSURE ESTABLISHES ITSELF OVER THE REGION SUNDAY EVENING....THUS WAVES SHOULD GET UP TO 4 TO 6 FT FOR A SHORT PERIOD SUN NIGHT IN THIS AREA. && .AVIATION (FOR THE 18 TAF ISSUANCE)... AREA OF RAIN OVER CENTRAL AND WEST UPPER MI WERE ASSOCIATED WITH MCV GENERATED BY CONVECTION OVER MN LAST NIGHT. ELEVATED INSTABILITY WAS JUST ENOUGH TO SUPPORT ISOLD TSRA OVER MAINLY SW UPPER MI. EXPECT THE SHRA/TSRA TO DISSIPATE THIS AFTERNOON. ANOTHER BAND OF SHRA/TSRA IS EXPECTED TO DEVELOP LATE THIS AFTERNOON AND EVENING AHEAD OF A COLD FRONT. THE FRONT AND ASSOCIATED SHRA/TSRA SHOULD MOVE THROUGH MAINLY BTWN 00Z-04Z WITH POTENTIAL FOR MVFR CIGS/VSBY ALONG WITH LCL STRONG WIND GUSTS. NW WINDS BEHIND THE FRONT SHOULD BRING CIGS/VSBYS BACK UP TO VFR BY DAYBREAK WITH GUSTY NW WINDS DEVELOPING DURING THE MORNING. && .MQT WATCHES/WARNINGS/ADVISORIES...NONE. && $$ DISCUSSION...VOSS AVIATION/MARINE...RJT
AREA FORECAST DISCUSSION...UPDATED
NWS DULUTH MN
1142 AM CDT SAT AUG 11 2007 .UPDATE... MINOR REVISIONS OF POPS AND TEMPERATURES THROUGHOUT THE AFTERNOON. && .DISCUSSION... SHOWERS AND THUNDERSTORMS ARE POPPING UP ALMOST AT RANDOM IN THE MOIST AIR AHEAD OF A COLD FRONT ATTM. THE DISORGANIZED AND WIDESPREAD NATURE OF THE SHOWERS WILL ACT TO MITIGATE THE THREAT OF VIGOROUS THUNDERSTORMS...ESPECIALLY OVER NORTHEAST MINNESOTA FOR THE NEXT SEVERAL HOURS. THE FRONT SHOULD CHASE PRECIPITATION EASTWARD AND OUT OF MOST AREAS LATE THIS EVENING. STRONG HIGH PRESSURE FROM SASKATCHEWAN WILL DRY THINGS OUT CSDRBLY LATE TONIGHT AND ON SUNDAY. && .PREV DISCUSSION... /ISSUED 1052 AM CDT SAT AUG 11 2007/ UPDATE...S/W TROF AXIS AND ASSOCIATED UPPER SPEED MAX AND SFC LOW CONTINUE TO TRANSLATE EASTWARD ACROSS THE DAKOTAS LATE THIS MORNING..WITH BEST AXIS OF LARGE SCALE FORCING FOR ASCENT APPARENTLY OVER THE ERN DAKOTAS AND WRN MN ATTM. HOWEVER..EFFECTS OF OVERNIGHT/MORNING CONVECTION AND RESIDUAL BOUNDARIES AND CLOUDS WILL MAKE FOR AN EXCEPTIONALLY COMPLICATED FORECAST FOR THE REST OF TODAY AND THIS EVENING...ESPECIALLY WITH RESPECT TO SEVERE POTENTIAL AND SURFACE-BASED STORMS IN THE DULUTH CWA. INTENSE OVERNIGHT MCS THAT AFFECTED THE I-94 CORRIDOR AND THE TWIN CITIES HAS LAID OUT AN OUTFLOW BOUNDARY THAT CURRENTLY EXTENDS FROM ECENT IOWA..NWWD TO NEAR ALBERT LEA AND MANKATO IN SRN MN..WITH A SECONDARY OUTFLOW BOUNDARY OVER WCENT/SW MN STILL PUSHING SWD..AS EVIDENCED BY STABLE ROLL CLOUD PER VIZ SAT FROM NEAR ST CLOUD TO REDWOOD FALLS. THE INITIAL BOUNDARY FROM THE OVERNIGHT STORMS APPEARS TO BE RATHER DEEP PER LATEST TAMDAR SOUNDINGS IN THE MSP AREA..AND APPARENT STEEP ISENTROPIC UPGLIDE ALONG THIS SURFACE LEADING TO NEW CONVECTIVE INITIATION TO THE SOUTH OF MSP RECENTLY. THE MAIN QUESTION OF THE DAY FOR THE DULUTH CWA IS HOW FAR NORTH WILL THESE BOUNDARIES RETREAT THIS AFTERNOON WITH AID FROM HEATING..AND ALSO FROM WARM ADVECTION AHEAD OF THE APPROACHING WAVE/FRONT. THE BEST BOUNDARY LAYER MOISTURE AND LLJ AXIS IS FORECASTED TO LIE FROM SCENT MN NEWD INTO NW WISCONSIN BY THE 21-03Z TIME FRAME..AND THIS APPEARS TO BE WHERE THE BEST COMBINATION OF CAPE /AOA 2500 J/KG/ DEEP LAYER WIND SHEAR /AOA 45 KTS/ AND LOW LEVEL MASS CONVERGENCE WILL BE LOCATED. IF THE RESIDUAL OUTFLOW BOUNDARY ACROSS SRN MN CAN MIX OUT AND RETREAT NWD AS A WARM FRONT..THE CHANCES FOR SFC BASED STORMS..INCLUDING SUPERCELLS..WILL INCREASE ACROSS THE SRN PART OF THE DLH CWA..PRIMAILY AREAS FROM PINE/CARLTON COUNTIES EWD ACROSS NW WISCONSIN. IF NOT..THE BEST SVR WX THREAT IS LIKELY TO REMAIN JUST SOUTH OF THE DLH CWA INTHE CAPE GRADIENT REGION ALONG THE I94 CORRIDOR. CONVERGENCE ALONG THE FRONT FROM THE BRAINERD LAKES AREA NWD TO VOYAGEURS NATIONAL PARK MAY ALSO BE SUFFICIENT FOR SOME SEVERE STORMS TO INITIATE AND MOVE EASTWARD INTO THE MN ARROWHEAD..WRN LAKE SUPERIOR AND THE TWIN PORTS AREA. UPDATES TO REFLECT ABOVE THINKING IN THE GRIDS AND ASSOCIATED TEXT PRODUCTS ARE ALREADY AVAILABLE..AND WE WILL UPDATE THE HWO IN THE NEXT COUPLE HOURS TO TRY AND REFINE THE THREAT AREAS AND TIMING. MILLER AVIATION...MVFR CEILINGS AND VISIBILITIES EXPECTED WITH SCATTERED THUNDERSTORMS THIS AFTERNOON AND EVENING..ESPECIALLY DLH AND HYR. LOW LEVEL JET WILL STRENGTHEN OVER NW WISCONSIN THIS AFTERNOON.. AND MAY RESULT IN MARGINAL LLWS CONDITIONS BY 00Z AND BEYOND. DLH WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. LS...NONE. PREV DISCUSSION... /ISSUED 308 AM CDT SAT AUG 11 2007/ DISCUSSION... VIGOROUS S/WV MAKING ITS WAY ACRS CWA ATTM AS SFC SYSTEM MOVES E ACRS CENTRAL PLAINS. STRONGEST STORMS JUST S OF OUR CWA NEAR GREATEST INSTABILITY IN AREA WHERE LOLVL JET IS RISING OVR WFNTL BNDRY. SEE SWODY1 FOR DETAILS. MODELS IN GOOD AGMT IN MOVG SYSTEM THRU OUR CWA BY LATE SAT. SUN SHUD BE FAIRLY QUIET AS SFC HIGH SLIDES ACRS THE REGION...WITH POPS INCREASING AGN ON MON AS LOLVL FLOW BECMS SLY ON BACK SIDE OF HIGH AND UPR RIDGE IS FLATTENS OUT BY S/WV MOVG ACRS SRN CN. CONVECTIVE ACTIVITY WILL DEPEND LARGELY ON AMT OF RETURN MSTR AND STRENGTH OF CAP...BUT SLGT OR LOW CHC POPS LOOK RSNBL FOR NOW. AVIATION... VFR CONDITIONS THROUGH THE PERIOD. HOWEVER...SCT THUNDERSTORMS EXPECTED THROUGHOUT THE DAY WITH GUSTY WINDS...MVFR CEILINGS AND VISIBILITIES ACCOMPANYING THE STRONGER STORMS. LLWS EARLY THIS MORNING IN VCNTY OF KDLH WS020/19040KT THROUGH 12Z. && POINT TEMPS/POPS... DLH 82 59 76 47 / 50 40 0 0 INL 82 55 74 45 / 50 10 0 0 BRD 85 60 79 55 / 60 20 10 0 HYR 85 61 83 47 / 40 60 0 0 ASX 83 61 78 48 / 40 60 0 0 && .DLH WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. LS...NONE. $$ EOM/MILLER
AREA FORECAST DISCUSSION
NWS NORTH PLATTE NE
308 PM CDT SAT AUG 11 2007 .SYNOPSIS... LOTS OF AC AROUND THIS MORNING...INDICATIVE OF THE DECENT MID LEVEL LAPSE RATES ACROSS THE CWA. HOWEVER...LARGE SCALE SUBSIDENCE LIMITING ANY FURTHER DEVELOPMENT ATTM WITH AC...AND KEEPING SKC IN THE WRN ZONES. COLD FRONTAL BOUNDARY MOVING INTO ERN ZONES ATTM AND APPROACHING BETTER INSTABILITY ALOFT. IN ADDITION...OUTFLOW BOUNDARY MOVING SWWD INTO C NEB...BUT CREATING AT LEAST SHORT TERM ADDITIONAL MESOSCALE SUBSIDENCE...AS EVIDENCED BY DECREASING THE AMOUNT OF AC BEHIND IT. FURTHER WEST...N TO NE WIND NOT SERVING TO FOCUS ANY CONVERGENCE BUT WILL ENHANCE UPSLOPE FLOW W OF CWA. WATER VAPOR IMAGERY SHOWING A DECENT SHORTWAVE TROF EXITING NRN NV AND TCU NOW SEEN ON VISIBLE IN SWRN WY. GOES DPI SHOWING AN OVERALL DRYING TREND THOUGH IN TOTAL PW IN WRN NEB. && .SHORT TERM DISCUSSION (TONIGHT THROUGH SUNDAY NIGHT)...WOULD EXPECT ISOLD CONVECTION...IF IT DEVELOPS FURTHER W...WOULD HAVE A SHOT TO MAKE IT INTO NWRN CWA OVERNIGHT AND HAVE REFLECTED GRIDS TO SHOW THIS. GENERAL TREND FOR TONIGHT THOUGH IS FOR DRY CONDITIONS. WILL ADJUST CLOUD COVER TO SHOW BETTER CHCS FOR STRATUS ESPECIALLY IN THE NORTH TONIGHT...AS DEW POINTS CONTINUE TO INCREASE OVERNIGHT AND UPPER RIDGE BUILDS IN THE W. WOULD THINK CHCS WOULD EXISTS FURTHER S FOR SUNDAY NIGHT...THOUGH MODELS NOT INDICATING THIS ATTM. AS SHORT WAVE BEGINS TO TOP THE RIDGE IN PLACE...A MORE PROMINENT LEE TROF DEVELOPS ACROSS WRN SD SUNDAY. WITH RETURN FLOW SETTING UP WOULD EXPECTED BETTER LL CONVERGENCE IN NWRN ZONES SUNDAY AFTERNOON AND HENCE A BETTER CHC OF TSRA IN THOSE AREAS. FURTHER S THOUGH...UPER LEVEL TEMPS WARM AND A LACK OF LL CONV SHOULD PRECLUDE WIDESPREAD TSRA DEVELOPMENT. .LONG TERM DISCUSSION (MONDAY THROUGH SATURDAY)...WITH UPPER RIDGE HOLDING IN LPACE...PERSISTENCE WOULD BE BEST TO FOLLOW FOR MID THROUGH END OF THE WEEK. MONDAY WOULD BE AN EXCEPTION TO THIS...AS LEE TROF BENDS EWD AND A MORE SWRLY FLOW TAKE OVER IN THE LOWER LEVELS. CLIMATOLOGICALLY WOULD TEND TO SEE HIGHER MAX TEMPS IN THIS CASE NEARER TO TROF AXIS...AND HAVE TRENDED THE GRIDS TWD THAT IDEA. WILL ALSO HAVE TO WATCH FOR POTENTIAL FIRE WX WATCH/RED FLAG WARNING HEADLINES AS LOWER RHS AND DRY LIGHTNING POTENTIAL TAKE SHAPE. TROF MAKES LITTLE PROGRESS SWD IN THE EVENING AS LLJ INCREASE WHICH SHOULD HELP GET HIGH BASED TSRA GOING IN THE N. BETTER LARGE SCALE SHEAR WOULD ALSO EXISTS IN THIS AREA LEADING TO BETTER AND MORE SUSTAINED UPDRAFTS. HOWEVER...UPPER LEVEL TEMPS WARM AHEAD OF THIS AND LEADS TO UNCERTAINTY IN THE PRECIP FORECAST. SREF REFLECTS THIS UNCERTAINTY AS WELL WITH LOW ENSEMBLE MEAN POPS. WILL HOLD OFF FOR NOW ON ADDING POPS UNTIL A BETTER IDEA OF CONVECTIVE TRENDS OVER THE REMANIING WEEKEND EVOLVE. 12Z ECMWF AND 00Z GFS SIMILAR IN THE IDEA OF DEVELOPING A MORE AMPLIFIED RIDGE W OF CWA BY MID WEEK AS HUDSON BAY LOW REMAINS AND TRIES TO CARVE A DEEPER TROF IN THE E. A MORE SUBSTANITIAL SHORT WAVE WILL TRAVEL THE PERIFERY OF THE RIDGE IN NRN ZONES WED AND HAVE INCLUDED POPS TO ACCOUNT FOR THIS. AGAIN...BETTER SHEAR SHOULD ALLOW A MORE ORGANIZED CONVECTIVE SYSTEM TO EVEOLVE ACROSS THE NRN ZONES...WHILE SRN ZONES REMAIN DRY. OBVIOUSLY...TIMING ISSUES PREVENT MUCH CONFIDENCE IN LOCATION BY LATE WEEK. && .AVIATION... VFR CONDITIONS SHOULD BE EXPECTED THROUGH THE LATE EVENING HOURS INTO THE EARLY MORNING HOURS ACROSS THE TWEB ROUTES. THUNDERSTORMS WILL BE POSSIBLE ALONG THE FRONT RANGE SO LIGHT AIRCRAFT SHOULD BE AWARE OF THESE CONDITIONS ALONG THE WESTERN PORITON OF THE 274 TWEB ROUTE. INCREASING LOW LEVEL MOISTURE WILL BE RETURNING TO CENTRAL NEBRASKA BEHIND A SFC BOUNDARY. THIS SHOULD LEAD TO STRATUS PRODUCTION NEAR SUNRISE OVER AT LEAST EASTERN PORTIONS OF THE LBF TWEB ROUTES. MFVR CONDTIONS COULD BE REALIZED AS CEILING DROP TO NEAR 2KFT AGL AND VSBYS DROP TO NEAR 4SM. THIS STRATUS SHOULD HOLD THROUGH MUCH OF THE MORNING BEFORE LIFTING AND SCATTERING TO VFR CONDITIONS BY TOMORROW AFTERNOON. && .LBF WATCHES/WARNINGS/ADVISORIES... NONE. && $$ JWS/13
AREA FORECAST DISCUSSION
NWS LA CROSSE WI
312 PM CDT SAT AUG 11 2007 .SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT FORECAST CONCERNS ARE ON PRECIPITATION CHANCES TONIGHT AND AGAIN MONDAY NIGHT AND TUESDAY MORNING. SEVERE WEATHER THREAT ALSO A CONCERN THIS EVENING. A VERY COMPLEX MESOSCALE ANALYSIS THIS AFTERNOON. 18Z SURFACE ANALYSIS SHOWS MAIN COLD FRONT EXTENDING FROM NEAR KINL TO KABR. THIS MORNINGS MCS HAS RESULTED IN A RESIDUAL OUTFLOW BOUNDARY ACROSS SOUTHERN WISCONSIN INTO NORTHEAST IOWA AND SOUTHERN MINNESOTA. MEANWHILE...WATER VAPOR IMAGERY SHOWING AN MCV SPINNING OVER NORTHERN IOWA. RICH LOW LEVEL MOISTURE EXTENDS FROM IOWA INTO SOUTHERN MINNESOTA AHEAD OF THE COLD FRONT. CLOUDS HAVE HAMPERED SURFACE HEATING...BUT LATEST LAPS ANALYSIS SHOWS MUCAPES OF 1500- 2000 J/KG ACROSS MUCH OF THE FORECAST AREA IN CLEAR AREA AHEAD OF FRONT. VISIBLE SATELLITE IMAGERY SHOWING BAND OF MID LEVEL CLOUDS DEVELOPING FROM NEAR KMSP TO KABR ALONG A MOISTURE CONVERGENCE AXIS. CURRENT CONVECTION...ALBEIT STRONG HAS REMAINED BELOW SEVERE LEVELS AND CONTINUES TO PUSH EASTWARD. STRONG CAP IN PLACE AS INDICATED BY TAMDAR SOUNDING AT KMSP. 12Z 11AUG07 MODELS IN GOOD AGREEMENT WITH THE OVERALL SYNOPTIC PATTERN THROUGH THE PERIOD. STILL SOME DIFFERENCES WITHIN THE QPF FIELDS ON PLACEMENT OF CONVECTION TONIGHT. THUS HAVE USED A BLEND BASED ON THE FORCING FIELDS. IN THE NEAR TERM...THE PRIMARY MID LEVEL TROUGH OVER SASKATCHEWAN AND MANITOBA WILL MOVE EASTWARD THROUGH THE MEAN RIDGE TO WESTERN ONTARIO TONIGHT. THE ASSOCIATED COLD FRONT THEN WILL PROGRESS SOUTHEASTWARD FROM THE DAKOTAS TO WISCONSIN LATER TONIGHT. BIGGEST QUESTION IN THE NEAR TERM IS ON DEVELOPMENT AND EVOLUTION OF ADDITIONAL CONVECTION THROUGH THE EVENING HOURS. STRONG CAP EXISTS FROM MINNESOTA INTO IOWA WITH RUC SHOWING 850-700MB AVERAGE TEMPERATURE NEAR 16 CELSIUS THROUGH 03Z WITH SOME WEAK COLD ADVECTION AT 700MB AFTER 03Z. CURRENT THINKING IS FOR INITIAL CONVECTION TO MOVE EAST OF THE AREA WITH A QUIET PERIOD LATE THIS AFTERNOON. THEN ADDITIONAL DEVELOPMENT LATE THIS AFTERNOON/EARLY EVENING NEAR A KMKT-EAST OF KDLH LINE AND THEN TRANSLATE EAST-SOUTHEAST TOWARD THE AREA. MOISTURE TRANSPORT HEAD OF THE APPROACHING FRONT CONTINUES FEEDING NORTHWARD INTO THE AREA THROUGH THE EVENING HOURS. BEST RAIN CHANCES LOOK TO BE ACROSS THE NORTHERN SECTIONS OF THE FORECAST AREA AND THUS HAVE CONFIGURED THE POPS GRID IN THIS MANNER. SEVERE WEATHER THREAT CONDITIONAL ON AMOUNT OF UPPER COOLING TO ERODE CAP AND HOW MUCH INSTABILITY REMAINS AT THAT TIME. FRONT TO PUSH OUT OF THE AREA BY SUNDAY WITH HIGH PRESSURE BUILDING IN FROM THE NORTHWEST. MODELS SHOWING DRIER AIR ADVECTING IN FROM THE NORTH WITH DECENT MIXING. HAVE LOWERED AFTERNOON DEW POINTS ACROSS THE SANDY AREAS NORTHEAST OF INTERSTATE 94. OTHERWISE A MOSTLY SUNNY DAY IS EXPECTED. THE HIGH SLIDES EAST SUNDAY NIGHT WITH MOISTURE TRANSPORT ON ITS BACK SIDE FUELING CONVECTION ACROSS MINNESOTA AND IOWA. DRIER EASTERLY FLOW WITH HIGH OVER THE AREA SHOULD KEEP PRECIPITATION CHANCES AT BAY ACROSS THE WESTERN ZONES. WARM ADVECTION/MOISTURE TRANSPORT INCREASE MONDAY AND MONDAY NIGHT AS NEXT SHORTWAVE MOVES ALONG THE CANADIAN BORDER. AS THE ASSOCIATED COLD FRONT MOVES TOWARD THE AREA RAIN CHANCES WILL BE INCREASING. FROPA LOOKS TO TAKE PLACE SOMETIME MONDAY NIGHT AND THUS HAVE PLACED THE HIGHEST POPS IN THIS TIME FRAME. BOUNDARY SETTLES TO THE SOUTH OF THE AREA TUESDAY AND TUESDAY NIGHT AS HIGH PRESSURE MOVES ACROSS THE WESTERN GREAT LAKES. .LONG TERM...WEDNESDAY THROUGH SATURDAY A NORTHWEST FLOW REGIME SETS UP ACROSS THE UPPER MIDWEST THROUGH THE PERIOD. MEDIUM RANGE OPERATIONAL MODELS ARE IN AGREEMENT AS CLOSED UPPER LOW FORMS OFF THE PACIFIC NORTHWEST AND BROAD HIGH PRESSURE RIDGE SPRAWLS ACROSS THE SOUTHERN AND CENTRAL CONUS SETTING UP THE MAIN BAND OF WESTERLIES ACROSS THE NORTHERN TIER OF STATES. BIGGEST FORECAST CHALLENGE IS THE TIMING ISSUES OF THE WEAK IMPULSES IN THE FAST UPPER FLOW. BOTH 06Z GFS AND 00Z ECMWF AND ENSEMBLES POINT TO MAIN BOUNDARY REMAINING TO THE SOUTH OF THE AREA WITH WEAK HIGH PRESSURE FARTHER NORTH. FIRST IMPULSE LOOKS TO TRANSLATE JUST SOUTH OF THE AREA ON WEDNESDAY AND THUS HAVE KEPT THE LOWER END POPS ACROSS THE SOUTH BOTH WEDNESDAY AND WEDNESDAY NIGHT. WITH WEAK HIGH THEN BUILDING ACROSS THE AREA THURSDAY AND FRIDAY AS MAIN MOISTURE TRANSPORT REMAINS ACROSS THE HIGH PLAINS. THIS AXIS TEN SHIFTS EASTWARD SATURDAY FOR A CHANCE OF SHRA/TSRA. && .AVIATION... DIFFICULT PRE-FRONTAL ENVIRONMENT OVER THE TAF SITES THIS AFTERNOON WITH MANY WEAK IMPULSES ENOUGH TO CAUSE CLUSTERS OF TSRA. MAIN COLD FRONT IS NOW SHIFTING SOUTH THROUGH MN AND WILL CAUSE A MORE LINEAR TSRA COMPLEX TO INITIATE ALONG A KMKT-EAST OF KDLH LINE THIS EVENING. BELIEVE THIS BROKEN LINE OF +TSRA WILL SAG THROUGH SE THROUGH THE TAF SITES. HOWEVER...THE CAP STRENGTH AND INITIATION TIME IS DIFFICULT AND THUS SO IS TIMING IN THE TAF. WILL PROVIDE A LATER AFTERNOON UPDATE TO TAFS TO TRY AND BUILD TIMING INTO THE SITES OF TSRA. && $$ .ARX WATCHES/WARNINGS/ADVISORIES... WI...NONE. MN...NONE. IA...NONE. && $$ SHORT/LONG TERM...RABERDING AVIATION..........BAUMGARDT