Forecast Discussions mentioning "ACARS", "MDCRS", "AIRCRAFT", "TAMDAR", or "AMDAR" received at FSL on 01/22/09

AREA FORECAST DISCUSSION...UPDATED
NWS MARQUETTE MI
1035 PM EST WED JAN 21 2009 .UPDATE... FCST WAS UPDATED TO EXPAND MENTION OF -FZDZ OVERNIGHT AND THU. -FZDZ AND/OR FLURRIES OVERNIGHT SHOULD MAINLY AFFECT THE KEWEENAW AND NE FCST AREA. MORE OF THE NRN FCST AREA SHOULD BE AFFECTED THU. DURING THE EVENING...THERE HAVE BEEN A FEW OBS BEGINNING TO INDICATE -FZDZ (CYXL/CYRL IN NRN ONTARIO TO THE NW OF LAKE SUPERIOR AND ALSO AT THE SOO). FCST SOUNDINGS INDICATE SHALLOW MOIST LAYER WILL BE FAVORABLE FOR THE POTENTIAL OF -FZDZ AS TEMPS IN THE MOIST LAYER SHOULD BE ABOVE -10C OVERNIGHT THRU MOST IF NOT ALL OF THU AFTN. 00Z RAOBS AND EVENING TAMDAR SOUNDINGS SUPPORT THE MODEL FCSTS. LOCATIONS THAT SEE UPSLOPING OFF LAKE SUPERIOR WILL BE MOST LIKELY TO SEE -FZDZ. WITH COLD FRONT DRIFTING INTO UPPER MI LATE TONIGHT AND THU...UPSLOPING AREAS WILL SHIFT FROM W TO NW FLOW FAVORED LOCATIONS TONIGHT TO N TO NE FLOW FAVORED LOCATIONS THU AFTN. && .SHORT TERM (TONIGHT AND THURSDAY)... ISSUED AT 415 PM EST VERY LITTLE WILL CHANGE AT THE UPPER LEVELS OVER THE NEXT 24 TO 36 HOURS. AT 500MB...NORTHWESTERLY FLOW WILL BECOME SLIGHTLY MORE WESTERLY...WITH THE LOW SLOWLY SAGGING SOUTHEASTWARD FROM HUDSON BAY THROUGH QUEBEC AND THE NEXT TROUGH MOVING THROUGH THE CENTRAL CANADIAN PROVINCES. THE 300MB JET MAX SITUATED OVER CENTRAL ONTARIO AND FAR WESTERN LAKE SUPERIOR THIS AFTERNOON WILL ALSO FLATTEN OUT AS IT SLIDES OVER SOUTHERN QUEBEC AND MAINE. AN ADDITIONAL BUT MUCH LESS DRAMATIC JET MAX IN THE SOUTHERN STREAM WILL MOVE FROM THE PACIFIC NORTHWEST AROUND TO EASTERN NORTH DAKOTA...NORTHERN MINNESOTA...AND NORTHERN WISCONSIN BY 00Z FRIDAY. AT THE SURFACE...A COLD FRONT IS CURRENTLY CUTTING ONTARIO INTO NORTH AND SOUTH HALVES. THE FRONT SHOULD DIVE SOUTHWARD ACROSS CENTRAL LAKE SUPERIOR BY 12Z THURSDAY...AND FARTHER DIVE OVER SOUTHERN AND EASTERN UPPER MICHIGAN BY 00Z FRIDAY. THIS IS WHERE THE APPROACHING 300MB JET WILL COME INTO ASSISTANCE...WITH THIS BOUNDARY...AND THE SURFACE LOW ACROSS THE CENTRAL PLAINS MOVING TO CENTRAL MINNESOTA AND WISCONSIN BY 00Z FRIDAY. 850MB TEMPERATURES REMAIN BORDERLINE OR TOO WARM FOR SIGNIFICANT LAKE EFFECT OR ENHANCED SNOWFALL...RANGING FROM NEAR 0C SOUTHWEST TO -10C FAR NORTH AND NORTHEAST. THE ONLY PLACES WHERE LAKE EFFECT SNOW COULD BE POSSIBLE GIVING THE RIGHT WIND DIRECTION AND AVAILABLE MOISTURE WOULD BE OVER THE KEWEENAW PENINSULA AND EASTERN ALGER...AND LUCE COUNTIES. TAKING THIS ALL INTO ACCOUNT...THE POTENTIAL FOR FREEZING DRIZZLE WAS ADDED TO THE SNOW SHOWERS THURSDAY AFTERNOON SOUTH. OTHER CHANGES INCLUDE TO INCREASE CLOUD COVER...GIVEN THE CURRENT OVC SKY FROM NORTHEASTERN MINNESOTA THROUGH THE ENTIRE MQT CWA AND MOST OF NORTHERN WISCONSIN. FEW OTHER CHANGES WERE NEEDED TO THE ONGOING FORECAST. .LONG TERM... THURSDAY NIGHT...AN INCREASINGLY SHEARED SHRTWAVE TROUGH IS EXPECTED TO MOVE FROM SRN SASK INTO NRN ONTARIO...WITH THE ASSOCIATED AREA OF MODERATE 700-300 QVECTOR CONV JUST BRUSHING UPPER MI. TEMPS IN THE MOIST LAYER TO ONLY AROUND -10C COULD KEEP SOME RESULT IN SOME -FZDZ BUT WITH ONLY MARGINAL TEMPS/RH PROFILE AND LOW POPS...ONLY -SN WAS MENTIONED FOR NOW. THE MODELS HAVE CONTINUED TO TREND SLOWER WITH THE TROUGH/FRONT PASSAGE. BY LATE THU NIGHT AS THE SFC TROUGH AND AXIS OF LOW LEVEL CONV MOVES INTO NW UPPER MI...SNOW AND LAKE ENHANCED SNOW (850 MB TEMPS TO AROUND -10C) IS EXPECTED TO DEVELOP WITH A FEW INCHES OF ACCUMULATION POSSIBLE. FRI...IN THE WAKE OF THE SFC LOW...COLDER AIR WILL SPILL INTO THE AREA OF NRLY WINDS. CONVERGENT NRLY FLOW INTO N UPPER MI AND DEEPER SYNOPTIC MOISTURE/LIFT WITH 800-600 MF FGEN IN THE MORNING SHOULD SUPPORT A PERIOD OF MODERATE SNOW ESPECIALLY FOR N WIND FAVORED LES SNOWBELTS. THE WINDOW WITH THE MOST FAVORABLE DGZ LAYER WITH THE BEST LIFT AND LOW LEVEL CONV WILL BE RELATIVELY BRIEF...LIMITING OVERALL SNOW ACCUMULATIONS WITH AMOUNTS GENERALLY IN THE 2 TO 4 INCH RANGE. FRI NIGHT INTO SAT...AS THE VERY COLD ARCTIC AIRMASS MOVES INTO THE AREA AND CAA PUSHES 850 MB TEMPS TO AROUND -25C OVERNIGHT THE SNOW GROWTH LAYER WILL ALSO SHRINK. SO...AS WINDS BACK...NW FLOW SNOWBELTS WILL CONTINUE TO MODERATE LES BUT WITH ACCUMULATIONS GENERALLY REMAINING IN THE 3-7 INCH RANGE OVERNIGHT. WIND CHILL VALUES WILL ALSO PLUMMET INTO THE 15 BELOW TO 25 BELOW ZERO RANGE. THE MODERATING INFLUECNE OF LAKE SUPERIOR SHOULD KEEP TEMPS OVER THE NRN PORTION OF UPPER MI FROM DROPPING OFF TOO FAR...GENERALLY FROM ZERO TO 5 BELOW ZERO. OVER THE INTERIOR WEST...TEMPS MAY DROP TO AROUND -10F. HOWEVER...WITH THE MIXING/RADIATIONAL COOLING BALANCE... AREAS WITH THE LOWER TEMPS SHOULD ALSO SEE SOMEWHAT LIGHTER WINDS. EXPECT WINDS TO BACK TO MORE WNW SAT WITH LES BANDS SHIFTING INTO THE KEWEENAW AND LOCATIONS EAST OF MUNISING. SUN-WED...ASIDE FROM THE CONTINUING LES FOR WRLY FLOW SNOWBELTS INTO TUE...A GENERALLY DRY PERIOD IS EXPECTED. THE ECMWF...GFS AND ESEMBLES SUGGEST WNW NRN STREAM FLOW WILL PREVAIL WITH ONLY WEAK SHORTWAVES MOVING THROUGH THE AREA WITH LITTLE AVBL MOISTURE. GREATER UNCERTAINTY BY WED WITH LOCATION/STRENGTH OF SHORTWAVES AND POTENTIAL INTERACTION WITH THE SRN STREAM. SO...ONLY LOWER END POPS WERE INCLUDED. && .AVIATION (FOR THE 00Z TAF ISSUANCE)... AT KCMX...IFR CIGS SHOULD PREVAIL UNDER MOIST UPSLOPING WRLY FLOW. CIGS SHOULD LIFT TO LOW MVFR IN THE WAKE OF COLD FROPA THU MORNING AS WINDS SHIFT TO A N/NE DIRECTION. AT KSAW...MVFR CIGS SHOULD PREVAIL UNTIL COLD FROPA LATE THU MORNING. LIGHT UPSLOPING N/NE FLOW OFF LAKE SUPERIOR AFTER FROPA SHOULD RESULT IN CIGS LOWERING TO IFR. UPSLOPING OF SHALLOW RELATIVELY WARM SUBFREEZING MOIST LAYER MAY ALSO RESULT IN SOME -FZDZ/-SN. && .MARINE (FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)... LOW PRESSURE ACROSS EASTERN CANADA WILL DRAG A TROUGH FROM ONTARIO THROUGH LAKE SUPERIOR BY LATE THURSDAY MORNING. LOW PRESSURE OVER THE CENTRAL PLAINS WILL THEN SURGE NORTHEASTWARD AND OVER UPPER MICHIGAN THURSDAY NIGHT INTO FRIDAY MORNING. BY LATE FRIDAY EVENING...THIS LOW PRESSURE SYSTEM WILL MOVE TO FAR SOUTHERN QUEBEC...WITH WINDS INCREASING TO 30 AND NEAR 35 KNOTS FRIDAY. HEAVY FREEZING SPRAY WILL ALSO BE POSSIBLE AS COLDER AIR FILLS OVER LAKE SUPERIOR. FOR THE WEEKEND...HIGH PRESSURE OVER WESTERN CANADA SHOULD BRING A RIDGE OF HIGH PRESSURE ACROSS LAKE SUPERIOR. BY MONDAY...THE LARGE HIGH PRESSURE SYSTEM OVER WESTERN CANADA SHOULD HAVE DOVE INTO THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI RIVER VALLEY. WILL NOT POST A GALE WATCH EAST FOR FRIDAY NIGHT...DUE TO THE MARGINAL AND LOCALIZED NATURE OF THE GALES THEMSELVES. THIS WILL NEED TO BE CHECKED BY PREVIOUS SHIFTS IF THERE ARE SIGNIFICANT CHANGES. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN...NONE. LAKE SUPERIOR...NONE. LAKE MICHIGAN...NONE. && $$ UPDATE...ROLFSON SHORT TERM...KF LONG TERM...JLB AVIATION...ROLFSON MARINE...KF
AREA FORECAST DISCUSSION...UPDATED
NWS MARQUETTE MI
1245 PM EST MON JAN 19 2009 UPDATED FOR 18Z AVIATION DISCUSSION .SYNOPSIS... 08Z WATER VAPOR LOOP AND RUC 500MB HEIGHT ANALYSIS STILL SHOWS A HIGH AMPLITUDE PATTERN ACROSS NORTH AMERICA...WITH STRONG RIDGING OVER THE WESTERN U.S. INTO SW CANADA...AND TROUGHING OVER SE CANADA INTO THE EASTERN U.S.. UPPER MI CONTINUES TO BE INFLUENCED BY THE TROUGH...AND AS SUCH 850MB TEMPS REMAIN ON THE COOL SIDE...AROUND -15C PER 00Z RAOBS. SINCE THE AIRMASS REMAINS COLD...LAKE EFFECT SNOW SHOWERS ALSO CONTINUE. ALL ACCUMULATIONS ARE VERY FLUFFY...WITH SNOW TO WATER RATIOS OF 50 TO 1 OR SO. THIS IS DUE TO THE LAKE EFFECT CLOUDS BEING COMPLETELY CONTAINED WITHIN THE DENDRITIC SNOW GROWTH ZONE (DGZ)...AS SHOWN BY A 02Z TAMDAR SOUNDING FROM SAW. BASICALLY...WE HAVE BEEN GETTING A LOT OF BANG FOR OUR BUCK...WITH A LOT OF SNOW TURNING UP FOR LITTLE QPF. THIS CONTINUES NOW...WITH SNOWFALL AMOUNTS FROM 7 PM TO 330 AM AT THE OFFICE OF 5.3 INCHES. POSITION OF THE LAKE EFFECT THE PAST FEW DAYS HAS BEEN FOCUSED A LOT BY MESOSCALE FACTORS...SUCH AS LAND BREEZES AND TROUGHS EXTENDING BACK FROM WEAK LOW PRESSURE IN MAINE. EVEN THE ICE THAT IS PRESENT ON LAKE SUPERIOR (NEAR THE APOSTLES AND COVERING A LOT OF OUR LSZ265 ZONE) MAY BE HELPING A BIT AS A CONVERGENCE FOCUSING MECHANISM. CURRENTLY...ONE OF THOSE TROUGHS EXTENDS FROM SOUTHERN LAKE HURON NW ACROSS ESC AND TO ONTONAGON. NORTH OF THIS TROUGH...A SFC RIDGE IS NOTED ALONG THE NORTH SHORE OF LAKE SUPERIOR. BETWEEN THESE TWO FEATURES...A NORTH TO NE FLOW HAS HELPED TO CONFINE THE LAKE EFFECT SNOW TO MARQUETTE/WRN ALGER COUNTIES. CONVERGENCE ALONG THE TROUGH IS ALSO BRINGING LAKE EFFECT INTO WRN GOGEBIC/ONTONAGON COUNTIES. AREAS THAT ARE STAYING QUIET IN THE U.P. ARE CRYSTAL FALLS...ISQ AND ERY...WITH MOSTLY CLEAR SKIES. TEMPS HAVE FALLEN TO AROUND ZERO IN ALL THREE PLACES...WITH TYPICAL COLD SPOTS NEAR THEM BELOW ZERO. FARTHER UP TO OUR NW...A SHRTWV IS MOVING SE DOWN THE TOP OF THE RIDGE TO NEAR CHURCHILL MANITOBA. 00Z RAOB AT CYQD HAD AN 850MB TEMP OF 3C...AND SOME OF THIS WARM AIR WILL LIKELY GET PULLED EASTWARD AS THIS SHRTWV DROPS SOUTH INTO THE TROUGH. && .DISCUSSION... MAIN HIGHLIGHT TO THE FORECAST IS THE TEMPORARY END OF THE LAKE EFFECT THIS AFTERNOON. TODAY...SHRTWV APPROACHING CHURCHILL MANITOBA WILL CONTINUE ITS DESCENT SOUTHWARD...REACHING FAR NORTHERN ONTARIO BY 00Z. BECAUSE THIS SHRTWV IS DROPPING SOUTH...THE HIGH PRESSURE RIDGE ALONG THE NORTH SHORE OF LAKE SUPERIOR WILL ALSO HAVE TO BE FORCED SOUTHWARD. IN FACT...BY 00Z IT SHOULD BE SITUATED DOWN IN SRN LOWER MI. THEREFORE WINDS ARE EXPECTED TO BACK THROUGH THE DAY...ALLOWING WARM ADVECTION TO TAKE HOLD. MUCH OF THE WARM TAKES PLACE ABOVE 950MB AND PEAKS AT 850MB...WHERE SOUNDINGS FOR CMX SHOW A 24 HOUR RISE OF 12C BY 00Z WITH A READING OF -4C. THIS WARMING CAUSES INVERSIONS TO CRASH SUBSTANTIALLY THROUGH THE DAY...SO LAKE EFFECT SHOULD COMPLETELY SHUT OFF OVER WESTERN SUPERIOR...MAYBE AS EARLY AS 18Z. WARMING TAKES LONGER TO CROSS EASTERN SUPERIOR...SO LAKE EFFECT PROBABLY DOES NOT SHUT OFF UNTIL 21Z OR 00Z. HOWEVER...LAKE EFFECT PCPN OVER LAND WILL BE DONE BY 18Z DUE TO WINDS BACKING TO THE WEST. SINCE THE LAKE EFFECT IS MOVING AND DIMINISHING THROUGH TIME...LOOK FOR ADDITIONAL ACCUMULATIONS TO BE LIGHT...PERHAPS PEAKING UP TO ANOTHER 3 INCHES IN ALGER COUNTY. GOING END TIMES OF HEADLINES SEEM REASONABLE. OUTSIDE OF THE LAKE EFFECT...DRY CONDITIONS WILL OCCUR WITH SUBSIDENCE AND DRY AIR. ALTHOUGH WE ARE WARMING ALOFT...THE IMPACT AT THE SFC IS EXPECTED TO BE LESS DUE TO THE VERY LOW SUN ANGLE THIS TIME OF YEAR. STAYED TOWARD THE LOW END OF GUIDANCE FOR HIGHS DUE TO THE STRONG SUBSIDENCE SEEN ON SOUNDINGS...AND EXPECTED INCREASE IN HIGH CLOUDS DURING THE AFTN. TONIGHT...UPPER RIDGE OVER THE WESTERN U.S. IS PROGGED TO BEGIN FLATTENING SOMEWHAT AS A SHRTWV TROUGH IN THE GULF OF ALASKA MOVES INLAND. THIS FLATTENING OF THE UPPER RIDGE WILL HELP TO KEEP THE SHRTWV THAT IS APPROACHING CHURCHILL WELL OFF TO OUR EAST...PROGGED TO REACH THE ONTARIO/QUEBEC LINE BY 12Z WED. HOWEVER...A LOW PRESSURE TROUGH WILL ACCOMPANY THE WAVE...MOVING FROM NW ONTARIO AT 00Z INTO UPPER MI BY 12Z. GIVEN HOW FAR EAST THE SHRTWV IS...ANY DPVA FORCING IS MINIMAL. ISENTROPIC LIFT PROGS LOOK QUIET AS WELL...WITH NEUTRAL LIFT AND ONLY SOME GRADUAL LOWERING IN CONDENSATION PRESSURE DEFICITS BY 12Z. THEREFORE...CHANCES FOR SYNOPTIC PCPN LOOK VERY LOW AT THIS POINT. EVEN IF PCPN COULD FALL...SOUNDINGS DEPICT A FAIRLY DRY LAYER PRESENT BTWN 900-700MB. THE ONLY AREA THAT SHOWS THIS LAYER MOISTENING IS OVER EASTERN SUPERIOR...AND THUS KEPT SOME 20 POPS THERE. REMOVED CHANCES FOR PCPN ELSEWHERE. TEMPS ARE TRICKY SINCE THERE SHOULD BE PLENTY OF HIGH CLOUDS AROUND...AS WELL AS INCREASE OF MID CLOUDS AND THEN LOW CLOUDS LATE IN THE NIGHT. IN ADDITION...THE APPROACH OF THE SFC TROUGH WILL HELP TO KEEP WIND SPEEDS UP. THEREFORE DECIDED TO STAY ON THE WARM SIDE OF GUIDANCE. ON A SIDE NOTE...WITH THE LOW CLOUDS COME IN LATE AND A WESTERLY FLOW...THERE COULD BE SOME FLURRIES DEVELOPING IN THE UPSLOPE AREAS OF THE WESTERN U.P.. WEDNESDAY...UPPER RIDGE IS SHOWN TO CONTINUE FLATTENING OUT AS THE SHRTWV CURRENTLY IN THE GULF OF ALASKA PUSHES SOUTHWARD THROUGH BRITISH COLUMBIA. FLOW OVER UPPER MI ALOFT ACTUALLY GOES FROM THE CURRENT DUE NORTH TO NORTHWEST BY 00Z THU. THIS NW FLOW WILL HELP TO KEEP RELATIVELY WARM AIR AT 850MB OVER THE CWA...RANGING FROM -2C WEST TO -8C EAST. OF MORE INTEREST IS BELOW 850MB...WITH MODELS HAVING PLENTY OF LOW LEVEL MOISTURE TRAPPED. MOST MODELS ARE ALSO PRINTING OUT LIGHT QPF WITH THIS MOISTURE...ESPECIALLY IN NW FLOW AREAS. IN FACT...IT IS CLOSE TO BEING UNSTABLE ENOUGH BELOW 850MB TO CALL IT LAKE EFFECT. FOR NOW...DECIDED TO FOLLOW THE PREVIOUS FCST AND JUST CALL IT FLURRIES FOR UPSLOPE NW FLOW AREAS...SINCE CLOUD DEPTHS ARE ONLY EXPECTED AROUND 2000 FT. LATER FCSTS MAY HAVE TO INCLUDE SOME LOW CHANCE POPS...THOUGH. THESE LOW CLOUDS SHOULD HELP KEEP TEMPS DOWN AS WELL...BUT READINGS ARE STILL EXPECTED TO CLIMB ABOVE NORMAL. STAYED WITH A BLEND OF GUIDANCE...WHICH HAS HIGHS IN THE MID TO UPPER 20S. WED NIGHT INTO THU...MODEL DIFFERENCES ARISE IN THE HANDLING OF THE BRITISH COLUMBIA SHRTWV. THE GFS/NAM AND UKMET ARE ALL PRETTY PROGRESSIVE...BRINGING IT TO AROUND THE INTERNATIONAL FALLS AREA BY 00Z FRI. ASSOCIATED WITH THIS SHRTWV IS A SFC LOW...WHICH WOULD REACH UPPER MI BY 00Z FRI ACCORDING TO THIS MODEL GROUP. THE 00Z ECMWF...ON THE OTHER HAND IS COMPLETELY DIFFERENT...WHICH WAS TRUE WITH THE 12Z RUN OF IT AS WELL. IT SUGGESTS THE SHRTWVS MAKES MORE OF A DIVE SOUTHWARD INTO SRN ALBERTA...WITH A WEAK NON-ASSOCIATED SFC LOW WELL TO THE EAST OVER SE MN AT 00Z FRI. AFTER COORDINATION WITH HPC...FOLLOWED THE ECMWF IDEA. ALL MODELS SHOW FOR WED NIGHT A COLD FRONT DROPPING SOUTH THROUGH NORTHERN ONTARIO...MOVING INTO LAKE SUPERIOR BY 12Z THU. MID-LEVEL FRONTOGENESIS ABOVE AND TO THE NORTH OF THIS FRONT MAY SUPPORT SOME LIGHT SYNOPTIC SNOW. WOULD EXPECT IT TO THEREFORE MOSTLY FALL ON LAKE SUPERIOR...PERHAPS BRUSHING THE EASTERN CWA. OTHERWISE...LOW CLOUDS HANGING AROUND COMBINED WITH WEST TO NW LOW LEVEL WINDS SUGGESTS KEEPING FLURRIES GOING IN UPSLOPE AREAS. THE CLOUDS WILL ALSO HELP TO KEEP TEMPS UP...AND THEREFORE STAYED ON THE WARM SIDE OF GUIDANCE WITH LOWS FROM THE MID TEENS TO LOW 20S. THESE READINGS COULD BE WARMED UP IN LATER FORECASTS IF IT ENDS UP COMPLETELY CLOUDY ON WEDNESDAY. FOR THU...THE FRONT AND MID-LEVEL FRONTOGENESIS SHIFT SOUTH IN RESPONSE TO FALLING HEIGHTS ALOFT. THEREFORE...SHIFTED THE LOW CHANCE POPS SOUTH AS WELL FOR THU. ECMWF 850MB TEMPS OF -8 TO -10C ARE TOO MARGINAL FOR LAKE EFFECT...THEREFORE DID NOT SHOW ANY LOCATION HAVING HIGHER POPS THAN 20. CLOUD COVER SHOULD BE PERSISTENT AGAIN...BUT WITH WARMER LOWS ON WED NIGHT AND NO SIGNIFICANT COOLING ON THU...THU SHOULD END UP BEING THE WARMEST DAY OF THE WEEK. GOING HIGHS LOOKED REASONABLE. THU NIGHT AND FRI...WHETHER YOU FOLLOW THE GFS...UKMET OR ECMWF...THERE IS A GENERAL IDEA OF LOW PRESSURE IN THE WESTERN GREAT LAKES AREA BY FRI MORNING...WHICH THEN SHIFTS OFF TO THE EASTERN GREAT LAKES DURING THE DAY FRI. IN THE WAKE OF THIS LOW...HIGH PRESSURE WHICH WILL BE BUILDING OVER THE NEXT COUPLE DAYS FROM NRN ALASKA INTO THE YUKON...IS EXPECTED TO NOSE DOWN THROUGH THE PLAINS. THIS MEANS ANOTHER SURGE OF ARCTIC AIR FOR UPPER MI...WHICH SHOULD ARRIVE BY 00Z SAT. ECMWF 850MB TEMPS FALL TO -12C BY 12Z FRI AND THEN TO -20C BY 00Z SAT. THESE FALLING 850MB TEMPS MEANS A RESURGENCE OF LAKE EFFECT...FIRST AFFECTING NORTH FLOW AREAS THU NIGHT INTO FRI MORNING...THEN SWITCHING TO NW FLOW AREAS FRI AFTN INTO FRI NIGHT. KEPT THE GENERAL IDEA OF THE PREVIOUS FORECAST THE SAME...WITH THE MAIN ADJUSTMENT TO SLOW DOWN THE HIGHER POPS IN THE NORTH CENTRAL U.P. THU NIGHT. ALSO ADDED SOME SMALL CHANCE POPS TO THE SOUTHERN U.P. THU NIGHT AND FRI WITH POTENTIAL OF SYNOPTIC SNOW AS INDICATED BY THE ECMWF. INITIALLY THE SNOW WILL LIKELY BE QUITE FLUFFY...THEN AS THE COLD AIR MOVES IN...THE SNOW SHOULD GET FINER AS THE DENDRITIC SNOW GROWTH ZONE FALLS BELOW THE CLOUD BASE. POTENTIAL DOES EXIST FOR MODERATE SNOW ACCUMULATIONS OVER HIGHER TERRAIN AREAS...AND WILL NOTE THIS IN THE HWO. REGARDING TEMPS...RAISED BOTH LOWS AND HIGHS UP A FEW DEGREES DURING THE PERIOD TO ACCOUNT FOR THE SLOWER SCENARIO OF COLD AIR COMING IN. FURTHER INCREASES MAY BE REQUIRED. HOWEVER...TEMPS SHOULD FALL FRIDAY AFTN. NO CHANGES MADE BEYOND FRI. STILL LOOKS COLD FOR THE WEEKEND INTO MONDAY. NEW ECMWF SHOWS THE ARCTIC HIGH THAT HAS BEEN NOSING DOWN INTO THE PLAINS MOVING OVERHEAD MONDAY NIGHT. IF THIS COMES TRUE...COULD SEE INLAND AREAS GETTING DOWN TO -20F AT LEAST. && .AVIATION (FOR THE 18Z TAF ISSUANCE)... KSAW...EXPECT VFR CONDITIONS TO PREVAIL THIS AFTERNOON INTO TONIGHT. WAA AHEAD OF A TROUGH APPROACHING THE AREA WILL BRING MVFR CIGS BACK INTO THE REGION LATE TONIGHT AND WED MORNING. KCMX...NORTHWEST WINDS WILL BACK SOUTHWEST THIS AFTERNOON. AS A RESULT...MVFR CONDITIONS ARE EXPECTED TO IMPROVE TO VFR LATE THIS AFTERNOON AS ANY LINGERING LAKE EFFECT SNOW ENDS. MVFR CIGS AND FLURRIES COULD MOVE BACK IN LATE TONIGHT AS WINDS SHIFT WEST AGAIN WITH A TROUGH PASSAGE. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)... NORTH WINDS THIS MORNING WILL BACK SOUTHWEST THIS AFTERNOON AS A HIGH PRESSURE RIDGE MOVES ACROSS THE AREA. A TIGHTENING SW GRADIENT AHEAD OF AN APPROACHING TROUGH WILL INCREASE WINDS TO 30 KT OVER THE WRN AND NCNTRL PORTIONS OF LAKE SUPERIOR TONIGHT RESULTING IN MODERATE FREEZING SPRAY. BEHIND THE PASSAGE OF A WEAK TROUGH LATE TONIGHT...WINDS WILL GENERALLY REMAIN 25 KTS OR LESS THROUGH THURSDAY. NORTHERLY WINDS WILL INCREASE TO 30 KT LATE THURSDAY NIGHT INTO SATURDAY BEHIND A COLD FRONTAL PASSAGE ALLOWING FOR THE FORMATION OF HEAVY FREEZING SPRAY. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... LAKE EFFECT SNOW ADVISORY UNTIL 9 AM EST THIS MORNING FOR MIZ006. LAKE EFFECT SNOW WARNING UNTIL 9 AM EST THIS MORNING FOR MIZ002- 005. LAKE EFFECT SNOW ADVISORY UNTIL 7 AM EST THIS MORNING FOR MIZ009. LAKE SUPERIOR...NONE. LAKE MICHIGAN...NONE. && $$ SYNOPSIS/DISCUSSION...AJ AVIATION...JLB MARINE...VOSS
AREA FORECAST DISCUSSION...UPDATED
NWS MARQUETTE MI
731 AM EST MON JAN 19 2009 UPDATED FOR 12Z AVIATION DISCUSSION .SYNOPSIS... 08Z WATER VAPOR LOOP AND RUC 500MB HEIGHT ANALYSIS STILL SHOWS A HIGH AMPLITUDE PATTERN ACROSS NORTH AMERICA...WITH STRONG RIDGING OVER THE WESTERN U.S. INTO SW CANADA...AND TROUGHING OVER SE CANADA INTO THE EASTERN U.S.. UPPER MI CONTINUES TO BE INFLUENCED BY THE TROUGH...AND AS SUCH 850MB TEMPS REMAIN ON THE COOL SIDE...AROUND -15C PER 00Z RAOBS. SINCE THE AIRMASS REMAINS COLD...LAKE EFFECT SNOW SHOWERS ALSO CONTINUE. ALL ACCUMULATIONS ARE VERY FLUFFY...WITH SNOW TO WATER RATIOS OF 50 TO 1 OR SO. THIS IS DUE TO THE LAKE EFFECT CLOUDS BEING COMPLETELY CONTAINED WITHIN THE DENDRITIC SNOW GROWTH ZONE (DGZ)...AS SHOWN BY A 02Z TAMDAR SOUNDING FROM SAW. BASICALLY...WE HAVE BEEN GETTING A LOT OF BANG FOR OUR BUCK...WITH A LOT OF SNOW TURNING UP FOR LITTLE QPF. THIS CONTINUES NOW...WITH SNOWFALL AMOUNTS FROM 7 PM TO 330 AM AT THE OFFICE OF 5.3 INCHES. POSITION OF THE LAKE EFFECT THE PAST FEW DAYS HAS BEEN FOCUSED A LOT BY MESOSCALE FACTORS...SUCH AS LAND BREEZES AND TROUGHS EXTENDING BACK FROM WEAK LOW PRESSURE IN MAINE. EVEN THE ICE THAT IS PRESENT ON LAKE SUPERIOR (NEAR THE APOSTLES AND COVERING A LOT OF OUR LSZ265 ZONE) MAY BE HELPING A BIT AS A CONVERGENCE FOCUSING MECHANISM. CURRENTLY...ONE OF THOSE TROUGHS EXTENDS FROM SOUTHERN LAKE HURON NW ACROSS ESC AND TO ONTONAGON. NORTH OF THIS TROUGH...A SFC RIDGE IS NOTED ALONG THE NORTH SHORE OF LAKE SUPERIOR. BETWEEN THESE TWO FEATURES...A NORTH TO NE FLOW HAS HELPED TO CONFINE THE LAKE EFFECT SNOW TO MARQUETTE/WRN ALGER COUNTIES. CONVERGENCE ALONG THE TROUGH IS ALSO BRINGING LAKE EFFECT INTO WRN GOGEBIC/ONTONAGON COUNTIES. AREAS THAT ARE STAYING QUIET IN THE U.P. ARE CRYSTAL FALLS...ISQ AND ERY...WITH MOSTLY CLEAR SKIES. TEMPS HAVE FALLEN TO AROUND ZERO IN ALL THREE PLACES...WITH TYPICAL COLD SPOTS NEAR THEM BELOW ZERO. FARTHER UP TO OUR NW...A SHRTWV IS MOVING SE DOWN THE TOP OF THE RIDGE TO NEAR CHURCHILL MANITOBA. 00Z RAOB AT CYQD HAD AN 850MB TEMP OF 3C...AND SOME OF THIS WARM AIR WILL LIKELY GET PULLED EASTWARD AS THIS SHRTWV DROPS SOUTH INTO THE TROUGH. && .DISCUSSION... MAIN HIGHLIGHT TO THE FORECAST IS THE TEMPORARY END OF THE LAKE EFFECT THIS AFTERNOON. TODAY...SHRTWV APPROACHING CHURCHILL MANITOBA WILL CONTINUE ITS DESCENT SOUTHWARD...REACHING FAR NORTHERN ONTARIO BY 00Z. BECAUSE THIS SHRTWV IS DROPPING SOUTH...THE HIGH PRESSURE RIDGE ALONG THE NORTH SHORE OF LAKE SUPERIOR WILL ALSO HAVE TO BE FORCED SOUTHWARD. IN FACT...BY 00Z IT SHOULD BE SITUATED DOWN IN SRN LOWER MI. THEREFORE WINDS ARE EXPECTED TO BACK THROUGH THE DAY...ALLOWING WARM ADVECTION TO TAKE HOLD. MUCH OF THE WARM TAKES PLACE ABOVE 950MB AND PEAKS AT 850MB...WHERE SOUNDINGS FOR CMX SHOW A 24 HOUR RISE OF 12C BY 00Z WITH A READING OF -4C. THIS WARMING CAUSES INVERSIONS TO CRASH SUBSTANTIALLY THROUGH THE DAY...SO LAKE EFFECT SHOULD COMPLETELY SHUT OFF OVER WESTERN SUPERIOR...MAYBE AS EARLY AS 18Z. WARMING TAKES LONGER TO CROSS EASTERN SUPERIOR...SO LAKE EFFECT PROBABLY DOES NOT SHUT OFF UNTIL 21Z OR 00Z. HOWEVER...LAKE EFFECT PCPN OVER LAND WILL BE DONE BY 18Z DUE TO WINDS BACKING TO THE WEST. SINCE THE LAKE EFFECT IS MOVING AND DIMINISHING THROUGH TIME...LOOK FOR ADDITIONAL ACCUMULATIONS TO BE LIGHT...PERHAPS PEAKING UP TO ANOTHER 3 INCHES IN ALGER COUNTY. GOING END TIMES OF HEADLINES SEEM REASONABLE. OUTSIDE OF THE LAKE EFFECT...DRY CONDITIONS WILL OCCUR WITH SUBSIDENCE AND DRY AIR. ALTHOUGH WE ARE WARMING ALOFT...THE IMPACT AT THE SFC IS EXPECTED TO BE LESS DUE TO THE VERY LOW SUN ANGLE THIS TIME OF YEAR. STAYED TOWARD THE LOW END OF GUIDANCE FOR HIGHS DUE TO THE STRONG SUBSIDENCE SEEN ON SOUNDINGS...AND EXPECTED INCREASE IN HIGH CLOUDS DURING THE AFTN. TONIGHT...UPPER RIDGE OVER THE WESTERN U.S. IS PROGGED TO BEGIN FLATTENING SOMEWHAT AS A SHRTWV TROUGH IN THE GULF OF ALASKA MOVES INLAND. THIS FLATTENING OF THE UPPER RIDGE WILL HELP TO KEEP THE SHRTWV THAT IS APPROACHING CHURCHILL WELL OFF TO OUR EAST...PROGGED TO REACH THE ONTARIO/QUEBEC LINE BY 12Z WED. HOWEVER...A LOW PRESSURE TROUGH WILL ACCOMPANY THE WAVE...MOVING FROM NW ONTARIO AT 00Z INTO UPPER MI BY 12Z. GIVEN HOW FAR EAST THE SHRTWV IS...ANY DPVA FORCING IS MINIMAL. ISENTROPIC LIFT PROGS LOOK QUIET AS WELL...WITH NEUTRAL LIFT AND ONLY SOME GRADUAL LOWERING IN CONDENSATION PRESSURE DEFICITS BY 12Z. THEREFORE...CHANCES FOR SYNOPTIC PCPN LOOK VERY LOW AT THIS POINT. EVEN IF PCPN COULD FALL...SOUNDINGS DEPICT A FAIRLY DRY LAYER PRESENT BTWN 900-700MB. THE ONLY AREA THAT SHOWS THIS LAYER MOISTENING IS OVER EASTERN SUPERIOR...AND THUS KEPT SOME 20 POPS THERE. REMOVED CHANCES FOR PCPN ELSEWHERE. TEMPS ARE TRICKY SINCE THERE SHOULD BE PLENTY OF HIGH CLOUDS AROUND...AS WELL AS INCREASE OF MID CLOUDS AND THEN LOW CLOUDS LATE IN THE NIGHT. IN ADDITION...THE APPROACH OF THE SFC TROUGH WILL HELP TO KEEP WIND SPEEDS UP. THEREFORE DECIDED TO STAY ON THE WARM SIDE OF GUIDANCE. ON A SIDE NOTE...WITH THE LOW CLOUDS COME IN LATE AND A WESTERLY FLOW...THERE COULD BE SOME FLURRIES DEVELOPING IN THE UPSLOPE AREAS OF THE WESTERN U.P.. WEDNESDAY...UPPER RIDGE IS SHOWN TO CONTINUE FLATTENING OUT AS THE SHRTWV CURRENTLY IN THE GULF OF ALASKA PUSHES SOUTHWARD THROUGH BRITISH COLUMBIA. FLOW OVER UPPER MI ALOFT ACTUALLY GOES FROM THE CURRENT DUE NORTH TO NORTHWEST BY 00Z THU. THIS NW FLOW WILL HELP TO KEEP RELATIVELY WARM AIR AT 850MB OVER THE CWA...RANGING FROM -2C WEST TO -8C EAST. OF MORE INTEREST IS BELOW 850MB...WITH MODELS HAVING PLENTY OF LOW LEVEL MOISTURE TRAPPED. MOST MODELS ARE ALSO PRINTING OUT LIGHT QPF WITH THIS MOISTURE...ESPECIALLY IN NW FLOW AREAS. IN FACT...IT IS CLOSE TO BEING UNSTABLE ENOUGH BELOW 850MB TO CALL IT LAKE EFFECT. FOR NOW...DECIDED TO FOLLOW THE PREVIOUS FCST AND JUST CALL IT FLURRIES FOR UPSLOPE NW FLOW AREAS...SINCE CLOUD DEPTHS ARE ONLY EXPECTED AROUND 2000 FT. LATER FCSTS MAY HAVE TO INCLUDE SOME LOW CHANCE POPS...THOUGH. THESE LOW CLOUDS SHOULD HELP KEEP TEMPS DOWN AS WELL...BUT READINGS ARE STILL EXPECTED TO CLIMB ABOVE NORMAL. STAYED WITH A BLEND OF GUIDANCE...WHICH HAS HIGHS IN THE MID TO UPPER 20S. WED NIGHT INTO THU...MODEL DIFFERENCES ARISE IN THE HANDLING OF THE BRITISH COLUMBIA SHRTWV. THE GFS/NAM AND UKMET ARE ALL PRETTY PROGRESSIVE...BRINGING IT TO AROUND THE INTERNATIONAL FALLS AREA BY 00Z FRI. ASSOCIATED WITH THIS SHRTWV IS A SFC LOW...WHICH WOULD REACH UPPER MI BY 00Z FRI ACCORDING TO THIS MODEL GROUP. THE 00Z ECMWF...ON THE OTHER HAND IS COMPLETELY DIFFERENT...WHICH WAS TRUE WITH THE 12Z RUN OF IT AS WELL. IT SUGGESTS THE SHRTWVS MAKES MORE OF A DIVE SOUTHWARD INTO SRN ALBERTA...WITH A WEAK NON-ASSOCIATED SFC LOW WELL TO THE EAST OVER SE MN AT 00Z FRI. AFTER COORDINATION WITH HPC...FOLLOWED THE ECMWF IDEA. ALL MODELS SHOW FOR WED NIGHT A COLD FRONT DROPPING SOUTH THROUGH NORTHERN ONTARIO...MOVING INTO LAKE SUPERIOR BY 12Z THU. MID-LEVEL FRONTOGENESIS ABOVE AND TO THE NORTH OF THIS FRONT MAY SUPPORT SOME LIGHT SYNOPTIC SNOW. WOULD EXPECT IT TO THEREFORE MOSTLY FALL ON LAKE SUPERIOR...PERHAPS BRUSHING THE EASTERN CWA. OTHERWISE...LOW CLOUDS HANGING AROUND COMBINED WITH WEST TO NW LOW LEVEL WINDS SUGGESTS KEEPING FLURRIES GOING IN UPSLOPE AREAS. THE CLOUDS WILL ALSO HELP TO KEEP TEMPS UP...AND THEREFORE STAYED ON THE WARM SIDE OF GUIDANCE WITH LOWS FROM THE MID TEENS TO LOW 20S. THESE READINGS COULD BE WARMED UP IN LATER FORECASTS IF IT ENDS UP COMPLETELY CLOUDY ON WEDNESDAY. FOR THU...THE FRONT AND MID-LEVEL FRONTOGENESIS SHIFT SOUTH IN RESPONSE TO FALLING HEIGHTS ALOFT. THEREFORE...SHIFTED THE LOW CHANCE POPS SOUTH AS WELL FOR THU. ECMWF 850MB TEMPS OF -8 TO -10C ARE TOO MARGINAL FOR LAKE EFFECT...THEREFORE DID NOT SHOW ANY LOCATION HAVING HIGHER POPS THAN 20. CLOUD COVER SHOULD BE PERSISTENT AGAIN...BUT WITH WARMER LOWS ON WED NIGHT AND NO SIGNIFICANT COOLING ON THU...THU SHOULD END UP BEING THE WARMEST DAY OF THE WEEK. GOING HIGHS LOOKED REASONABLE. THU NIGHT AND FRI...WHETHER YOU FOLLOW THE GFS...UKMET OR ECMWF...THERE IS A GENERAL IDEA OF LOW PRESSURE IN THE WESTERN GREAT LAKES AREA BY FRI MORNING...WHICH THEN SHIFTS OFF TO THE EASTERN GREAT LAKES DURING THE DAY FRI. IN THE WAKE OF THIS LOW...HIGH PRESSURE WHICH WILL BE BUILDING OVER THE NEXT COUPLE DAYS FROM NRN ALASKA INTO THE YUKON...IS EXPECTED TO NOSE DOWN THROUGH THE PLAINS. THIS MEANS ANOTHER SURGE OF ARCTIC AIR FOR UPPER MI...WHICH SHOULD ARRIVE BY 00Z SAT. ECMWF 850MB TEMPS FALL TO -12C BY 12Z FRI AND THEN TO -20C BY 00Z SAT. THESE FALLING 850MB TEMPS MEANS A RESURGENCE OF LAKE EFFECT...FIRST AFFECTING NORTH FLOW AREAS THU NIGHT INTO FRI MORNING...THEN SWITCHING TO NW FLOW AREAS FRI AFTN INTO FRI NIGHT. KEPT THE GENERAL IDEA OF THE PREVIOUS FORECAST THE SAME...WITH THE MAIN ADJUSTMENT TO SLOW DOWN THE HIGHER POPS IN THE NORTH CENTRAL U.P. THU NIGHT. ALSO ADDED SOME SMALL CHANCE POPS TO THE SOUTHERN U.P. THU NIGHT AND FRI WITH POTENTIAL OF SYNOPTIC SNOW AS INDICATED BY THE ECMWF. INITIALLY THE SNOW WILL LIKELY BE QUITE FLUFFY...THEN AS THE COLD AIR MOVES IN...THE SNOW SHOULD GET FINER AS THE DENDRITIC SNOW GROWTH ZONE FALLS BELOW THE CLOUD BASE. POTENTIAL DOES EXIST FOR MODERATE SNOW ACCUMULATIONS OVER HIGHER TERRAIN AREAS...AND WILL NOTE THIS IN THE HWO. REGARDING TEMPS...RAISED BOTH LOWS AND HIGHS UP A FEW DEGREES DURING THE PERIOD TO ACCOUNT FOR THE SLOWER SCENARIO OF COLD AIR COMING IN. FURTHER INCREASES MAY BE REQUIRED. HOWEVER...TEMPS SHOULD FALL FRIDAY AFTN. NO CHANGES MADE BEYOND FRI. STILL LOOKS COLD FOR THE WEEKEND INTO MONDAY. NEW ECMWF SHOWS THE ARCTIC HIGH THAT HAS BEEN NOSING DOWN INTO THE PLAINS MOVING OVERHEAD MONDAY NIGHT. IF THIS COMES TRUE...COULD SEE INLAND AREAS GETTING DOWN TO -20F AT LEAST. && .AVIATION (FOR THE 12Z TAF ISSUANCE)... KSAW...NORTH WINDS WILL BACK NORTHWEST THIS MORNING AND THEN WESTERLY THIS AFTERNOON. AS A RESULT...IFR TO OCNL LIFR CONDITIONS IN LAKE EFFECT SNOW WILL IMPROVE TO MVFR BY 14Z AND THEN TO VFR THIS AFTERNOON AS SNOW ENDS AND SKIES BCM SCT. KCMX...NORTHWEST WINDS WILL BACK SOUTHWEST THIS AFTERNOON. AS A RESULT...MVFR CONDITIONS IN LAKE EFFECT SNOW WILL IMPROVE TO VFR THIS AFTERNOON AS SNOW ENDS. MVFR CIGS AND FLURRIES COULD MOVE BACK IN LATE TONIGHT AS WINDS SHIFT WEST AGAIN WITH A TROUGH PASSAGE. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)... NORTH WINDS THIS MORNING WILL BACK SOUTHWEST THIS AFTERNOON AS A HIGH PRESSURE RIDGE MOVES ACROSS THE AREA. A TIGHTENING SW GRADIENT AHEAD OF AN APPROACHING TROUGH WILL INCREASE WINDS TO 30 KT OVER THE WRN AND NCNTRL PORTIONS OF LAKE SUPERIOR TONIGHT RESULTING IN MODERATE FREEZING SPRAY. BEHIND THE PASSAGE OF A WEAK TROUGH LATE TONIGHT...WINDS WILL GENERALLY REMAIN 25 KTS OR LESS THROUGH THURSDAY. NORTHERLY WINDS WILL INCREASE TO 30 KT LATE THURSDAY NIGHT INTO SATURDAY BEHIND A COLD FRONTAL PASSAGE ALLOWING FOR THE FORMATION OF HEAVY FREEZING SPRAY. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... LAKE EFFECT SNOW ADVISORY UNTIL 9 AM EST THIS MORNING FOR MIZ006. LAKE EFFECT SNOW WARNING UNTIL 9 AM EST THIS MORNING FOR MIZ002- 005. LAKE EFFECT SNOW ADVISORY UNTIL 7 AM EST THIS MORNING FOR MIZ009. LAKE SUPERIOR...NONE. LAKE MICHIGAN...NONE. && $$ SYNOPSIS/DISCUSSION...AJ AVIATION...VOSS MARINE...VOSS
AREA FORECAST DISCUSSION
NWS MARQUETTE MI
424 AM EST MON JAN 19 2009 .SYNOPSIS... 08Z WATER VAPOR LOOP AND RUC 500MB HEIGHT ANALYSIS STILL SHOWS A HIGH AMPLITUDE PATTERN ACROSS NORTH AMERICA...WITH STRONG RIDGING OVER THE WESTERN U.S. INTO SW CANADA...AND TROUGHING OVER SE CANADA INTO THE EASTERN U.S.. UPPER MI CONTINUES TO BE INFLUENCED BY THE TROUGH...AND AS SUCH 850MB TEMPS REMAIN ON THE COOL SIDE...AROUND -15C PER 00Z RAOBS. SINCE THE AIRMASS REMAINS COLD...LAKE EFFECT SNOW SHOWERS ALSO CONTINUE. ALL ACCUMULATIONS ARE VERY FLUFFY...WITH SNOW TO WATER RATIOS OF 50 TO 1 OR SO. THIS IS DUE TO THE LAKE EFFECT CLOUDS BEING COMPLETELY CONTAINED WITHIN THE DENDRITIC SNOW GROWTH ZONE (DGZ)...AS SHOWN BY A 02Z TAMDAR SOUNDING FROM SAW. BASICALLY...WE HAVE BEEN GETTING A LOT OF BANG FOR OUR BUCK...WITH A LOT OF SNOW TURNING UP FOR LITTLE QPF. THIS CONTINUES NOW...WITH SNOWFALL AMOUNTS FROM 7 PM TO 330 AM AT THE OFFICE OF 5.3 INCHES. POSITION OF THE LAKE EFFECT THE PAST FEW DAYS HAS BEEN FOCUSED A LOT BY MESOSCALE FACTORS...SUCH AS LAND BREEZES AND TROUGHS EXTENDING BACK FROM WEAK LOW PRESSURE IN MAINE. EVEN THE ICE THAT IS PRESENT ON LAKE SUPERIOR (NEAR THE APOSTLES AND COVERING A LOT OF OUR LSZ265 ZONE) MAY BE HELPING A BIT AS A CONVERGENCE FOCUSING MECHANISM. CURRENTLY...ONE OF THOSE TROUGHS EXTENDS FROM SOUTHERN LAKE HURON NW ACROSS ESC AND TO ONTONAGON. NORTH OF THIS TROUGH...A SFC RIDGE IS NOTED ALONG THE NORTH SHORE OF LAKE SUPERIOR. BETWEEN THESE TWO FEATURES...A NORTH TO NE FLOW HAS HELPED TO CONFINE THE LAKE EFFECT SNOW TO MARQUETTE/WRN ALGER COUNTIES. CONVERGENCE ALONG THE TROUGH IS ALSO BRINGING LAKE EFFECT INTO WRN GOGEBIC/ONTONAGON COUNTIES. AREAS THAT ARE STAYING QUIET IN THE U.P. ARE CRYSTAL FALLS...ISQ AND ERY...WITH MOSTLY CLEAR SKIES. TEMPS HAVE FALLEN TO AROUND ZERO IN ALL THREE PLACES...WITH TYPICAL COLD SPOTS NEAR THEM BELOW ZERO. FARTHER UP TO OUR NW...A SHRTWV IS MOVING SE DOWN THE TOP OF THE RIDGE TO NEAR CHURCHILL MANITOBA. 00Z RAOB AT CYQD HAD AN 850MB TEMP OF 3C...AND SOME OF THIS WARM AIR WILL LIKELY GET PULLED EASTWARD AS THIS SHRTWV DROPS SOUTH INTO THE TROUGH. && .DISCUSSION... MAIN HIGHLIGHT TO THE FORECAST IS THE TEMPORARY END OF THE LAKE EFFECT THIS AFTERNOON. TODAY...SHRTWV APPROACHING CHURCHILL MANITOBA WILL CONTINUE ITS DESCENT SOUTHWARD...REACHING FAR NORTHERN ONTARIO BY 00Z. BECAUSE THIS SHRTWV IS DROPPING SOUTH...THE HIGH PRESSURE RIDGE ALONG THE NORTH SHORE OF LAKE SUPERIOR WILL ALSO HAVE TO BE FORCED SOUTHWARD. IN FACT...BY 00Z IT SHOULD BE SITUATED DOWN IN SRN LOWER MI. THEREFORE WINDS ARE EXPECTED TO BACK THROUGH THE DAY...ALLOWING WARM ADVECTION TO TAKE HOLD. MUCH OF THE WARM TAKES PLACE ABOVE 950MB AND PEAKS AT 850MB...WHERE SOUNDINGS FOR CMX SHOW A 24 HOUR RISE OF 12C BY 00Z WITH A READING OF -4C. THIS WARMING CAUSES INVERSIONS TO CRASH SUBSTANTIALLY THROUGH THE DAY...SO LAKE EFFECT SHOULD COMPLETELY SHUT OFF OVER WESTERN SUPERIOR...MAYBE AS EARLY AS 18Z. WARMING TAKES LONGER TO CROSS EASTERN SUPERIOR...SO LAKE EFFECT PROBABLY DOES NOT SHUT OFF UNTIL 21Z OR 00Z. HOWEVER...LAKE EFFECT PCPN OVER LAND WILL BE DONE BY 18Z DUE TO WINDS BACKING TO THE WEST. SINCE THE LAKE EFFECT IS MOVING AND DIMINISHING THROUGH TIME...LOOK FOR ADDITIONAL ACCUMULATIONS TO BE LIGHT...PERHAPS PEAKING UP TO ANOTHER 3 INCHES IN ALGER COUNTY. GOING END TIMES OF HEADLINES SEEM REASONABLE. OUTSIDE OF THE LAKE EFFECT...DRY CONDITIONS WILL OCCUR WITH SUBSIDENCE AND DRY AIR. ALTHOUGH WE ARE WARMING ALOFT...THE IMPACT AT THE SFC IS EXPECTED TO BE LESS DUE TO THE VERY LOW SUN ANGLE THIS TIME OF YEAR. STAYED TOWARD THE LOW END OF GUIDANCE FOR HIGHS DUE TO THE STRONG SUBSIDENCE SEEN ON SOUNDINGS...AND EXPECTED INCREASE IN HIGH CLOUDS DURING THE AFTN. TONIGHT...UPPER RIDGE OVER THE WESTERN U.S. IS PROGGED TO BEGIN FLATTENING SOMEWHAT AS A SHRTWV TROUGH IN THE GULF OF ALASKA MOVES INLAND. THIS FLATTENING OF THE UPPER RIDGE WILL HELP TO KEEP THE SHRTWV THAT IS APPROACHING CHURCHILL WELL OFF TO OUR EAST...PROGGED TO REACH THE ONTARIO/QUEBEC LINE BY 12Z WED. HOWEVER...A LOW PRESSURE TROUGH WILL ACCOMPANY THE WAVE...MOVING FROM NW ONTARIO AT 00Z INTO UPPER MI BY 12Z. GIVEN HOW FAR EAST THE SHRTWV IS...ANY DPVA FORCING IS MINIMAL. ISENTROPIC LIFT PROGS LOOK QUIET AS WELL...WITH NEUTRAL LIFT AND ONLY SOME GRADUAL LOWERING IN CONDENSATION PRESSURE DEFICITS BY 12Z. THEREFORE...CHANCES FOR SYNOPTIC PCPN LOOK VERY LOW AT THIS POINT. EVEN IF PCPN COULD FALL...SOUNDINGS DEPICT A FAIRLY DRY LAYER PRESENT BTWN 900-700MB. THE ONLY AREA THAT SHOWS THIS LAYER MOISTENING IS OVER EASTERN SUPERIOR...AND THUS KEPT SOME 20 POPS THERE. REMOVED CHANCES FOR PCPN ELSEWHERE. TEMPS ARE TRICKY SINCE THERE SHOULD BE PLENTY OF HIGH CLOUDS AROUND...AS WELL AS INCREASE OF MID CLOUDS AND THEN LOW CLOUDS LATE IN THE NIGHT. IN ADDITION...THE APPROACH OF THE SFC TROUGH WILL HELP TO KEEP WIND SPEEDS UP. THEREFORE DECIDED TO STAY ON THE WARM SIDE OF GUIDANCE. ON A SIDE NOTE...WITH THE LOW CLOUDS COME IN LATE AND A WESTERLY FLOW...THERE COULD BE SOME FLURRIES DEVELOPING IN THE UPSLOPE AREAS OF THE WESTERN U.P.. WEDNESDAY...UPPER RIDGE IS SHOWN TO CONTINUE FLATTENING OUT AS THE SHRTWV CURRENTLY IN THE GULF OF ALASKA PUSHES SOUTHWARD THROUGH BRITISH COLUMBIA. FLOW OVER UPPER MI ALOFT ACTUALLY GOES FROM THE CURRENT DUE NORTH TO NORTHWEST BY 00Z THU. THIS NW FLOW WILL HELP TO KEEP RELATIVELY WARM AIR AT 850MB OVER THE CWA...RANGING FROM -2C WEST TO -8C EAST. OF MORE INTEREST IS BELOW 850MB...WITH MODELS HAVING PLENTY OF LOW LEVEL MOISTURE TRAPPED. MOST MODELS ARE ALSO PRINTING OUT LIGHT QPF WITH THIS MOISTURE...ESPECIALLY IN NW FLOW AREAS. IN FACT...IT IS CLOSE TO BEING UNSTABLE ENOUGH BELOW 850MB TO CALL IT LAKE EFFECT. FOR NOW...DECIDED TO FOLLOW THE PREVIOUS FCST AND JUST CALL IT FLURRIES FOR UPSLOPE NW FLOW AREAS...SINCE CLOUD DEPTHS ARE ONLY EXPECTED AROUND 2000 FT. LATER FCSTS MAY HAVE TO INCLUDE SOME LOW CHANCE POPS...THOUGH. THESE LOW CLOUDS SHOULD HELP KEEP TEMPS DOWN AS WELL...BUT READINGS ARE STILL EXPECTED TO CLIMB ABOVE NORMAL. STAYED WITH A BLEND OF GUIDANCE...WHICH HAS HIGHS IN THE MID TO UPPER 20S. WED NIGHT INTO THU...MODEL DIFFERENCES ARISE IN THE HANDLING OF THE BRITISH COLUMBIA SHRTWV. THE GFS/NAM AND UKMET ARE ALL PRETTY PROGRESSIVE...BRINGING IT TO AROUND THE INTERNATIONAL FALLS AREA BY 00Z FRI. ASSOCIATED WITH THIS SHRTWV IS A SFC LOW...WHICH WOULD REACH UPPER MI BY 00Z FRI ACCORDING TO THIS MODEL GROUP. THE 00Z ECMWF...ON THE OTHER HAND IS COMPLETELY DIFFERENT...WHICH WAS TRUE WITH THE 12Z RUN OF IT AS WELL. IT SUGGESTS THE SHRTWVS MAKES MORE OF A DIVE SOUTHWARD INTO SRN ALBERTA...WITH A WEAK NON-ASSOCIATED SFC LOW WELL TO THE EAST OVER SE MN AT 00Z FRI. AFTER COORDINATION WITH HPC...FOLLOWED THE ECMWF IDEA. ALL MODELS SHOW FOR WED NIGHT A COLD FRONT DROPPING SOUTH THROUGH NORTHERN ONTARIO...MOVING INTO LAKE SUPERIOR BY 12Z THU. MID-LEVEL FRONTOGENESIS ABOVE AND TO THE NORTH OF THIS FRONT MAY SUPPORT SOME LIGHT SYNOPTIC SNOW. WOULD EXPECT IT TO THEREFORE MOSTLY FALL ON LAKE SUPERIOR...PERHAPS BRUSHING THE EASTERN CWA. OTHERWISE...LOW CLOUDS HANGING AROUND COMBINED WITH WEST TO NW LOW LEVEL WINDS SUGGESTS KEEPING FLURRIES GOING IN UPSLOPE AREAS. THE CLOUDS WILL ALSO HELP TO KEEP TEMPS UP...AND THEREFORE STAYED ON THE WARM SIDE OF GUIDANCE WITH LOWS FROM THE MID TEENS TO LOW 20S. THESE READINGS COULD BE WARMED UP IN LATER FORECASTS IF IT ENDS UP COMPLETELY CLOUDY ON WEDNESDAY. FOR THU...THE FRONT AND MID-LEVEL FRONTOGENESIS SHIFT SOUTH IN RESPONSE TO FALLING HEIGHTS ALOFT. THEREFORE...SHIFTED THE LOW CHANCE POPS SOUTH AS WELL FOR THU. ECMWF 850MB TEMPS OF -8 TO -10C ARE TOO MARGINAL FOR LAKE EFFECT...THEREFORE DID NOT SHOW ANY LOCATION HAVING HIGHER POPS THAN 20. CLOUD COVER SHOULD BE PERSISTENT AGAIN...BUT WITH WARMER LOWS ON WED NIGHT AND NO SIGNIFICANT COOLING ON THU...THU SHOULD END UP BEING THE WARMEST DAY OF THE WEEK. GOING HIGHS LOOKED REASONABLE. THU NIGHT AND FRI...WHETHER YOU FOLLOW THE GFS...UKMET OR ECMWF...THERE IS A GENERAL IDEA OF LOW PRESSURE IN THE WESTERN GREAT LAKES AREA BY FRI MORNING...WHICH THEN SHIFTS OFF TO THE EASTERN GREAT LAKES DURING THE DAY FRI. IN THE WAKE OF THIS LOW...HIGH PRESSURE WHICH WILL BE BUILDING OVER THE NEXT COUPLE DAYS FROM NRN ALASKA INTO THE YUKON...IS EXPECTED TO NOSE DOWN THROUGH THE PLAINS. THIS MEANS ANOTHER SURGE OF ARCTIC AIR FOR UPPER MI...WHICH SHOULD ARRIVE BY 00Z SAT. ECMWF 850MB TEMPS FALL TO -12C BY 12Z FRI AND THEN TO -20C BY 00Z SAT. THESE FALLING 850MB TEMPS MEANS A RESURGENCE OF LAKE EFFECT...FIRST AFFECTING NORTH FLOW AREAS THU NIGHT INTO FRI MORNING...THEN SWITCHING TO NW FLOW AREAS FRI AFTN INTO FRI NIGHT. KEPT THE GENERAL IDEA OF THE PREVIOUS FORECAST THE SAME...WITH THE MAIN ADJUSTMENT TO SLOW DOWN THE HIGHER POPS IN THE NORTH CENTRAL U.P. THU NIGHT. ALSO ADDED SOME SMALL CHANCE POPS TO THE SOUTHERN U.P. THU NIGHT AND FRI WITH POTENTIAL OF SYNOPTIC SNOW AS INDICATED BY THE ECMWF. INITIALLY THE SNOW WILL LIKELY BE QUITE FLUFFY...THEN AS THE COLD AIR MOVES IN...THE SNOW SHOULD GET FINER AS THE DENDRITIC SNOW GROWTH ZONE FALLS BELOW THE CLOUD BASE. POTENTIAL DOES EXIST FOR MODERATE SNOW ACCUMULATIONS OVER HIGHER TERRAIN AREAS...AND WILL NOTE THIS IN THE HWO. REGARDING TEMPS...RAISED BOTH LOWS AND HIGHS UP A FEW DEGREES DURING THE PERIOD TO ACCOUNT FOR THE SLOWER SCENARIO OF COLD AIR COMING IN. FURTHER INCREASES MAY BE REQUIRED. HOWEVER...TEMPS SHOULD FALL FRIDAY AFTN. NO CHANGES MADE BEYOND FRI. STILL LOOKS COLD FOR THE WEEKEND INTO MONDAY. NEW ECMWF SHOWS THE ARCTIC HIGH THAT HAS BEEN NOSING DOWN INTO THE PLAINS MOVING OVERHEAD MONDAY NIGHT. IF THIS COMES TRUE...COULD SEE INLAND AREAS GETTING DOWN TO -20F AT LEAST. && .AVIATION (FOR THE 06Z TAF ISSUANCE)... KSAW...CONVERGENT NORTHERLY FLOW TONIGHT WILL KEEP OCNL MODERATE SNOW SHOWERS GOING WITH IFR TO OCNL MVFR CONDITIONS. WINDS BACKING NW LATE TONIGHT AHEAD OF APPROACHING RDG FROM THE NRN PLAINS WILL SHIFT HEAVIER LES BANDS EAST AND IMPROVE CONDITIONS TO MVFR AGAIN. BY TUE AFTERNOON...WEST WINDS WILL PUSH LAKE EFFECT WELL EAST AND VFR CONDITIONS RETURN THROUGH THE REST OF THE PERIOD. KCMX...THE COMBINATION OF A SHORTWAVE TROUGH AND NRLY FLOW WILL RESULT IN PERSISTENT LES WITH IFR CONDITIONS TONIGHT. FLOW BACKING NW LATE TONIGHT AHEAD OF APPROACHING RDG WILL IMPROVE CONDITIONS AGAIN TO MVFR IN WEAKER LES BANDS WHICH WILL LAST THROUGH THE REST OF THE PERIOD. && .MARINE (FOR THE 4 AM LAKE SUPERIOR FORECAST ISSUANCE)... NORTH WINDS THIS MORNING WILL BACK SOUTHWEST THIS AFTERNOON AS A HIGH PRESSURE RIDGE MOVES ACROSS THE AREA. A TIGHTENING SW GRADIENT AHEAD OF AN APPROACHING TROUGH WILL INCREASE WINDS TO 30 KT OVER THE WRN AND NCNTRL PORTIONS OF LAKE SUPERIOR TONIGHT RESULTING IN MODERATE FREEZING SPRAY. BEHIND THE PASSAGE OF A WEAK TROUGH LATE TONIGHT...WINDS WILL GENERALLY REMAIN 25 KTS OR LESS THROUGH THURSDAY. NORTHERLY WINDS WILL INCREASE TO 30 KT LATE THURSDAY NIGHT INTO SATURDAY BEHIND A COLD FRONTAL PASSAGE ALLOWING FOR THE FORMATION OF HEAVY FREEZING SPRAY. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN... LAKE EFFECT SNOW ADVISORY UNTIL 9 AM EST THIS MORNING FOR MIZ006. LAKE EFFECT SNOW WARNING UNTIL 9 AM EST THIS MORNING FOR MIZ002- 005. LAKE EFFECT SNOW ADVISORY UNTIL 7 AM EST THIS MORNING FOR MIZ009. LAKE SUPERIOR...NONE. LAKE MICHIGAN...NONE. && $$ SYNOPSIS/DISCUSSION...AJ AVIATION...07 MARINE...VOSS
AREA FORECAST DISCUSSION
NWS DULUTH MN
937 PM CST WED JAN 21 2009 .UPDATE...QUITE A TEMPERATURE VARIATION ACROSS THE CWA THIS EVENING...WITH TEMPS IN THE CLEAR AIR IN THE SINGLE DIGITS AND TEMPERATURES IN THE CLOUDS IN THE LOWER 20S IN SPOTS. THE CLOUDS ARE GRADUALLY DROPPING SOUTHWARD AGAIN...AND SHOULD CONTINUE TO DO SO OVERNIGHT. HAVE DROPPED TEMPS SOME 10-15 DEGREES IN SPOTS DUE TO THE CLEARING...BUT TEMPERATURES SHOULD MODERATE SOMEWHAT AS CLOUDS FILL IN/MOVE IN AGAIN. OTHER THAN THAT...THERE HAS BEEN SOME FZDZ NORTH OF THE BORDER THIS EVENING. WILL CONTINUE TO MENTION PATCHY FREEZING DRIZZLE ACROSS THE CWA OVERNIGHT...AND WILL HAVE TO WATCH FOR DROPPING VSBYS AS A SIGN OF FZDZ. SO FAR...KHIB HAS DROPPED TO 1/4 MILE...ON THE EDGE OF THE CLOUDS...SO WILL SEE SOME PATCHY DENSE FOG AS WELL. OTHERWISE... NO MAJOR CHANGES WITH ZONES/GRIDS IN GOOD SHAPE. && .PREV DISCUSSION... /ISSUED 301 PM CST WED JAN 21 2009/ DISCUSSION...LOW STRATUS DECK THAT HAS BEEN OVER THE FA ALL DAY IS ERODING FROM THE WEST. EDGE OF THE CLOUD DECK HAS REACHED NW WI AND THE TWIN PORTS...BUT ALREADY BEGINNING TO SEE SIGNS OF THE STRATUS REFORMING. EXPECT THIS TREND TO CONTINUE AND WHERE THE CLOUDS HAVE CLEARED...TO FILL BACK IN. FORECAST SOUNDINGS ARE SUGGESTING THAT -FZDZ IS POSSIBLE TONIGHT ALONG WITH SOME FOG. SREF PROBABILITIES OF FROZEN PCPN ALSO POINTING TOWARDS -FZDZ POTENTIAL TONIGHT. HAVE LEFT GRIDS AS IS IN REGARDS TO THE -FZDZ. ADDED PATCHY FOG EVERYWHERE AS THE INVERSION STRENGTHENS ONCE AGAIN TONIGHT. -FZDZ POTENTIAL EXISTS THROUGH THURSDAY MORNING ACROSS THE NORTHERN THIRD OF THE FA PER FORECAST SOUNDINGS...DROPPING SOUTHWARD IN THE AFTERNOON. SREF PROBABILITIES ALSO INDICATING THE FOG MAY PERSIST THROUGH THE DAY. HAVE OPTED TO LEAVE THE FOG OUT FOR NOW IN ANTICIPATION OF CLEARING SIMILAR TO TODAY. MAY SEE SOME FLURRIES DEVELOP IN THE AFTERNOON ACROSS THE NORTHERN PORTION WITH THE APPROACH OF UPPER LEVEL WAVE/SFC COLD FRONT. BETTER CHANCE OF -SN TO OCCUR THURSDAY NIGHT AS THE UPPER WAVE CROSSES THE FA AND ANOTHER ROUND OF VERY COLD ARCTIC AIR DESCENDS UPON THE FA. INTERACTION OF THE WAVE ON THE FRONT AND THE RELATIVELY MOIST BOUNDARY LAYER SHOULD PRODUCE SOME LIGHT ACCUMULATION. GREATEST AREAL COVERAGE OF THIS -SN SHOULD BE THE MN ARROWHEAD WHICH WILL BE ON THE N SIDE OF THE SFC LOW THAT MOVES THROUGH THE FA. THIS BLAST OF ARCTIC AIR WILL BE SHORT LIVED...ROUGHLY 36 HOURS...AND MIN TEMPS REFLECT THIS WITH MINUS TEENS TO 20S F FRIDAY NIGHT AND SATURDAY NIGHT. SFC HIGH WILL SETTLE IN AS WELL. WIND CHILL MAY BECOME A FACTOR DEPENDING ON WIND STRENGTH. LONG TERM...SAT NIGHT THRU TUESDAY.. FAIRLY QUIET AND CHILLY PATTERN AS CWA REMAINS UNDERNEATH BRISK WNW MID LVL FLOW. SPLIT FLOW IN WESTERLIES FEATURES ACTIVE SRN BRANCH SPLITTING OFF PACNW COAST AND REEMERGING OVER SOCAL AND EAST INTO SRN PLAINS. THIS KEEPS NORTHLAND WELL NORTH OF MAIN BAROCLINIC ZONE AND SIGNIFICANT STORM POTENTIAL. CONFLUENCE BETWEEN TWO BRANCHES OF WESTERLIES WILL BE CENTERED NEAR NRN PLAINS. THIS SHOULD PERPETUATE SFC HIGH FROM WRN PLAINS OF CANADA SOUTHEAST TOWARDS MIDWEST. WITH BELOW NORMAL HTS/TEMPS AT 50H/85H...COLDER THAN TYPICAL MAX/MINS. AVIATION...LARGE AREA OF LOW STRATUS COVERS ALL TERMINALS EXCEPT BRD. MVFR BASES OCCURRING OVER NW WISCONSIN THIS AFTERNOON...WHILE CLOUD DECK LOWERS TO IFR AT INL/HIB/DLH.TAMDAR NEAR HIB AT 20Z INDICATES TOP OF STRATUS NEAR 4.5 KFT. BACK EDGE OF STRATUS DECK HAS BEEN EDGING EAST AND CURRENT SPEED WOULD ALLOW SOME BREAKS BY LATE AFTERNOON OVER HIB/DLH TERMINALS. FOR OVERNIGHT PERIOD WILL PLAY PESSIMISTIC ROUTE GIVEN OVERALL SYNOPTIC REGIME...MODIFIED PACIFIC AIR ADVECTING OVER SUBSTANTIAL SNOW PACK. SUSPECT THAT ANY CLEARING WILL BE TEMPORARY AS STRATUS REFORMS OVERNIGHT. MDL TIME/HEIGHT XSECTS SHOW FAIRLY STRONG INVERSION WILL EXIST THROUGH ALL OF TAF PERIOD. && POINT TEMPS/POPS... DLH 17 23 4 8 / 10 10 30 20 INL 17 18 -7 -1 / 10 10 30 20 BRD 7 25 1 5 / 10 10 20 20 HYR 10 25 9 15 / 10 10 20 20 ASX 15 24 13 17 / 10 10 30 20 && .DLH WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. $$ DAP
AREA FORECAST DISCUSSION
NWS DULUTH MN
301 PM CST WED JAN 21 2009 .DISCUSSION...LOW STRATUS DECK THAT HAS BEEN OVER THE FA ALL DAY IS ERODING FROM THE WEST. EDGE OF THE CLOUD DECK HAS REACHED NW WI AND THE TWIN PORTS...BUT ALREADY BEGINNING TO SEE SIGNS OF THE STRATUS REFORMING. EXPECT THIS TREND TO CONTINUE AND WHERE THE CLOUDS HAVE CLEARED...TO FILL BACK IN. FORECAST SOUNDINGS ARE SUGGESTING THAT -FZDZ IS POSSIBLE TONIGHT ALONG WITH SOME FOG. SREF PROBABILITIES OF FROZEN PCPN ALSO POINTING TOWARDS -FZDZ POTENTIAL TONIGHT. HAVE LEFT GRIDS AS IS IN REGARDS TO THE -FZDZ. ADDED PATCHY FOG EVERYWHERE AS THE INVERSION STRENGTHENS ONCE AGAIN TONIGHT. -FZDZ POTENTIAL EXISTS THROUGH THURSDAY MORNING ACROSS THE NORTHERN THIRD OF THE FA PER FORECAST SOUNDINGS...DROPPING SOUTHWARD IN THE AFTERNOON. SREF PROBABILITIES ALSO INDICATING THE FOG MAY PERSIST THROUGH THE DAY. HAVE OPTED TO LEAVE THE FOG OUT FOR NOW IN ANTICIPATION OF CLEARING SIMILAR TO TODAY. MAY SEE SOME FLURRIES DEVELOP IN THE AFTERNOON ACROSS THE NORTHERN PORTION WITH THE APPROACH OF UPPER LEVEL WAVE/SFC COLD FRONT. BETTER CHANCE OF -SN TO OCCUR THURSDAY NIGHT AS THE UPPER WAVE CROSSES THE FA AND ANOTHER ROUND OF VERY COLD ARCTIC AIR DESCENDS UPON THE FA. INTERACTION OF THE WAVE ON THE FRONT AND THE RELATIVELY MOIST BOUNDARY LAYER SHOULD PRODUCE SOME LIGHT ACCUMULATION. GREATEST AREAL COVERAGE OF THIS -SN SHOULD BE THE MN ARROWHEAD WHICH WILL BE ON THE N SIDE OF THE SFC LOW THAT MOVES THROUGH THE FA. THIS BLAST OF ARCTIC AIR WILL BE SHORT LIVED...ROUGHLY 36 HOURS...AND MIN TEMPS REFLECT THIS WITH MINUS TEENS TO 20S F FRIDAY NIGHT AND SATURDAY NIGHT. SFC HIGH WILL SETTLE IN AS WELL. WIND CHILL MAY BECOME A FACTOR DEPENDING ON WIND STRENGTH. .LONG TERM...SAT NIGHT THRU TUESDAY.. FAIRLY QUIET AND CHILLY PATTERN AS CWA REMAINS UNDERNEATH BRISK WNW MID LVL FLOW. SPLIT FLOW IN WESTERLIES FEATURES ACTIVE SRN BRANCH SPLITTING OFF PACNW COAST AND REEMERGING OVER SOCAL AND EAST INTO SRN PLAINS. THIS KEEPS NORTHLAND WELL NORTH OF MAIN BAROCLINIC ZONE AND SIGNIFICANT STORM POTENTIAL. CONFLUENCE BETWEEN TWO BRANCHES OF WESTERLIES WILL BE CENTERED NEAR NRN PLAINS. THIS SHOULD PERPETUATE SFC HIGH FROM WRN PLAINS OF CANADA SOUTHEAST TOWARDS MIDWEST. WITH BELOW NORMAL HTS/TEMPS AT 50H/85H...COLDER THAN TYPICAL MAX/MINS. && .AVIATION...LARGE AREA OF LOW STRATUS COVERS ALL TERMINALS EXCEPT BRD. MVFR BASES OCCURRING OVER NW WISCONSIN THIS AFTERNOON...WHILE CLOUD DECK LOWERS TO IFR AT INL/HIB/DLH.TAMDAR NEAR HIB AT 20Z INDICATES TOP OF STRATUS NEAR 4.5 KFT. BACK EDGE OF STRATUS DECK HAS BEEN EDGING EAST AND CURRENT SPEED WOULD ALLOW SOME BREAKS BY LATE AFTERNOON OVER HIB/DLH TERMINALS. FOR OVERNIGHT PERIOD WILL PLAY PESSIMISTIC ROUTE GIVEN OVERALL SYNOPTIC REGIME...MODIFIED PACIFIC AIR ADVECTING OVER SUBSTANTIAL SNOW PACK. SUSPECT THAT ANY CLEARING WILL BE TEMPORARY AS STRATUS REFORMS OVERNIGHT. MDL TIME/HEIGHT XSECTS SHOW FAIRLY STRONG INVERSION WILL EXIST THROUGH ALL OF TAF PERIOD. && POINT TEMPS/POPS... DLH 17 23 4 8 / 10 10 30 20 INL 13 18 -7 -1 / 10 10 30 20 BRD 12 25 1 5 / 10 10 20 20 HYR 15 25 9 15 / 10 10 20 20 ASX 17 24 13 17 / 10 10 30 20 && .DLH WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. LS...NONE. $$ GSF/CANNON
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
229 PM CST WED JAN 21 2009 .DISCUSSION... MODEL TRENDS TODAY STILL INDICATE THE UPPER RIDGE THAT IN PLACE OVER THE MIDWEST...WILL CONTINUE TO ERODE AND BREAK DOWN ACROSS THE UPPER MIDWEST. THIS WILL ALLOW SOME ARCTIC AIR TO BEGIN TO OOZE DOWN OVER SOUTH CENTRAL CANADA OVER THE NEXT DAY OR SO BEFORE PLUNGING DOWN ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES REGION BEFORE THE WEEKEND. BY SUNDAY MORNING...OVERNIGHT LOWS WILL VARY FROM 20 BELOW ZERO TO 10 BELOW ZERO OVER MUCH OF CWA WITH DAYTIME HIGHS IN THE SINGLE DIGITS ON SUNDAY. THE LATEST SREF HAS -20 SFC DEWPOINT PRESS SOUTH OVER NORTHEAST HALF OF CWA BY THAT PERIOD. THE NEW ARCTIC BLAST EXPECTED TO BE SHORT-LIVED AS UPPER RIDGE BUILDS OVER WESTERN AND CENTRAL CANADA BY MID WEEK OF NEXT WEEK. IN THE NEAR TERM...STRATUS CLOUDS WILL TEMPORARILY MOVE OUT OF EAST CENTRAL MN AND PART OF WEST CENTRAL WISCONSIN EARLY THIS EVENING. CLOUDS ARE EXPECTED TO ROLL BACK OVER THE AREA AND ADVANCE WEST AND NORTH TONIGHT. && .AVIATION.../18Z TAF ISSUANCE/ LOW IFR CEILING REMAIN ACROSS EASTERN AREAS LATE MORNING. NOTICING SOME EROSION IN THE WESTERN AREAS AROUND KMSP LAST FEW FOG PRODUCT SATELLITE IMAGERY. TAMDAR SOUNDING SHOWING LARGE INVERSION WITH CLOUD LAYER AVERAGING ABOUT 1K FT THICK. MODELS SHOWING NW FLOW AT 925MB LEVEL...WHERE MUCH OF CLOUD LAYER RESIDES. MORE OF A PUSH TO THE WESTERN CLOUD EDGE OVER NORTHERN METRO TOWARD KJMR/KCBG AREA. THIS ADVANCES EAST THIS AFTERNOON...WITH QUESTION REMAINING AS TO HAVE FAR EAST THIS EDGE WILL WORK TODAY. WINDS REMAIN RATHER LIGHT ACROSS THE TAF AREA...AND SHOULD SEE IFR/LOW MVFR CIGS REMAIN AT KRNH/KEAU THROUGH THE NIGHT. DIFFICULT TO DISCERN IF FOG DEVELOPMENT WILL OVERTAKE REGION OVERNIGHT. WILL SEE SOME MELTING TO THE FAR WEST...BUT LOW LEVEL DEWPOINTS REMAIN QUITE DRY. WILL MENTION SOME MVFR VSBYS IN FOG AT MOST SITES DEVELOPING MAINLY AFTER 06Z PER MODEL TREND. KMSP WILL BE ON THE EDGE OF LOW CLOUDS THIS EVENING...AND WITH LIGHT WINDS REMAINING OVER THE REGION... FOG/STRATUS DEVELOPMENT...OR CLOUD EDGE MAY DEVELOPMENT BACK WEST AGAIN OVERNIGHT. HAD TO KEEP MENTION OF THIS POSSIBILITY IN TAF FOR NOW. EXPECT CLOUDS/FOG TO MOVE OUT THU MORNING...WITH VFR CONDS ANTICIPATED IN WESTERN AREAS AFTER 15Z AND THE FAR EAST AROUND 18Z. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. && $$ JM/DWE
AREA FORECAST DISCUSSION
NWS TWIN CITIES/CHANHASSEN MN
1145 AM CST WED JAN 21 2009 .UPDATE... UPDATED TO INCLUDE 18Z AVIATION DISCUSSION BELOW. && .DISCUSSION... HIGHLY AMPLIFIED UPPER LEVEL PATTERN FINALLY BREAKING DOWN THIS MORNING...AS EVIDENCED BY WIDESPREAD H5 HEIGHT FALLS AT 00Z WITHIN THE WESTERN RIDGE. AT THE SURFACE...A WEAK SURFACE TROUGH IS MOVING THROUGH THE UPPER MIDWEST THIS MORNING AND WARM ADVECTION OUT AHEAD OF IT IS LEADING TO STRATUS ACROSS EXTREME EASTERN MINNESOTA AND WISCONSIN. THIS SHOULD SHOULD CLEAR OUT THROUGH THE MORNING...AS WARMER AND DRIER AIR WORKS ITS WAY IN FROM THE WEST BEHIND THE TROUGH. HIGHS TODAY SHOULD BE A GOOD 5 DEGREES WARMER THAN YESTERDAY...WHICH WILL ALLOW MOST OF THE MINNESOTA CWA TO FLIRT WITH THE 30 DEGREE MARK...WITH NEAR FREEZING TEMPERATURES POSSIBLE IN THE FAR SOUTHWEST CWA. FOR HIGHS...TRENDED TOWARD THE COOLER MET...WHICH SEEMS TO BE MORE IN LINE WITH HOW TEMPERATURES HAVE ACTED THE LAST COUPLE OF DAYS. MILD WEATHER WILL CONTINUE THROUGH THURSDAY UNTIL A STRONG ARCTIC COLD FRONT PUTS THE AREA INTO WELL BELOW NORMAL TEMPERATURES ONCE AGAIN FRIDAY. CURRENT MODEL TRENDS HAVE THE FRONT MOVING COMPLETELY THROUGH THE CWA BY AROUND NOON FRIDAY. THIS WILL LIKELY RESULT IN FALLING TEMPERATURES THROUGHOUT MOST OF THE DAY...AS 1050 MB SURFACE HIGH COMES ROARING INTO THE CWA. PRESSURE GRADIENT WILL BE QUIET STRONG IMMEDIATELY BEHIND THE FRONT...SO WENT ABOVE GUIDANCE FOR WINDS DURING THE DAY FRIDAY. FOR THE FRIDAY THROUGH SUNDAY MORNING PERIOD...TOOK ANOTHER 2 TO 4 DEGREES OFF OF INHERITED FORECAST...TRENDING TOWARD MUCH COOLER BIAS CORRECTED VALUES...WHICH WOULD SUGGEST WE COULD SEE SOME -20 OR COLDER LOWS AGAIN SATURDAY AND SUNDAY WITH HIGHS SATURDAY STAYING BELOW ZERO. AFTER SUNDAY MORNING...WE LOOSE OUR GOOD FEED OF ARCTIC AIR...WHICH WILL ALLOW TEMPERATURES TO MODERATE SOME INTO THE BEGINNING OF NEXT WEEK. ALTHOUGH WE WILL HAVE A STRONG ARCTIC COLD FRONT MOVE THROUGH FRIDAY...THERE ARE NO SYSTEMS OF SIGNIFICANCE THAT WILL EFFECT THE CWA OVER THE NEXT WEEK. FORCING FOR THE FRONT ON FRIDAY IS SHALLOW AND CONFINED MAINLY TO THE SURFACE AND IS LAKING MUCH MOISTURE. AS A RESULT...NOT ANTICIPATING MUCH MORE THAN FLURRIES WITH FRONT ATTM. BEST CHANCES FOR SNOW WILL BE OFF TO OUR EAST...WHERE A WEAK SURFACE WILL MOVE FROM MANITOBA INTO NORTHERN MICHIGAN. OTHER THAN THAT...AMPLIFIED PATTERN FLATTENS OUT...RESULTING IN MAINLY ZONAL FLOW ACROSS THE CONUS...WITH MOST OF THE ACTIVITY SHIFTING SOUTH. && .AVIATION.../18Z TAF ISSUANCE/ LOW IFR CEILING REMAIN ACROSS EASTERN AREAS LATE MORNING. NOTICING SOME EROSION IN THE WESTERN AREAS AROUND KMSP LAST FEW FOG PRODUCT SATELLITE IMAGERY. TAMDAR SOUNDING SHOWING LARGE INVERSION WITH CLOUD LAYER AVERAGING ABOUT 1K FT THICK. MODELS SHOWING NW FLOW AT 925MB LEVEL...WHERE MUCH OF CLOUD LAYER RESIDES. MORE OF A PUSH TO THE WESTERN CLOUD EDGE OVER NORTHERN METRO TOWARD KJMR/KCBG AREA. THIS ADVANCES EAST THIS AFTERNOON...WITH QUESTION REMAINING AS TO HAVE FAR EAST THIS EDGE WILL WORK TODAY. WINDS REMAIN RATHER LIGHT ACROSS THE TAF AREA...AND SHOULD SEE IFR/LOW MVFR CIGS REMAIN AT KRNH/KEAU THROUGH THE NIGHT. DIFFICULT TO DISCERN IF FOG DEVELOPMENT WILL OVERTAKE REGION OVERNIGHT. WILL SEE SOME MELTING TO THE FAR WEST...BUT LOW LEVEL DEWPOINTS REMAIN QUITE DRY. WILL MENTION SOME MVFR VSBYS IN FOG AT MOST SITES DEVELOPING MAINLY AFTER 06Z PER MODEL TREND. KMSP WILL BE ON THE EDGE OF LOW CLOUDS THIS EVENING...AND WITH LIGHT WINDS REMAINING OVER THE REGION... FOG/STRATUS DEVELOPMENT...OR CLOUD EDGE MAY DEVELOPMENT BACK WEST AGAIN OVERNIGHT. HAD TO KEEP MENTION OF THIS POSSIBILITY IN TAF FOR NOW. EXPECT CLOUDS/FOG TO MOVE OUT THU MORNING...WITH VFR CONDS ANTICIPATED IN WESTERN AREAS AFTER 15Z AND THE FAR EAST AROUND 18Z. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...NONE. WI...NONE. && $$ MG/DWE
AREA FORECAST DISCUSSION
NWS PORTLAND OR
230 AM PST TUE JAN 20 2009 .SYNOPSIS...A STRONG UPPER LEVEL RIDGE WILL CONTINUE TO DOMINATE THE PACIFIC NORTHWEST THROUGH TODAY...CENTERED NEAR IDAHO. THE UPPER RIDGE WILL THEN WEAKEN AND MOVE OFF TO THE EAST FOR THE REMAINDER OF THE WEEK. THE STRONG SURFACE HIGH PRESSURE AREA EAST OF THE CASCADES WILL ALSO WEAKEN...ESPECIALLY TUESDAY NIGHT AND WEDNESDAY WITH DECREASING EAST WINDS. THE FIRST PACIFIC WEATHER SYSTEM TO APPROACH IN QUITE SOME WHILE WILL SPLIT AND WEAKEN AS IT NEARS THE COAST WEDNESDAY NIGHT AND THURSDAY...THEN EVENTUALLY PUSH THROUGH OUR FORECAST AREA ABOUT FRIDAY. A SERIES OF WEATHER SYSTEMS MAY BEGIN PUSHING THROUGH THE PACIFIC NORTHWEST THIS WEEKEND AND EARLY NEXT WEEK AS THE UPPER AIR PATTERN FINALLY CHANGES. && .SHORT TERM...THE KTTD-KDLS OFFSHORE PRESSURE GRADIENT HAS FINALLY FALLEN TO LESS THAN 10 MB THIS MORNING...BUT THE DECREASE IS SLOW AND WINDS ARE STILL QUITE GUSTY THIS MORNING IN AND NEAR THE COLUMBIA RIVER GORGE AND IN THE EAST COUNTY AREAS THOUGH WIND SPEEDS HAVE FALLEN BELOW ADVISORY CRITERIA AND WILL CONTINUE TO DIMINISH TODAY. TROUTDALE WAS STILL GUSTING TO AROUND 30 MPH THIS MORNING. DEWPOINTS REMAIN VERY LOW ACROSS THE FORECAST AREA THIS MORNING AND THINK THE BEST CHANCE OF ANY FOG WILL BE DOWN NEAR EUGENE AND POSSIBLY UP NEAR CASTLE ROCK...BUT THEN PATCHY AT BEST ANYWHERE ELSE. WINDS WILL LET UP A LOT MORE TONIGHT AND WEDNESDAY AND THINK THE FOG WILL BEGIN EXPANDING MORE THEN. THE SURFACE PRESSURE GRADIENT IS STILL OFFSHORE THROUGH THE GORGE AROUND 6 OR 7 MB ON THE NAM12 TONIGHT AND WEDNESDAY...SO THERE WILL STILL BE SOME WIND IN THE GORGE AND NEAR TROUTDALE. THAT WOULD STILL SUPPORT PEAK GUSTS OF 40 TO 50 MPH IN THE GORGE. PRESSURE GRADIENTS LET UP TO AROUND 5 MB WEDNESDAY NIGHT WITH GUSTS UP TO 30 OR 35 MPH TOPS IN THE GORGE. EXPECT MORE FOG IN THE VALLEYS WEDNESDAY NIGHT AS WELL. THE GRADIENTS ARE WEAKENING AS THE UPPER RIDGE WEAKENS AND THE FIRST PACIFIC WEATHER SYSTEM IN QUITE SOME TIME APPROACHES...BUT THAT FRONT WILL BE SPLITTING AND WEAKENING AS IT APPROACHES. THE SOUTHERN PART HEADS TOWARD CALIFORNIA. THE NORTHERN PART SETS UP OFF THE WASHINGTON AND OREGON COAST WEDNESDAY NIGHT AND THURSDAY. AS IT DOES...A MARINE LAYER MAY DEVELOP ALONG THE COAST FROM THE SOUTH LATE WEDNESDAY AND THURSDAY. SOME MOISTURE FROM THE SOUTHERN PART OF THIS SPLITTING SYSTEM MAY LIFT BACK NORTH THROUGH CENTRAL AND EASTERN OREGON AND MAY BRUSH A PART OF OUR AREA. ADDED A SLIGHT CHANCE OF SHOWERS TO THE LANE COUNTY CASCADES THEN. THE LEFTOVER NORTHERN LOW MAY FINALLY MOVE ONSHORE AROUND FRIDAY... THOUGH LOOKS LIKE IT WILL MOVE SOUTH ALONG THE COAST. WILL NOT MAKE ANY CHANGES FOR THAT YET. WILLSON .LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS... A LOT OF UNCERTAINTY IN THE EXTENDED FORECAST. LATEST RUNS OF THE ECMWF AND GFS TRY TO SHOW A PATTERN CHANGE BEGINNING SAT. ENSEMBLE FORECASTS SHOW A WIDE RANGE OF SOLUTIONS FOR DAYS 5-7. THERE ARE HINTS THAT A RETURN TO A COLDER AND MORE ACTIVE PATTERN WILL OCCUR SUN AND CONTINUE THROUGH EARLY NEXT WEEK. WOULD TEND TO LEAN TOWARD THE ECMWF MODEL FOR THE EXTENDED BASED ON ITS PAST PERFORMANCE. HEDGED MORE TOWARD CLIMO POPS STARTING SUN. WEISHAAR && .AVIATION...DRY OFFSHORE FLOW CONTINUES...WITH MAINLY VFR CONDITIONS PREVAILING THIS MORNING. ONLY EXCEPTION MAY BE SOME PATCHY FG/FZFG IN THE INTERIOR VALLEYS AWAY FROM THE GORGE AS WINDS GO CALM. GUSTS 35-45 KT CONTINUE NEAR THE WEST END OF THE GORGE...WITH GUSTS TO 30-35 KT CONTINUING NEAR KTTD. AIRCRAFT SOUNDINGS SUGGEST CORE OF STRONG WINDS IS MAINLY CONFINED TO 2000 FT MSL AND BELOW...WITH MUCH LIGHTER SE FLOW ABOVE. WINDS EASE SLIGHTLY TODAY...BUT GUSTS 25-30 KT STILL POSSIBLE AT KTTD THROUGH THE DAY. KPDX AND APPROACHES...VFR CONDITIONS PREVAIL TODAY. WINDS ARE EASING AT KPDX...BUT JUST EAST OF THE RUNWAYS GORGE WINDS CONTINUE WITH EAST WIND GUSTS 25-35 KT NEAR KTTD. EXPECT SOME SLIGHT EASING IN THESE WINDS AS THE DAY PROGRESSES. && .MARINE...STRONG HIGH PRESSURE OVER THE INLAND NORTHWEST IS BEGINNING TO WEAKEN...BUT OFFSHORE FLOW CONTINUES TO PRODUCE LOCALLY GUSTY WINDS TO 25 KT BELOW GAPS AND COASTAL CANYONS THIS MORNING. AS HIGH PRESSURE WEAKENS EXPECT WINDS TO EASE OVER THE NEXT 24 HOURS. VERY WEAK DISTURBANCE WILL TRACK UP THE OREGON COAST WED...POSSIBLY CAUSING A SHIFT TO LIGHT-MODERATE S-SE WINDS FOR THE COASTAL WATERS. SEAS EXPECTED TO REMAIN BELOW 10 FT THROUGH AT LEAST FRIDAY. WEAGLE && .PQR WATCHES/WARNINGS/ADVISORIES... OR/WA...AIR STAGNATION ADVISORY UNTIL WED MORNING FOR SOUTH WILLAMETTE VALLEY...THE UPPER HOOD RIVER VALLEY...THE WESTERN COLUMBIA RIVER GORGE NEAR HOOD RIVER...AND THE LOWER COLUMBIA AND I5 CORRIDOR OF SW WASHINGTON && $$ MORE WEATHER INFORMATION ONLINE AT... Http://weather.gov/portland THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY REFERRED TO AS THE FORECAST AREA.
AREA FORECAST DISCUSSION
NWS SALT LAKE CITY UT
321 AM MST TUE JAN 20 2009 .SYNOPSIS...STRONG HIGH PRESSURE WILL REMAIN OVER THE INTERIOR WEST THROUGH TUESDAY THEN START TO WEAKEN AND MOVE TO THE EAST. A WEAK BUT MOIST PACIFIC STORM SYSTEM WILL AFFECT THE REGION THURSDAY INTO FRIDAY. && .DISCUSSION...WATER VAPOR LOOP SHOWS A RIDGE DOMINATING THE NORTHERN ROCKIES...WITH MOISTURE ALOFT BEING PULLED NORTHWARD INTO THE RIDGE. THE NEXT DISTURBANCE IS WORKING EAST TOWARD 135W/35N. AN UPPER LOW WAS LOCATED NEAR 170W/50N. ACARS 400-250MB WIND OBSERVATIONS REVEAL LIGHT FLOW ALOFT WITH THE RIDGE IN PLACE OVER THE ROCKIES. 00Z 700MB ANALYSIS INDICATED COOL ADVECTION INITIATING WITH +4C AT KSLC AND +1C UPSTREAM AT KRIW. 00Z KSLC RAOB INDICATES NEARLY NEUTRAL ADVECTION DURING THE PAST 24 HOURS...EXCEPT +5C OF WARMING NEAR 800MB. THE PRECIPITABLE WATER VALUE HAS DROPPED TO A TENTH OF AN INCH. THE LOW LEVEL INVERSION HAS LOWERED TO 860MB. INVERSION REMAINS THE MAIN WEATHER CONCERN INTO THE MEDIUM RANGE. BUFKIT MODEL FORECAST SOUNDINGS CONTINUE TO BE TOO MOIST IN THE BOUNDARY LAYER ALONG THE WASATCH FRONT...PARTICULARLY THE NAM. VISIBILITIES AT SLC CREPT UP TO 6SM DURING THE EARLY OVERNIGHT HOURS...DESPITE A STRONG LOW LEVEL INVERSION IN PLACE. WHILE PARTICULATES CONTINUE TO INCREASE IN THE VALLEY...THE MOISTURE HAS NOT. THE AMOUNT OF SNOW COVER IN THE VALLEY CONTINUES TO RECEDE. THE THOUGHT AROUND THE OFFICE IS PERHAPS THE CROSS BARRIER FLOW FROM THE EAST MAY HAVE BEEN ENOUGH TO BRING DOWN SOME DRIER AIR WHEN DRAINAGE FLOW SET UP LAST EVENING. VISIBILITIES HAVE SINCE FALLEN BACK INTO THE 3-4SM RANGE...AND CLIMATOLOGY SUPPORTS LESS THAN A 20 PERCENT CHANCE OF THE AIRPORT FALLING TO OR BELOW 1SM. THERE WILL HOWEVER BE PATCHY FOG ALONG THE WASATCH EARLY THIS MORNING. ELSEWHERE...FOG HAS REDEVELOPED IN THE CACHE VALLEY...UTAH COUNTY...WEST CENTRAL UTAH AND THE UINTA BASIN. 11-3.9U SATELLITE IMAGERY SHOWS BEST AERIAL COVERAGE IN THE UINTA BASIN AND WEST OF DELTA. A FEW WEB CAMS NEAR PROVO (INCLUDING INTERSTATE 15 ALONG PROVO BAY) SHOW DENSE FOG...ALTHOUGH IT CANT BE CHARACTERIZED AS WIDESPREAD. WILL LEAVE THE DENSE FOG ADVISORY IN PLACE GIVEN THE METEOROLOGICAL SETUP AND CURRENT OBSERVATIONS. OTHERWISE ANOTHER SUNNY AND HAZY DAY AS THE FOG DECAYS DURING THE MID TO LATE MORNING HOURS. SOME HIGH LEVEL MOISTURE BEGINS TO AFFECT SOUTHERN UTAH AS THE BACKSIDE OF THE RIDGE INCREASES IN MOISTURE. FOR HIGH TEMPERATURES...MADE ONLY A FEW CHANGES TO YESTERDAYS OBSERVED HIGHS AS MODEL GUIDANCE IS NOT PICKING UP THE INVERTED VALLEY COOLING TRENDS. FOG REDEVELOPS TONIGHT...ALTHOUGH HIGH BASED CLOUDS BEGIN TO INCREASE FROM THE SOUTHWEST. TEMPERATURES AT 800MB ATOP THE LOW LEVEL INVERSION ARE WARMEST THIS EVENING...AND BEGIN TO COOL LATER TONIGHT. RIDGE BEGINS TO BREAK DOWN WEDNESDAY. EXPECT HAZY CONDITIONS UNDER INCREASING CLOUDS. HAVE STARTED WITH YESTERDAYS OBSERVED HIGHS...AND TWEAKED WITH BIAS CORRECTED MAV MOS TO INTRODUCE SOME UNCERTAINTY. PRECIPITATION SPREADS IN FROM THE WEST LATER IN THE MIDWEEK...HOWEVER THE EUROPEAN DIFFERS FROM THE NAM/GFS IN HOW STRONG THE APPROACHING SYSTEM REMAINS. THIS INTRODUCES TIMING DIFFERENCES AND AT THIS POINT AM GOING WITH THE SLOWER AND WEAKER SOLUTION OF THE EUROPEAN GIVEN THE STRENGTH OF THE DEPARTING RIDGE. LIGHT ACCUMULATING SNOW WILL BE POSSIBLE IN THE MOUNTAINS...WITH A QUESTION MARK OF HOW MUCH QPF REACHES THE VALLEYS BASED ON THE DRY AIR CURRENTLY IN PLACE. WILL ALSO HAVE TO KEEP AN EYE ON THE COLD AIR ENTRENCHED ACROSS THE CACHE VALLEY AND NEAR PROVO AS PRECIPITATION MOVES IN...AS ANY RAIN ALOFT WOULD FREEZE SHOULD THE COLD AIR REMAIN IN PLACE THURSDAY MORNING. THE GFS IS TRENDING TOWARD THE EUROPEAN IN THE EXTENDED. AFTER RIDGING PASSES DURING THE LATE WORK WEEK...A SERIES OF DISTURBANCES ALOFT CARVE A BROAD CONUS TROUGH NEXT WEEK. THIS WOULD BRING COOLER/CLOUDIER AND PERHAPS SNOWIER CONDITIONS TO THE REGION NEXT WEEK...WITH A QUICK SYSTEM EVERY OTHER DAY OR SO. THE ARRIVAL OF THE COLD AIR ALOFT LATE THIS WEEKEND SHOULD ALSO MIX OUT THE INVERSION CURRENTLY IN PLACE. && .AVIATION...MVFR VISIBILITIES IN HAZE ARE EXPECTED TO CONTINUE THROUGH THE TAF PERIOD AT KSLC TERMINAL. DENSE FOG FORMATION IS NOT EXPECTED AT THIS TIME BUT A 30 PERCENT CHANCE EXISTS FOR TOMORROW NIGHT. WINDS WILL FOLLOW THEIR NORMAL DIURNAL PATHS BUT REMAIN VERY LIGHT. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...DENSE FOG ADVISORY UNTIL 11 AM TUESDAY FOR UTZ001-UTZ004-UTZ011- UTZ015. WY...NONE. && $$ PUBLIC...ROGOWSKI AVIATION...YOUNG FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT... HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
AREA FORECAST DISCUSSION
NWS GREEN BAY WI
333 PM CST WED JAN 21 2009 .SYNOPSIS...UPR RIDGE ACRS WRN NOAM WL SHIFT WWD A BIT DURING THE FIRST PART OF THE FCST PERIOD. THAT WL ALLOW DOWNSTREAM TROF TO PULL BACK INTO THE GREAT LAKES RGN. THE OVERALL PATTERN WL LOSE SOME AMPLITUDE AND THE FLOW OVER THE ERN 1/2 OF NOAM SHOULD WEAKEN LATER IN THE FCST PERIOD...AS DEEP VORTEX WITHIN THE TROF HEADS OFF TOWARD GREENLAND. RETROGRESSION OF THE UPR FEATURES WL ALLOW ANOTHER ARCTIC AIR MASS TO SURGE ACRS THE AREA FOR THE UPCOMING WEEKEND...THEN MODERATION EXPECTED AGAIN NEXT WK AS THE FLOW FLATTENS. POTENTIAL FOR WIDESPREAD SIG PCPN WL BE LOW DURING THE FIRST PART OF THE FCST PERIOD. THE POTENTIAL EXISTS FOR A SIG PCPN PRODUCING STORM THE HEAD EWD OUT OF THE PLAINS NEXT WK...BUT THERE IS UNCERTAINTY ON THE NWD EXTENT OF THE PCPN. && .SHORT TERM...TNGT/THU. CLDS FCST WL CAUSE PROBLEMS THE NEXT FEW PERIODS. WIDESPREAD ST/SC ACRS THE AREA...BUT SOME A FEW SUBSTANTIAL BREAKS. LARGEST BREAK IS IN WK DOWNSLOPE FLOW OVER NERN WI. 12Z GRB RAOB AND AFTN AIRCRAFT SOUNDINGS SHOWED STG INVERSION IN PLACE...WITH PLENTY OF MOISTURE TRAPPED BENEATH. THUS STUCK WITH A PRETTY CLOUDY FCST. HELD MIN TEMPS UP FOR TNGT WITH THE IDEAS THAT THERE WOULD BE PLENY OF CLDS. BUT NEED TO BE CAREFUL BECAUSE IF ANY SIG BREAKS ARE PRESENT AFTER DARK....WINDS WL BE LGT AND WITH WIDESPREAD SNOWCOVER....TEMPS COULD QUICKLY CRASH 10-15 DEGREES. EVENING SHIFT WL HAVE TO WATCH FOR THIS...BUT BEST BET SEEMED TO BE TO GO WITH THE IDEA THAT THERE WOULD BE PLENTY OF CLDS...AND WARMER TEMPS. WL MENTION SOME FG AS WELL. SEEMS LIKE FLURRIES WL BE SHIFTG OFF TO THE SE...SO WILL KEEP THOSE OUT OF THE FCST FOR TNGT. FZDZ MIGHT ALSO BE POSSIBLE...BUT WOULD LIKE TO SEE A LITTLE MORE INDICATION OF LIFT IN THE CLOUD LAYER BEFORE TOSSING THAT ALL OVER THE FCST. WK SFC PRESSURE GRADIENT AGAIN TOMORROW MAKES IT DIFFICULT TO BELIEVE WE/LL GET MORE THAN SOME BREAKS IN THE CLDS. LIKE TDA...THAT SHOULD HOLD TEMPS BACK. COULD BE SOME WEAK ISENT LIFT IN THE LOWER LEVELS...AND THAT WOULD BE MORE FAVORABLE FOR FZDZ. BUT BEST LIFT WOULD SEEM TO BE TO THE SW OF THE FCST AREA...WHERE AIR IS PROGGED TO BE A LITTLE DRIER. WL LEAVE OUT FOR NOW. .LONG TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY. 12Z MODELS RUNS WERE SHOWING THE ARCTIC FRONT...THAT WAS EXPECTED TO PASS THROUGH THE FORECAST AREA ON FRIDAY...THROUGH MOST OR ALL OF THE AREA BY 12Z FRIDAY. 1000-500MB THICKNESSES AND 850MB TEMPERATURES CRASH DURING THE DAY ON FRIDAY BUT MOS GUIDANCE PRODUCTS STILL HAD MAX TEMPERATURES AROUND 18Z ACROSS MUCH OF THE AREA...AND ABOUT 15Z...ACROSS THE NORTH. CONTINUED THE CHANCE OF SNOW SHOWERS ACROSS NORTH-CENTRAL WISCONSIN WITH COLD NORTHERLY FLOW ACROSS THE WARMER WATERS OF WESTERN LAKE SUPERIOR. DID NOT GO WITH HIGH POPS DUE TO INITIAL SURFACE TO 850MB DIRECTIONAL SHEAR AND WINDS QUICKLY BACKING ON FRIDAY NIGHT...BECOMING LESS FAVORABLE FOR LAKE EFFECT SNOW SHOWERS IN THE FORECAST AREA. HAVE HELD OFF ANY MENTION OF SNOW UNTIL GOING WITH LOW CHANCE OR SLIGHT CHANCE POPS AROUND THE MIDDLE OF NEXT WEEK. MODELS WERE SHOWING SIGNIFICANT DIFFERENCES BY THIS TIME SO THE APPROACH TAKEN FOR THAT PART OF THE FORECAST WAS MORE MIDDLE OF THE ROAD...WITH MINIMAL CHANGES TO THE PRECIPITATION FORECAST FOR CONTINUITY AND CONSISTENCY WITH OTHER FORECASTS FROM ADJACENT NWS OFFICES. OTHERWISE TEMPERATURES COLDER THAN GUIDANCE ARE THE RULE DURING THE LONG TERM AS ARCTIC OUTBREAKS ARE NOT HANDLED WELL BY MOS. && .AVIATION...MET GUID LOWER THAN MAV IN TERMS OF CIGS OVERNIGHT. LOWER SEEMED BETTER GIVEN THE INVERSION AND CURRENT METARS. GENERALLY WENT WITH LIFR CONDITIONS OVERNIGHT. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SKOWRONSKI/MG
AREA FORECAST DISCUSSION...CORRECTED
NWS LOUISVILLE KY
230 AM EST THU JAN 22 2009 .SHORT TERM (TODAY AND TONIGHT)... THE UPPER AIR PATTERN HAS FLATTENED CONSIDERABLY OVER THE PAST 24 HOURS AS AN UPPER TROUGH MOVES EAST OF NEW ENGLAND. SURFACE TROUGHING ACROSS THE GREAT LAKES OVER THE NEXT DAY WILL ALLOW SOUTHWEST LOW LEVEL FLOW. SOUTHWEST FLOW WILL ALSO BE AIDED BY HIGH PRESSURE CENTERED OVER FLORIDA. SATELLITE SHOWS A VERY DRY AIRMASS OVER THE ENTIRE EASTERN CONUS WITH CLEAR SKIES ACROSS THE GULF COAST AND TENNESSEE VALLEY. EXPECT MOSTLY CLEAR SKIES TODAY AND TONIGHT WITH JUST SOME PASSING CIRRUS TODAY. AS FORECAST 925MB TEMPERATURES RISE FROM JUST BELOW FREEZING CURRENTLY TO NEAR 8C BY EARLY FRIDAY...TEMPERATURES WILL BECOME QUITE A BIT MILDER. ALREADY EARLY THIS MORNING TEMPERATURES HAVE STEADIED IN THE LOWER TO MIDDLE 20S. THIS AFTERNOON`S HIGHS WILL RANGE FROM 9 TO 13 DEGREES WARMER THAN YESTERDAY`S. OVERNIGHT LOWS EARLY TOMORROW MAY STAY ABOVE FREEZING. WINDS THIS AFTERNOON WILL INCREASE TO 10 MPH FROM THE SOUTHWEST...AND WILL RELAX TO AROUND 5 TO 8 MPH FROM THE SOUTH OVERNIGHT. .LONG TERM (FRIDAY THROUGH WEDNESDAY)... FRIDAY-FRIDAY NIGHT... WARM CHANGING TO COLD... FRIDAY WILL BE THE WARMEST DAY WE HAVE SEEN IN A WHILE. SHORT-LIVED RIDGING WILL COME TO AN END AS NORTHWEST FLOW DIVES DOWN ACROSS THE NRN CONUS. BEFORE THIS HAPPENS...TEMPS SHOULD WARM UP INTO THE UPPER 40S N TO MID 50S SOUTH. THE NW FLOW WILL HELP PUSH A SFC LOW OVER THE GREAT LAKES AND ASSOCIATED COLD FRONT SEWD ACROSS OUR REGION. WITH OUR AREA BEING ON THE TAIL END OF THE FRONT...AND MOS GUIDANCE ONLY INDICATING SLT CHC POPS...WILL LOWER POPS IN THE GRIDS TO SLT CHC RAIN SHOWERS...WITH THE BEST CHC BEING OVER THE ERN CWA FRIDAY AFTN AND EVE AND OVER THE SOUTH FRI NIGHT. FRONT WILL BE THROUGH THE CWA FRIDAY NIGHT...WITH COLDER AIR BEHIND CHANGING ANY RAIN SHOWERS TO LIGHT SNOW. THERE MAY BE AN ENHANCED CHC OF PRECIP AFTER MIDNIGHT FRIDAY NIGHT AS OVER-RUNNING PRECIP FROM A LOW OVER THE SRN PLAINS HELPS ADD MOISTURE TO THE FRONTAL BOUNDARY. MAY BUMP UP OUR SERN CWA TO 30 POPS LATE FRIDAY NIGHT SINCE ENSEMBLE GUIDANCE AGREES. EITHER WAY WILL END ALL POPS BY 12Z SAT. SATURDAY-MONDAY... CHILLY AND MOSTLY DRY... THIS PERIOD MARKS A TRANSITION FROM A WARM BUT SHORT-LIVED AMPLIFIED PATTERN TO A ZONAL FLOW ALOFT FOR OUR AREA. THIS FAST FLOW WILL BE RELATIVELY DRY UNTIL EARLY NEXT WEEK. THE COLD AIR BEHIND THE FRIDAY NIGHT FRONT WILL KEEP TEMPS NEARLY STEADY TO BARELY RISING ON SATURDAY. HIGHS WILL BE AROUND FREEZING. TEMPERATURES FOR SUNDAY AND MONDAY WILL BE SIMILAR SINCE LOW-LEVEL THICKNESSES AND FLOW PATTERN ALOFT STAYS RELATIVELY THE SAME. WEAK SFC HIGH PRESSURE EXTENDING FROM THE NRN PLAINS WILL HELP KEEP CONDITIONS DRY OVER THE WEEKEND INTO MONDAY. BY MONDAY NIGHT...OVER-RUNNING PRECIP FROM AN INVERTED SFC TROUGH MAY REACH INTO OUR CWA FROM THE SW. WITH THE HIGHEST POPS FROM GUIDANCE IN THE TUES-WED TIME FRAME AND THE LAST FOUR MODEL RUNS SHOWING A SLIGHT SLOW DOWN IN PRECIP ONSET...MAY REMOVE ALL POPS THROUGH MONDAY AND WILL LOWER MONDAY NIGHT POPS SIGNIFICANTLY. AT THIS POINT ANY PRECIP STARTING MONDAY NIGHT WILL BE MAINLY OVER THE WEST AND EITHER A MIXED BAG OR MAINLY SNOW. TUESDAY-WEDNESDAY... GETTING WARMER AND A BETTER CHANCE FOR PRECIP IN THIS PERIOD... NO CHANGES MADE TO THIS PERIOD. MEDIUM-RANGE FORECAST MODELS ARE COMING IN BETTER AGREEMENT WITH THE PATTERN FOR NEXT WEEK. LARGE UPPER LOW OFF THE WRN CONUS WILL MOVE EASTWARD INTO THE SOUTHWEST US. THIS WILL HELP AMPLIFY THE FLOW...POSSIBLY SWITCHING US OVER TO A SOUTHWESTERLY FLOW MIDDLE OF THE WEEK...WHICH MEANS WARMER TEMPS BUT A MORE ACTIVE PATTERN. BEFORE THIS TAKES PLACE HOWEVER...INVERTED TROUGH SCENARIO STILL AT QUESTION FOR THE TUES-WED TIME FRAME. THE EURO AND GFS BOTH INDICATE THE BULK OF THE PRECIP COMING WEDNESDAY AND BEYOND. THIS IS LIKELY DUE TO SWRN CONUS UPPER LOW FINALLY KICKING OUT AND HELPING AID IN MOISTURE ADVECTION AND SURGING THE SFC LOW EASTWARD. EITHER WAY...MIDDLE OF NEXT WEEK LOOKS LIKE THE BEST CHC FOR PRECIP AND THE BEST CHC FOR ANOTHER SHORT-LIVED WARM-UP. && .AVIATION (06Z TAFS)... VFR CONDITIONS EXPECTED FOR THIS FORECAST PERIOD WITH MAINLY CLEAR SKIES. HIGH PRESSURE WILL SETTLE ACROSS THE GULF COAST STATES PROVIDING A WESTERLY LOW LEVEL FLOW. BASED ON LATEST ACARS SOUNDINGS LLWS IS MARGINAL BUT WE DO SEE ABOUT A 25KT DIFFERENCE BETWEEN THE SURFACE AND 2K FT AGL SO WE WILL HOLD ONTO THE LLWS UNTIL 13Z. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...NONE. IN...NONE. && $$ WEATHER.GOV/LOUISVILLE SHORT TERM...JSD LONG TERM....AL AVIATION.....JSD
AREA FORECAST DISCUSSION
NWS LOUISVILLE KY
1145 PM EST WED JAN 21 2009 .UPDATE FOR 06Z TAF,S... SHORT TERM (TONIGHT AND THU)... WARMING TREND WILL CONTINUE AND STRENGTHEN... BACKING UPR FLO NOTED THRU THIS PERIOD WITH SIGNIFICANT HEIGHT RISES AS FLATTENING RIDGE MOVES EWD FROM THE ROCKIES. CLOCKWISE/SW FLO WILL CONTINUE AT THE SFC/LOWER LEVELS AROUND HIGH PRES SPRAWLED ACRS THE GULF. THIS WILL LIMIT TEMP FALLS TNGT/ENCOURAGE RISES THU... ALONG WITH SUNSHINE. THU MAX TEMPS SHUD BE SOME 10-15 DEGS WARMER THAN TDA WITH INSIGNIFICANT OR NON-EXISTENT CLOUDS THRU THE PERIOD. PREFER THE GFS MOS TEMPS OVER THE NAM MOS FOR TNGT-COLDER (DUE TO A FCST OF LOWER DEWPOINTS-WHICH CURRENT OBS VERIFY. MOST OF THE TEMP FALL WILL BE EARLY TNGT WITH NEAR STEADY TEMPS OR ONLY SLIGHT FALLS AFTER MIDNIGHT. WILL COMPROMISE ON MAXS THU WITH BWG LIKELY NEAR 50. .LONG TERM (THURSDAY NIGHT THROUGH WEDNESDAY)... THURSDAY NIGHT THROUGH SUNDAY NIGHT... FCST PD WILL START OFF QUIET AS FAIRLY ZONAL FLOW AND SFC RIDGING WILL KEEP THE WEATHER DRY AROUND HERE. HAVE BEEN MONITORING A WEAK SYSTEM MOVING WITHIN THE FLOW THAT LOOKS TO IMPACT THE REGION IN THE FRIDAY TO EARLY SATURDAY TIME FRAME. SFC FRONTAL BOUNDARY LOOKS TO MOVE THROUGH THE REGION WITH A QUICK WARM UP AHEAD OF THE SYSTEM AND ANOTHER SHOT OF REINFORCING COLD AIR BEHIND IT. SOME LIGHT PRECIPITATION DOES LOOK TO IMPACT THE AREA. SUITE OF MED-LONG RANGE GUIDANCE HAS A BIT OF SPREAD WITH THIS SYSTEM. FEEL THAT LOW CHANCE POPS ARE REQUIRED FOR FRIDAY AS FRONTAL BOUNDARY SHOULD PROMOTE ENOUGH LIFT FOR SCT RAIN SHOWERS. SOME MOISTURE REMAINS ON THE BACKSIDE FOR A LITTLE SNOW. AFTER THE FRONTAL PASSAGE...FAIRLY STRONG HIGH PRESSURE SYSTEM LOOKS TO DRIFT INTO THE NORTHERN PLAINS AND UPPER MIDWEST WHICH WILL KEEP LOW-LEVEL COLD AIRMASS IN PLACE THROUGH SUNDAY. AS FOR TEMPERATURES...WARMEST DAY LOOKS TO BE FRIDAY WITH TEMPS STARTING OFF IN THE LOW TO MID 30S WITH HIGHS IN THE UPPER 40S IN THE FAR NORTH TO AROUND 50 IN THE CENTRAL SECTIONS AND LOWER 50S ACROSS THE SOUTH. TEMPS WILL THEN FALL QUICKLY BEHIND THE FRONT WITH LOWS SAT MORNING IN THE LOWER TO MID 20S IN THE NORTH WITH AROUND 30 IN THE SOUTH. HIGHS SAT WILL NOT WARM ALL THAT MUCH WITH READINGS IN THE LOW TO MID 30S. SUNDAY MORNING LOOK QUITE CHILLY AGAIN WITH LOWS IN THE UPPER TEENS TO AROUND 20 AND HIGHS IN THE LOW TO MID 30S. MONDAY THROUGH WEDNESDAY... VERY ACTIVE WEATHER PATTERN SETTING UP IN THIS TIME PERIOD AS MAJOR PATTERN CHANGE WILL BE WELL UNDERWAY. THE POTENTIAL FOR A SIGNIFICANT PRECIPITATION EVENT STILL EXISTS FOR EARLY NEXT WEEK. HOWEVER A COUPLE OF THINGS ARE GOING HERE THAT WILL MAKE THE FORECAST VERY DIFFICULT. FIRST...THE UPPER LEVEL PATTERN WILL BE STILL UNDERGOING A CHANGE...WHICH WILL INDUCE LARGE AMOUNTS OF SPREAD IN THE MODELS INCLUDING THE ENSEMBLES. SECONDLY...WE WILL BE ENTERING A PERIOD OF SPLIT FLOW WHICH THE MODELS DO NOT HANDLE ALL THAT WELL. MUCH OF OUR FORECAST WILL CONTINUE TO FOCUS ON THE DEVELOPMENT OF A STRONG WAVE DIGGING FROM THE PACIFIC NORTHWEST INTO CALIFORNIA. VARIOUS MODEL SOLUTIONS TODAY SHOW A NUMBER OF SOLUTIONS. BOTH 12Z GFS AND EURO SOLUTIONS DIG THE WAVE ACROSS THE WESTERN U.S. BUT THE GFS IS NOT AS AGGRESSIVE AS THE EURO IN THAT IT APPEARS THAT IT IS CATCHING ON TO THE STRONG PACIFIC JET THAT WILL CONTINUE TO FORCE A MORE PROGRESSIVE PATTERN ALOFT. THE EURO DIGS AND RETROGRADES THE LOW A LITTLE BIT AND THEN LETS IT COME EAST. FROM A METEOROLOGICAL STANDPOINT THATS NOT LIKELY TO HAPPEN IN SUCH A PROGRESSIVE FLOW. IN GENERAL...WE HAVE LEANED A BIT CLOSER TO THE 12Z GFS WHICH GIVES US PRETTY GOOD CONTINUITY WITH THE FCSTS FROM 24 HOURS AGO. WITH THAT SAID...STRONG WAVE OUT IN THE SOUTHWEST U.S. WILL LIKELY END UP SENDING A SERIES OF UPPER LEVEL DISTURBANCES EASTWARD WITHIN THE MEAN FLOW. THE COMBINATION OF THE SW WAVE AND THE STRONGLY CONFLUENT FLOW ALOFT OVER THE GREAT LAKES LOOKS TO KEEP THE SOUTHEAST RIDGE IN CHECK AND ALLOW THE SHALLOW PRE-EXISTING AIRMASS IN PLACE THROUGH MUCH OF THE PD. FROM A PATTERN RECOGNITION STAND POINT...THE INGREDIENTS SEEM TO BE COMING TOGETHER FOR A DECENT OVERRUNNING PRECIPITATION EVENT. OVERALL FORECASTER CONFIDENCE IS HIGH ON THIS KIND OF EVENT HAPPENING. HOWEVER...THERE IS STILL UNCERTAINTY IN REGARDS TO HOW STRONG THE WARM AIR ADVECTION WILL BE AND WHAT EFFECT IT WILL HAVE ON PRECIPITATION TYPE. OVERALL TREND IN THE OPERATIONAL MODELS HAS BEEN SLIGHTLY COLDER WITH TEMPS. ON THE OTHER HAND...THE GFS ENSEMBLES ARE SLIGHTLY WARMER AND RESULT IN MORE OF A MIXED PRECIPITATION EVENT. GFS ENSEMBLE PLUME CHARTS CONTINUE TO SHOW A LARGE SPREAD IN PRECIPITATION ARRIVAL. SO WE HAVE BACKED OFF POPS SLIGHTLY FOR MONDAY AND TRENDED THINGS SLIGHTLY SLOWER WITH MORE EMPHASIS ON MONDAY NIGHT AND TUESDAY FOR PRECIPITATION. PRECIPITATION LOOKS TO DIMINISH A BIT AND POSSIBLY END BY WEDNESDAY. FOR TEMPS...HAVE TRENDED THINGS CLOSE TO THE 12Z OP GFS AND THE 12Z ENSEMBLE MEAN. THIS RESULTS IN A SLIGHTLY COOLER TEMP FCST...BUT CARRIES GOOD CONTINUITY FROM THE PREVIOUS TWO FCSTS. && .AVIATION (06Z TAFS)... VFR CONDITIONS EXPECTED FOR THIS FORECAST PERIOD WITH MAINLY CLEAR SKIES. HIGH PRESSURE WILL SETTLE ACROSS THE GULF COAST STATES PROVIDING A WESTERLY LOW LEVEL FLOW. BASED ON LATEST ACARS SOUNDINGS LLWS IS MARGINAL BUT WE DO SEE ABOUT A 25KT DIFFERENCE BETWEEN THE SURFACE AND 2K FT AGL SO WE WILL HOLD ONTO THE LLWS UNTIL 13Z. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...NONE. IN...NONE. && $$ WEATHER.GOV/LOUISVILLE SHORT TERM...KIRKPATRICK LONG TERM....MRJ AVIATION.....JA
AREA FORECAST DISCUSSION...UPDATED
NWS MARQUETTE MI
1230 AM EST THU JAN 22 2009 UPDATED AVIATION DISCUSSION FOR 06Z TAF ISSUANCE .UPDATE... ISSUED AT 1035 PM EST FCST WAS UPDATED TO EXPAND MENTION OF -FZDZ OVERNIGHT AND THU. -FZDZ AND/OR FLURRIES OVERNIGHT SHOULD MAINLY AFFECT THE KEWEENAW AND NE FCST AREA. MORE OF THE NRN FCST AREA SHOULD BE AFFECTED THU. DURING THE EVENING...THERE HAVE BEEN A FEW OBS BEGINNING TO INDICATE -FZDZ (CYXL/CYRL IN NRN ONTARIO TO THE NW OF LAKE SUPERIOR AND ALSO AT THE SOO). FCST SOUNDINGS INDICATE SHALLOW MOIST LAYER WILL BE FAVORABLE FOR THE POTENTIAL OF -FZDZ AS TEMPS IN THE MOIST LAYER SHOULD BE ABOVE -10C OVERNIGHT THRU MOST IF NOT ALL OF THU AFTN. 00Z RAOBS AND EVENING TAMDAR SOUNDINGS SUPPORT THE MODEL FCSTS. LOCATIONS THAT SEE UPSLOPING OFF LAKE SUPERIOR WILL BE MOST LIKELY TO SEE -FZDZ. WITH COLD FRONT DRIFTING INTO UPPER MI LATE TONIGHT AND THU...UPSLOPING AREAS WILL SHIFT FROM W TO NW FLOW FAVORED LOCATIONS TONIGHT TO N TO NE FLOW FAVORED LOCATIONS THU AFTN. && .SHORT TERM (TONIGHT AND THURSDAY)... ISSUED AT 415 PM EST VERY LITTLE WILL CHANGE AT THE UPPER LEVELS OVER THE NEXT 24 TO 36 HOURS. AT 500MB...NORTHWESTERLY FLOW WILL BECOME SLIGHTLY MORE WESTERLY...WITH THE LOW SLOWLY SAGGING SOUTHEASTWARD FROM HUDSON BAY THROUGH QUEBEC AND THE NEXT TROUGH MOVING THROUGH THE CENTRAL CANADIAN PROVINCES. THE 300MB JET MAX SITUATED OVER CENTRAL ONTARIO AND FAR WESTERN LAKE SUPERIOR THIS AFTERNOON WILL ALSO FLATTEN OUT AS IT SLIDES OVER SOUTHERN QUEBEC AND MAINE. AN ADDITIONAL BUT MUCH LESS DRAMATIC JET MAX IN THE SOUTHERN STREAM WILL MOVE FROM THE PACIFIC NORTHWEST AROUND TO EASTERN NORTH DAKOTA...NORTHERN MINNESOTA...AND NORTHERN WISCONSIN BY 00Z FRIDAY. AT THE SURFACE...A COLD FRONT IS CURRENTLY CUTTING ONTARIO INTO NORTH AND SOUTH HALVES. THE FRONT SHOULD DIVE SOUTHWARD ACROSS CENTRAL LAKE SUPERIOR BY 12Z THURSDAY...AND FARTHER DIVE OVER SOUTHERN AND EASTERN UPPER MICHIGAN BY 00Z FRIDAY. THIS IS WHERE THE APPROACHING 300MB JET WILL COME INTO ASSISTANCE...WITH THIS BOUNDARY...AND THE SURFACE LOW ACROSS THE CENTRAL PLAINS MOVING TO CENTRAL MINNESOTA AND WISCONSIN BY 00Z FRIDAY. 850MB TEMPERATURES REMAIN BORDERLINE OR TOO WARM FOR SIGNIFICANT LAKE EFFECT OR ENHANCED SNOWFALL...RANGING FROM NEAR 0C SOUTHWEST TO -10C FAR NORTH AND NORTHEAST. THE ONLY PLACES WHERE LAKE EFFECT SNOW COULD BE POSSIBLE GIVING THE RIGHT WIND DIRECTION AND AVAILABLE MOISTURE WOULD BE OVER THE KEWEENAW PENINSULA AND EASTERN ALGER...AND LUCE COUNTIES. TAKING THIS ALL INTO ACCOUNT...THE POTENTIAL FOR FREEZING DRIZZLE WAS ADDED TO THE SNOW SHOWERS THURSDAY AFTERNOON SOUTH. OTHER CHANGES INCLUDE TO INCREASE CLOUD COVER...GIVEN THE CURRENT OVC SKY FROM NORTHEASTERN MINNESOTA THROUGH THE ENTIRE MQT CWA AND MOST OF NORTHERN WISCONSIN. FEW OTHER CHANGES WERE NEEDED TO THE ONGOING FORECAST. .LONG TERM... THURSDAY NIGHT...AN INCREASINGLY SHEARED SHRTWAVE TROUGH IS EXPECTED TO MOVE FROM SRN SASK INTO NRN ONTARIO...WITH THE ASSOCIATED AREA OF MODERATE 700-300 QVECTOR CONV JUST BRUSHING UPPER MI. TEMPS IN THE MOIST LAYER TO ONLY AROUND -10C COULD KEEP SOME RESULT IN SOME -FZDZ BUT WITH ONLY MARGINAL TEMPS/RH PROFILE AND LOW POPS...ONLY -SN WAS MENTIONED FOR NOW. THE MODELS HAVE CONTINUED TO TREND SLOWER WITH THE TROUGH/FRONT PASSAGE. BY LATE THU NIGHT AS THE SFC TROUGH AND AXIS OF LOW LEVEL CONV MOVES INTO NW UPPER MI...SNOW AND LAKE ENHANCED SNOW (850 MB TEMPS TO AROUND -10C) IS EXPECTED TO DEVELOP WITH A FEW INCHES OF ACCUMULATION POSSIBLE. FRI...IN THE WAKE OF THE SFC LOW...COLDER AIR WILL SPILL INTO THE AREA OF NRLY WINDS. CONVERGENT NRLY FLOW INTO N UPPER MI AND DEEPER SYNOPTIC MOISTURE/LIFT WITH 800-600 MB FGEN IN THE MORNING SHOULD SUPPORT A PERIOD OF MODERATE SNOW ESPECIALLY FOR N WIND FAVORED LES SNOWBELTS. THE WINDOW WITH THE MOST FAVORABLE DGZ LAYER WITH THE BEST LIFT AND LOW LEVEL CONV WILL BE RELATIVELY BRIEF...LIMITING OVERALL SNOW ACCUMULATIONS WITH AMOUNTS GENERALLY IN THE 2 TO 4 INCH RANGE. FRI NIGHT INTO SAT...AS THE VERY COLD ARCTIC AIRMASS MOVES INTO THE AREA AND CAA PUSHES 850 MB TEMPS TO AROUND -25C OVERNIGHT THE SNOW GROWTH LAYER WILL ALSO SHRINK. SO...AS WINDS BACK...NW FLOW SNOWBELTS WILL CONTINUE TO MODERATE LES BUT WITH ACCUMULATIONS GENERALLY REMAINING IN THE 3-7 INCH RANGE OVERNIGHT. WIND CHILL VALUES WILL ALSO PLUMMET INTO THE 15 BELOW TO 25 BELOW ZERO RANGE. THE MODERATING INFLUENCE OF LAKE SUPERIOR SHOULD KEEP TEMPS OVER THE NRN PORTION OF UPPER MI FROM DROPPING OFF TOO FAR...GENERALLY FROM ZERO TO 5 BELOW ZERO. OVER THE INTERIOR WEST...TEMPS MAY DROP TO AROUND -10F. HOWEVER...WITH THE MIXING/RADIATIONAL COOLING BALANCE... AREAS WITH THE LOWER TEMPS SHOULD ALSO SEE SOMEWHAT LIGHTER WINDS. EXPECT WINDS TO BACK TO MORE WNW SAT WITH LES BANDS SHIFTING INTO THE KEWEENAW AND LOCATIONS EAST OF MUNISING. SUN-WED...ASIDE FROM THE CONTINUING LES FOR WRLY FLOW SNOWBELTS INTO TUE...A GENERALLY DRY PERIOD IS EXPECTED. THE ECMWF...GFS AND ENSEMBLES SUGGEST WNW NRN STREAM FLOW WILL PREVAIL WITH ONLY WEAK SHORTWAVES MOVING THROUGH THE AREA WITH LITTLE AVBL MOISTURE. GREATER UNCERTAINTY BY WED WITH LOCATION/STRENGTH OF SHORTWAVES AND POTENTIAL INTERACTION WITH THE SRN STREAM. SO...ONLY LOWER END POPS WERE INCLUDED. && .AVIATION (FOR THE 06Z TAF ISSUANCE)... AT KCMX...IFR CIGS SHOULD PREVAIL IN MOIST UPSLOPING WNW FLOW UNDER SHARP INVERSION. THERE HAVE BEEN A FEW OBS UPSTREAM IN NRN ONTARIO REPORTING -FZDZ/-SN. MAY SEE INTERMITTENT -FZDZ/-SN LATE IN THE NIGHT/EARLY MORNING PRIOR TO COLD FROPA AND A WIND SHIFT TO THE NE. WITH WINDS SHIFTING TO THE NE AFTER FROPA...CIGS SHOULD LIFT TO LOW MVFR. IFR CIGS MAY RETURN IN THE EVENING AS WINDS VEER TO AN UPSLOPING ERLY DIRECTION. APPROACHING DISTURBANCE SHOULD BRING -SN (MVFR VIS) TOWARD THE END OF THIS FCST PERIOD. AT KSAW...IFR CIGS SHOULD PREVAIL THRU THE NIGHT INTO THE AFTN HRS. LIGHT UPSLOPING N/NE FLOW OFF LAKE SUPERIOR AFTER COLD FROPA LATE MORNING SHOULD RESULT IN SOME -FZDZ/-SN DEVELOPING DUE TO UPSLOPING OF SHALLOW RELATIVELY WARM SUBFREEZING MOIST LAYER. AS WINDS VEER TO A MORE GRADUAL UPSLOPING ERLY DIRECTION...EXPECT LIGHT PCPN TO END WITH CIGS RISING SLIGHTLY TO LOW MVFR LATE AFTN. && .MARINE (FOR THE 4 PM LAKE SUPERIOR FORECAST ISSUANCE)... LOW PRESSURE ACROSS EASTERN CANADA WILL DRAG A TROUGH FROM ONTARIO THROUGH LAKE SUPERIOR BY LATE THURSDAY MORNING. LOW PRESSURE OVER THE CENTRAL PLAINS WILL THEN SURGE NORTHEASTWARD AND OVER UPPER MICHIGAN THURSDAY NIGHT INTO FRIDAY MORNING. BY LATE FRIDAY EVENING...THIS LOW PRESSURE SYSTEM WILL MOVE TO FAR SOUTHERN QUEBEC...WITH WINDS INCREASING TO 30 AND NEAR 35 KNOTS FRIDAY. HEAVY FREEZING SPRAY WILL ALSO BE POSSIBLE AS COLDER AIR FILLS OVER LAKE SUPERIOR. FOR THE WEEKEND...HIGH PRESSURE OVER WESTERN CANADA SHOULD BRING A RIDGE OF HIGH PRESSURE ACROSS LAKE SUPERIOR. BY MONDAY...THE LARGE HIGH PRESSURE SYSTEM OVER WESTERN CANADA SHOULD HAVE DOVE INTO THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI RIVER VALLEY. WILL NOT POST A GALE WATCH EAST FOR FRIDAY NIGHT...DUE TO THE MARGINAL AND LOCALIZED NATURE OF THE GALES THEMSELVES. THIS WILL NEED TO BE CHECKED BY PREVIOUS SHIFTS IF THERE ARE SIGNIFICANT CHANGES. && .MQT WATCHES/WARNINGS/ADVISORIES... UPPER MICHIGAN...NONE. LAKE SUPERIOR...NONE. LAKE MICHIGAN...NONE. && $$ UPDATE...ROLFSON SHORT TERM...KF LONG TERM...JLB AVIATION...ROLFSON MARINE...KF
AREA FORECAST DISCUSSION
NWS LOUISVILLE KY
600 AM EST THU JAN 22 2009 .AFD CONCERNS 12Z TAFS... && .SHORT TERM (TODAY AND TONIGHT)... THE UPPER AIR PATTERN HAS FLATTENED CONSIDERABLY OVER THE PAST 24 HOURS AS AN UPPER TROUGH MOVES EAST OF NEW ENGLAND. SURFACE TROUGHING ACROSS THE GREAT LAKES OVER THE NEXT DAY WILL ALLOW SOUTHWEST LOW LEVEL FLOW. SOUTHWEST FLOW WILL ALSO BE AIDED BY HIGH PRESSURE CENTERED OVER FLORIDA. SATELLITE SHOWS A VERY DRY AIRMASS OVER THE ENTIRE EASTERN CONUS WITH CLEAR SKIES ACROSS THE GULF COAST AND TENNESSEE VALLEY. EXPECT MOSTLY CLEAR SKIES TODAY AND TONIGHT WITH JUST SOME PASSING CIRRUS TODAY. AS FORECAST 925MB TEMPERATURES RISE FROM JUST BELOW FREEZING CURRENTLY TO NEAR 8C BY EARLY FRIDAY...TEMPERATURES WILL BECOME QUITE A BIT MILDER. ALREADY EARLY THIS MORNING TEMPERATURES HAVE STEADIED IN THE LOWER TO MIDDLE 20S. THIS AFTERNOON`S HIGHS WILL RANGE FROM 9 TO 13 DEGREES WARMER THAN YESTERDAY`S. OVERNIGHT LOWS EARLY TOMORROW MAY STAY ABOVE FREEZING. WINDS THIS AFTERNOON WILL INCREASE TO 10 MPH FROM THE SOUTHWEST...AND WILL RELAX TO AROUND 5 TO 8 MPH FROM THE SOUTH OVERNIGHT. .LONG TERM (FRIDAY THROUGH WEDNESDAY)... FRIDAY-FRIDAY NIGHT... WARM CHANGING TO COLD... FRIDAY WILL BE THE WARMEST DAY WE HAVE SEEN IN A WHILE. SHORT-LIVED RIDGING WILL COME TO AN END AS NORTHWEST FLOW DIVES DOWN ACROSS THE NRN CONUS. BEFORE THIS HAPPENS...TEMPS SHOULD WARM UP INTO THE UPPER 40S N TO MID 50S SOUTH. THE NW FLOW WILL HELP PUSH A SFC LOW OVER THE GREAT LAKES AND ASSOCIATED COLD FRONT SEWD ACROSS OUR REGION. WITH OUR AREA BEING ON THE TAIL END OF THE FRONT...AND MOS GUIDANCE ONLY INDICATING SLT CHC POPS...WILL LOWER POPS IN THE GRIDS TO SLT CHC RAIN SHOWERS...WITH THE BEST CHC BEING OVER THE ERN CWA FRIDAY AFTN AND EVE AND OVER THE SOUTH FRI NIGHT. FRONT WILL BE THROUGH THE CWA FRIDAY NIGHT...WITH COLDER AIR BEHIND CHANGING ANY RAIN SHOWERS TO LIGHT SNOW. THERE MAY BE AN ENHANCED CHC OF PRECIP AFTER MIDNIGHT FRIDAY NIGHT AS OVER-RUNNING PRECIP FROM A LOW OVER THE SRN PLAINS HELPS ADD MOISTURE TO THE FRONTAL BOUNDARY. MAY BUMP UP OUR SERN CWA TO 30 POPS LATE FRIDAY NIGHT SINCE ENSEMBLE GUIDANCE AGREES. EITHER WAY WILL END ALL POPS BY 12Z SAT. SATURDAY-MONDAY... CHILLY AND MOSTLY DRY... THIS PERIOD MARKS A TRANSITION FROM A WARM BUT SHORT-LIVED AMPLIFIED PATTERN TO A ZONAL FLOW ALOFT FOR OUR AREA. THIS FAST FLOW WILL BE RELATIVELY DRY UNTIL EARLY NEXT WEEK. THE COLD AIR BEHIND THE FRIDAY NIGHT FRONT WILL KEEP TEMPS NEARLY STEADY TO BARELY RISING ON SATURDAY. HIGHS WILL BE AROUND FREEZING. TEMPERATURES FOR SUNDAY AND MONDAY WILL BE SIMILAR SINCE LOW-LEVEL THICKNESSES AND FLOW PATTERN ALOFT STAYS RELATIVELY THE SAME. WEAK SFC HIGH PRESSURE EXTENDING FROM THE NRN PLAINS WILL HELP KEEP CONDITIONS DRY OVER THE WEEKEND INTO MONDAY. BY MONDAY NIGHT...OVER-RUNNING PRECIP FROM AN INVERTED SFC TROUGH MAY REACH INTO OUR CWA FROM THE SW. WITH THE HIGHEST POPS FROM GUIDANCE IN THE TUES-WED TIME FRAME AND THE LAST FOUR MODEL RUNS SHOWING A SLIGHT SLOW DOWN IN PRECIP ONSET...MAY REMOVE ALL POPS THROUGH MONDAY AND WILL LOWER MONDAY NIGHT POPS SIGNIFICANTLY. AT THIS POINT ANY PRECIP STARTING MONDAY NIGHT WILL BE MAINLY OVER THE WEST AND EITHER A MIXED BAG OR MAINLY SNOW. TUESDAY-WEDNESDAY... GETTING WARMER AND A BETTER CHANCE FOR PRECIP IN THIS PERIOD... NO CHANGES MADE TO THIS PERIOD. MEDIUM-RANGE FORECAST MODELS ARE COMING IN BETTER AGREEMENT WITH THE PATTERN FOR NEXT WEEK. LARGE UPPER LOW OFF THE WRN CONUS WILL MOVE EASTWARD INTO THE SOUTHWEST US. THIS WILL HELP AMPLIFY THE FLOW...POSSIBLY SWITCHING US OVER TO A SOUTHWESTERLY FLOW MIDDLE OF THE WEEK...WHICH MEANS WARMER TEMPS BUT A MORE ACTIVE PATTERN. BEFORE THIS TAKES PLACE HOWEVER...INVERTED TROUGH SCENARIO STILL AT QUESTION FOR THE TUES-WED TIME FRAME. THE EURO AND GFS BOTH INDICATE THE BULK OF THE PRECIP COMING WEDNESDAY AND BEYOND. THIS IS LIKELY DUE TO SWRN CONUS UPPER LOW FINALLY KICKING OUT AND HELPING AID IN MOISTURE ADVECTION AND SURGING THE SFC LOW EASTWARD. EITHER WAY...MIDDLE OF NEXT WEEK LOOKS LIKE THE BEST CHC FOR PRECIP AND THE BEST CHC FOR ANOTHER SHORT-LIVED WARM-UP. && .AVIATION (12Z TAFS)... DRY CONTINENTAL AIR HAS BROUGHT A CLEAR NIGHT ALL THE WAY FROM THE LOWER OHIO VALLEY THROUGH THE WESTERN GULF. VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD WITH MOSTLY CLEAR SKIES TODAY AND TONIGHT EXCEPT FOR SOME OCCASIONAL SCATTERED MID LEVEL CLOUDS ABOVE 15KFT. A 10Z ACARS SOUNDING CURRENTLY SHOWS WINDS FROM THE WEST-SOUTHWEST AROUND 34KT AT 2000FT. THIS WILL CONTINUE A MARGINAL WIND SHEAR SCENARIO THROUGH 13 OR 14Z THIS MORNING. THIS AFTERNOON SOUTHWEST WINDS WILL INCREASE TO 10 TO 14 MPH. WIND SHEAR WILL LIKELY DEVELOP AFTER 04Z FRIDAY AS SOUTHWEST WINDS INCREASE TO 35KT AROUND 2000FT. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...NONE. IN...NONE. && $$ WEATHER.GOV/LOUISVILLE SHORT TERM...JSD LONG TERM....AL AVIATION.....JSD
AREA FORECAST DISCUSSION
NWS SALT LAKE CITY UT
401 AM MST THU JAN 22 2009 .SYNOPSIS...A COUPLE OF WEAK BUT MOIST PACIFIC STORM SYSTEMS WILL AFFECT THE REGION THROUGH SATURDAY. A STRONGER SYSTEM WILL DEVELOP ALONG THE WEST COAST ON SUNDAY...POTENTIALLY IMPACTING THE INTERMOUNTAIN WEST EARLY NEXT WEEK. && .DISCUSSION...WATER VAPOR LOOP SHOWS THE UPPER LEVEL RIDGE BREAKING DOWN...ALLOWING THE APPROACH OF A TROUGH FROM THE EASTERN PACIFIC. COMPRISED WITHIN THE TROUGH ARE DISTURBANCES WEST OF NORTHERN CALIFORNIA AND BAJA CALIFORNIA. THE NEXT SHEARED TROUGH WAS LOCATED FROM NEAR 140W/35N TO 160W/60N. A WAVE WAS BEING PULLED WESTWARD ALONG 50N WEST OF BRITISH COLUMBIA...AS ANOTHER DISTURBANCE DIGS SOUTHEAST ACROSS WESTERN CANADA. ACARS 400-250MB WIND OBSERVATIONS REVEAL LIGHT ANTICYCLONIC FLOW ALOFT HAS BEEN DAMPENED SOUTH ALONG THE PLAINS. 00Z 700MB ANALYSIS PLACED THE RIDGE NOW CENTERED IN NORTHERN MEXICO...WITH RIDGING NORTHWARD INTO THE GREAT BASIN. MOIST SOUTHWEST FLOW WAS ENSUING...BECOMING STRONGER FURTHER WEST ALONG THE PACIFIC COAST. 00Z KSLC RAOB INDICATES 3-5C OF COLD ADVECTION DURING THE PAST 24 HOURS ABOVE 800MB. THE PRECIPITABLE WATER VALUE HAS RISEN ABOVE A QUARTER OF AN INCH. THE LOW LEVEL INVERSION HAS REMAINED AT 860MB...BUT HAS WEAKENED DURING THE PAST 24 HOURS. PATCHY LIGHT FOG HAS REDEVELOPED ACROSS PORTIONS OF CENTRAL AND NORTHERN UTAH EARLY THIS MORNING AS HIGH CLOUDS CONTINUE TO STREAM IN FROM THE SOUTHWEST. ITS MUCH WARMER THIS MORNING ACROSS MOST LOCATIONS...OUTSIDE OF THE CACHE VALLEY WHERE LOGAN IS IN THE MIDDLE TEENS. EXPECT THE NORTHERN CALIFORNIA DISTURBANCE TO SHEAR EASTWARD ACROSS THE GREAT BASIN TONIGHT AND DISSIPATE OVER THE CENTRAL ROCKIES FRIDAY. BLENDED TOTAL PRECIPITABLE WATER LOOP SHOWS A NICE CORRIDOR OF 1-1.5" VALUES ADVANCING NORTHWARD INTO CALIFORNIA AHEAD OF THE TROUGH. WILL TAKE SOME TIME FOR THE MOISTURE TO AFFECT UTAH THIS MORNING...WITH A MORE LIKELY ONSET TIME DURING THE AFTERNOON HOURS. THERMAL PROFILES BY THAT TIME SHOULD SUPPORT VALLEY RAIN. IN THE CACHE VALLEY...AM CONCERNED THE COLD AIR REMAINS TRAPPED. WHILE 00Z KSLC RAOB SUGGESTS TEMPERATURES ALOFT WOULD SUPPORT RAIN...EVAPORATIVE COOLING WOULD MAKE SNOW MORE LIKELY (ALTHOUGH CANNOT TOTALLY RULE A BRIEF LIGHT PERIOD OF FREEZING RAIN ACROSS THE CACHE VALLEY AT ONSET). THIS IS WHAT THE 00/06Z NAM WOULD SUGGEST. 00Z NAM THERMAL PROFILE VERIFIED MUCH BETTER AT KSLC THAN THE GFS WHICH WAS 5-10C TOO WARM IN THE LOWER LEVELS. BEST QPF LOOKS TO BE IN NORTHERN UTAH UNDER SHEARING WAVE TONIGHT INTO FRIDAY. WITH THE POSSIBILITY OF BRIEF LIGHT FREEZING RAIN AT ONSET AND MARGINAL SNOW TOTALS IN THE FORECAST...DECIDED TO GO WITH A WINTER WEATHER ADVISORY FOR UTZ001 LATE TODAY INTO FRIDAY MORNING. A RIDGE QUICKLY TRANSLATES OVER THE REGION LATE FRIDAY AND FRIDAY NIGHT...AHEAD OF A DEEPENING LOW OVER THE CALIFORNIA COAST. GIVEN THE DEPTH OF THE SYSTEM...A TROPICAL MOISTURE TELECONNECTION WOULD BE LIKELY BY SUNDAY AND MONDAY. THE INCREASING SOUTHERLY FLOW SHOULD SUPPORT AN EROSION OF REMAINING INVERTED VALLEYS LATER THIS WEEKEND. IT ALSO MEANS A HIGHER THAN CLIMATOLOGY CHANCE OF PRECIPITATION...WITH SNOW IN THE MOUNTAINS AND COOLER VALLEYS...AND RAIN ELSEWHERE. WILL HAVE TO KEEP AN EYE OUT FOR POTENTIAL FLASH FLOODING ACROSS SOUTHERN UTAH LATE THIS WEEKEND AND EARLY NEXT WEEK. IT WILL DEPEND ON THE POSITION/TRANSLATION SPEED OF THE UPPER LOW AND MOISTURE PLUME ADVECTING NORTHWARD. DID NOT SPEND TOO MUCH TIME ON THE FORECAST BEYOND MONDAY...AS GLOBAL MODELS AND ENSEMBLES HAVE HAD POOR RUN-TO-RUN CONTINUITY. && .AVIATION...MVFR VISIBILITIES ARE EXPECTED TO CONTINUE THROUGH MUCH OF THE TAF PERIOD AT THE SLC TERMINAL. RAIN SHOWERS ARE FORECAST TO BUILD INTO THE AREA MAINLY AFTER 22Z...LOWERING CEILINGS TO NEAR 4000 FT AGL. THERE IS A 30 PERCENT CHANCE OF MVFR CEILINGS IN ASSOCIATION WITH THESE SHOWERS BETWEEN AFTER 22Z. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...WINTER WEATHER ADVISORY FROM NOON THURSDAY TO 11 AM FRIDAY FOR UTZ001. WY...NONE. && $$ PUBLIC...ROGOWSKI AVIATION...KRUSE FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT... HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)