AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
120 PM PST FRI DEC 5 2008
.SYNOPSIS...
OFFSHORE FLOW WILL PREVAIL THROUGH SATURDAY FOR FAIR AND DRY WEATHER
CONDITIONS. A WEAK UPPER LEVEL LOW WILL MOVE ACROSS SOUTHERN
CALIFORNIA SUNDAY...CAUSING AN INCREASE IN CLOUDS. HIGH PRESSURE
REBUILDING ALONG THE COAST MONDAY WILL LEAD TO ANOTHER ROUND OF
MODERATE SANTA ANA WINDS BY TUESDAY. DRY WEATHER AND A WARMING TREND
WILL RETURN MONDAY THROUGH THURSDAY.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM...TONIGHT THROUGH SUNDAY...
SINCE NOON OFFSHORE PRESSURE GRADIENTS HAVE BEGUN TO RELAX...THOUGH
NOT AS RAPIDLY AS EARLIER FORECAST. AS OF 1300 PST THERE WAS STILL
-12 MB BETWEEN ORANGE COUNTY COAST AND NORTHEAST NEVADA...WHILE A
WEAK ONSHORE PRESSURE GRADIENT AROUND 1 MB BETWEEN THE COAST AND THE
INLAND VALLEYS WAS MAINTAINING A 400 FOOT DEEP MARINE LAYER AND
KEEPING THE OFFSHORE WINDS FROM SURFACING THERE. ABOVE THE MARINE
LAYER AND INLAND TO THE MOUNTAINS REPORTED WIND GUSTS...DISCOUNTING
KSDM... HAVE RANGED BETWEEN 35 AND 47 MPH. LATEST ACARS/PROFILER
SOUNDINGS AND KSOX VAD WINDS...NOW SHOWING EAST 20 KT IN THE
3000-6000 FT LAYER...DOWN FROM 30 KT EARLIER THIS MORNING. THIS
DOWNWARD TREND SUPPORTS THE MODEL GUIDANCE AND CLIMATOLOGY SO WILL
LET THE WIND ADVISORY EXPIRE AT 1400 PST. FOR TONIGHT THROUGH
SATURDAY...WEAK OFFSHORE FLOW WILL PREVAIL...GENERALLY EAST 10 MPH
WITH GUSTS UP TO 25 MPH IN WIND PRONE AREAS. THE RESIDUAL MARINE
LAYER IS EXPECTED TO SCOUR OUT/MOVE OFFSHORE AFTER MIDNIGHT WITH
LAND BREEZES COMBINING WITH THE SYNOPTIC FLOW SO NOT FORECASTING FOG
FOR TONIGHT. WITH DRIER AIR IN PLACE FOR ALL AREAS...WIND SHELTERED
LOCATIONS SHOULD EXPERIENCE MUCH COOLER OVERNIGHT TEMPERATURES.
CONVERSELY DAYTIME TEMPERATURES SATURDAY SHOULD BE 5 DEGREES OVER
TODAYS READINGS FOR MOST LOCATIONS. SATURDAY NIGHT THROUGH SUNDAY
NIGHT A MOISTENING TREND WITH A MODERATION IN TEMPERATURES... DUE TO
THE CLOSED LOW MOVING BACK TOWARDS THE COAST AND ONSHORE. THE 05/12Z
RUN OF THE GFS MODEL AND THE 05/00Z RUN OF THE ECMWF BOTH GENERATED
PRECIPITATION WITH THE LOW AS IT MOVES ONSHORE SUNDAY. THE 05/12Z
RUN OF THE NAM12 WAS FASTER ON THE MOVEMENT AND DRY. THE 05/18Z RUN
NOW SHOWS SOME VERY LIGHT PRECIPITATION AMOUNTS AGAINST THE COASTAL
SLOPES OF SAN DIEGO COUNTY MOUNTAINS SUNDAY EVENING. I RAISED THE
POPS EVER SO SLIGHTLY...TO AROUND 13 PERCENT AND INCREASED CLOUD
COVER...BUT STILL USING A FORECAST SCENARIO OF MARINE LAYER
DEEPENING BACK TO AROUND 2000 FEET...WHILE ABOVE THIS...FROM 2000 TO
15000 FEET AIR MASS REMAINS RELATIVELY DRY.
.LONG TERM...MONDAY THROUGH NEXT FRIDAY
FOR MOST OF THIS PERIOD A DRYING AND WARMING TREND WILL BE OCCURRING
DUE TO STRONG HIGH PRESSURE RIDGE ALONG WEST COAST. THE PATTERN IS
FAVORABLE FOR MODERATE SANTA ANA WINDS MONDAY NIGHT INTO TUESDAY.
HOWEVER BY THURSDAY THE RIDGE IS FLATTENED AS A FAST MOVING...MOSTLY
DRY...COLD FRONT THAT PUSHES THROUGH PACIFIC NORTHWEST AND INTO
GREAT BASIN. THE SURFACE PRESSURE DOES NOT HAVE LONG TO REBUILD ON
FRIDAY TO SUPPORT ANOTHER ROUND OF SANTA ANA WINDS BEFORE A STRONG
AND WET COLD FRONT BLASTS ONTO THE PACIFIC NW COAST AND BEGINS TO
SWEEP SOUTHEAST THROUGH CALIFORNIA. THIS IS THE START OF A MAJOR
SHIFT IN THE LONG WAVE TROUGH POSITIONS THAT HAS BEEN ADVERTISED FOR
SOME TIME...WITH A TROUGH BECOMING ANCHORED ALONG THE COAST BY MID
DECEMBER. SO THOUGH A DRY PATTERN WILL PERSIST FOR NEXT SEVEN
DAYS...BEYOND THIS LOOKS COOL AND WET FOR SOUTHERN CALIFORNIA.
&&
.AVIATION...
052130Z...THIS EVENING THERE WILL BE LOCALLY GUSTY NORTHEAST TO EAST
WINDS EFFECTING MAINLY AREAS BELOW CANYONS AND PASSES. LOW LEVEL
WIND SHEAR IS POSSIBLE THIS EVENING. TONIGHT THROUGH SATURDAY THE
WINDS SHOULD CONTINUE TO WEAKEN. CLEAR SKIES AND UNRESTRICTED
VISIBILITIES ARE EXPECTED. SMALL
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WIND ADVISORY UNTIL 2 PM PST THIS AFTERNOON FOR RIVERSIDE
COUNTY MOUNTAINS-SAN BERNARDINO COUNTY MOUNTAINS-SAN BERNARDINO
AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE-SAN DIEGO
COUNTY MOUNTAINS-SAN DIEGO COUNTY VALLEYS-SANTA ANA MOUNTAINS
AND FOOTHILLS.
HIGH RIP CURRENT RISK TODAY FOR THE ORANGE COUNTY AND SAN DIEGO
COUNTY BEACHES.
PZ...NONE.
&&
$$
PUBLIC/FIRE WEATHER...BALFOUR
AVIATION/MARINE...SMALL
NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
920 AM PST FRI DEC 5 2008
.SYNOPSIS...
OFFSHORE FLOW WILL BRING GUSTY EAST TO NORTHEAST WINDS THROUGH AND
BELOW PASSES AND CANYONS TODAY...OTHERWISE FAIR AND DRY WEATHER WILL
CONTINUE THROUGH SATURDAY. A WEAK UPPER LEVEL LOW WILL MOVE ACROSS
SOUTHERN CALIFORNIA SUNDAY...CAUSING AN INCREASE IN CLOUDS. HIGH
PRESSURE REBUILDING ALONG THE COAST MONDAY WILL LEAD TO ANOTHER
ROUND OF MODERATE SANTA ANA WINDS BY TUESDAY. DRY WEATHER AND A
WARMING TREND IS EXPECTED FROM MONDAY THROUGH THURSDAY.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
.SHORT TERM...TODAY THROUGH SUNDAY...
NOT TOO OFTEN GET TO OBSERVE A VERY NARROW TROUGH BEFORE IT FILLS OR
SPINS UP INTO A CLOSED LOW. COMPARE THE SOUNDINGS FROM
KVBG...KDRA...AND KNKX THIS MORNING WHICH ARE ONLY SEPARATED BY 2.5
TO 3.5 DEGREES LATITUDE. FROM 15000 TO 40000 FEET THE WIND
DIRECTIONS ARE ABOUT 180 DEGREES OPPOSED AND AT 30000 FEET THERE IS
ABOUT 150 KTS OF WIND SHEAR. CLOSER TO THE GROUND AND MAIN FORECAST
CONCERN TODAY IS LOCATION/STRENGTH/DURATION OF OFFSHORE WINDS.
PRESSURE GRADIENT BETWEEN ORANGE COUNTY COAST AND NORTHEAST NEVADA
IS ABOUT 15 MB AT 0800 PST WHILE STILL ABOUT 1 MB ONSHORE ACROSS SAN
DIEGO COUNTY. ACARS/MESONET OBSERVATIONS SHOW SUSTAINED EAST WINDS
20 MPH WITH GUSTS AROUND 40 MPH ABOVE 1500 FEET WHILE FOG AND HAZE
WAS STILL PRESENT OVER COASTAL PLAIN AND WESTERN VALLEYS BELOW 500
FOOT ELEVATION. A WEAK ONSHORE PRESSURE GRADIENT...0.5 TO 1 MB IS
MAINTAINED BETWEEN THE COASTAL AND INLAND VALLEYS ALL DAY...SO
COMPLETE SCOURING OUT OF THE MARINE LAYER BELOW 500 FEET ELEVATION
IS UNLIKELY TODAY. FOR THE INLAND VALLEYS/FOOTHILLS/MOUNTAINS...BY
1300 PST THE SURFACE PRESSURE GRADIENT IS ABOUT HALF AS STRONG AS
THIS MORNING. EAST TO NORTHEAST WINDS THESE LOCATIONS SHOULD PEAK
BETWEEN 1000-1200 PST THEN FALL OFF QUICKLY DURING THE AFTERNOON.
FOR TONIGHT THROUGH SATURDAY...WEAK OFFSHORE FLOW CONTINUES...
GENERALLY EAST 10 MPH OR LESS. WITH DRIER AIR AND MORE WIND
SHELTERING...OVERNIGHT TEMPERATURES SHOULD BE MUCH COOLER.
CONVERSELY DAYTIME TEMPERATURES SATURDAY SHOULD BE 5 DEGREES OVER
TODAYS READINGS FOR MOST LOCATIONS. SATURDAY NIGHT THROUGH SUNDAY
NIGHT A MOISTENING TREND WITH A MODERATION IN TEMPERATURES...
DUE TO THE CLOSED LOW MOVING BACK TOWARDS THE COAST AND ONSHORE. THE
05/12Z RUN OF THE GFS MODEL AND THE 05/00Z RUN OF THE ECMWF BOTH
GENERATED PRECIPITATION WITH THE LOW AS IT MOVES ONSHORE SUNDAY. THE
05/12Z RUN OF THE NAM12 WAS FASTER ON THE MOVEMENT AND DRY. CURRENT
GRIDS HAVE 10 PERCENT POPS AND DO NOT PLAN ON INCREASING THEM ANY
HIGHER. FORECAST SCENARIO WILL BE DEEPENING OF THE MARINE
LAYER...BACK TO AROUND 2000 FEET...WHILE ABOVE THIS...FROM 2000 TO
15000 FEET AIR MASS REMAINS DRY.
.LONG TERM...MONDAY THROUGH NEXT FRIDAY
FOR MOST OF THIS PERIOD A DRYING AND WARMING TREND WILL BE OCCURRING
DUE TO STRONG HIGH PRESSURE RIDGE ALONG WEST COAST. THE PATTERN IS
FAVORABLE FOR MODERATE SANTA ANA WINDS MONDAY NIGHT INTO TUESDAY.
HOWEVER BY THURSDAY THE RIDGE IS FLATTENED AS A FAST MOVING...MOSTLY
DRY...COLD FRONT THAT PUSHES THROUGH PACIFIC NORTHWEST AND INTO
GREAT BASIN. THE SURFACE PRESSURE DOES NOT HAVE LONG TO REBUILD ON
FRIDAY TO SUPPORT ANOTHER ROUND OF SANTA ANA WINDS BEFORE A STRONG
AND WET COLD FRONT BLASTS ONTO THE PACIFIC NW COAST AND BEGINS TO
SWEEP SOUTHEAST THROUGH CALIFORNIA. THIS IS THE START OF A MAJOR
SHIFT IN THE LONG WAVE TROUGH POSITIONS THAT HAS BEEN ADVERTISED FOR
SOME TIME...WITH A TROUGH BECOMING ANCHORED ALONG THE COAST BY MID
DECEMBER. SO THOUGH A DRY PATTERN WILL PERSIST FOR NEXT SEVEN
DAYS...BEYOND THIS LOOKS COOL AND WET FOR SOUTHERN CALIFORNIA.
&&
.AVIATION...
051730Z...TODAY THERE WILL BE LOCALLY STRONG NORTHEAST TO EAST WINDS
EFFECTING MAINLY INLAND AREAS. THIS SHOULD CLEAR OUT ANY RESIDUAL
FOG...LEAVING CLEAR SKIES OVER THE REGION. SOME BRIEF LOW LEVEL WIND
SHEAR IS POSSIBLE TODAY. TONIGHT THROUGH SATURDAY WEAK OFFSHORE
FLOW...CLEAR SKIES AND UNRESTRICTED VISIBILITIES ARE EXPECTED. SMALL
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...WIND ADVISORY UNTIL 2 PM PST THIS AFTERNOON FOR RIVERSIDE
COUNTY MOUNTAINS-SAN BERNARDINO COUNTY MOUNTAINS-SAN BERNARDINO
AND RIVERSIDE COUNTY VALLEYS-THE INLAND EMPIRE-SAN DIEGO
COUNTY MOUNTAINS-SAN DIEGO COUNTY VALLEYS-SANTA ANA MOUNTAINS
AND FOOTHILLS.
HIGH RIP CURRENT RISK TODAY FOR THE ORANGE COUNTY AND SAN DIEGO
COUNTY BEACHES.
PZ...NONE.
&&
$$
PUBLIC/FIRE WEATHER...BALFOUR
AVIATION/MARINE...SMALL
NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
AREA FORECAST DISCUSSION
NWS GRAND RAPIDS MI
1040 AM EST THU DEC 4 2008
LATEST UPDATE...SHORT TERM AND MARINE...
.SYNOPSIS...(412 AM EST THU DEC 4 2008)
COLDER AIR WILL CONTINUE MOVING IN OVER THE GREAT LAKES INTO THE DAY
ON FRIDAY. THIS WILL ALLOW FOR LAKE EFFECT SNOW SHOWERS TO BE
EXPECTED RIGHT ON THROUGH THE REMAINDER OF THE WEEK. SIGNIFICANT
AMOUNTS OF LAKE EFFECT ARE NOT EXPECTED...HOWEVER SOME AREAS WILL
SEE THE SNOWPACK GRADUALLY BUILD. AN AREA OF LOW PRESSURE WILL MOVE
IN ACROSS THE REGION LATE FRIDAY NIGHT AND DURING THE DAY ON
SATURDAY. THIS SYSTEM WILL BRING SOME SNOW TO MOST OF THE
AREA...WITH LAKE ENHANCEMENT INCREASING AMOUNTS A BIT ALONG MOST OF
THE LAKESHORE.
&&
.SHORT TERM...(1040 AM EST THU DEC 4 2008)
(REST OF TODAY THROUGH SATURDAY)
I HAVE UPDATED THE FORECAST TO INCREASE THE AREA OF CONDITIONAL POP
THROUGH THIS AFTERNOON. I ALSO INCREASED THE FORECAST SNOWFALL
AMOUNTS FOR TODAY TO 1 TO 2 INCHES CENTERED ON US-131. THAT WAS
BASED ON RADAR TRENDS AND THE IR AND WATER VAPOR IMAGES CONFERMING
WHAT THE 12Z RUC SUGGESTS.... THAT IS CORE OF THE POLAR JET HAS
PASSED EAST OF THE SOUTWEST MICHIGAN. WITH THE VAD WIND SUGGESTS THE
INVERSION HEIGHT HAS INCREASED ABOUT 1000 FT FROM 5000 FT PRIOR TO
14Z TO ABOUT 6000 FT AT 15Z. TAMDAR SOUNDINGS SHOWS SIMILAR
TRENDS. 850 MB TEMP CONTINUES TO FALL FROM AROUND -13C AT 12Z OVER
LAKE MICHIGAN TO NEAR -15C BY 18Z. SFC OBS SHOW 1TO MILE VIS AT GRR
LAN AZO RQB AT 15Z. ALSO THE RUC SHOWS THE DGZ HAS BECOME SATURATED
AND WILL REMAIN SO THE REST OF THE DAY. THE BEST LIFT IS BETWEEN NOW
AND 20Z. THE MEAN BOUNDARY LAYER WIND IS 270 DEGREES AROUND 25
KNOTS. THUS I BELIEVE WE WILL SEE SNOW ALL DAY OVER MOST OF THE CWA
DOWN WIND OF LAKE MICHIGAN BETWEEN ROUTE 10 AND I-94. SOUTH OF I-94
WINDS ARE NOT OVER THE LAKE LONG ENOUGH TO REALLY DO MUCH IN TERMS
OF SNOWFALL.
NEXT SPEED MAX/SHORT WAVE TROUGH IS NOW DIVING SOUTHEAST OVER THE
DAKOTAS AND MN. THIS SYSTEM WILL BE ENOUGH TO SEND THE POLAR JET
SOUTH OF THE AREA TONIGHT. WITH THE APPROACH OF THE UPPER
SYSTEMS....INVERSION HTS ARE EXPECTED TO INCREASE TO AROUND 8-9K FT.
LOW LEVEL FLOW IS EXPECTED TO REMAIN MAINLY WNW THROUGH THE NIGHT.
THE SYNOPTIC FORCING IN ADDITION TO THE FAVORABLE OVER-LAKE
INSTABILITY WILL INCREASE THE INTENSITY OF THE SNOW SHOWERS. MODELS
ARE INDICATING THAT A GOOD DEAL OF LOW LEVEL CONVERGENCE WILL
DEVELOP LATE THIS EVENING AND LAST INTO THE OVERNIGHT HOURS. THE
FAVORED AREAS WILL BE ROUGHLY SOUTH OF A LINE FROM GRAND HAVEN TO
CHARLOTTE. THE LIMITED INVERSION HTS SHOULD KEEP THIS PICKUP IN LAKE
EFFECT FROM GETTING TOO OUT OF HAND. WE DO NOT HAVE THE CONFIDENCE
ANY LOCATION WILL SEE WARNING CRITERIA ACCUMS...HOWEVER WE DO
BELIEVE THERE IS A GOOD CHANCE THAT AN ADVISORY MAY BE NEEDED. WE
HAVE TRENDED AMOUNTS UP...AND ENOUGH TIME EXISTS THAT THE DAY SHIFT
CAN TAKE ANOTHER LOOK AT POSSIBLE HEADLINES.
INVERSION HTS WILL FALL A BIT AS THE SHORT WAVE MOVES AWAY FROM THE
AREA ON FRI MORNING. WINDS ARE EXPECTED TO SHIFT FROM THE WNW TO
MORE SW BY LATE FRI AFTERNOON. THIS WILL HELP TO KEEP ANY ONE AREA
FROM SEEING MUCH SNOW. THE FOCUS OF BETTER SNOW ACCUMS WILL
TRANSITION FROM THE SW CORNER OF THE CWFA TO THE NW CORNER.
THE NEXT COUPLE OF SHORT WAVES WILL THEN DIVE SE TOWARD THE AREA
LATE FRI NIGHT AND DURING THE DAY ON SAT. IT WILL BE THE SECOND
SHORT WAVE THAT WILL BRING A CLIPPER TYPE SFC LOW ACROSS THE NRN
PORTION OF THE STATE. THE SYSTEM ITSELF WILL BE POTENT...AND WOULD
BRING A COUPLE OF INCHES OF SNOW BY ITSELF. H850 TEMPS DO NOT WARM
ALL THAT MUCH AHEAD OF IT...LEAVING DELTA T/S AT LEAST IN THE MID
TEENS ACROSS THE AREA. THE SW FLOW COMBINED WITH ALMOST A
NON-EXISTENT INVERSION AND THE OVER-LAKE INSTABILITY WILL SET UP
WHAT LOOKS TO BE A POTENTIALLY SIGNIFICANT LAKE ENHANCEMENT EVENT
FOR THE NW PORTION OF THE CWFA. SOME DETAILS WILL NEED TO BE WORKED
OUT...BUT THERE IS POTENTIAL FOR SOME WARNING CRITERIA SNOWS. THIS
WILL BE LATE 4TH PERIOD/5TH PERIOD...SO WE WILL HOLD OFF ON ANY
WATCH FOR NOW.
&&
.LONG TERM...(412 AM EST THU DEC 4 2008)
(SATURDAY NIGHT THROUGH WEDNESDAY)
MAIN STORY IN THE LONG TERM WILL BE SNOW AND COLD. SURGES OF COLD
AIR WILL PUSH INTO SOUTHWEST LOWER MICHIGAN DURING WEEKEND AND INTO
THE MIDDLE OF NEXT WEEK. THE FIRST SURGE WILL RUSH IN SATURDAY NIGHT
IN THE WAKE OF A CLIPPER SYSTEM MOVING OFF TO THE EAST. 850MB TEMPS
ARE FORECAST TO PLUNGE INTO THE MIDDLE TEENS C BELOW ZERO. LAKE
EFFECT WILL CONTINUE INTO SUNDAY...BEFORE RIDGING ENDS MUCH OF THE
ACTIVITY INTO SUNDAY NIGHT.
ANOTHER CLIPPER WILL MOVE THROUGH THE REGION MONDAY AND MONDAY
NIGHT. THE ASSOCIATED COLD FRONT PUSHES THROUGH THE AREA TUESDAY
MORNING. ARCTIC AIR POURS INTO THE GREAT LAKES REGION INTO MID
WEEK...WITH 850MB TEMPS PLUNGING WELL INTO THE 20S BELOW ZERO C.
SOME SYNOPTIC SCALE SNOW CAN BE EXPECTED MONDAY AND MONDAY NIGHT AS
THE SYSTEM MOVES THROUGH...FOLLOWED BY GOOD CHANCES FOR LAKE EFFECT
TUESDAY INTO WEDNESDAY.
TRIED TO NUDGE DOWN TEMPS IN THE EXTENDED...GIVEN WHAT HAS BEEN A
PERSISTENT SIGNAL BY THE GFS TO FORECAST A COLD PERIOD. TEMPERATURES
FOR THE MIDDLE OF NEXT WEEK MAY VERY WELL BE DEEP WINTER TYPE
NUMBERS WITH HIGHS IN THE TEENS AND LOWS DIPPING TOWARD ZERO. DID
NOT GO THAT COLD YET...BUT HAVE BEGUN THE TREND IN THAT DIRECTION.
&&
.MARINE...(1040 AM EST THU DEC 4 2008)
I EXTENED THE SCA UNTIL 00Z SATURDAY SINCE THE WINDS AND WAVES ARE
MORE THAN STRONG AND OR LARGE ENOUGH. WE MAY END UP WITH A GALE
WARNING FOR LATE FRIDAY NIGHT ON LATER FORECASTS DUE THE STRONG
SYSTEM COMING IN FROM THE NORTHWEST FOR SATURDAY. FREEZING SPRAY
POTENTIAL WILL INCREASE AT THAT TIME WITH COLDER AIR MOVING IN.
&&
.AVIATION...(655 AM EST THU DEC 4 2008)
MAIN BATCH OF SNOW THAT MOVED THROUGH THE TAF SITES OVERNIGHT IS
SLIDING EAST/DECREASING IN INTENSITY THIS MORNING. NOT EXPECTING
MUCH IN THE WAY OF SNOW THROUGH THE DAY TODAY. LAKE EFFECT CLOUDS
WILL CONTINUE TO BE IN PLACE ABOVE ALL THE TAF SITES HOWEVER. A
GRADUAL LIFTING OF THE CEILING HEIGHTS IS EXPECTED...RISING FROM
AROUND 2500FT THIS MORNING TO 3500FT THIS AFTERNOON.
LAKE EFFECT SNOW IS EXPECTED TO INCREASE IN COVERAGE AND INTENSITY
AS WE HEAD INTO THE EVENING HOURS. KMKG...KGRR AND KAZO SHOULD ALL
SEE MVFR VISIBILITIES DEVELOP ONCE AGAIN AS SNOW SHOWERS MOVE
THROUGH THOSE LOCATIONS. INLAND...TOWARD KLAN AND KJXN...IT SHOULD
MAINLY BE FLURRIES. CEILINGS AREA WIDE SHOULD DIP BACK INTO THE MVFR
CATEGORY ONCE AGAIN TONIGHT.
&&
.HYDROLOGY...(412 AM EST THU DEC 4 2008)
WITH TEMPERATURES EXPECTED TO GENERALLY BE BELOW FREEZING THROUGH
THE NEXT WEEK...LITTLE TO NO RUNOFF CAN BE EXPECTED INTO AREA
STREAMS AND RIVERS. IT DOES APPEAR THAT WE WILL BUILD A SNOWPACK
WITH LAKE EFFECT SNOW SHOWERS EXPECTED MOST DAYS AND A FEW SYSTEMS
MOVING THROUGH.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY IN EFFECT THROUGH 00Z SATURDAY.
&&
$$
SYNOPSIS: NJJ
SHORT TERM: NJJ / WDM
LONG TERM: DUKE
MARINE: NJJ / WDM
AVIATION: DUKE
HYDROLOGY: NJJ
AREA FORECAST DISCUSSION
NWS GAYLORD MI
1028 AM EST THU DEC 4 2008
.SYNOPSIS.../ISSUED AT 413 AM/
COLD AIR FLOWING ACROSS THE RELATIVELY WARM WATERS OF THE GREAT
LAKES WILL PRODUCE LAKE EFFECT AND LAKE ENHANCED SNOWFALL THROUGH
THE UPCOMING WEEKEND. LAKE EFFECT SNOW SHOWERS WILL INTENSIFY THIS
AFTERNOON AND TONIGHT AS AN UPPER LEVEL DISTURBANCE PUSHES ACROSS
THE REGION. A CLIPPER SYSTEM IS FORECAST TO CROSS THE STATE
SATURDAY...WHICH WILL BRING MORE WIDESPREAD SNOWFALL TO NORTHERN
MICHIGAN...AS WELL AS A PERIOD OF HEAVIER ENHANCED SNOWFALL OFF OF
LAKE MICHIGAN FRIDAY NIGHT INTO SATURDAY.
KAS
&&
.SHORT TERM.../ISSUED AT 1026 AM/...TODAY
MUCH ANTICIPATED LAKE EFFECT SNOW EVENT TRYING TO GETS IT ACT
TOGETHER THIS MORNING...WITH LOCAL RADAR SHOWING SOMEWHAT BETTER
BANDING STRUCTURES BECOMING EVIDENT IN WEST-NORTHWEST FLOW
REGIME...WITH POCKETS OF INCH PER HOUR SNOWFALL RATES
(ALTHOUGH...THESE ARE STILL HIGHLY TRANSITORY). HOWEVER...DESPITE
GREAT OVER-WATER INSTABILITY (PUSHING 20C)...LOW INVERSION LEVELS
(12Z KGRB SOUNDING INVERSION OF ONLY 860MB)...NO LAKE SUPERIOR
CONNECTION...AND LACK OF SYNOPTIC SUPPORT ARE KEEPING THINGS
RELATIVELY IN-CHECK OVER NORTHWEST LOWER. A LITTLE DIFFERENT STORY
NORTH OF THE MIGHTY MAC...WITH ENHANCED CONVERGENCE ALONG SOUTHWEST
INTRUDING REMNANT ONTARIO COLD AIR DRAINAGE FLOW LEADING TO A RATHER
HEALTHY EASTERN LAKE SUPERIOR BAND PIVOTING INTO LUCE COUNTY...ALL
THE WHILE KEEPING JUST SCATTERED LIGHTER SNOW SHOWER ACTIVITY OVER
MUCH OF EASTERN UPPER. ADDITIONAL SNOWFALL AMOUNTS AND HEADLINE
MANAGEMENT REMAIN FOREFRONT FOR THE REST OF THE DAY...ESPECIALLY AS
RATHER IMPRESSIVE UPSTREAM WAVE BEGINS TO FLEX ITS MUSCLE OVER THE
LAKE WATERS.
FOR LAKE MICHIGAN...UPSTREAM ACARS AND RAOB SOUNDINGS CONFIRM LATEST
MODEL GUIDANCE OF A RAPID INCREASE IN INVERSION LEVELS THIS
AFTERNOON (PUSHING 11KFT BY EVENING) AND MAX OMEGA IN FAVORABLE DGZ.
THIS SHOULD ALLOW THE LAKE MACHINE TO INCREASE IN INTENSITY THROUGH
THE AFTERNOON...WITH PERSISTENT WNW FLOW (290ISH) TARGETING THE
TRADITIONAL SNOWBELTS NORTH OF M-72 AND ALONG AND WEST OF I-75.
THEREFORE...WILL LEAVE INHERITED SNOWFALL AMOUNTS OF AN ADDITIONAL 3
TO 4 INCHES IN THIS AREA UNTOUCHED. AS ALWAYS...LOCALLY HEAVIER
AMOUNTS ARE CERTAINLY POSSIBLE...ESPECIALLY WITH THE BELIEF BANDING
STRUCTURES SHOULD REMAIN THROUGH THE AFTERNOON WITH DEEP NORTHWEST
LOWER MICHIGAN SNOWPACK AND LOW SUN ANGLE PREVENTING MUCH DIURNAL
DISRUPTION. HAVE SOME CONCERN ALONG THE M-55 CORRIDOR COUNTIES WITH
LIMITED FETCH LENGTH (~60 MILES) POSSIBLY HINDERING SNOWFALL
ACCUMULATIONS. STILL...WOULD LIKE TO SEE HOW EVERYTHING TRANSPIRES
WITH PASSAGE OF AFOREMENTIONED WAVE THIS AFTERNOON BEFORE CUTTING
ACCUMULATIONS IN THIS AREA. IN A NUTSHELL...WILL LEAVE CURRENT
HEADLINE AND SNOW AMOUNTS AS IS FOR NORTHWEST LOWER MICHIGAN.
FOR LAKE SUPERIOR...MUCH LIKE LAKE MICHIGAN...A RAPID INCREASE IN
INVERSION LEVELS IS EXPECTED THIS AFTERNOON...WITH MAX OMEGA PEGGED
IN THE FLUFF PRODUCING DGZ. WOULD ALSO EXPECT A QUICK BACKING OF
WINDS TO THE WNW AS DRAINAGE FLOW CEASES WITH DIURNAL RESPONSE.
850MB-700MB STREAMLINE ANALYSIS CONTINUES TO POINT TO AREAS NORTH OF
M-28 AS UNDER THE GUN...INCLUDING THE SOO BY LATER THIS AFTERNOON.
WITH EXCELLENT UPSTREAM FETCH LENGTH...EXPECT AN INCH PER HOUR
SNOWFALL RATES TO EASILY BE ATTAINED AT TIMES...WITH ADDITIONAL
SNOWFALL AMOUNTS APPROACHING 6 INCHES NEAR THE POINT AND 2 TO 3
INCHES AT THE SOO. THUS...CURRENT WARNING WILL REMAIN IN
EFFECT.
AS NORTHERN MICHIGANDER ARE USED TO...AWAY FROM THE FAVORED LAKE
AREAS EXPECT JUST SCATTERED SNOW SHOWERS WITH LIGHT ACCUMULATIONS.
QUICK PEEK AT TONIGHT CONTINUES TO SHOW EXCELLENT LAKE SNOW
PARAMETERS THROUGH ABOUT 9Z IN AREAS FAVORED BY 280 TO 290 DEGREE
FLOW...WITH SEVERAL ADDITIONAL INCHES EXPECTED.
MSB
&&
.LONG TERM.../ISSUED AT 413 AM/...TONIGHT AND BEYOND
MODELS ARE CERTAINLY IN DECENT AGREEMENT HEADING INTO THE UPCOMING
WEEKEND...SO WILL TAKE A BLENDED APPROACH.
FLOW REMAINS 280-290 THROUGH TONIGHT...WITH ENHANCED SNOWFALL
CONTINUING IN THE SNOWBELTS. THE BEST SNOW ACCUMULATIONS WILL OCCUR
TONIGHT WITH AN ADDITIONAL 4 TO 7 INCHES EXPECTED NORTH OF M-72 IN
THE WARNING AREA AND NEAR WHITEFISH BAY IN EASTERN UPPER.
FLOW WILL BEGIN TO BACK AROUND TO THE SOUTHWEST ON FRIDAY WITH
DRY AIR AGAIN INVADING THE MID LEVELS...PUSHING INVERSION HEIGHTS
DOWN TO AROUND 5KFT. STILL PLENTY COLD ENOUGH FOR LAKE EFFECT
SNOW...BUT WE SHOULD SEE A SIGNIFICANT REDUCTION IN INTENSITY WITH
RELATIVELY MINOR SNOW ACCUMULATIONS.
AS THE CLIPPER PUSHES IN THE WESTERN LAKES FRIDAY NIGHT...WE WILL
LIKELY SEE AN ENHANCED BAND OF SNOWFALL DEVELOP ACROSS THE LONG AXIS
OF LAKE MICHIGAN...POINTED INTO MACKINAC AND CHIPPEWA COUNTIES. AT
THIS TIME...IT DOES NOT APPEAR THE BAND WILL SET UP LONG ENOUGH TO
PRODUCE WARNING CRITERIA SNOWFALL...BUT WILL LIKELY BE A SOLID
ADVISORY EVENT. HOWEVER...NOT PLANNING TO HOIST ANY ADDITIONAL
HEADLINES AT THIS TIME...SO WE CAN REMAIN MORE FOCUSED ON THE
ONGOING HEADLINES. AS THE ALBERTA CLIPPER DRAGS A SURFACE TROUGH
ACROSS THE AREA...THE BAND OF ENHANCED SNOWFALL WILL LIKELY BE
DRAGGED ONSHORE INTO NORTHWEST LOWER MICHIGAN ON SATURDAY...
PRODUCING A PERIOD OF LOW VISIBILITIES AND HEAVY SNOWFALL DURING
THE MORNING TO EARLY AFTERNOON HOURS ACROSS NORTHWEST LOWER
MICHIGAN. REGARDLESS...ALL OF NORTHERN MICHIGAN WILL SEE A PERIOD
OF SNOWFALL WITH THE LARGE SCALE ASCENT PROVIDED BY THE CLIPPER
SYSTEM. FINALLY AS THE SYSTEM DEPARTS SATURDAY EVENING...WE WILL
TRANSITION TO LAKE EFFECT SNOW IN THE NNW FLOW FAVORED SNOWBELTS.
ALL IN ALL...MUCH BELOW NORMAL TEMPERATURES AND SNOWY CONDITIONS
WILL CONTINUE TROUGH THE UPCOMING WEEKEND AND LIKELY BEYOND THE
WEEKEND.
NO CHANGES MADE WERE MADE TO THE FORECAST BEYOND SATURDAY NIGHT.
KAS
&&
.MARINE.../ISSUED AT 413 AM/
WNW WINDS CONTINUE TO GUST UP OVER 20 KNOTS OCCASIONALLY IN THE
NEARSHORE AREAS. HOWEVER...WINDS HAVE WEAKENED ENOUGH ACROSS THE
SOUTHERN SHORES OF MACKINAC COUNTY TO ALLOW THE SCA TO BE CANCELLED
FOR THESE ZONES...INCLUDING THE STRAITS. ALSO...WENT AHEAD AND
CANCELLED THE STURGEON POINT TO ALABASTER ZONE. ALL OTHER ZONES
WILL CONTINUE TO SEE WIND GUSTS UP TO 25 KNOTS THROUGH THURSDAY
NIGHT AND EXTENDED THE SCA ACCORDINGLY.
WILL NEED TO CONTINUE TO MONITOR THE POTENTIAL FOR GALES FRIDAY
NIGHT INTO SATURDAY AS THE GRADIENT TIGHTENS UP AHEAD OF OUR NEXT
LOW PRESSURE DISTURBANCE. HOWEVER...PREFERRING TO WAIT AT LEAST ONE
MORE FORECAST PACKAGE BEFORE ANY HEADLINES ARE ISSUED.
KAS
&&
.AVIATION.../ISSUED AT 615 AM/...VALID FOR 12Z TAFS
LAKE EFFECT SNOW SHOWERS WILL KEEP ALL SITES ALTERNATING FROM VFR
TO MVFR CONDITIONS OVER THE NEXT 24 HOURS...WITH OCCASIONALLY
IFR/LIFR CONDITIONS IN THE HEAVIEST SNOW SHOWERS.
KAS
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 4 AM EST FRIDAY FOR MIZ023-029-
031>033.
WINTER STORM WARNING UNTIL 4 AM EST FRIDAY FOR MIZ016-017-
019>022-025>028.
LAKE EFFECT SNOW WARNING UNTIL 10 AM EST FRIDAY FOR MIZ008.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST FRIDAY FOR LMZ323-342-
344>346.
LH...SMALL CRAFT ADVISORY UNTIL 7 AM EST FRIDAY FOR LHZ347-348.
LS...SMALL CRAFT ADVISORY UNTIL 7 AM EST FRIDAY FOR LSZ321-322.
&&
$$
AREA FORECAST DISCUSSION
NWS RALEIGH NC
300 PM EST FRI DEC 5 2008
.SYNOPSIS...
A FRONT THAT IS STALLED OUT ALONG NORTH CAROLINA COASTAL SECTIONS
WILL GRADUALLY SHIFT EAST AWAY FROM THE AREA THROUGH TONIGHT... AS
CHILLY HIGH PRESSURE BUILDS IN FROM THE WEST. THIS HIGH WILL MOVE
OVERHEAD AND WEAKEN BY LATE SATURDAY... AND THEN AN ALBERTA CLIPPER
SWINGS THROUGH THE MID ATLANTIC REGION SATURDAY EVENING. COLD HIGH
PRESSURE WILL AGAIN BUILD INTO THE AREA ON SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 215 PM FRIDAY...
THE LATEST SURFACE ANALYSIS SHOWS THE PRIMARY SURFACE FRONT ALONG
THE SE EDGE OF THE CWA... WITH THE SECONDARY FRONT A BIT FARTHER NW
THROUGH THE EASTERN PIEDMONT... AND IT IS THIS FRONT THAT IS THE
LEADING EDGE OF THE VERY DRY AIR. RESIDUAL MOISTURE IN THE LOWEST
SEVERAL THOUSAND FEET COMBINED WITH WEAK MIXING HAVE HELPED HOLD
CLOUDS OVER THE EASTERN CWA TODAY... BUT AS A SHEARED MID LEVEL LOBE
OF VORTICITY APPROACHES FROM THE WEST AND THE UPPER JET CORE TO OUR
NORTH SHIFTS EASTWARD... THE 850 MB FRONT SHOULD BE PROPELLED
EASTWARD... ALL RESULTING IN CLEARING SKIES BY MID EVENING. BOTH THE
NAM AND GFS HOWEVER DEPICT A POCKET OF ISENTROPIC UPGLIDE AT 285K
OVER THE NW CWA LATE TONIGHT INTO SUNDAY MORNING AS THE WEAK 850 MB
FRONT HEADS BACK NORTH... SO WILL BRING BACK AN AREA OF SCATTERED
CLOUDS HERE OVERNIGHT. WITH SURFACE RIDGING NEARLY OVERHEAD BY
MORNING... EXPECT LOWS OF 24-30... MILDER IN THE URBAN AREAS WITH
SHELTERED AND RURAL AREAS OF THE PIEDMONT LIKELY TO DROP OFF QUICKLY
GIVEN THE INCIPIENT DRY AIR. -GIH
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 235 PM FRIDAY...
FOR SATURDAY/SATURDAY NIGHT: SATURDAY SHOULD BEGIN WITH A GOOD BIT
OF SUNSHINE BUT WITH INCREASING HIGH CLOUDS TOWARD MIDDAY. A CLIPPER
SYSTEM IS STILL EXPECTED TO DROP THROUGH THE MIDWEST LATE FRIDAY
NIGHT INTO SATURDAY MORNING... THEN PASS THROUGH NC AND OFF COAST
SATURDAY NIGHT. THE NAM REMAINS MORE SUBDUED WITH THIS VORTICITY
MAXIMUM AS COMPARED TO THE GFS... WEAKENING IT IN FAVOR OF A
STRONGER MAXIMUM TO ITS NW... HOWEVER THERE HAS BEEN A GENERAL MODEL
TREND TOWARD A STRONGER WAVE WITH MORE DYNAMIC LIFT AS IT
APPROACHES. THE 12Z WRF-ARW IS GENERATING LIGHT PRECIP AMOUNTS
ACROSS NORTH CENTRAL NC VERY LATE SATURDAY AFTERNOON THROUGH THE
EVENING... AND THE 12Z GFS HAS TRENDED TOWARD GREATER QPF AS WELL...
GENERATING SEVERAL HUNDREDTHS LIQUID ACROSS THE ENTIRE PIEDMONT.
GIVEN THIS TREND... WILL SLIGHTLY EXPAND AREALLY THE SLIGHT CHANCE
POPS SATURDAY AFTERNOON... SWEEPING THEM EAST AND RAISING THEM TO
20-30% SATURDAY EVENING. FORECAST WET BULB PROFILES ARE PRIMARILY
BELOW FREEZING EXCEPT FOR THE LOWEST COUPLE THOUSAND FEET WHERE THE
AIR IS ALSO MARKEDLY DRIER. BUT GFS FORECAST SOUNDINGS SHOW NEAR
SATURATION UP TO -20C... SO A PRECIP TYPE OF LIGHT RAIN AT ONSET AND
A MIXTURE OF LIGHT RAIN AND LIGHT SNOW IN THE EVENING NORTH OF
HIGHWAY 64 WILL BE RETAINED. THE LOW LEVEL DRY AIR AND APPARENT LACK
OF CONCENTRATED STRONG FORCING FOR ASCENT SHOULD LIMIT AMOUNTS SO AS
TO BE INSIGNIFICANT... HOWEVER IF IT APPEARS THAT LIFT WILL BE
BRIEFLY ENHANCED... WE MAY SEE A SHORT PERIOD OF MOSTLY SNOW MAINLY
NEAR THE VA BORDER... BUT AGAIN THE BREVITY OF ANY SUCH OCCURRENCE
SHOULD RENDER IT INSIGNIFICANT FOR TRAVELERS. THICKNESSES AND
STATISTICAL GUIDANCE AGREE ON HIGHS OF 45-52. LOWS SATURDAY NIGHT
26-34 WITH INCREASING COLD ADVECTION BEHIND THE EXITING WAVE.
FOR SUNDAY: THE MID LEVEL LONGWAVE TROUGH AXIS SHIFTS TO OUR NE
SUNDAY MORNING AS THE POLAR HIGH BUILDS IN FROM THE NW... AND
CONSIDERABLE SUNSHINE IS EXPECTED. WITH RAPIDLY DEEPENING SURFACE
PRESSURES OVER THE NORTHEAST STATES... THE RESULTING TIGHTENING MSLP
GRADIENT WILL PRODUCE BLUSTERY SURFACE WINDS AROUND 15 MPH WITH
GUSTS TO AROUND 25 MPH POSSIBLE (SEE FIRE WEATHER DISCUSSION BELOW).
WITH STRONG COLD ADVECTION AND CONSIDERING THE POLAR SOURCE OF THE
INCOMING SURFACE HIGH... HAVE LOWERED HIGHS A BIT TO 41-48. -GIH
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AS OF 300 PM FRIDAY...
MONDAY:
THE LATEST 12Z MODEL RUNS CONTINUE TO SHOW SFC HIGH PRESSURE
BUILDING ACROSS THE AREA FROM THE WEST ON SUNDAY NIGHT AND
MONDAY...WITH UNIDIRECTIONAL FLOW ALOFT. CLEAR SKIES AND NEAR CALM
WINDS WILL ALLOW EXCELLENT RADIATIONAL COOLING MON MORNING...AND
EXPECT VERY CHILLY LOW TEMP READINGS IN THE LOWER/MID 20S. CLEAR
SKIES WILL EVENTUALLY GIVE WAY TO INCREASING MID/UPPER LEVEL CLOUDS
BY THE AFT/EVE AS UPPER LEVEL MOISTURE ADVECTS DOWNSTREAM OF AN AREA
OF LOW PRESSURE EXPECTED TO DEVELOP ACROSS THE LOWER MIDWEST. FOR
TEMPS...WENT WITH A BLEND OF MOS GUIDANCE AND THICKNESSES (1285-
1295M AT 12Z MON UP TO 1310-1325M BY 00Z TUE)...WHICH SUGGEST HIGHS
RANGING FROM THE MID 40S TO LOWER 50S.
TUESDAY THROUGH FRIDAY:
AN UNSETTLED WEATHER PATTERN IS STILL EXPECTED DURING THIS PORTION
OF THE FORECAST. HOWEVER...SPECIFICS REMAIN DIFFICULT TO PIN DOWN
DUE TO CONTINUED DIFFERENCES IN HOW THE LONG RANGE MODELS HANDLE
NORTHERN/SOUTHERN STREAM PHASING. ON TUESDAY AN UPPER LEVEL WAVE IS
EXPECTED TO DIG SOUTH THROUGH THE INTERMOUNTAIN WEST...INTO THE FAR
WESTERN GOMEX BY WED. THIS WILL HELP PUSH A FRONTAL ZONE TOWARD THE
AREA FROM THE WEST...IN ADDITION TO ALLOWING A MOIST SOUTHWEST FLOW
ALOFT (FROM THE GOMEX) TO SETUP OVER THE SOUTHEAST STATES. AS OF THE
LATEST 12Z MODEL RUNS...WED LOOKS LIKE A BETTER CHANCE FOR PRECIP
THAN TUE...ALTHOUGH QUITE A BIT OF UNCERTAINTY REMAINS THROUGH
MID/LATE WEEK. BOTH THE GFS/ECMWF SHOW THE UPPER LEVEL WAVE THAT
DIGS INTO THE WESTERN GOMEX CLOSING OFF INTO AN UPPER LOW
THURSDAY...WHICH SUBSEQUENTLY MOVES EAST ACROSS THE NORTHERN GOMEX
AND THEN NORTHEAST THROUGH THE SOUTHEAST STATES...WITH A SFC LOW
DEVELOPING IN THE GULF AND MOVING NORTHEAST ALONG THE SOUTHEAST
COAST ON THU/FRI. ALTHOUGH THE GFS/ECMWF ARE NOW SHOWING A MORE
SIMILAR PATTERN THROUGH MID/LATE NEXT WEEK...THERE ARE STILL TIMING
DIFFERENCES...AND THERE IS ENOUGH UNCERTAINTY TO LEAVE THE EXTENDED
FORECAST MORE OR LESS AS IS...WITH THE EXCEPTION OF SOME MINOR
TWEAKING TO POPS AND TEMPS. WILL BASICALLY SHOW CHANCE POPS FROM TUE
THROUGH FRI...WITH MOSTLY CLOUDY OR OVERCAST SKIES DURING THE ENTIRE
PERIOD. TEMPERATURES REMAIN DIFFICULT TO FCST IN THIS PERIOD SINCE
THEY WILL HIGHLY DEPEND ON THE TIMING OF FRONTAL PASSAGES...
ONSET/DURATION OF PRECIP...AND THE TRACK OF ANY SFC LOW THAT MAY
DEVELOP BY MID/LATE WEEK. AT THIS TIME WILL SHOW NEAR NORMAL TEMPS
ON TUE/WED...WITH BELOW NORMAL TEMPS ON THU/FRI. -VINCENT
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AS OF 1255 PM FRIDAY...
PERIODS OF MVFR CIGS ARE LIKELY AT RDU/FAY/RWI FOR THE REST OF THE
AFTERNOON... OTHERWISE VFR CONDITIONS ARE EXPECTED AT CENTRAL NC
TERMINALS THROUGH MIDDAY SATURDAY. A SURFACE FRONT REMAINS STALLED
ACROSS EASTERN NC AS A CHILLY HIGH PRESSURE ATTEMPTS TO PUSH IN FROM
THE WEST. RESIDUAL MOISTURE IN THE LOWEST 5000 FT AGL... NOTED ON
AMDAR AIRCRAFT SOUNDINGS OVER THE AREA LATE THIS MORNING... AND WEAK
MIXING HAVE HELPED HOLD CLOUDS WITH 2000-4000 FT AGL BASES OVER THE
RDU/FAY/RWI AREAS. ONCE AN UPPER LEVEL JET TO OUR NORTH SHIFTS EAST
LATER THIS AFTERNOON... STRONGER MIXING WILL ENSUE AND THESE CLOUDS
SHOULD DISSIPATE... LEAVING ONLY HIGH CLOUDS ABOVE 12000 FT AGL OVER
CENTRAL NC THROUGH TONIGHT. MINOR AMOUNTS OF MOISTURE NOTED ON
FORECAST SOUNDINGS AROUND 3500-4000 FT AGL MAY PRODUCE SCATTERED
CLOUDS AT INT/GSO LATE TONIGHT... BUT NO CIGS ARE EXPECTED. MID
LEVEL CLOUDINESS ABOVE 12000 FT AGL WILL START TO INCREASE TOWARD
MIDDAY SATURDAY FROM WEST TO EAST AHEAD OF AN ALBERTA CLIPPER SYSTEM
DIVING IN FROM THE NW. VSBYS ARE EXPECTED TO REMAIN VFR THROUGH
EARLY SATURDAY AFTERNOON.
LOOKING BEYOND MIDDAY SATURDAY... THE AFOREMENTIONED CLIPPER SYSTEM
IS EXPECTED TO BRING A PERIOD OF BROKEN VFR CLOUD COVER MAINLY TO
INT/GSO/RDU/RWI LATE SATURDAY AFTERNOON THROUGH EVENING. THE
POTENTIAL WILL EXIST FOR VIRGA AND A LITTLE RAIN/SNOW MIX DURING
THIS TIME FRAME... ESPECIALLY NEAR THE VA BORDER AND INTO THE
NORTHERN NC TERMINAL SITES. VFR CONDITIONS WILL THEN PREVAIL
SATURDAY NIGHT INTO MONDAY NIGHT. COMPUTER MODELS CONTINUE TO SHOW A
DEVELOPING STORM SYSTEM WELL TO OUR SOUTHWEST TOWARD MID WEEK THAT
MAY PRODUCE VARIOUS ADVERSE AVIATION CONDITIONS FROM TUESDAY THROUGH
WEDNESDAY AND POSSIBLY BEYOND... SO AVIATION INTERESTS SHOULD STAY
TUNED FOR LATER FORECASTS. -GIH
&&
.FIRE WEATHER...
MARGINALLY ADVERSE FIRE WEATHER CONDITIONS ARE POSSIBLE ON SUNDAY.
THE COMBINATION OF DEEPENING LOW PRESSURE AND STRONG HIGH PRESSURE
BUILDING IN FROM THE WEST WILL PRODUCE SUSTAINED WINDS AROUND 15 MPH
AND GUSTS TO AROUND 25 MPH ON SUNDAY. IN ADDITION... AS VERY DRY LOW
LEVEL AIR SPILLS INTO THE AREA... RELATIVE HUMIDITIES WILL BOTTOM
OUT AT 21-26 PERCENT IN THE EARLY TO MID AFTERNOON. THOSE WITH FIRE
WEATHER INTERESTS SHOULD KEEP A CLOSE EYE ON THE LATEST FORECASTS
AND CONDITIONS HEADING THROUGH THE WEEKEND. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...HARTFIELD
LONG TERM...VINCENT
AVIATION...HARTFIELD
FIRE WEATHER...HARTFIELD
AREA FORECAST DISCUSSION
NWS RALEIGH NC
235 PM EST FRI DEC 5 2008
.SYNOPSIS...A FRONT THAT IS STALLED OUT ALONG NORTH CAROLINA COASTAL
SECTIONS WILL GRADUALLY SHIFT EAST AWAY FROM THE AREA THROUGH
TONIGHT... AS CHILLY HIGH PRESSURE BUILDS IN FROM THE WEST. THIS
HIGH WILL MOVE OVERHEAD AND WEAKEN BY LATE SATURDAY... AND THEN AN
ALBERTA CLIPPER SWINGS THROUGH THE MID ATLANTIC REGION SATURDAY
EVENING. COLD HIGH PRESSURE WILL AGAIN BUILD INTO THE AREA ON SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 215 PM FRIDAY...
THE LATEST SURFACE ANALSYS SHOWS THE PRIMARY SURFACE FRONT ALONG THE
SE EDGE OF THE CWA... WITH THE SECONDARY FRONT A BIT FARTHER NW
THROUGH THE EASTERN PIEDMONT... AND IT IS THIS FRONT THAT IS THE
LEADING EDGE OF THE VERY DRY AIR. RESIDUAL MOISTURE IN THE LOWEST
SEVERAL THOUSAND FEET COMBINED WITH WEAK MIXING HAVE HELPED HOLD
CLOUDS OVER THE EASTERN CWA TODAY... BUT AS A SHEARED MID LEVEL LOBE
OF VORTICITY APPROACHES FROM THE WEST AND THE UPPER JET CORE TO OUR
NORTH SHIFTS EASTWARD... THE 850 MB FRONT SHOULD BE PROPELLED
EASTWARD... ALL RESULTING IN CLEARING SKIES BY MID EVENING. BOTH THE
NAM AND GFS HOWEVER DEPICT A POCKET OF ISENTROPIC UPGLIDE AT 285K
OVER THE NW CWA LATE TONIGHT INTO SUNDAY MORNING AS THE WEAK 850 MB
FRONT HEADS BACK NORTH... SO WILL BRING BACK AN AREA OF SCATTERED
CLOUDS HERE OVERNIGHT. WITH SURFACE RIDGING NEARLY OVERHEAD BY
MORNING... EXPECT LOWS OF 24-30... MILDER IN THE URBAN AREAS WITH
SHELTERED AND RURAL AREAS OF THE PIEDMONT LIKELY TO DROP OFF QUICKLY
GIVEN THE INCIPIENT DRY AIR. -GIH
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 235 PM FRIDAY...
FOR SATURDAY/SATURDAY NIGHT: SATURDAY SHOULD BEGIN WITH A GOOD BIT
OF SUNSHINE BUT WITH INCREASING HIGH CLOUDS TOWARD MIDDAY. A CLIPPER
SYSTEM IS STILL EXPECTED TO DROP THROUGH THE MIDWEST LATE FRIDAY
NIGHT INTO SATURDAY MORNING... THEN PASS THROUGH NC AND OFF COAST
SATURDAY NIGHT. THE NAM REMAINS MORE SUBDUED WITH THIS VORTICITY
MAXIMUM AS COMPARED TO THE GFS... WEAKENING IT IN FAVOR OF A
STRONGER MAXIMUM TO ITS NW... HOWEVER THERE HAS BEEN A GENERAL MODEL
TREND TOWARD A STRONGER WAVE WITH MORE DYNAMIC LIFT AS IT
APPROACHES. THE 12Z WRF-ARW IS GENERATING LIGHT PRECIP AMOUNTS
ACROSS NORTH CENTRAL NC VERY LATE SATURDAY AFTERNOON THROUGH THE
EVENING... AND THE 12Z GFS HAS TRENDED TOWARD GREATER QPF AS WELL...
GENERATING SEVERAL HUNDREDTHS LIQUID ACROSS THE ENTIRE PIEDMONT.
GIVEN THIS TREND... WILL SLIGHTLY EXPAND AREALLY THE SLIGHT CHANCE
POPS SATURDAY AFTERNOON... SWEEPING THEM EAST AND RAISING THEM TO
20-30% SATURDAY EVENING. FORECAST WET BULB PROFILES ARE PRIMARILY
BELOW FREEZING EXCEPT FOR THE LOWEST COUPLE THOUSAND FEET WHERE THE
AIR IS ALSO MARKEDLY DRIER. BUT GFS FORECAST SOUNDINGS SHOW NEAR
SATURATION UP TO -20C... SO A PRECIP TYPE OF LIGHT RAIN AT ONSET AND
A MIXTURE OF LIGHT RAIN AND LIGHT SNOW IN THE EVENING NORTH OF
HIGHWAY 64 WILL BE RETAINED. THE LOW LEVEL DRY AIR AND APPARENT LACK
OF CONCENTRATED STRONG FORCING FOR ASCENT SHOULD LIMIT AMOUNTS SO AS
TO BE INSIGNIFICANT... HOWEVER IF IT APPEARS THAT LIFT WILL BE
BRIEFLY ENHANCED... WE MAY SEE A SHORT PERIOD OF MOSTLY SNOW MAINLY
NEAR THE VA BORDER... BUT AGAIN THE BREVITY OF ANY SUCH OCCURRENCE
SHOULD RENDER IT INSIGNIFICANT FOR TRAVELERS. THICKNESSES AND
STATISTICAL GUIDANCE AGREE ON HIGHS OF 45-52. LOWS SATURDAY NIGHT
26-34 WITH INCREASING COLD ADVECTION BEHIND THE EXITING WAVE.
FOR SUNDAY: THE MID LEVEL LONGWAVE TROUGH AXIS SHIFTS TO OUR NE
SUNDAY MORNING AS THE POLAR HIGH BUILDS IN FROM THE NW... AND
CONSIDERABLE SUNSHINE IS EXPECTED. WITH RAPIDLY DEEPENING SURFACE
PRESSURES OVER THE NORTHEAST STATES... THE RESULTING TIGHTENING MSLP
GRADIENT WILL PRODUCE BLUSTERY SURFACE WINDS AROUND 15 MPH WITH
GUSTS TO AROUND 25 MPH POSSIBLE (SEE FIRE WEATHER DISCUSSION BELOW).
WITH STRONG COLD ADVECTION AND CONSIDERING THE POLAR SOURCE OF THE
INCOMING SURFACE HIGH... HAVE LOWERED HIGHS A BIT TO 41-48. -GIH
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AS OF 430 AM FRIDAY...
UNSETTLED WEATHER PATTERN EXPECTED THIS PERIOD ACROSS CENTRAL NC.
SPLIT FLOW REGIME BECOMES ESTABLISHED ACROSS TH WESTERN AND CENTRAL
U.S. EARLY NEXT WEEK WITH MEDIUM RANGE GUIDANCE SUGGESTING A MORE
ACTIVE THAN NORMAL SOUTHERN STREAM. MODELS GENERALLY HAVE A TENDENCY
TO HAVE TIMING ISSUES WITH SYSTEMS IN AN ACTIVE SOUTHERN STREAM AND
THIS SEEMS TO BE THE CASE WITH THIS EVOLVING SYSTEM.
DISTURBANCES ALOFT WILL SLOWLY STRENGTHEN AN UPPER LEVEL LOW IN
VICINITY OF THE TX PANHANDLE BY TUESDAY MORNING. THIS SYSTEM IN
CONJUNCTION WITH RETREATING HIGH PRESSURE OFF THE ATLANTIC COAST
WILL RESULT IN A MOIST SLY RETURN FLOW OVER CENTRAL NC BY EARLY
TUESDAY. THIS TYPE OF LOW LEVEL WARM AIR ADVECTION REGIME USUALLY
PRODUCES PATCHES OF LIGHT PRECIP AS THE LOW LEVEL SLY FLOW COMES IN
CONTACT AND OVERRIDES THE COOL DRY STABLE AIR NEAR SURFACE (COURTESY
OF THE RETREATING HIGH (POSSIBLY ARCTIC IN ORIGIN)). PARTIAL
THICKNESSES AND MODEL SOUNDINGS SUGGEST THAT IF THE PRECIP DEVELOPS
DURING THE OVERNIGHT HOURS MONDAY NIGHT...IT MAY START OUT AS LIGHT
FREEZING RAIN IN THE NW PIEDMONT BEFORE THE COLUMN MOISTENS/WARMS
SUFFICIENTLY IN THE LOWER LEVELS. DUE TO THE NARROW WINDOW OF
OPPORTUNITY AND THE PROBABILITY A LOT MAY CHANGE BETWEEN NOW AND
THEN...HAVE NOT MENTIONED WINTRY PRECIP IN THE FORECAST. HOWEVER
WILL MENTION IN THE HWO SO THAT DOT OFFICIALS ARE ALERTED TO THE
POTENTIAL NOW AND NOT MONDAY MORNING.
DEEPENING/STRENGTHENING S-SW FLOW WILL PULL GULF MOISTURE INTO THE
REGION TUESDAY-WEDNESDAY. DUE TO THE EXPECTED SLOW EASTWARD
TRANSLATION OF UPPER SYSTEM IN SOUTHERN STREAM...THIS COULD HAVE THE
POTENTIAL TO PRODUCE HEAVY/EXCESSIVE AMOUNTS OF RAIN...ESPECIALLY
IMMEDIATELY W-SW OF CENTRAL NC. PER LATEST 00Z ECMWF/GFS...GFS
CONTINUES TO BE FASTER AND DEEPER WITH THE UPPER LEVEL
SYSTEM..MAINTAINING A CLOSED UPPER LEVEL CIRCULATION FROM THE
TX-NORTHERN GULF OF MEXICO-CAROLINA COAST TUESDAY THROUGH THU. THE
MAGNITUDE AND EXTREME SOUTHERN TRAJECTORY DEPICTED BY THE GFS VERY
ABNORMAL. SCENARIO OFFERED BY THE ECMWF A LITTLE MORE PLAUSIBLE BUT
STILL DEPICTS A STRONG UPPER LEVEL LOW THAT SLOWLY EJECTS E-NE FROM
TX INTO THE DEEP SOUTH WED INTO THU THEN OPENS UP AND MOVE NE THU
NIGHT AND FRI ACROSS THE SE U.S. AS A PIECE OF ENERGY DIVES SE ALONG
THE SPINE OF THE ROCKIES.
DUE TO THE TIMING DIFFERENCES AND POTENTIAL HIGH IMPACT OF THIS
SYSTEM...MADE FEW IF ANY CHANGES TO THE FORECAST BEYOND TUESDAY.
HIGH CHANCE POPS IN ORDER FOR TUESDAY INTO WEDNESDAY AS INITIAL WARM
AIR SURGE SHOULD RESULT IN SOME RAIN. WILL LIKELY SEE A LULL IN
PRECIP SOMETIME WED INTO THU BEFORE NEXT ROUND OF PRECIP AFFECTS
REGION LATE THU INTO FRI (IF TIMING OF ECMWF CORRECT). MAX TEMPS WED
INTO THU MAY LIKELY NEED TO BE RAISED ONE-TWO CATEGORIES.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AS OF 1255 PM FRIDAY...
PERIODS OF MVFR CIGS ARE LIKELY AT RDU/FAY/RWI FOR THE REST OF THE
AFTERNOON... OTHERWISE VFR CONDITIONS ARE EXPECTED AT CENTRAL NC
TERMINALS THROUGH MIDDAY SATURDAY. A SURFACE FRONT REMAINS STALLED
ACROSS EASTERN NC AS A CHILLY HIGH PRESSURE ATTEMPTS TO PUSH IN FROM
THE WEST. RESIDUAL MOISTURE IN THE LOWEST 5000 FT AGL... NOTED ON
AMDAR AIRCRAFT SOUNDINGS OVER THE AREA LATE THIS MORNING... AND WEAK
MIXING HAVE HELPED HOLD CLOUDS WITH 2000-4000 FT AGL BASES OVER THE
RDU/FAY/RWI AREAS. ONCE AN UPPER LEVEL JET TO OUR NORTH SHIFTS EAST
LATER THIS AFTERNOON... STRONGER MIXING WILL ENSUE AND THESE CLOUDS
SHOULD DISSIPATE... LEAVING ONLY HIGH CLOUDS ABOVE 12000 FT AGL OVER
CENTRAL NC THROUGH TONIGHT. MINOR AMOUNTS OF MOISTURE NOTED ON
FORECAST SOUNDINGS AROUND 3500-4000 FT AGL MAY PRODUCE SCATTERED
CLOUDS AT INT/GSO LATE TONIGHT... BUT NO CIGS ARE EXPECTED. MID
LEVEL CLOUDINESS ABOVE 12000 FT AGL WILL START TO INCREASE TOWARD
MIDDAY SATURDAY FROM WEST TO EAST AHEAD OF AN ALBERTA CLIPPER SYSTEM
DIVING IN FROM THE NW. VSBYS ARE EXPECTED TO REMAIN VFR THROUGH
EARLY SATURDAY AFTERNOON.
LOOKING BEYOND MIDDAY SATURDAY... THE AFOREMENTIONED CLIPPER SYSTEM
IS EXPECTED TO BRING A PERIOD OF BROKEN VFR CLOUD COVER MAINLY TO
INT/GSO/RDU/RWI LATE SATURDAY AFTERNOON THROUGH EVENING. THE
POTENTIAL WILL EXIST FOR VIRGA AND A LITTLE RAIN/SNOW MIX DURING
THIS TIME FRAME... ESPECIALLY NEAR THE VA BORDER AND INTO THE
NORTHERN NC TERMINAL SITES. VFR CONDITIONS WILL THEN PREVAIL
SATURDAY NIGHT INTO MONDAY NIGHT. COMPUTER MODELS CONTINUE TO SHOW A
DEVELOPING STORM SYSTEM WELL TO OUR SOUTHWEST TOWARD MID WEEK THAT
MAY PRODUCE VARIOUS ADVERSE AVIATION CONDITIONS FROM TUESDAY THROUGH
WEDNESDAY AND POSSIBLY BEYOND... SO AVIATION INTERESTS SHOULD STAY
TUNED FOR LATER FORECASTS. -GIH
&&
.FIRE WEATHER...
MARGINALLY ADVERSE FIRE WEATHER CONDITIONS ARE POSSIBLE ON SUNDAY.
THE COMBINATION OF DEEPENING LOW PRESSURE AND STRONG HIGH PRESSURE
BUILDING IN FROM THE WEST WILL PRODUCE SUSTAINED WINDS AROUND 15 MPH
AND GUSTS TO AROUND 25 MPH ON SUNDAY. IN ADDITION... AS VERY DRY LOW
LEVEL AIR SPILLS INTO THE AREA... RELATIVE HUMIDITIES WILL BOTTOM
OUT AT 21-26 PERCENT IN THE EARLY TO MID AFTERNOON. THOSE WITH FIRE
WEATHER INTERESTS SHOULD KEEP A CLOSE EYE ON THE LATEST FORECASTS
AND CONDITIONS HEADING THROUGH THE WEEKEND. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...HARTFIELD
FIRE WEATHER...HARTFIELD
AREA FORECAST DISCUSSION
NWS RALEIGH NC
215 PM EST FRI DEC 5 2008
.SYNOPSIS...A FRONT THAT IS STALLED OUT ALONG NORTH CAROLINA COASTAL
SECTIONS WILL GRADUALLY SHIFT EAST AWAY FROM THE AREA THROUGH
TONIGHT... AS CHILLY HIGH PRESSURE BUILDS IN FROM THE WEST. THIS
HIGH WILL MOVE OVERHEAD AND WEAKEN BY LATE SATURDAY... AND THEN AN
ALBERTA CLIPPER SWINGS THROUGH THE MID ATLANTIC REGION SATURDAY
EVENING. COLD HIGH PRESSURE WILL AGAIN BUILD INTO THE AREA ON SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 215 PM FRIDAY...
THE LATEST SURFACE ANALSYS SHOWS THE PRIMARY SURFACE FRONT ALONG THE
SE EDGE OF THE CWA... WITH THE SECONDARY FRONT A BIT FARTHER NW
THROUGH THE EASTERN PIEDMONT... AND IT IS THIS FRONT THAT IS THE
LEADING EDGE OF THE VERY DRY AIR. RESIDUAL MOISTURE IN THE LOWEST
SEVERAL THOUSAND FEET COMBINED WITH WEAK MIXING HAVE HELPED HOLD
CLOUDS OVER THE EASTERN CWA TODAY... BUT AS A SHEARED MID LEVEL LOBE
OF VORTICITY APPROACHES FROM THE WEST AND THE UPPER JET CORE TO OUR
NORTH SHIFTS EASTWARD... THE 850 MB FRONT SHOULD BE PROPELLED
EASTWARD... ALL RESULTING IN CLEARING SKIES BY MID EVENING. BOTH THE
NAM AND GFS HOWEVER DEPICT A POCKET OF ISENTROPIC UPGLIDE AT 285K
OVER THE NW CWA LATE TONIGHT INTO SUNDAY MORNING AS THE WEAK 850 MB
FRONT HEADS BACK NORTH... SO WILL BRING BACK AN AREA OF SCATTERED
CLOUDS HERE OVERNIGHT. WITH SURFACE RIDGING NEARLY OVERHEAD BY
MORNING... EXPECT LOWS OF 24-30... MILDER IN THE URBAN AREAS WITH
SHELTERED AND RURAL AREAS OF THE PIEDMONT LIKELY TO DROP OFF QUICKLY
GIVEN THE INCIPIENT DRY AIR. -GIH
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 310 AM FRIDAY...
MODEL GUIDANCE HAS DEVIATED LITTLE FROM EARLIER SCENARIO. GFS STILL
MORE ROBUST WITH THE VORT MAXIMA DIVING INTO THE BASE OF THE L/W
TROUGH WHILE ECMWF HAS THIS FEATURE A LITTLE FARTHER TO THE NORTH
AND THE NAM REMAINS RATHER WEAK. NOT SURPRISINGLY...GFS ALSO WETTER
ALOFT ALONG WITH BETTER LIFT. DEPTH OF MOISTURE THROUGH THE FAVORED
ICE NUCLEATION REGION COUPLED WITH MODERATE LIFT SUGGEST THAT WHERE
HEAVIER PRECIP OCCURS...WET SNOW IS FAVORED OVER RAIN. ONE BIG
NEGATIVE FOR PRECIP IS THAT THE SUB CLOUD LAYER IS QUITE DRY. THUS
MOST OF THE THE PRECIP THAT FALLS WILL GO TO SATURATING THE LOWER
LEVELS. BY THE TIME THAT IS ACHIEVED...BEST DYNAMICS ALOFT ARE
SCOOTING TO THE E-NE. WILL CONTINUE TREND MOSTLY/PARTLY SUNNY SKIES
IN THE MORNING FOLLOWED THICKENING CLOUDS FROM NW-SE LATE SATURDAY
INTO SATURDAY EVENING. USING THE WORST CASE SCENARIO (GFS)...WILL
CONFINE POPS TO THE NORTHERN THIRD OF THE CWA AND MENTION LIGHT RAIN
EARLY THEN EITHER LIGHT RAIN OR LIGHT SNOW. AS TIME APPROACHES AND
APPEARS THAT GFS IS MORE CORRECT...THEN CAN CHANGE EMPHASIS ON
PRECIP TO MORE SNOW THAN RAIN. IF ALL SNOW WERE TO OCCUR...AMOUNTS
WILL BE LIGHT AND MELT ON IMPACT WITH THE EXCEPTION OF SOME LIGHT
ACCUMULATION ON CARS/GRASSY AREAS.
COLD HIGH PRESSURE WILL BUILD INTO REGION FROM THE NW IN WAKE OF
EXITING SYSTEM SUNDAY. TIGHT PRESSURE GRADIENT INDICATES A BLUSTERY
DAY WITH SUSTAINED WINDS 10-15MPH AND GUSTS 20-25MPH. GFS
THICKNESSES SUGGEST MAX TEMPS NO HIGHER THAN MID 30S IN THE NW
PIEDMONT. THIS APPEARS TOO EXTREME AT THIS TIME. NAM THICKNESSES
SUGGEST LOWER 40S NW TO THE UPPER 40S SE.
CHILLY SUNDAY NIGHT WITH HIGH NOSING INTO REGION. DECENT
RADIATION COOLING SUGGEST MIN TEMPS IN THE MID 20S MOST PLACES
WITH THE COLDER LOCALES NEAR 20 PROBABLE.
CONTINUED COOL AND DRY MONDAY WITH UPPER LEVEL FLOW BECOMING
WESTERLY AS L/W TROUGH EXITS THE EASTERN SEABOARD AND A SERIES OF
DISTURBANCES IN THE SPLIT FLOW WEST OF US TRAVERSE EAST.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AS OF 430 AM FRIDAY...
UNSETTLED WEATHER PATTERN EXPECTED THIS PERIOD ACROSS CENTRAL NC.
SPLIT FLOW REGIME BECOMES ESTABLISHED ACROSS TH WESTERN AND CENTRAL
U.S. EARLY NEXT WEEK WITH MEDIUM RANGE GUIDANCE SUGGESTING A MORE
ACTIVE THAN NORMAL SOUTHERN STREAM. MODELS GENERALLY HAVE A TENDENCY
TO HAVE TIMING ISSUES WITH SYSTEMS IN AN ACTIVE SOUTHERN STREAM AND
THIS SEEMS TO BE THE CASE WITH THIS EVOLVING SYSTEM.
DISTURBANCES ALOFT WILL SLOWLY STRENGTHEN AN UPPER LEVEL LOW IN
VICINITY OF THE TX PANHANDLE BY TUESDAY MORNING. THIS SYSTEM IN
CONJUNCTION WITH RETREATING HIGH PRESSURE OFF THE ATLANTIC COAST
WILL RESULT IN A MOIST SLY RETURN FLOW OVER CENTRAL NC BY EARLY
TUESDAY. THIS TYPE OF LOW LEVEL WARM AIR ADVECTION REGIME USUALLY
PRODUCES PATCHES OF LIGHT PRECIP AS THE LOW LEVEL SLY FLOW COMES IN
CONTACT AND OVERRIDES THE COOL DRY STABLE AIR NEAR SURFACE (COURTESY
OF THE RETREATING HIGH (POSSIBLY ARCTIC IN ORIGIN)). PARTIAL
THICKNESSES AND MODEL SOUNDINGS SUGGEST THAT IF THE PRECIP DEVELOPS
DURING THE OVERNIGHT HOURS MONDAY NIGHT...IT MAY START OUT AS LIGHT
FREEZING RAIN IN THE NW PIEDMONT BEFORE THE COLUMN MOISTENS/WARMS
SUFFICIENTLY IN THE LOWER LEVELS. DUE TO THE NARROW WINDOW OF
OPPORTUNITY AND THE PROBABILITY A LOT MAY CHANGE BETWEEN NOW AND
THEN...HAVE NOT MENTIONED WINTRY PRECIP IN THE FORECAST. HOWEVER
WILL MENTION IN THE HWO SO THAT DOT OFFICIALS ARE ALERTED TO THE
POTENTIAL NOW AND NOT MONDAY MORNING.
DEEPENING/STRENGTHENING S-SW FLOW WILL PULL GULF MOISTURE INTO THE
REGION TUESDAY-WEDNESDAY. DUE TO THE EXPECTED SLOW EASTWARD
TRANSLATION OF UPPER SYSTEM IN SOUTHERN STREAM...THIS COULD HAVE THE
POTENTIAL TO PRODUCE HEAVY/EXCESSIVE AMOUNTS OF RAIN...ESPECIALLY
IMMEDIATELY W-SW OF CENTRAL NC. PER LATEST 00Z ECMWF/GFS...GFS
CONTINUES TO BE FASTER AND DEEPER WITH THE UPPER LEVEL
SYSTEM..MAINTAINING A CLOSED UPPER LEVEL CIRCULATION FROM THE
TX-NORTHERN GULF OF MEXICO-CAROLINA COAST TUESDAY THROUGH THU. THE
MAGNITUDE AND EXTREME SOUTHERN TRAJECTORY DEPICTED BY THE GFS VERY
ABNORMAL. SCENARIO OFFERED BY THE ECMWF A LITTLE MORE PLAUSIBLE BUT
STILL DEPICTS A STRONG UPPER LEVEL LOW THAT SLOWLY EJECTS E-NE FROM
TX INTO THE DEEP SOUTH WED INTO THU THEN OPENS UP AND MOVE NE THU
NIGHT AND FRI ACROSS THE SE U.S. AS A PIECE OF ENERGY DIVES SE ALONG
THE SPINE OF THE ROCKIES.
DUE TO THE TIMING DIFFERENCES AND POTENTIAL HIGH IMPACT OF THIS
SYSTEM...MADE FEW IF ANY CHANGES TO THE FORECAST BEYOND TUESDAY.
HIGH CHANCE POPS IN ORDER FOR TUESDAY INTO WEDNESDAY AS INITIAL WARM
AIR SURGE SHOULD RESULT IN SOME RAIN. WILL LIKELY SEE A LULL IN
PRECIP SOMETIME WED INTO THU BEFORE NEXT ROUND OF PRECIP AFFECTS
REGION LATE THU INTO FRI (IF TIMING OF ECMWF CORRECT). MAX TEMPS WED
INTO THU MAY LIKELY NEED TO BE RAISED ONE-TWO CATEGORIES.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AS OF 1255 PM FRIDAY...
PERIODS OF MVFR CIGS ARE LIKELY AT RDU/FAY/RWI FOR THE REST OF THE
AFTERNOON... OTHERWISE VFR CONDITIONS ARE EXPECTED AT CENTRAL NC
TERMINALS THROUGH MIDDAY SATURDAY. A SURFACE FRONT REMAINS STALLED
ACROSS EASTERN NC AS A CHILLY HIGH PRESSURE ATTEMPTS TO PUSH IN FROM
THE WEST. RESIDUAL MOISTURE IN THE LOWEST 5000 FT AGL... NOTED ON
AMDAR AIRCRAFT SOUNDINGS OVER THE AREA LATE THIS MORNING... AND WEAK
MIXING HAVE HELPED HOLD CLOUDS WITH 2000-4000 FT AGL BASES OVER THE
RDU/FAY/RWI AREAS. ONCE AN UPPER LEVEL JET TO OUR NORTH SHIFTS EAST
LATER THIS AFTERNOON... STRONGER MIXING WILL ENSUE AND THESE CLOUDS
SHOULD DISSIPATE... LEAVING ONLY HIGH CLOUDS ABOVE 12000 FT AGL OVER
CENTRAL NC THROUGH TONIGHT. MINOR AMOUNTS OF MOISTURE NOTED ON
FORECAST SOUNDINGS AROUND 3500-4000 FT AGL MAY PRODUCE SCATTERED
CLOUDS AT INT/GSO LATE TONIGHT... BUT NO CIGS ARE EXPECTED. MID
LEVEL CLOUDINESS ABOVE 12000 FT AGL WILL START TO INCREASE TOWARD
MIDDAY SATURDAY FROM WEST TO EAST AHEAD OF AN ALBERTA CLIPPER SYSTEM
DIVING IN FROM THE NW. VSBYS ARE EXPECTED TO REMAIN VFR THROUGH
EARLY SATURDAY AFTERNOON.
LOOKING BEYOND MIDDAY SATURDAY... THE AFOREMENTIONED CLIPPER SYSTEM
IS EXPECTED TO BRING A PERIOD OF BROKEN VFR CLOUD COVER MAINLY TO
INT/GSO/RDU/RWI LATE SATURDAY AFTERNOON THROUGH EVENING. THE
POTENTIAL WILL EXIST FOR VIRGA AND A LITTLE RAIN/SNOW MIX DURING
THIS TIME FRAME... ESPECIALLY NEAR THE VA BORDER AND INTO THE
NORTHERN NC TERMINAL SITES. VFR CONDITIONS WILL THEN PREVAIL
SATURDAY NIGHT INTO MONDAY NIGHT. COMPUTER MODELS CONTINUE TO SHOW A
DEVELOPING STORM SYSTEM WELL TO OUR SOUTHWEST TOWARD MID WEEK THAT
MAY PRODUCE VARIOUS ADVERSE AVIATION CONDITIONS FROM TUESDAY THROUGH
WEDNESDAY AND POSSIBLY BEYOND... SO AVIATION INTERESTS SHOULD STAY
TUNED FOR LATER FORECASTS. -GIH
&&
.FIRE WEATHER...
MARGINALLY ADVERSE FIRE WEATHER CONDITIONS ARE POSSIBLE ON SUNDAY.
THE COMBINATION OF DEEPENING LOW PRESSURE AND STRONG HIGH PRESSURE
BUILDING IN FROM THE WEST WILL PRODUCE SUSTAINED WINDS AROUND 15 MPH
AND GUSTS TO AROUND 25 MPH ON SUNDAY. IN ADDITION... AS VERY DRY LOW
LEVEL AIR SPILLS INTO THE AREA... RELATIVE HUMIDITIES WILL BOTTOM
OUT AT 21-26 PERCENT IN THE EARLY TO MID AFTERNOON. THOSE WITH FIRE
WEATHER INTERESTS SHOULD KEEP A CLOSE EYE ON THE LATEST FORECASTS
AND CONDITIONS HEADING THROUGH THE WEEKEND. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...HARTFIELD
FIRE WEATHER...HARTFIELD
AREA FORECAST DISCUSSION
NWS RALEIGH NC
1255 PM EST FRI DEC 5 2008
.SYNOPSIS...A FRONT THAT IS STALLED OUT ALONG NORTH CAROLINA COASTAL
SECTIONS WILL GRADUALLY SHIFT EAST AWAY FROM THE AREA THROUGH
TONIGHT... AS CHILLY HIGH PRESSURE BUILDS IN FROM THE WEST. THIS
HIGH WILL MOVE OVERHEAD AND WEAKEN BY LATE SATURDAY... AND THEN AN
ALBERTA CLIPPER SWINGS THROUGH THE MID ATLANTIC REGION SATURDAY
EVENING. COLD HIGH PRESSURE WILL AGAIN BUILD INTO THE AREA ON SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 1045 AM FRIDAY...
ANALYSES OF 12Z UPPER AIR DATA... PARTICULARLY AT 925 MB AND 850
MB... SHOW THE LOW LEVEL COOLER AND DRIER TAKING ITS TIME TO WORK
INTO THE CWA... AS EVIDENCED BY THE MILD 850 MB TEMPS AT MHX/CHS AND
THE PERSISTENT STRATOCUMULUS COVERING THE EASTERN CWA. NEAR TERM SKY
FORECAST HAS BEEN ADJUSTED TO ACCOUNT FOR THE PROLONGED CLOUDINESS
HERE. THE PRIMARY SURFACE FRONT IS LOCATED ALONG THE SE EDGE OF THE
CWA AT 14Z... ALTHOUGH DUE TO THE MOUNTAINS THE COLD AIR IS SPILLING
SLOWLY IN FROM THE NORTH AND AROUND THE SW. A SECONDARY FRONT IS A
BIT FARTHER NW THROUGH THE EASTERN PIEDMONT... AND IT IS BEHIND THIS
FRONT THAT SURFACE DEW POINTS DROP INTO THE LOWER 20S AND UPPER
TEENS. THE VERY DRY NATURE OF THIS INCOMING SURFACE AIR WAS NOT WELL
HANDLED BY EARLIER GUIDANCE AND THESE TOO HAVE BEEN ADJUSTED
SIGNIFICANTLY DOWNWARD ESPECIALLY IN THE NW CWA THROUGH TONIGHT. AS
THE POLAR UPPER JET TO OUR NORTH PIVOTS EASTWARD... ITS RIGHT
ENTRANCE REGION FINALLY PASSES OVER AND EAST OF CENTRAL NC... AND
THIS SHOULD ALLOW THE BULK OF THE CHILLY LOW LEVEL AIR TO FINALLY
PUSH WELL INTO THE CWA. TEMPS ARE ROUGH TODAY AS SOUTHEAST SECTIONS
OF THE CWA BEGAN THE DAY CLOSE TO THE PROJECTED HIGHS... AND IN THE
TRIAD... COLD ADVECTION SHOULD ALLOW JUST A 5-8 DEGREE RISE FOR THE
REST OF THE DAY... IF THAT. HAVE ADJUSTED HOURLY TEMP READINGS AND
THE DAYTIME HIGHS TO ACCOUNT FOR A MINIMAL RISE... ONLY PEAKING IN
THE MID 40S TO AROUND 50 WHEN ALL IS SAID AND DONE. -GIH
TONIGHT...SURFACE HIGH SETTLES OVERHEAD. APPEARS ENOUGH DRIER AIR
WILL WORK ITS WAY TO THE SURFACE IN THE EAST TO ERODE CLOUDS.
CHILLIEST MIN TEMPS EXPECTED IN THE NW PIEDMONT CLOSE TO THE CENTER
OF THE HIGH. (MID 20S NW TO THE LOWER 30S SE). -WSS
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 310 AM FRIDAY...
MODEL GUIDANCE HAS DEVIATED LITTLE FROM EARLIER SCENARIO. GFS STILL
MORE ROBUST WITH THE VORT MAXIMA DIVING INTO THE BASE OF THE L/W
TROUGH WHILE ECMWF HAS THIS FEATURE A LITTLE FARTHER TO THE NORTH
AND THE NAM REMAINS RATHER WEAK. NOT SURPRISINGLY...GFS ALSO WETTER
ALOFT ALONG WITH BETTER LIFT. DEPTH OF MOISTURE THROUGH THE FAVORED
ICE NUCLEATION REGION COUPLED WITH MODERATE LIFT SUGGEST THAT WHERE
HEAVIER PRECIP OCCURS...WET SNOW IS FAVORED OVER RAIN. ONE BIG
NEGATIVE FOR PRECIP IS THAT THE SUB CLOUD LAYER IS QUITE DRY. THUS
MOST OF THE THE PRECIP THAT FALLS WILL GO TO SATURATING THE LOWER
LEVELS. BY THE TIME THAT IS ACHIEVED...BEST DYNAMICS ALOFT ARE
SCOOTING TO THE E-NE. WILL CONTINUE TREND MOSTLY/PARTLY SUNNY SKIES
IN THE MORNING FOLLOWED THICKENING CLOUDS FROM NW-SE LATE SATURDAY
INTO SATURDAY EVENING. USING THE WORST CASE SCENARIO (GFS)...WILL
CONFINE POPS TO THE NORTHERN THIRD OF THE CWA AND MENTION LIGHT RAIN
EARLY THEN EITHER LIGHT RAIN OR LIGHT SNOW. AS TIME APPROACHES AND
APPEARS THAT GFS IS MORE CORRECT...THEN CAN CHANGE EMPHASIS ON
PRECIP TO MORE SNOW THAN RAIN. IF ALL SNOW WERE TO OCCUR...AMOUNTS
WILL BE LIGHT AND MELT ON IMPACT WITH THE EXCEPTION OF SOME LIGHT
ACCUMULATION ON CARS/GRASSY AREAS.
COLD HIGH PRESSURE WILL BUILD INTO REGION FROM THE NW IN WAKE OF
EXITING SYSTEM SUNDAY. TIGHT PRESSURE GRADIENT INDICATES A BLUSTERY
DAY WITH SUSTAINED WINDS 10-15MPH AND GUSTS 20-25MPH. GFS
THICKNESSES SUGGEST MAX TEMPS NO HIGHER THAN MID 30S IN THE NW
PIEDMONT. THIS APPEARS TOO EXTREME AT THIS TIME. NAM THICKNESSES
SUGGEST LOWER 40S NW TO THE UPPER 40S SE.
CHILLY SUNDAY NIGHT WITH HIGH NOSING INTO REGION. DECENT
RADIATION COOLING SUGGEST MIN TEMPS IN THE MID 20S MOST PLACES
WITH THE COLDER LOCALES NEAR 20 PROBABLE.
CONTINUED COOL AND DRY MONDAY WITH UPPER LEVEL FLOW BECOMING
WESTERLY AS L/W TROUGH EXITS THE EASTERN SEABOARD AND A SERIES OF
DISTURBANCES IN THE SPLIT FLOW WEST OF US TRAVERSE EAST.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AS OF 430 AM FRIDAY...
UNSETTLED WEATHER PATTERN EXPECTED THIS PERIOD ACROSS CENTRAL NC.
SPLIT FLOW REGIME BECOMES ESTABLISHED ACROSS TH WESTERN AND CENTRAL
U.S. EARLY NEXT WEEK WITH MEDIUM RANGE GUIDANCE SUGGESTING A MORE
ACTIVE THAN NORMAL SOUTHERN STREAM. MODELS GENERALLY HAVE A TENDENCY
TO HAVE TIMING ISSUES WITH SYSTEMS IN AN ACTIVE SOUTHERN STREAM AND
THIS SEEMS TO BE THE CASE WITH THIS EVOLVING SYSTEM.
DISTURBANCES ALOFT WILL SLOWLY STRENGTHEN AN UPPER LEVEL LOW IN
VICINITY OF THE TX PANHANDLE BY TUESDAY MORNING. THIS SYSTEM IN
CONJUNCTION WITH RETREATING HIGH PRESSURE OFF THE ATLANTIC COAST
WILL RESULT IN A MOIST SLY RETURN FLOW OVER CENTRAL NC BY EARLY
TUESDAY. THIS TYPE OF LOW LEVEL WARM AIR ADVECTION REGIME USUALLY
PRODUCES PATCHES OF LIGHT PRECIP AS THE LOW LEVEL SLY FLOW COMES IN
CONTACT AND OVERRIDES THE COOL DRY STABLE AIR NEAR SURFACE (COURTESY
OF THE RETREATING HIGH (POSSIBLY ARCTIC IN ORIGIN)). PARTIAL
THICKNESSES AND MODEL SOUNDINGS SUGGEST THAT IF THE PRECIP DEVELOPS
DURING THE OVERNIGHT HOURS MONDAY NIGHT...IT MAY START OUT AS LIGHT
FREEZING RAIN IN THE NW PIEDMONT BEFORE THE COLUMN MOISTENS/WARMS
SUFFICIENTLY IN THE LOWER LEVELS. DUE TO THE NARROW WINDOW OF
OPPORTUNITY AND THE PROBABILITY A LOT MAY CHANGE BETWEEN NOW AND
THEN...HAVE NOT MENTIONED WINTRY PRECIP IN THE FORECAST. HOWEVER
WILL MENTION IN THE HWO SO THAT DOT OFFICIALS ARE ALERTED TO THE
POTENTIAL NOW AND NOT MONDAY MORNING.
DEEPENING/STRENGTHENING S-SW FLOW WILL PULL GULF MOISTURE INTO THE
REGION TUESDAY-WEDNESDAY. DUE TO THE EXPECTED SLOW EASTWARD
TRANSLATION OF UPPER SYSTEM IN SOUTHERN STREAM...THIS COULD HAVE THE
POTENTIAL TO PRODUCE HEAVY/EXCESSIVE AMOUNTS OF RAIN...ESPECIALLY
IMMEDIATELY W-SW OF CENTRAL NC. PER LATEST 00Z ECMWF/GFS...GFS
CONTINUES TO BE FASTER AND DEEPER WITH THE UPPER LEVEL
SYSTEM..MAINTAINING A CLOSED UPPER LEVEL CIRCULATION FROM THE
TX-NORTHERN GULF OF MEXICO-CAROLINA COAST TUESDAY THROUGH THU. THE
MAGNITUDE AND EXTREME SOUTHERN TRAJECTORY DEPICTED BY THE GFS VERY
ABNORMAL. SCENARIO OFFERED BY THE ECMWF A LITTLE MORE PLAUSIBLE BUT
STILL DEPICTS A STRONG UPPER LEVEL LOW THAT SLOWLY EJECTS E-NE FROM
TX INTO THE DEEP SOUTH WED INTO THU THEN OPENS UP AND MOVE NE THU
NIGHT AND FRI ACROSS THE SE U.S. AS A PIECE OF ENERGY DIVES SE ALONG
THE SPINE OF THE ROCKIES.
DUE TO THE TIMING DIFFERENCES AND POTENTIAL HIGH IMPACT OF THIS
SYSTEM...MADE FEW IF ANY CHANGES TO THE FORECAST BEYOND TUESDAY.
HIGH CHANCE POPS IN ORDER FOR TUESDAY INTO WEDNESDAY AS INITIAL WARM
AIR SURGE SHOULD RESULT IN SOME RAIN. WILL LIKELY SEE A LULL IN
PRECIP SOMETIME WED INTO THU BEFORE NEXT ROUND OF PRECIP AFFECTS
REGION LATE THU INTO FRI (IF TIMING OF ECMWF CORRECT). MAX TEMPS WED
INTO THU MAY LIKELY NEED TO BE RAISED ONE-TWO CATEGORIES.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AS OF 1255 PM FRIDAY...
PERIODS OF MVFR CIGS ARE LIKELY AT RDU/FAY/RWI FOR THE REST OF THE
AFTERNOON... OTHERWISE VFR CONDITIONS ARE EXPECTED AT CENTRAL NC
TERMINALS THROUGH MIDDAY SATURDAY. A SURFACE FRONT REMAINS STALLED
ACROSS EASTERN NC AS A CHILLY HIGH PRESSURE ATTEMPTS TO PUSH IN FROM
THE WEST. RESIDUAL MOISTURE IN THE LOWEST 5000 FT AGL... NOTED ON
AMDAR AIRCRAFT SOUNDINGS OVER THE AREA LATE THIS MORNING... AND WEAK
MIXING HAVE HELPED HOLD CLOUDS WITH 2000-4000 FT AGL BASES OVER THE
RDU/FAY/RWI AREAS. ONCE AN UPPER LEVEL JET TO OUR NORTH SHIFTS EAST
LATER THIS AFTERNOON... STRONGER MIXING WILL ENSUE AND THESE CLOUDS
SHOULD DISSIPATE... LEAVING ONLY HIGH CLOUDS ABOVE 12000 FT AGL OVER
CENTRAL NC THROUGH TONIGHT. MINOR AMOUNTS OF MOISTURE NOTED ON
FORECAST SOUNDINGS AROUND 3500-4000 FT AGL MAY PRODUCE SCATTERED
CLOUDS AT INT/GSO LATE TONIGHT... BUT NO CIGS ARE EXPECTED. MID
LEVEL CLOUDINESS ABOVE 12000 FT AGL WILL START TO INCREASE TOWARD
MIDDAY SATURDAY FROM WEST TO EAST AHEAD OF AN ALBERTA CLIPPER SYSTEM
DIVING IN FROM THE NW. VSBYS ARE EXPECTED TO REMAIN VFR THROUGH
EARLY SATURDAY AFTERNOON.
LOOKING BEYOND MIDDAY SATURDAY... THE AFOREMENTIONED CLIPPER SYSTEM
IS EXPECTED TO BRING A PERIOD OF BROKEN VFR CLOUD COVER MAINLY TO
INT/GSO/RDU/RWI LATE SATURDAY AFTERNOON THROUGH EVENING. THE
POTENTIAL WILL EXIST FOR VIRGA AND A LITTLE RAIN/SNOW MIX DURING
THIS TIME FRAME... ESPECIALLY NEAR THE VA BORDER AND INTO THE
NORTHERN NC TERMINAL SITES. VFR CONDITIONS WILL THEN PREVAIL
SATURDAY NIGHT INTO MONDAY NIGHT. COMPUTER MODELS CONTINUE TO SHOW A
DEVELOPING STORM SYSTEM WELL TO OUR SOUTHWEST TOWARD MID WEEK THAT
MAY PRODUCE VARIOUS ADVERSE AVIATION CONDITIONS FROM TUESDAY THROUGH
WEDNESDAY AND POSSIBLY BEYOND... SO AVIATION INTERESTS SHOULD STAY
TUNED FOR LATER FORECASTS. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD/WSS
SHORT TERM...WSS
LONG TERM...WSS
AVIATION...HARTFIELD
AREA FORECAST DISCUSSION
NWS SALT LAKE CITY UT
326 AM MST THU DEC 4 2008
.SYNOPSIS...A WEAK STORM SYSTEM WILL MOVE SOUTH ACROSS UTAH AND
SOUTHWEST WYOMING TODAY. HIGH PRESSURE ALOFT WILL BUILD INTO THE
AREA FRIDAY AND REMAIN THROUGH THE WEEKEND. THE NEXT STORM SYSTEM
IS FORECAST TO CROSS THE REGION EARLY NEXT WEEK.
&&
.DISCUSSION...WATER VAPOR LOOP SHOWS A SERIES OF WEAK DISTURBANCES
DROPPING SOUTH ACROSS THE NORTHERN ROCKIES...AS AN UPPER LOW MOVES
SOUTHWARD ALONG 130W. RIDGING IS DEVELOPING OVER WESTERN CANADA
BEHIND THESE SYSTEMS. ACARS 400-250MB OBSERVATIONS REVEAL A 80-120KT
NORTHERLY JET OVER THE PACIFIC NORTHWEST. 00Z 700MB ANALYSIS
INDICATES WEAK WARM ADVECTION OVER THE REGION...WITH A MUCH COLDER
AIRMASS SETTLING ACROSS THE NORTHERN ROCKIES AND UPPER MIDWEST ON
BROAD NORTHWEST FLOW.
00Z KSLC RAOB INDICATED 10C OF WARM ADVECTION BETWEEN 500-400MB WITH
LITTLE ADVECTION NOTED BELOW 650MB DURING THE PREVIOUS 24 HOURS.
0435Z ACARS ASCENT SOUNDING SHOWS WINDS BACKING IN THE LOWER LEVELS
LAST EVENING. THIS IS IN RESPONSE TO THE APPROACH OF THE WEAK
DISTURBANCES FROM THE NORTH. IR SATELLITE IMAGERY HAS INDICATED
COOLING CLOUD TOPS ACROSS SOUTHERN IDAHO AND NORTHERN UTAH
OVERNIGHT...WITH SEVERAL UP REPORTS SPOTTED AT 9Z.
GFS INDICATES WEAK FRONTOGENETIC FORCING BETWEEN 700-500MB EARLY
THIS MORNING AS THE FIRST WAVE MOVES THROUGH. SATELLITE PRESENTATION
AND MODELS INDICATE THIS FIRST WAVE QUICKLY EXITS BY LATE THIS
MORNING OR MIDDAY. THE SECOND WAVE SHOULD SETTLE SOUTH ACROSS
EASTERN UTAH THIS AFTERNOON...BUT IT APPEARS MORE MOISTURE STARVED
THAN THE FIRST JUDGING BY IR SATELLITE AND MODEL TRENDS.
ACCUMULATING SNOW SHOULD BE LIMITED TO THE MOUNTAINS OF NORTHERN AND
PERHAPS CENTRAL UTAH WITH MOISTURE BEING A LIMITING FACTOR ACROSS
THE VALLEYS. WITH FLOW BECOMING NORTHERLY LATER TODAY AND A LACK OF
INSTABILITY...NOT EXPECTING MUCH IN THE MOUNTAINS EITHER.
CLEARING SKIES AND MUCH COOLER TONIGHT BEHIND THE COLD FRONT AS HIGH
PRESSURE SETTLES INTO THE REGION. WHILE WINDS COULD BECOME GUSTY IN
THE SOUTHWEST CANYONS TONIGHT...PRESSURE GRADIENT AND 700MB FLOW DO
NOT SUGGEST WINDS SHOULD APPROACH ADVISORY CRITERIA. STABLE AIRMASS
REMAINS IN PLACE INTO THE WEEKEND AS WARM ADVECTION OCCURS ON
NORTHWESTERLY FLOW ALOFT. BOTH THE GFS AND EUROPEAN INDICATE THE
NEXT SYSTEM DROPS SOUTHEAST FROM THE PACIFIC NORTHWEST ACROSS THE
GREAT BASIN FOR THE EARLY WORK WEEK. LOOKS LIKE NORTHWEST FLOW
CONTINUES THROUGH MIDWEEK...WITH THE EUROPEAN TRYING TO BUILD THE
LONG WAVE TROUGH A LITTLE BIT FURTHER WEST ALONG THE ROCKIES THAN
THE GFS AT THIS TIME. 00Z GFS ENSEMBLE MEMBERS ARE EXHIBITING GREATER
THAN TYPICAL SPREAD AT 500MB BEGINNING ON DAY 5 OVER THE WESTERN
CONUS....WHICH SPREADS EAST ACROSS THE CONUS BY DAY 7. THUS
CONFIDENCE IS LOWER THAN NORMAL BEYOND THE EARLY WEEK SYSTEM.
&&
.AVIATION...SOUTHERLY DRAINAGE WINDS WILL SHIFT TO THE NORTHWEST
AROUND 12Z AS A COLD FRONT CROSSES THE REGION. EXPECT CEILINGS TO
LOWER BELOW 7K FT AROUND TIME OF FRONTAL PASSAGE. BEST MOISTURE AND
LIFT PROGGED TO REMAIN NORTH OF TERMINAL AREA...BUT A CHANCE EXISTS
FOR A BRIEF PERIOD OF MVFR CEILINGS AND IFR VISIBILITIES WITH A SNOW
SHOWER FROM 12Z THROUGH 18Z. EXPECT CEILINGS TO RISE ABOVE CRITICAL
7K FT LEVEL BY LATE AFTERNOON.
&&
.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...NONE.
&&
$$
PUBLIC...ROGOWSKI
AVIATION...BARJENBRUCH
FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)
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