FXUS63 KGRB 072151
AFDGRB
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
351 PM CST MON DEC 7 2009
.SHORT TERM...TONIGHT AND TUESDAY.
THE MAIN FORECAST CONCERN IS SNOW WITH THE STORM SYSTEM THAT WAS
DEVELOPING OVER THE SOUTHWEST CONUS THIS AFTERNOON. 12Z MODELS
WERE IN GOOD AGREEMENT...SHOWING QPF SPREADING ACROSS THE SOUTHERN
PART OF THE FORECAST BETWEEN 12Z AND 18Z TUESDAY...THEN ACROSS THE
REST OF THE CWA BY 00Z WEDNESDAY. HPC GUIDANCE INDICATED ONE TO
TWO INCHES GENERALLY SOUTHWEST OF A MERRILL TO GREEN BAY TO
MANITOWOC LINE BETWEEN 00Z TUESDAY THROUGH 00Z WEDNESDAY.
THE 2 INCH CONTOUR FROM HPC WAS NOT FAR SOUTHWEST OF THE FORECAST
AREA AND MODELS BROUGHT QPF TO THE AREA RATHER RAPIDLY. AS A
RESULT...HAVE GONE WITH A FEW TENTHS OF AN INCH OF SNOW FOR THE
SOUTHWEST CWA DURING THE MORNING...THEN 1.0 TO 1.5 INCH FOR MOST
LOCATIONS DURING THE AFTERNOON.
TEMPERATURES ARE COLD ENOUGH BUT WINDS TONIGHT DID NOT APPEAR
FAVORABLE FOR LAKE EFFECT IN NORTH-CENTRAL WISCONSIN. THOUGHT
ABOUT LEAVING OUT ANY MENTION OF LAKE EFFECT IN THE NORTH
TONIGHT...BUT POPS WERE IN THE CHANCE CATEGORY TO THE NORTH AND
WEST...SO HAVE MENTIONED ISOLATED SNOW SHOWERS FOR VILAS THIS
EVENING...BUT NOTHING AFTER 06Z.
.LONG TERM...TUESDAY NIGHT THRU NEXT MONDAY.
AN EXTENDED PERIOD OF BELOW AVERAGE TEMPERATURES REMAINS IN STORE
FOR THE WESTERN GREAT LAKES REGION THROUGH END OF THE WEEKEND.
ROBUST OMEGA BLOCK OVER ALASKA WILL GRADUALLY WEAKEN BY THE END OF
THE WEEK...AS RIDGING OVER THE ARCTIC REASSERTS ITSELF AND DISLODGES
THE POLAR VORTEX SOUTHWARD FOR THIS WEEKEND. HOWEVER...WITH THE
ARRIVAL OF THE ARCTIC AIRMASS...QUIET CONDITIONS WILL RETURN AFTER
THE POTENT LOW PRESSURE SYSTEM DEPARTS LATE WEDNESDAY. LATEST MODEL
RUNS LOOK TO BE IN BETTER THAN AVERAGE AGREEMENT THROUGH THIS
EXTENDED FORECAST. WILL THEREFORE TAKE A BLEND OF THE 00Z ECMWF AND
06Z GFS THROUGH FRIDAY AT 12Z BEFORE TRENDING TOWARDS THE 00Z GFS
ENSEMBLE THEREAFTER.
TUESDAY NIGHT AND WEDNESDAY...12Z GFS AND ECMWF ARE IN GOOD
AGREEMENT WITH THE TRACK AND TIMING OF THE FIRST WINTER STORM OF THE
YEAR. STRONG SHORTWAVE CURRENTLY DIGGING SOUTHWARD ACROSS
CALIFORNIA WILL MOVE FROM THE SOUTH-CENTRAL PLAINS TO THE
MID-MISSISSIPPI VALLEY TUESDAY NIGHT BEFORE REACHING THE EASTERN
GREAT LAKES ON WEDNESDAY. AHEAD OF THE SHORTWAVE...A DYNAMIC
SURFACE LOW WILL GAIN STRENGTH AS IT REACHES SOUTHERN LAKE MICHIGAN
BY WED 12Z AND CENTRAL LAKE HURON BY 00Z THU. SOUTHERLY TO
SOUTHEASTERLY WINDS ALOFT AND 20-30KTS OF ISENTROPIC ASCENT ON THE
290-295K SURFACES WITH A WIDE OPEN GULF WILL TRANSPORT MIXING RATIOS
OF 2-3 G/KG ACROSS THE STATE...AND SHOULD SEE A LARGE AREA OF SNOW
CONTINUE TO SURGE NORTH ACROSS THE FORECAST AREA FOR THE ENTIRE
NIGHT. EASTERLY 1000-850MB FLOW WITH DELTA T/S 10-12C WILL SUPPORT
LAKE ENHANCEMENT FOR THE ENTIRE NIGHT AS WELL. IN ADDITION...AS THE
SHORTWAVE AND SURFACE LOW APPROACHES FROM THE SOUTHWEST...QG FORCING
WILL INCREASE AFTER MIDNIGHT AND WIDESPREAD LIGHT SNOW WILL BECOME
HEAVY. THE TRACK/TIMING OF THE LOWS PASSAGE WOULD SUGGEST THE
HEAVIEST SNOW FALLING BETWEEN WED 09-15Z BEFORE SUBSIDENCE STARTS TO
MOVE IN BEHIND THE SHORTWAVE. DUE TO THE LONGER DURATION OF
POSSIBLE LAKE ENHANCEMENT (21Z TUE-15Z WED)...THE FOX VALLEY AND
LAKE MICHIGAN SHORELINE STAND TO RECEIVE THE MOST SNOW...POSSIBLY UP
TO 10 TO 14 INCHES USING A SNOW LIQUID RATIO OF 13:1. SOME
ENHANCEMENT WILL ALSO BE POSSIBLE ACROSS NORTH-CENTRAL WISCONSIN AS
WINDS SWING AROUND FROM THE NORTHEAST TO THE NORTHWEST DURING THE
AFTERNOON. MORE QUESTION MARKS HERE...AS WINDS SEEM TO BE TRANSIENT
AND SHOULD NOT GET A STATIONARY DOMINANT LAKE ENHANCED BAND.
INSTEAD...THINK ANY DOMINANT BAND WILL HAVE POTENTIAL TO DROP A
QUICK ONE TO THREE INCHES IN ADDITION TO THE SYNOPTIC SNOW. OUTSIDE
THE FOX VALLEY...HIGHER SNOW LIQUID RATIOS OF 17:1 STILL SUGGEST
8-10 INCHES ARE POSSIBLE. FORTUNATELY...MAX OMEGA IS NOT WELL
COINCIDENT WITH THE DENDRITIC GROWTH ZONE AND THERE IS NOT MUCH
ELEVATED INSTABILITY (COULD NOT FIND NEGATIVE EPV). AWAY FROM LAKE
SUPERIOR LAKE ENHANCEMENT...SNOW WILL BE WINDING DOWN IN THE
AFTERNOON...BUT NORTHWEST WINDS WILL BE RAMPING UP. COULD SEE GUSTS
UP TO 30 MPH INLAND AND 40 MPH NEAR THE LAKE SHORE WHICH WOULD LEAD
TO BLOWING AND DRIFTING SNOW. PHEW...ALL THIS SAID...WITH UPGRADE
WATCH TO A WINTER STORM WARNING FOR THE ENTIRE AREA.
WEDNESDAY NIGHT...MOST OF THE SNOW SHOULD HAVE DISSIPATED/EXITED THE
AREA BY 00Z THU EXCEPT FOR SNOW SHOWERS OVER N-C WISCONSIN AND
POSSIBLY A FEW FLURRIES ELSEWHERE. EVEN THE LAKE ENHANCED SNOWS
WILL BE WINDING DOWN THOUGH...AS WINDS BACK AROUND TO THE WEST AND WILL
CONFINE ANY BANDS TO THE UPPER PENINSULA. MAY ACTUALLY SEE SOME
CLEARING SKIES LATE ACROSS CENTRAL WISCONSIN. HOWEVER...FRIGID
ARCTIC AIR (850MB TEMPS -20C) BROUGHT IN BY BRISK WEST WINDS WILL
DROP TEMPS NEAR ZERO DEGREES EVERYWHERE BY MORNING. WIND CHILL
READINGS MAY APPROACH 20 BELOW OVER CENTRAL WISCONSIN.
THURSDAY THROUGH MONDAY...LOW PRESSURE WILL PULL AWAY TO THE EAST OR
NORTHEAST ACROSS QUEBEC ON THURSDAY...WHILE HIGH PRESSURE MOVES
ACROSS THE AREA. BREEZY WEST-NORTHWEST WINDS WILL CONTINUE TO
FUNNEL ARCTIC AIR ACROSS THE STATE...KEEPING H850 TEMPS IN THE -20
TO -25C RANGE. AS A RESULT...TEMPS WILL STRUGGLE TO GET OUT OF THE
SINGLE DIGITS ABOVE ZERO AND WILL CONTINUE THE TREND OF LOWERING MAX
TEMPS...BY ONLY A DEGREE OR TWO THOUGH. THE COLDEST NIGHT LOOKS TO
BE THURSDAY NIGHT AS THE PRESSURE GRADIENT SEEMS TO SLACKEN
SOMEWHAT...BUT STILL LOOKS LIKE THERE WILL BE ENOUGH WIND TO PREVENT
TEMPS FROM REALLY PLUMMETING (LIKE BELOW -20F). SOME MODERATION OF
THE ARCTIC AIR WILL OCCUR ON FRIDAY AS THE POLAR VORTEX DROPS INTO
SOUTH-CENTRAL CANADA AND WINDS BACK TO MORE OF A SOUTHERLY DIRECTION
AHEAD OF AN ASSOCIATED WEAK BOUNDARY. WILL SIDE A LITTLE MORE ON
THE WARMER SIDE OF GUIDANCE FOR FRIDAY...BUT TEMPS IN THE TEENS
STILL LOOK APPROPRIATE. THE ARCTIC BOUNDARY MOVES ACROSS THE REGION
ON SATURDAY OR EARLY SATURDAY NIGHT WITHOUT MUCH MOISTURE TO WORK
WITH. WILL KEEP A DRY FORECAST IN TACT. ARCTIC HIGH THEN BUILDS IN
SUNDAY INTO MONDAY. STILL SEEING WEAK SIGNALS OF CONFLUENT FLOW
OVER THESE TWO DAYS...BUT NOT ENOUGH CONFIDENCE TO ADD PRECIP.
HIGHS POSSIBLY BACK INTO THE 20S.
&&
.AVIATION...EXPECT SOME MVFR CEILINGS FROM LAKE EFFECT CLOUDS
DURING THE EVENING...BUT THESE SHOULD DIMINISH ONCE WINDS ALOFT
BACK AND NO LONGER BECOME FAVORABLE FOR THE LOWER CLOUDS AND
ASSOCIATED LIGHT SNOW SHOWERS/FLURRIES. OTHERWISE MVFR CEILINGS TO
THE SOUTH OF THE FORECAST AREA APPEARED TO BE DEPARTING TO THE
EAST. AS A RESULT...VFR CIGS/VSBYS ARE EXPECTED TO PREVAIL
THROUGHOUT THE NIGHT. AFTER THAT CIGS START TO LOWER AS THE WINTER
STORM APPROACHES. MVFR CONDITIONS WILL RAPIDLY DETERIORATE TO
IFR...MAINLY DUE TO LOWER VSBYS WITH THE SNOW...BEFORE CIGS ALSO
LOWER.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING FROM NOON TUESDAY TO MIDNIGHT CST WEDNESDAY
NIGHT FOR WIZ030-031-035>040-045-048>050.
WINTER STORM WARNING FROM 3 PM TUESDAY TO MIDNIGHT CST WEDNESDAY
NIGHT FOR WIZ005-010>013-018>022-073-074.
&&
$$
MG/MPC
