FXUS63 KGRB 052102
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
302 PM CST SAT DEC 5 2009

.SYNOPSIS...DOMINANT FEATURE CONTROLLING THE WX ACRS NOAM DURING
THE FCST PERIOD WL BE STG RIDGE ALONG THE WEST COAST. DEEP VORTEX
WL WORK INTO POSN OVER NOAM JUST E OF THE RIDGE BY MID-WEEK. THE
EVOLUTION OFTHE LARGE SCALE PATTERN BEYOND THAT POINT IS MORE
COMPLEX AND UNCERTAIN. FLOW BECOMES SPLIT AS A BRANCH OF
WESTERLIES FM THE PAC UNDERCUTS THE WRN RIDGE. BUT DEEP VORTEX
LOCKED IN E OF THE RIDGE SHOULD KEEP AT LEAST SOME BROAD TROFFING
OVER MUCH OF NOAM. RESULT WL BE A LOWER AMPLITUDE FLOW ACRS THE
CONUS...BUT WITH TROF POSN STILL SOMEWHERE OVER THE N-C STATES OR
GREAT LAKES RGN. THAT SHOULD KEEP COLD HIGH PRESSURE AT LEAST
RIDGING INTO THE NRN PLAINS...SO THE INFLUX OF MILDER PAC AIR
INTO THE MIDWEST WL BE DELAYED.

ACTIVE SWLY UPR FLOW WL BRING A SERIES OF SYSTEMS ACRS THE
REGION. ADVISORY CRITERIA SNOWS FOR E-C WI SHOULD ACCOMPANY THE
SYSTEM ON SUN NGT/MON. MAJOR WINTER STORM STILL ON TRACK TO AFFECT
THE AREA MID-WEEK. MOST AREAS SHOULD END UP WITH ABV NORMAL PCPN
BY THE TIME THOSE SYSTEMS MOVE THROUGH. TEMPS WL REMAIN A LITTLE
BLO NORMAL EARLY IN THE PERIOD...THEN EXPECT A BRIEF BUT FAIRLY
INTENSE SHOT OF COLD AIR BEHIND THE MID-WEEK STORM. CONFIDENCE IN
TEMPERATURE TRENDS BEYOND THAT HAVE DECREASED THE PAST FEW
DAYS...BUT MOST LIKELY SCENARIO IS FOR READINGS TO REBOUND AT
LEAST SOMEWHAT FOR THE LATTER PART OF THE FCST PERIOD.
&&

.SHORT TERM...TNGT AND SUN. INVERTED TROF DEVELOPING NEWD FM THE
SRN PLAINS SHOULD WORK INTO THE AREA TNGT. TO SOME EXTENT...ALL
THE MODELS SENDING SIGNALS FOR LIFT AND GENERATING LGT QPF ACRS A
PORTION OF THE FCST AREA. WEAK QG FORCING SEEMS TO OVERLAP MID-LVL
FRONTOGENETIC FORCING BEST IN NERN WI LATE TNGT. THAT SEEMS TO BE
WHERE MOST OF THE GUID IS PRODUCING LGT QPF. LATE AFTN RADAR
MOSAIC SHOWED RETURNS ACRS THE NRN PLAINS STREAMING EWD...AND NOW
EVIDENT N OF MPX. EXTRAPOLATION WOULD TAKE THEM INTO THE FCST
AREA LATER TNGT. GIVEN ALL THAT...AND THE FACT IT HASN/T BEEN VERY
DIFFICULT TO GET IT TO SNOW THE PAST FEW DAYS...DECIDED TO GO WITH
HIGH PROBABILITY/LOW AMNT EVENT FOR NERN WI TNGT. BOOSTED POPS IN
THE NE UP TO LIKELY AFTER MIDNIGHT. WL MENTION UP TO AN INCH OF
ACCUMULATION THERE. WL SURROUND THAT AREA WITH JUST A CHC OF LIGHT
SNOW AND FLURRIES.

PCPN SHOULD SHIFT EWD EARLY SUN. SHOULD BE MOSTLY CLOUDY BUT
QUIET...AT LEAST UNTIL THE NEXT SYSTEM ARRIVES SUN NGT.

.LONG TERM...SUNDAY NIGHT THRU NEXT SATURDAY. AN ACTIVE PERIOD OF
WEATHER EXPECTED AS AT LEAST TWO SYSTEMS WILL BRING ACCUMULATING
SNOW TO THE FORECAST AREA. 

THE FIRST SYSTEM IS THE RESULT OF JET ENERGY MOVING SOUTH THROUGH
CALIFORNIA. IT SHOULD LIFT NORTHEAST FROM SOUTHWEST UNITED STATES
TOWARDS THE MIDWEST AND GREAT LAKES SUNDAY. THE LEFT EXIT REGION
OF THE JET APPROACHES THE AREA SUNDAY NIGHT AND EARLY
MONDAY...WHILE IN THE LOWER LEVELS WE HAVE WARM ADVECTION AND
CONVERGENCE. MODEL QPFS ARE GENERALLY ABOUT A QUARTER TO THIRD OF
AN INCH IN THE FOX VALLEY AND LAKESHORE COUNTIES...WHICH SHOULD BE
ENOUGH TO YIELD 2 TO 5 INCHES OF SNOW GIVEN A 14 TO 1 OR GREATER
SNOW TO WATER RATIO. MODELS DEPICT A MESOSCALE CIRCULATION FORMING
OVER THE NORTHERN PORTION OF THE LAKE AND COASTAL CONVERGENCE
WHICH SHOULD ENHANCE SNOWFALL NEAR THE LAKE. THERE IS EVEN A
PERIOD OF TIME MONDAY WHERE WINDS AND TEMPERATURES ALOFT ARE
FAVORABLE FOR ENHANCED SNOW FROM THE BAY. YOU DON/T SEE THAT TOO
MUCH AND IT IS DIFFICULT TO PREDICT BUT SEEMS POSSIBLE IN THIS
CASE. WILL ISSUE A WINTER WEATHER ADVISORY FOR THE FOX VALLEY AND
LAKESHORE FOR SUNDAY NIGHT AT MIDNIGHT THROUGH NOON MONDAY.

MODELS HAVE BEEN VERY CONSISTENT WITH THE STORM FOR THE MIDDLE OF
THE WEEK CONSIDERING IT WILL BE THE RESULT OF TWO STRONG JETS THAT
ARE SO FAR AWAY. ONE STRONG JET (170KTS AT 300MB) WAS AROUND 35N
NEAR THE DATELINE WHILE THE OTHER (140KTS) WAS ROUNDING THE
WESTERN RIDGE NORTH OF ALASKA. CONSIDERING THESE JETS ARE OVER
SOME OF THE MOST DATA SPARSE AREAS IT IS AMAZING THAT THE MODELS
HAVE BEEN FAIRLY CONSISTENT WITH THIS SYSTEM. BUT I WOULD NOT BE
SURPISED TO SEE SHIFTS IN THE STORM TRACK SUNDAY AND MONDAY. IF IT
MATERIALIZES AS NOW FORECAST BY THE GFS AND ECMWF WE WILL HAVE
HEAVY SNOW OVER OUR FORECAST AREA TUESDAY NIGHT THROUGH
WEDNESDAY...WITH CONSIDERABLE BLOWING AND DRIFTING SNOW. IT WILL
BE INTERESTING TO SEE HOW THIS ALL WORKS OUT.

ARTIC AIR IS DRIVEN INTO THE REGION THURSDAY ON STRONG NORTHWEST
WINDS. SURFACE TEMPERATURES NEAR ZERO F SHOWN BY BUFKIT THURSDAY
EVENING WITH WINDS NEARLY SUFFICIENT TO PRODUCE WIND CHILL
ADVISORY CRITERIA. 850 MB WINDS LOOK LIKE THEY WILL HAVE TOO MUCH
WESTERLY COMPONENT FOR SIGNIFICANT LAKE EFFECT SNOW IN VILAS
COUNTY.
&&

.AVIATION...ALTHOUGH MVFR LINGERED OVER THE N...GENERALLY WENT
WITH IMPROVING CIGS THIS AFTN. EXPECT MID-CLDS TO MOVE BACK INTO
THE RGN AND LOWER THIS EVENING. BUT TAF SITES WL GENERALLY BE S
AND W OF THE AREA MOST LIKELY TO HAVE SNOW TNGT. SO EDGED CIGS
DOWNWARD...BUT GENERALLY ONLY INTO LOWER-END OF THE VFR CATEGORY.
&&

.MARINE...A PROLONGED PERIOD OF GALE FORCE OR STRONGER WINDS
POSSIBLE TUESDAY NIGHT THROUGH THURSDAY IN ASSOCIATION WITH THE
WINTER STORM MOVING THROUGH THE REGION.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...

WINTER WEATHER ADVISORY FROM 06Z-18Z MON
WIZ022-038>040-048>050-

&&

$$
SKOWRONSKI/RDM