FXUS63 KGRB 260235 AAB
AFDGRB

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GREEN BAY WI
835 PM CST FRI DEC 25 2009

.UPDATE...RADAR RETURNS ACRS THE FCST AREA SEEM TO HAVE DECREASED
AND LOST SOME ORGANIZATION DURING THE PAST HOUR OR SO. AFTER
COORDINATING WITH MQT...WL ALLOW THE ADVISORY FOR N-C WI TO
EXPIRE. N-C WI IS THE FARTHEST FROM THE COLDER AIR WRAPPING IN FM
THE S...SO THAT AREA IS ALSO LEAST SUSCEPTIBLE TO HAVING ROADWAYS
ICE OVER. 

A LITTLE MORE CONCERNED ABOUT THE SRN PART OF THE FCST AREA.
MODELS SHOW STG VORT LIFTG TOWARD THAT AREA TNGT...BUT NEVER SEEM
TO REALLY DEVELOP MUCH OF AN ORGANIZED PCPN BAND WITH IT. RADAR
MOSAIC...HOWEVER...SHOWS BAND OF SNOW DEVELOPING IN NRN IL. VSBYS
AT KFEP AND KRFD DOWN TO 3/4 AND 1 3/4 SM IN THE PAST HR. WOULD
SEEM THAT BAND OF PCPN SHOULD HEAD UP TOWARD THE SRN PART OF THE
FCST AREA. WL WATCH THAT A BIT LONGER...BUT WL PROBABLY BUMP
SNOWFALL TOTALS UP A TOUCH OVER THE SRN PART OF THE FCST AREA.

SHOULD HAVE UPDATED PRODUCE SUITE OUT WITHIN 30-45 MINUTES.

SKOWRONSKI
&&

.PREV DISCUSSION...ISSUED AT 711 PM CST FRI DEC 25 2009...

UPDATE...COLDER AIR AT LOW-LEVELS STARTING TO SURGE NWD INTO THE
AREA. IN ADDITION...CAA ALOFT CAUSING PCPN TO CHG BACK TO SNOW
ACRS PARTS OF C/N-C WI WHERE BOUNDARY LAYER WAS ALREADY WITHIN A
FEW DEGREES OF FREEZING. SHOULD SEE TRANSITION TO SNOW ACRS MOST
OF THE AREA WITHIN THE NEXT FEW HRS...WITH PERHAPS DOOR COUNTY
HOLDING OUT A BIT LONGER.

RADAR MOSAIC STILL SHOWS A LOT OF PCPN ACRS THE AREA. MODELS
SUGGEST PCPN WL WANE AFTER MIDNIGHT...BUT PCPN FILLING BACK IN
OVER SRN WI AND NRN IL DON/T EXACTLY FIT WITH THAT IDEA. GOING
FCST OKAY FOR NOW...BUT MAY NEED TO EDGE OVERNIGHT SNOW TOTALS UP
A BIT OF CURRENT TRENDS CONTINUE.

WL NEED TO MAKE A DECISION IN THE NEXT COUPLE HRS ON WHAT TO DO
WITH THE ADVISORY FOR N-C WI. GIVEN CURRENT RADARS...LEANING
TOWARD EXTENDING IT FOR THE REST OF THE NIGHT. BUT WL WAIT AND SEE
HOW THINGS EVOLVE IN THE NEXT HR OR SO BEFORE MAKING FINAL
DECISION.

ALREADY SENT UPDATED GRIDS. UPDATED ZONES WITH FRESHENED UP
WORDING WL BE OUT SHORTLY.

DISCUSSION ISSUED AT 339 PM CST FRI DEC 25 2009...

SHORT TERM...TONIGHT THROUGH SATURDAY. THE NAM SEEMED TO DO VERY
WELL WITH FORECASTING THE WESTWARD EXTENT OF THE ELEVATED ABOVE
FREEZING LAYER WITH THIS STORM...MUCH BETTER THAN THE GFS AND
ECMWF. THIS MILD AIR HAS MADE IT ALL THE WAY WEST TO THE
MINNEAPOLIS AREA THIS AFTERNOON. THE ABOVE FREEZING TEMPERATURES
WILL BE SOON REPLACED BY MORE SEASONABLE AIR THAT WAS ROCKETING
NORTHEASTWARD FROM ILLINOIS AT 21Z.

THE AIR ALOFT HAS COOLED ENOUGH FOR SNOW ACROSS MOST OF THE REGION
ALREADY...BUT WARM AIR NEAR THE GROUND IS CAUSING IT MELT OVER ALL
BUT THE FAR NORTH. THE RAIN SHOULD CHANGE TO SNOW FROM SOUTH TO
NORTH WITH THE ARRIVAL OF COLDER BOUNDARY LAYER AIR THIS EVENING.
THE BEST SNOWS WILL BE IN THE NORTH WITH THE GREATER FORCING AND COLDER
BOUNDARY LAYER.

THE OCCLUDED SYSTEM IS FORECAST TO DRIFT INTO SOUTHERN WISCONSIN
SATURDAY AND SET UP SUITABLE CONDITIONS FOR LAKE ENHANCED SNOWFALL
ALONG THE LAKE MICHIGAN COUNTIES AND PERHAPS AS FAR WEST AS THE FOX
VALLEY. LAKE SURFACE TO 850MB TEMPERATURE DIFFERENCES ARE FORECAST
TO BE 15C TO 17C WITH INVERSION HEIGHTS ABOVE 8000 FEET. SYNOPTIC
SCALE SNOW WILL HELP SEED THE LAKE EFFECT BANDS MAKING THEM MORE
EFFICIENT. THINK THAT 2 TO 3 INCHES IS LIKELY IN THE LAKESHORE
COUNTIES WITH AN INCH OR TWO IN THE FOX VALLEY. THERE IS AT LEAST
A CHANCE OF ADVISORY CRITERIA SNOW ALONG THE LAKE...BUT THE LAKE
ENHANCEMENT HINGES ON SYNOPTIC SCALE WIND DIRECTION. AND THAT
HINGES ON THE MODELS HAVING THE OCCLUDED SYSTEM MOVING INTO
SOUTHERN WISCONSIN. LATER SHIFTS MIGHT HAVE TO INCREASE SNOW
AMOUNTS IF WINDS LOOK FAVORABLE.

LONG TERM...SAT NGT THRU NXT FRI. SEVERAL FCST PBLMS TO SORT OUT
DURING THE LONG-TERM PERIOD. FIRST...WHEN WL THIS SYSTEM FINALLY
DEPART? SECOND...WL THERE BE ANY LK EFFECT SAT NGT NEAR LK MI AS
WNDS BACK FROM SE TO NE WITH TIME? FINALLY...ANY POTENTIAL SYSTEM
ON THE HORIZON FOR LTR NXT WEEK? 

AS THE CLOSED UPR LOW ROTATES SOUTH...THEN SE INTO SRN WI SAT NGT...
THE SFC LOW IS EXPECTED TO PIVOT NE INTO W-CNTRL SECTIONS OF LK MI.
MAIN FCST PBLM IS POTENTIAL OF LK EFFECT SNOW SHWRS ON TOP OF THE
SYNOPTIC SNOW NEAR LK MI. FCST SNDNGS ARE INITIALLY UNSTABLE WITH
LK-INDUCED CAPES OF 300 J/KG AND NO REAL LOW-LVL INVERSIONS TO SPEAK
OF UNTIL 8K FT. CONDITIONS BECOME MORE UNFAVORABLE LTR IN THE NGT AS
WNDS CONT TO BACK AND EVENTUALLY BECOME OFFSHORE. HAVE RAISED POPS
TO CATEGORICAL OVR E-CNTRL WI...BUT KEPT LIKELY POPS GOING FOR THE
REMAINDER OF THE FCST AREA. A COUPLE OF INCHES OF ACCUMULATION WL BE
PSBL NEAR THE LAKE WITH LESSER AMTS FARTHER INLAND.

ENTIRE SYSTEM FINALLY MAKES AN EWD SHIFT TOWARD THE ERN GREAT LKS ON
SUNDAY...BUT NOT BEFORE DROPPING ADDL LGT SNOW ON NE WI. THIS IS DUE
TO BEING ON THE CYCLONIC SIDE OF THE DEPARTING SYSTEM WITH MSTR
STILL WRAPPING AROUND. MOST ACCUMULATIONS WL BE LIMITED TO LESS THAN
AN INCH...SO TRAVEL SHOULD NOT BE OVERLY IMPACTED. HAVE KEPT TEMPS
TOWARD THE COOLER SIDE OF GUID AS WEAK CAA TAKES OVR THE AREA.

A PREDOMINANT NW FLOW REMAINS OVR THE FCST AREA SUNDAY NGT...THUS
SOME LK EFFECT SNOW SHWRS ARE PSBL FOR VILAS CNTY WITH JUST SCT
FLURRIES AROUND ELSEWHERE. A CDFNT APPROACHES NRN WI LATE IN THE
NGT...BUT HAVE LITTLE AFFECT ON OUR WEATHER INITIALLY. THIS CDFNT
COMPLETES ITS DRIVE SWD THRU WI MON MORNING AND VEERS THE WNDS MORE
N-NW WITH TIME. INFLUX OF COLDER AIR BEHIND THE FNT SENDS 8H TEMPS
DOWN TO AROUND -15C OVR WRN LK SUPERIOR BY MON AFTERNOON LEADING TO
LK EFFECT POTENTIAL FOR N-CNTRL WI (I.E. VILAS CNTY). PBLM FOR
ACCUMULATING SNOW IS THAT BY THE TIME THE AIR GETS COLD ENUF...
INVERSION HGTS DROP AND DRIER AIR BEGINS TO MIX INTO THE SNDNG. 
THUS...DO NOT SEE THIS AS A MAJOR LK EFFECT SITN AND KEPT VILAS CNTY
IN CHC CATEGORY (NW CORNER) AND LITTLE ELSEWHERE. MAX TEMPS STILL
CLOSE TO NORMAL DESPITE THE FROPA MAINLY DUE TO 'MILD' START TO THE
DAY.

HI PRES TO BUILD INTO THE GREAT LKS RGN MON NGT AND ALREADY BE ON
THE VERGE OF EXITING THE RGN ON TUE. IT COULD BE A COLD NGT OVR THE
FCST AREA MON NGT DEPENDING ON FINAL SNOW TOTALS FROM CURRENT STORM
AND EXACTLY WHERE THE HI PRES RESIDES. COOLEST READINGS PLACED OVR
N-CNTRL WI WHERE MORE SNOW ON THE GROUND. ON TUE...WNDS ARE EXPECTED
TO ALREADY BE BACKING TO THE SOUTH AND ALLOW FOR WARMER AIR ALOFT
TO RETURN TO WI. LOOK FOR SOME INCREASE IN MID/HI CLDS BY TUE
AFTERNOON AS THE WARMER AIR OVERRUNS THE COOLER AIR AT THE SFC. 

MDLS ARE IN PRETTY GOOD AGREEMENT THRU TUE BEFORE THE GFS SHOWS A
FLATTER MEAN FLOW VERSUS A MORE AMPLIFIED EMCWF/CANADIAN. ENUF RUN-
TO-RUN DIFFERENCES ARE EVIDENT TO NOT TOTALLY BUY ONE MODEL OVR
ANOTHER. JUST EXPECT A BIT MORE UNSETTLED WEATHER PATN FROM WED
ONWARD WITH TEMPS AVERAGING AT OR SLIGHTLY ABV NORMAL. ANTICIPATE
CLDS TO THICKEN TUE NGT AS A WEAK NRN STREAM SHRTWV TROF MOVS INTO
THE NRN PLAINS AND A SRN STREAM UPR TROF PUSHES ACROSS THE FOUR
CORNERS. AS THE NRN STREAM TROF REACHES THE UPR MIDWEST ON TUE...IT
WL SHOVE A CDFNT INTO WI AND COULD PROVIDE FOR A WDLY SCT LGT SNOW
OR FLURRIES EVENT INTO NE WI. HATE TO YO-YO ON POPS...BUT FEEL
COMPELLED TO ADD A SLGT CHC BACK INTO THE FCST FOR WED.

LATTER PART OF NXT WEEK'S FCST WL COME DOWN TO HOW MUCH AMPLIFICATION
TAKES PLACE IN THE MEAN FLOW. THE FLATTER FLOW WOULD KEEP A CHC OF
SNOW IN THE FCST THRU THU AS THE UPR TROF MOVS THRU AND THEN DRYING
OUT FOR FRI. AN AMPLIFIED PATN WOULD PROVIDE FOR A BREAK IN THE SNOW
IN THE FCST THRU THU (BEHIND THE CDFNT/AHD OF A CLOSING UPR LOW) AND
THEN BRING A CHC OF SNOW SHWRS TO THE RGN ON FRI. ENDED UP USING THE
ECMWF ENSEMBLE MEAN WHICH WAS CLOSER TO THE GFS. THUS...MAINTAINED A
CHC OF LGT SNOW THU AND GONE DRY FOR FRI (EXPECT LK EFFECT CHC FOR
N-CNTRL WI).

AVIATION...IFR CONDITIONS WILL CONTINUE IN MOST PLACES THROUGH
THE EVENING HOURS...THEN CIGS AND VSBYS SHOULD GRADUALLY INCREASE
LATE TONIGHT AND SATURDAY. RAIN WILL CHANGE TO WET SNOW THIS
EVENING AND DIMINISH OVERNIGHT. LAKE EFFECT SNOWS EXPECTED
SATURDAY AT MTW AND SUE AND TO A LESSER EXTENT AT GRB/ATW/OSH
WHERE LOCAL IFR/MVFR POSSIBLE. ELSEHERE IT SHOULD BE VFR.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$