FXUS63 KGRB 221012
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
412 AM CST TUE DEC 22 2009

.SHORT TERM...TODAY THROUGH WEDNESDAY...MAIN FCST CONCERNS ARE MINOR
SNOW CHCS AND TEMPS.

S/W TROF OVER NE IA WAS GENERATING A SWATH OF LIGHT SNOW OVER SW
WI. THE NORTHERN EDGE OF THIS SNOW HAS CREPT CLOSE TO OUR FAR SW
COUNTIES OVERNIGHT...BUT SO FAR...NOTHING HAS BEEN REPORTED ON THE
ISW/Y50 OBSERVATIONS. MOST MODELS KEEP MEASURABLE SNOW JUST SOUTH
OF GRB CWA...BUT THE RUC SUGGESTS THAT THE H8 BAROCLINIC ZONE MAY
TIGHTEN UP THIS MORNING...WITH ISENT LIFT DEVELOPING AS LLVL WINDS
VEER SE. TO ACCOUNT FOR THIS POSSIBILITY...HAVE KEPT A CHC POP FOR
LIGHT SNOW OVER OUR SOUTHERN COUNTIES FOR THE MORNING HOURS. THE
OTHER CONCERN IS LK-EFFECT SNOW SHOWERS. RADAR SHOWS A NORTH TO
SOUTH ORIENTED BAND OF SNOW SHOWERS OVER CNTRL LK MICH...GRADUALLY
SPREADING WEST TOWARD OUR LKSHR COUNTIES. INSTABILITY IS NOT
EXPECTED TO BE GREAT (LK-H8 DELTA-T'S OF 14-16 C)...SYNOPTIC
FORCING SHD REMAIN TO THE SOUTH...AND H8 RH DECREASES AS THE DAY
PROGRESSES...SO WILL ONLY RAISE POPS TO 40 PERCENT ALONG THE LKSHR
FOR NOW. HOWEVER...IF THE CURRENT BAND HOLDS TOGETHER...MAY NEED
TO BOOST POPS AND ADD SOME SMALL ACCUMS LATER IN THE SHIFT.

MUCH DRIER H8 AIR MOVES INTO NE WI TONIGHT INTO WEDS...WITH H8
RH'S DROPPING TO 10-20 PERCENT ALONG THE LKSHR DURING THE DAY ON
WEDS. EXPECT ANY LK-EFFECT THAT OCCURS TODAY TO DIMINISH TO
FLURRIES THIS EVG...THEN COME TO AN END OVERNIGHT. THE DRY EAST
FLOW SHOULD HOLD OFF ANY SNOW WITH THE INCOMING SYSTEM UNTIL WEDS
NGT.

USED A BLEND OF MOSGUIDE/MOSGUIDEBC FOR MAX TEMPS...AS THEY HAVE
BEEN THE BEST PERFORMERS LATELY. MIN TEMPS TONIGHT ARE TRICKY...
AS LESS CLOUD COVER IS ANTICIPATED NORTH...BUT EAST FLOW OFF LK
MICHIGAN COULD FILL IN ANY BREAKS WITH LOW CLOUDS. HAVE OPTED
TO CONTINUE THE FCST OF MIN TEMPS BLO MET/MAV GUIDANCE IN NC/FAR
NE WI...AND AT OR A LITTLE ABOVE GUIDANCE FOR OUR SOUTHERN AND
EASTERN COUNTIES.

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY.

A LARGE UPPER CYCLONE AND SURFACE LOW PRESSURE SYSTEM ARE THE MAIN
PLAYERS DURING THIS PART OF THE FORECAST. ONSET OF PRECIPITATION
IS THE FIRST CONCERN AS THE SURFACE SYSTEM MAKES ITS WAY TOWARD
THE REGION FROM THE PLAINS. MEDIUM RANGE MODELS ARE FAIRLY
CONSISTENT IN PLACING MINOR QPF IN THE EXTREME SOUTHWEST PART OF
THE CWA ON WEDNESDAY NIGHT. QPF SHOULD THEN SPREAD ACROSS THE
REST OF THE FORECAST AREA ON THURSDAY BUT THE PROBLEM THEN BECOMES
PRECIPITATION TYPE. THE SYSTEM WILL HAVE PLENTY OF WARM ADVECTION
TO ITS EAST. CRITICAL THICKNESS VALUES FROM VARIOUS MEDIUM RANGE
MODELS INDICATED THE POTENTIAL FOR FREEZING RAIN...SLEET OR MIXED
PRECIPITATION ACROSS ABOUT THE SOUTHEAST HALF OF THE AREA...UNTIL
ENOUGH COLD AIR WRAPS AROUND THE SYSTEM TO CHANGE ANY
PRECIPITATION TO SNOW.

THOUGH TRAVEL CONDITIONS COULD BE UGLY AROUND CHRISTMAS EVE OR
CHRISTMAS DAY...THERE IS ENOUGH UNCERTAINTY TO LEAVE OUT ANY
HEADLINES FOR NOW. MADE CHANGES TO THE WEDNESDAY NIGHT FORECAST
TO INCREASE POPS IN THE SOUTHWEST. AFTER THAT ONLY MINOR CHANGES
WERE MADE TO THE GRIDS DUE TO THE RATHER LOW LEVEL OF FORECASTER
CONFIDENCE.
&&

.AVIATION...MVFR CIGS OVER NC WI WERE SHIFTING WEST EARLY THIS MORNING...
AND LOOK LIKE THEY WILL MOVE OUT OF THE FORECAST AREA. LIGHT SNOW OVER
SW WI MAY BRUSH PARTS OF CENTRAL WI THIS MORNING...BRINGING A BRIEF
PERIOD OF MVFR CIGS/VSBYS TO AREAS SOUTH OF A LINE FROM MFI TO OSH.
LK- EFFECT SNOW SHOWERS OVER CNTRL LK MICH SHOULD REACH THE LKSHR
COUNTIES LATER THIS MORNING/AFTERNOON...AS LLVL WINDS TURN EAST.
MUCH DRIER AIR AT 850 MB WILL ADVECT INTO EASTERN WI TONIGHT...
WHICH SHOULD DIMINISH THE LK-EFFECT SNOW SHOWERS TO FLURRIES DURING
THE EVG...THEN CAUSE THEM TO END OVERNIGHT. WITH CONTINUED EAST
FLOW TONIGHT...MAY HAVE TO CONTEND WITH MORE LOW CLOUD DEVELOPMENT...
WITH CIGS MAINLY IN THE MVFR CATEGORY.
&&

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

$$
KIECKBUSCH/MG