FXUS63 KGRB 212057
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
257 PM CST MON DEC 21 2009

.SYNOPSIS...EXTREMELY BLOCKY PATTERN IN PLACE ACRS NOAM AND THE ATL.
ENERGY DIGGING DOWN EAST SIDE OF WEST COAST RIDGE WL BOTTOM OUT IN
THE DESERT SW...THEN HEAD INTO THE PLAINS AND GENERATE A SIG STORM
SYSTEM. TRACK OF THE SYSTEM STILL COMPLICATED BY ALL THE DOWNSTREAM
BLOCKING...THOUGH IT HAS BECOME CLEAR THAT THE WORST OF THE STORM
WILL BE SW OF THE FCST AREA. STILL...THE SYSTEM WL BRING A SIG PCPN
EVENT JUST IN TIME FOR THE PEAK HOLIDAY TRAVEL PERIOD. TREND OF THE
MED RANGE MODELS SEEMS TO BE FOR A MORE PROGRESSIVE BUT SPLIT FLOW
REGIME BY THE END OF THE PERIOD. TEMPS WL REMAIN NR NORMAL UNTIL THE
STORM CROSSES THE RGN...THEN THERE SHOULD BE AT LEAST A BRIEF SHOT
OF COLD AIR IN THE WAKE OF THE SYSTEM.
&&

.SHORT TERM...TONIGHT AND TUESDAY. 

LATEST RUC ANALYSIS AND VIS/IR/WV/RADAR IMAGERY SHOW A SHORTWAVE 
TROUGH EMBEDDED WITHIN NW FLOW ALOFT AND ITS ASSOCIATED SURFACE LOW 
SPINNING OVER LAKE SUPERIOR THIS AFTERNOON.  SNOW SHOWERS ACROSS 
NORTHERN WISCONSIN HAVE BEEN FAIRLY PERSISTENT ALL DAY...AND HAVE 
RECENTLY ADDED SOME MINOR LAKE ENHANCEMENT COMBINED WITH A WEAKISH 
SURFACE TROUGH THAT PRODUCED AN UPTICK IN SNOW SHOWER INTENSITY AT 
IRONWOOD.  LUCKILY...1000-850MB WIND SPEEDS HAVE BEEN BETWEEN 10-15 
KTS WHICH HAVE PREVENTED THESE HEAVIER SNOW SHOWERS FROM REACHING 
INTO VILAS COUNTY.  SPOTTER REPORTS AND A CALL TO LAW ENFORCEMENT IN 
VILAS COUNTY EARLIER THIS AFTERNOON REVEALED AROUND AN INCH OF 
LIGHT/FLUFFY SNOW SINCE EARLY THIS MORNING.  THINK WILL NOT SEE MUCH 
MORE THAN AN ADDITIONAL HALF INCH TO INCH THROUGH EARLY THIS EVENING 
AS LOW LEVEL WINDS WEAKEN A BIT AND VEER AROUND TO THE NORTH. 
OTHERWISE... BKN/OVC STRATUS EXISTS ALL THE WAY BACK INTO EASTERN MN 
WITH SOME FLURRIES WITHIN THE CYCLONIC FLOW.  FARTHER 
UPSTREAM...COLD CLOUD TOPS ARE NOW PUSHING ACROSS SD INTO SW 
MINNESOTA ALONG A TIGHTENING THERMAL GRADIENT.  WITH THE FLURRY 
ACTIVITY AND UPSTREAM BAROCLINIC ZONE...PRECIP CHANCES ARE THE MAIN 
FORECAST CONCERN THROUGH TOMORROW.

TONIGHT...ARCTIC HIGH PRESSURE WILL BE BUILDING INTO THE AREA 
TONIGHT...WITH THE BOUNDARY BETWEEN AIRMASSES SETTING UP ACROSS 
SOUTHERN MINNESOTA INTO SE WISCONSIN.  FIRST THOUGH...DRIER 
MID-LEVEL AIR WILL ADVECT SE INTO THE NORTHEAST HALF OF WISCONSIN 
TONIGHT.  LOW LEVEL CYCLONIC FLOW WILL HANG TOUGH THROUGH THE 
EVENING...SO IT WILL TAKE A WHILE BEFORE THE LOW CLOUDS SCATTER 
OUT.  ONCE WINDS SHIFT TO THE NORTH AND THEN NORTHEAST...UPSTREAM 
INDICATIONS SUGGEST WE WILL SEE SOME PARTIAL CLEARING ACROSS N-C AND 
FAR NE WISCONSIN LATE IN THE EVENING AND OVERNIGHT.  FARTHER 
SOUTH...MOISTURE WILL BE MORE PLENTIFUL CLOSER TO THE DEFORMATION 
AXIS AND WILL REMAIN MORE ON THE BKN TO OVC SIDE FOR MOST OF THE 
NIGHT.  MODELS DEPICT THE NORTHERN EDGE OF THE FGEN BAND REACHING 
INTO WISCONSIN RAPIDS TO WAUTOMA CORRIDOR AND WILL INTRODUCE A SMALL 
CHANCE OF LIGHT SNOW DURING THE OVERNIGHT HOURS INTO THE FORECAST.  
TEMPERATURES ARE DIFFICULT TONIGHT...ESPECIALLY UP NORTH...AND 
DEPEND ON HOW MUCH CLEARING WE WILL SEE.  WITH FULL CLEARING...THINK 
THAT LOW TEMPS COULD FALL WELL BELOW ZERO.  HOWEVER...SATELLITE 
IMAGES SUGGEST WILL HAVE SOME MID AND HIGH CLOUDS TO CONTEND WITH 
AND WILL HAVE TEMPS FALLING NEAR ZERO AT THE COLD SPOTS.

TUESDAY...THE BAROCLINIC ZONE REMAINS RELATIVELY STATIONARY ACROSS 
CENTRAL TO SOUTHEAST WISCONSIN...AND WILL LINGER A SMALL CHANCE OF 
LIGHT SNOW SHOWERS OVER CENTRAL WISCONSIN FOR THE MORNING HOURS.  IN 
THE AFTERNOON...THE BEST CONVERGENCE ALONG THE BOUNDARY WILL SHIFT 
TO THE SOUTHEAST...AND SNOW CHANCES SEEM SMALL ENOUGH TO KEEP A DRY 
FORECAST IN TACT.  OTHERWISE...NORTHEAST LOW LEVEL WINDS SHIFT 
AROUND TO THE EAST DURING THE DAY AND WILL DRAW INCREASING MOISTURE 
OFF LAKE MICHIGAN INLAND.  850-700MB AIR IS VERY DRY (20-30% 
RH)...SO WILL PROBABLY SEE SOME LAKE CLOUDS DEVELOP WITH JUST A FEW 
FLURRIES.  PREVIOUS SHIFT HAD THIS COVERED PRETTY WELL AND WILL ONLY 
MAKE A FEW TWEAKS FOR COLLABORATION PURPOSES.  AREAS OVER N-C WISCONSIN 
SHOULD SEE A PARTLY SUNNY ASSUMING LOW CLOUDS SCT OUT AS ANTICIPATED 
TONIGHT.

.LONG TERM...TUE NGT THRU NEXT MON. MAJOR STORM SYSTEM WILL BE
AFFECTING THE AREA DURING THE LATTER PART OF THIS WEEK. BUT THIS
ISN/T GOING TO BE A REPEAT OF THE DEC 8-9 STORM. WE ARE UNLIKELY TO
GET AS MUCH SNOW. IT WILL FALL OVER A LONGER PERIOD OF TIME. AND
WINDS WILL DECREASE INSTEAD OF INCREASE AS THE STORM WEARS ON. MAIN
MESSAGE I/LL TRY TO GET OUT WITH THIS FCST PKG IS THAT ALTHOUGH THE
STORM WILL COME THROUGH DURING THE PEAK HOLIDAY TRAVEL PERIOD AND
CAUSE DISRUPTIONS...IT WON/T BE OF THE SAME CLASS AS THE PREVIOUS
STORM. NO HEADLINES AT THIS TIME.

STORM STILL EXPECTED TO REACH PEAK INTENSITY IN THE PLAINS...THEN
WEAKEN AS IT HEADS NE INTO WI. BUT SUBTLE CHANGES HAVE OCCURRED
SINCE YDA. TREND ON MODELS HAS BEEN TO SHIFT A LITTLE SEWD WITH THE
TRACK OF THE LOW. THESE CHANGES MOST PRONOUNCED ON THE CANADIAN
MODEL...AND FIT WELL WITH IDEA THAT SYSTEM WL BE FORCED TO TRACK S
OF STRONGEST BLOCKING THAT WAS OVER NERN NOAM. 

MAIN CHGS TO THE FCST WERE TO DELAY THE ONSET OF PCPN. WL PROBABLY
HAVE LEAD BAND OF PCPN TRY TO WORK NEWD WED NGT INTO THU. BUT IT WL
RUN INTO VERY DRY AIR ACRS THE AREA...AND THAT DRY AIR AT LOW-LEVELS
WL BE GETTING REINFORCED FM THE NE. SO SLOWED ONSET OF PCPN...ESP
MORE SIG PCPN. MODEL FCST SOUNDINGS SUGGEST MULTIPLE PCPN TYPES
POSSIBLE. ALSO ADDED SOME FZDZ TO THE FCST FOR MOST AREAS AS IT
APPEARS MID-LVL MOISTURE MAY NOT BE SUFFICIENT TO INTRODUCE ICE
CRYSTALS INTO LOWER CLOUDS. SFC TEMPS OVER E-C WI MAY RISE ENOUGH TO
RESULT IN JUST DZ OR RAIN AT TIMES.

PCPN SHOULD TURN BACK TO ALL SNOW LATER FRI NGT. EXPECT SNOW TO CONT
INTO SAT...THOUGH IT PROBABLY WON/T BE THAT HEAVY. NEED TO WATCH FOR
THE POSSIBILITY OF A SMALL SCALE VORT WRAPPING AROUND THE UPR LOW
AND PRODUCING A SMALL AREA OF HEAVIER SNOW...BUT NO WAY TO PINPOINT
WHERE OR EVEN IF THAT WL HAPPEN THIS FAR OUT.
&&

.AVIATION...PREVAILING MVFR CIGS AND VSBYS THROUGH EARLY THIS 
EVENING WITH A MOIST BOUNDARY LAYER AHEAD OF AN ARCTIC FRONT.  
THEREAFTER...DRIER NORTHERLY WINDS WILL SHIFT A CLEANER AIRMASS INTO 
THE REGION...FIRST REACHING RHI/CWA/AUW AND THEN GRB A FEW HOURS 
LATER.  MODEL DEPICT THIS DRIER AIR SCATTERING OUT THE MVFR CLOUD 
DECK...ALTHOUGH WE WILL STILL HAVE A CIRRUS SHIELD OVERHEAD.  AS LOW 
LEVEL WINDS SHIFT TO THE NORTHEAST LATE TONIGHT THEN TO THE EAST 
TOMORROW...MOISTURE WILL GET PICKED UP FROM LAKE MICHIGAN LEADING TO 
A POSSIBLE MVFR CLOUD DECK RETURNING BY LATE MORNING AT GRB...AND IN 
THE AFTERNOON AT AUW/CWA/RHI.  SOME FLURRIES WILL BE ALSO POSSIBLE 
AT GRB TOMORROW AFTERNOON.
&&

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

$$
MPC/SKOWRONSKI