FXUS63 KMKX 252134
AFDMKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
334 PM CST WED NOV 25 2009

HUGE FORECAST CHALLENGE TODAY WITH UNCERTAINTY IN PRECIP TYPE FOR 
TONIGHT AND THANKSGIVING MORNING. 

.SYNOPSIS...19Z WATER VAPOR LOOP AND RUC ANALYSIS SHOW A SHORTWAVE 
LIFTING OUT OF THE LAKE SUPERIOR/LAKE HURON REGION AND ANOTHER 
SHORTWAVE DROPPING INTO SOUTHERN MN OUT OF THE EASTERN DAKOTAS. AT 
THE SFC...THE CENTER OF AN OCCLUDED LOW PRESSURE SYSTEM WAS SITTING 
OVER NORTHERN LAKE MICHIGAN.

AS THE UPPER LOW DROPS SOUTHEAST INTO EASTERN IA AND NORTHERN IL 
THIS EVENING...A SHORTWAVE WILL PIVOT AROUND THE LOW ACROSS SOUTHERN 
WI. THE SHORTWAVE IS ENHANCED BY THE LEFT EXIT REGION OF THE JET 
DIVING DOWN ACROSS THE UPPER MIDWEST.
 
&&

.SHORT TERM...
LATE THIS AFTERNOON...SHOWERS ASSOCIATED WITH THE APPROACHING UPPER 
LEVEL SHORTWAVE AND INHERENT NEGATIVE OMEGA AND UPPER LEVEL 
DIVERGENCE WILL CONTINUE TO EXPAND OVER SOUTHERN WI THROUGH EARLY 
EVENING. 

TONIGHT...THE SFC LOW WILL RAPIDLY DROP A TROUGH DOWN ACROSS WI FROM 
NORTH TO SOUTH AS ANOTHER SHORTWAVE PIVOTS AROUND THE UPPER LOW. A 
CONCENTRATED AREA OF 700MB NEGATIVE OMEGA WILL ALSO PIVOT ALONG THE 
SHORTWAVE ACROSS SOUTHERN WI OVERNIGHT. THE AREA OF RAIN IN THE 
MINNEAPOLIS AREA LATE THIS AFTERNOON WILL THE BE THE AREA OF FOCUS 
FOR SOUTHERN WI TONIGHT. SINCE THE SECOND SHORTWAVE IS EXPECTED TO 
CATCH UP WITH THE FIRST...WE ARE NOT EXPECTING MUCH OF A BREAK IN 
PRECIP OVER THE CWA THIS EVENING. 

MODELS AGREE THAT THE DEEPEST MOISTURE...BEST FORCING AND THEREFORE 
HEAVIEST PRECIP WILL FALL ALONG THE SFC TROUGH...HITTING THE 
NORTHERN CWA BY 03Z...THE CENTRAL CWA FROM FLD TO MSN TO MRJ BY 
06Z...AND THEN SHIFT EASTWARD ACROSS CENTRAL AND SOUTHERN CWA 
THROUGH 12Z. 

THE MOST DIFFICULT PART OF THE FORECAST IS PRECIP TYPE. THE LOCAL 
MODELS AND TO A LESSER EXTENT THE NAM SEEM TO HANDLE THE COLD AIR 
WRAPPING INTO THE SYSTEM FROM THE SOUTHWEST OVERNIGHT. IT LOOKS LIKE 
THE STRONGEST DYNAMICS...BEST OMEGA AND COINIDENT QVECTOR CONV AND 
NEG EPV HIT THE SOUTHERN CWA AND NORTHEAST IA BY THIS EVENING. 
WITHIN THAT AREA IS WHERE THE MODELS SHOW 925MB TEMPS COLLAPSING THE 
QUICKEST...WHICH IS WHERE THE BEST CHANCE FOR RAIN CHANGING OVER TO 
SNOW FOR A BRIEF TIME COULD OCCUR. AFTER MIDNIGHT...WENT WITH ALL 
SNOW FOR THE FAR SOUTHWEST COUNTIES AND EXPANDED THAT AREA INTO 
SOUTHWEST DANE COUNTY AND UP TO THE DELLS AND EAST TO LAKE GENEVA 
AFTER 09Z. 

SNOW ACCUMULATIONS COULD BE UP TO A QUICK INCH IN THE SOUTHWEST CWA 
OVERNIGHT...MAINLY ON GRASS SURFACES. WITH GROUND TEMPS AS WARM AS 
THEY ARE...EXPECT SNOW TO MELT QUICKLY. HOWEVER...FREEZING TEMPS 
TOWARD MORNING COULD CREATE SLICK ROADS.

TEMPERATURES IN THE FAR NORTHEAST PART OF THE CWA ARE EXPECTED TO 
REMAIN ABOVE FREEZING. THIS IS THE AREA CLOSEST TO THE CENTER OF THE 
LOW AND SHOULD STAY RAIN FOR THE ENTIRE NIGHT.

THURSDAY...MODELS LINGER PRECIP ACROSS THE SOUTHEAST CWA THROUGH 
15Z THU MORNING. MORNING TEMPS DROP TO AROUND OR BELOW FREEZING 
EARLY...THEN QUICKLY REBOUND INTO THE UPPER 30S AND LOWER 40S. THE 
FAR NORTHEAST THAT SHOULD BE RAIN ALL NIGHT HAS A SHOT AT LIGHT SNOW 
EARLY THU MORNING AS THE PRECIP TAPERS OFF. THE SOUTHEAST CWA NEAR 
KENOSHA COULD SEE HEAVIER PRECIP FALLING AS UP TO A HALF INCH OF 
SNOW AROUND THE 8 AM HOUR. THIS COULD CAUSE A LITTLE HAZARDOUS 
TRAVEL WEATHER WITH THE EXPECTED HEAVY HOLIDAY TRAFFIC. AGAIN...WITH 
WARM GROUND TEMPS...EXPECT SNOW TO MELT QUICKLY. 

THURSDAY NIGHT...CLOUDS COULD LINGER...BUT PRECIP SHOULD BE WELL OFF 
SHORE AS HIGH PRESSURE APPROACHES THE GREAT LAKES REGION.

.LONG TERM...
A RIDGE OF HIGH PRESSURE WILL SETTLE IN ON FRIDAY AND SATURDAY. 
TEMPS WILL BE ON THE RISE FOR SAT AS 850MB TEMPS INCREASE TO +8 TO 
+10C WITH THE RETURN FLOW AROUND THE HIGH. A WEAK SFC LOW IS 
EXPECTED TO DEVELOP ALONG A 500MB SHORTWAVE CROSSING THE US/CAN 
BORDER SAT NIGHT. 

PRECIP IS POSSIBLE ON SUN AS THE LOW DIPS DOWN ACROSS THE UPPER 
GREAT LAKES AND DRAGS A COLD FRONT ACROSS WI. 850MB TEMPS DIP DOWN 
TO -6C IN SOUTH CENTRAL WI BY MON MORNING. THIS WOULD MAKE ANY 
PRECIP CHANCES BE A MIX OF RAIN OR SNOW ON SUN...THEN MAINLY SNOW 
SUN NIGHT EXCEPT NEAR THE LAKESHORE. A LITTLE LINGERING WRAP AROUND 
MOISTURE IS POSSIBLE IN THE EASTERN CWA ON MON AND WOULD BE RAIN OR 
SNOW...DEPENDING ON THE BOUNDARY LAYER TEMPS. 

THERE WAS A LARGE DIFFERENCE BETWEEN THE 06Z GFS AND THE 00Z ECMWF 
MODEL SOLNS FOR TUE THROUGH THU AND HPC PREFERRED THE MORE 
CONSISTENT ECMWF...BUT LATEST 12Z GFS IS IN LINE WITH THE 00Z ECMWF. 
THE CONSENSUS IS FOR HIGH PRESSURE TO SPRAWL ACROSS THE EASTERN 
CONUS AND AN UPPER LOW WILL SWING ANOTHER SFC LOW ACROSS THE US/CAN 
BORDER TUE NIGHT INTO WED. THIS GIVES MORE CONFIDENCE IN GOING WITH 
A DRY FCST FROM MON NIGHT THROUGH WED NIGHT.

&&

.AVIATION...
IFR VISIBILITIES AND NUMEROUS AREAS OF LIFR CEILINGS WILL CONTINUE 
THIS EVENING AND OVERNIGHT DUE TO AN UPPER LOW/TROF DROPPING IN FROM 
THE NORTHWEST. WHILE UPPER LEVELS COOL...BOUNDARY LAYER WILL 
REMAIN RATHER WARM...SO EXPECT RAIN THROUGH 06Z AND A CHANGEOVER TO 
A RAIN/SNOW MIX IN SOUTHWESTERN WISCONSIN AROUND 12Z WITH LITTLE 
ACCUMULATION. A RAIN/SNOW MIX MAY BRIEFLY OCCUR ACCROSS SOUTHEASTERN 
WISCONSIN AROUND 12Z THANKSGIVING DAY.

&&

.MARINE...
BRISK NORTHWEST WINDS AND WAVES 2 TO 4 FEET ARE EXPECTED THURSDAY AND 
THURSDAY NIGHT...AS THE SURFACE PRESSURE GRADIENT TIGHTENS AND COLD 
AIR MOVES ACROSS THE WATERS FROM THE NORTHWEST. HOWEVER...WINDS AND 
SEAS IN THE NEARSHORE WATERS WILL REMAIN BELOW SMALL CRAFT ADVISORY 
CRITERIA. 

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...NONE.
&&

$$

SHORT/LONG TERM...13/MRC
AVIATION/MARINE...23/BRUESKE