FXUS63 KARX 290943
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
343 AM CST SUN NOV 29 2009

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

MAIN FORECAST CONCERNS ARE WITH PRECIPITATION CHANCES TODAY AND 
MONDAY INTO MONDAY EVENING.

CURRENTLY AS OF 09Z...WATER VAPOR AND RUC 500MB HEIGHT ANALYSIS 
SHOWED RIDGING OVER THE EASTERN U.S. AND OVER THE PACIFIC 
NORTHWEST...AN UPPER LOW IN SOUTHWEST ARIZONA...AND A TROUGH OVER 
SOUTH CENTRAL CANADA INTO THE NORTHERN PLAINS. AHEAD OF THIS 
TROUGH...A 110 KT JET AT 250MB WAS PRESENT FROM DULUTH ACROSS 
WESTERN LAKE SUPERIOR...PLACING THE FORECAST AREA IN AN AREA OF 
UPPER LEVEL DIVERGENCE. A MID-LEVEL FRONTOGENESIS ZONE ALSO EXISTED 
FROM NORTHEAST NEBRASKA INTO NORTHWEST WISCONSIN...WHICH IS 
REFLECTED BY SUB 30 DBZ RETURNS ON RADAR IMAGERY. SURFACE OBS 
INDICATE THAT MOSTLY AREAS ALONG AND NORTH OF I-90 ARE SEEING 
SNOW...WHERE DEEPER MOISTURE EXISTS. SOME REPORTS INCLUDE 0.25 TO 
0.5 INCH IN SAWYER COUNTY WI AND 0.1 TO 0.2 INCHES IN POLK COUNTY 
WI. 00Z SOUNDINGS FROM INL AND MPX SHOW THE MOISTURE DIFFERENCE... 
WHERE MPX HAD 10-15C DEWPOINT DEPRESSIONS BETWEEN 700-900MB. IN THE 
WAKE OF THE PRECIPITATION... 11-3.9UM SATELLITE IMAGERY AND SURFACE 
OBS SHOWED STRATUS COVERING MUCH OF THE EASTERN DAKOTAS INTO WEST 
AND NORTHERN MINNESOTA. AT THE SURFACE...A TROUGH OF LOW PRESSURE 
EXTENDED FROM CENTRAL OKLAHOMA TO SOUTHERN LAKE MICHIGAN...AND HIGH 
PRESSURE COVERED MUCH OF THE NORTHERN ROCKIES INTO THE WESTERN 
DAKOTAS. NORTHWEST WINDS BETWEEN THE HIGH AND TROUGH ARE DRIVING 
COLDER AIR SOUTHEAST...ESPECIALLY AT 850MB WHERE 00Z SOUNDINGS 
SHOWED -4C AT BIS COMPARED TO +5C AT MPX.

TODAY AND TONIGHT...UPPER TROUGH OVER THE NORTHERN PLAINS IS 
FORECAST TO DIG INTO THE AREA TODAY...THEN HEAD TOWARDS THE OHIO 
VALLEY TONIGHT. WITH ITS PROGRESSION...ANTICIPATE THE AREA OF LIGHT 
SNOW ENTERING THE NORTHWEST SECTIONS OF THE FORECAST AREA WILL PUSH 
EAST-SOUTHEAST FAIRLY QUICKLY TODAY...WHICH ARE BEING FORCED 
DYNAMICALLY BY THE UPPER TROUGH. THIS HAS BEEN SHOWN THE PAST FEW 
DAYS...BUT IS A LITTLE STRONGER. NET RESULT WAS A NEED TO RAISE 
PROBABILITIES OF PRECIPITATION THIS MORNING TO A HIGH LEVEL...BUT 
ONLY A LITTLE QPF AND SNOW. ALSO SHOWN THE PAST FEW DAYS IS THE 
STRATUS DECK TO FOLLOW IN THE PRECIPITATION\S WAKE...WHICH SHOULD 
ENCOMPASS MUCH OF THE AREA TODAY. LOW LEVEL WINDS BACK A LITTLE MORE 
WESTERLY TONIGHT COMPARED TO THE NORTHWEST TODAY...WHICH SHOULD HELP 
TO DRIVE DRIER AIR CURRENTLY OVER THE WESTERN DAKOTAS EASTWARD. 
THEREFORE...SOME CLEARING IS EXPECTED...ESPECIALLY WEST OF THE 
MISSISSIPPI RIVER. THIS CLEARING WILL BE NEGATED SOME TOWARDS 12Z 
MONDAY. THIS IS DUE TO AN AREA OF HIGH BASED ISENTROPIC LIFT ACROSS 
MUCH OF THE STATE OF MINNESOTA...AHEAD OF A SHORTWAVE PROGGED OVER 
LAKE WINNIPEG AT 12Z MONDAY. REGARDING TEMPERATURES...LITTLE RISE IS 
ANTICIPATED TODAY WITH THE EXTENSIVE CLOUD COVER AND COLD ADVECTION 
IN PLACE. IN FACT...850MB TEMPS SHOULD STAY ON A FALLING TREND 
THROUGH THE DAY...DROPPING FROM AROUND 0C AT 12Z TO -5C AT 00Z. 
TONIGHT...THE CLEARING DOES CAUSE SOME CONCERN FOR TEMPS TO 
PLUMMET...THOUGH THE PRESSURE GRADIENT NEVER REALLY RELAXES ENOUGH 
FOR WIDESPREAD DECOUPLING TO OCCUR. NONETHELESS...NIGHT TIME COOLING 
SHOULD ALLOW READINGS TO FALL INTO THE 20S.

MONDAY AND MONDAY NIGHT...UPPER TROUGH OVER THE OHIO VALLEY LOOKS TO 
REMAIN PROGRESSIVE...IN RESPONSE TO ANOTHER MORE POTENT TROUGH 
DROPPING DOWN THROUGH ALBERTA AND SASKATCHEWAN DURING THIS TIME 
FRAME. IN FACT...SOME WEAK RIDGING COULD START BUILDING INTO THE 
AREA AHEAD OF THIS POTENT TROUGH BY 12Z TUESDAY. UNTIL THEN...THE 
ONLY ITEM OF FOCUS IS THE SHORTWAVE OVER LAKE WINNIPEG AT 12Z 
MONDAY...WHICH MODELS SHOW QUICKLY HEADING INTO THE PROGRESSIVE OHIO 
VALLEY TROUGH...REACHING NORTHERN WISCONSIN BY 00Z TUESDAY AND 
PENNSYLVANIA BY 12Z TUESDAY. WARM ADVECTION/ISENTROPIC LIFT AHEAD OF 
THIS SHORTWAVE IS EXPECTED TO SPREAD SOME LIGHT SNOW ACROSS NORTHERN 
MINNESOTA AND NORTHERN WISCONSIN. ADDED A 20 PERCENT CHANCE OF SNOW 
TO AREAS NORTH AND EAST OF I-94...TO ACCOUNT FOR THE WARM ADVECTION. 
AREAS EAST OF THE MISSISSIPPI RIVER SHOULD ALSO SEE AN INCREASE OF 
CLOUDS...ALONG WITH A RE-ENFORCING SHOT OF COLD AIR. THEREFORE... 
TEMPERATURES WILL LIKELY STRUGGLE TO GET MUCH ABOVE FREEZING FOR 
AREAS NORTH AND EAST OF I-94. WEST OF THE MISSISSIPPI RIVER...850MB 
TEMPS ARE PROGGED TO HOLD STEADY BETWEEN -2 AND -4C...AND WITH A 
LITTLE MORE SUNSHINE (OBSCURED SOMEWHAT BY CIRRUS CLOUDS) SHOULD 
RESULT IN HIGHS AT LEAST IN THE LOW 40S. FOR MONDAY NIGHT...FLOW 
BACKS AGAIN TOWARDS THE WEST WITH THE UPPER RIDGE BUILDING IN...BUT 
THIS TIME FROM THE SURFACE INTO THE MID LEVELS. THEREFORE...EXPECT 
ANOTHER DRY AIR SURGE TO COME IN...WITH MAYBE SOME CIRRUS MOVING IN 
LATE AHEAD OF THE POTENT TROUGH. PRESSURE GRADIENT LOOKS TO HAVE A 
CHANCE TO RELAX SOME AS A WEAK SURFACE RIDGE MOVES ACROSS. THUS...A 
FEW HOURS OF DECOUPLING AND MOSTLY CLEAR SKIES APPEARS POSSIBLE... 
SUGGESTING LOWS AT SOME LOCATIONS POSSIBLY GETTING DOWN INTO THE LOW 
20S.

TUESDAY AND TUESDAY NIGHT...THIS PERIOD LOOKS TO HAVE A LOT OF 
CHANGE IN THE WEATHER...MAINLY WITH TEMPERATURES AND WINDS AS 
MOISTURE IS SERIOUSLY LACKING. ALL OF IT IS A RESULT OF THAT POTENT 
TROUGH OVER ALBERTA AND SASKATCHEWAN AT 12Z TUESDAY. MODELS ARE IN 
SURPRISINGLY GOOD AGREEMENT ON THE HANDLING OF THIS POTENT 
TROUGH...SHOWING IT DIG INTO THE NORTHERN PLAINS ON TUESDAY...THEN 
HEADING AND EXPANDING EAST ACROSS THE UPPER MISSISSIPPI REGION 
TUESDAY NIGHT. A FAIRLY STRONG LOW WILL ACCOMPANY THE TROUGH...WITH 
A 997MB SURFACE LOW CROSSING SOUTH CENTRAL CANADA INTO ONTARIO 
DURING THE PERIOD. THE ASSOCIATED COLD FRONT LOOKS TO REACH KTOB 
AROUND 20Z...KLSE AROUND 00Z WEDNESDAY...THEN CLEAR THE REST OF THE 
AREA BY 06Z. AHEAD OF THE FRONT...A SURGE OF DOWNSLOPED WARM AIR 
WILL ENTER THE AREA...WITH 850MB TEMPS CLIMBING TO 3-6C (WARMEST IN 
NORTHEAST IOWA). SOME CIRRUS IS ANTICIPATED THROUGH THE DAY... 
ESPECIALLY NORTH OF I-90...ALONG WITH A NARROW BAND OF ALTOSTRATUS 
ALONG THE FRONT. THEREFORE...WARMEST READINGS SHOULD OCCUR SOUTH OF 
I-90...AND OVERALL FOR MUCH OF THE FORECAST AREA END UP BEING A MILD 
DAY. IN THE WAKE OF THE COLD FRONT...NORTHWEST WINDS ARE GOING TO 
KICK UP...DRIVING 850MB TEMPS DOWN TO -4 TO -8C BY 12Z WEDNESDAY... 
IF NOT COOLER. COLDEST READINGS...PERHAPS AS LOW AS THE LOW 
20S...EXPECTED ACROSS SOUTHEAST MINNESOTA AND TAYLOR-CLARK COUNTIES 
OF WISCONSIN. READINGS SHOULD ONLY FALL TO AROUND 30 TOWARD FAR 
SOUTHWEST WISCONSIN WHERE THE FRONT PASSES LAST. LAST ITEM TO NOTE 
IS THAT SOME STRATUS FROM THE NORTHWEST MAY START ENTERING THE 
PICTURE LATE TUESDAY NIGHT...ESPECIALLY OVER TAYLOR COUNTY.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

FULL LATITUDE TROUGHING IS FORECAST BY ALL MODELS AND ENSEMBLES TO 
DEVELOP FROM NORTHERN QUEBEC INTO THE CENTRAL PLAINS BY 12Z 
THURSDAY...ALLOWING FOR THE FIRST SURGE OF ARCTIC-ISH AIR TO FLOW 
SOUTH INTO THE CENTRAL U.S.. SINCE IT IS EARLY DECEMBER...THE AIR IS 
NOT OF THE TRUE WINTER ARCTIC...BUT 850MB TEMPS ARE PROGGED TO 
FALL TO -8 TO -10C BY 00Z THURSDAY AND -12 TO -14C BY 00Z FRIDAY. 
THE FULL LATITUDE TROUGH DEVELOPMENT IS A RESULT OF FIRST THAT 
POTENT TROUGH THAT MOVED INTO THE UPPER MISSISSIPPI VALLEY TUESDAY 
NIGHT...AND A RE-ENFORCING SHORTWAVE DROPPING DOWN INTO THE TROUGH 
FROM SASKATCHEWAN ON WEDNESDAY. OVERALL...PRECIPITATION CHANCES LOOK 
MINIMAL THROUGH FRIDAY...SINCE THE COOL AIRMASS LOOKS FAIRLY DRY 
BESIDES THE ISSUE OF STRATUS ON THE COLD FRONTAL INVERSION. 
HOWEVER...WITH THE UPPER LEVEL TROUGH FULLY SITUATED OVER THE 
FORECAST AREA ON THURSDAY... SOME DIURNAL SNOW SHOWERS CANNOT BE 
RULED OUT. THEREFORE...THE LOW CHANCE PROBABILITIES OF PRECIPITATION 
REMAIN FOR THURSDAY. COOL AIR APPEARS TO LINGER INTO FRIDAY AS 
WELL...WITH 850MB TEMPS HOVERING IN THE -12 TO -14C RANGE. ADJUSTED 
HIGHS AND LOWS DOWN SLIGHTLY FROM THE PREVIOUS FORECAST TO FIT 
BETTER WITH LATEST GUIDANCE. 

FOR NEXT WEEKEND...THE 29.00Z GFS APPEARS TO BE AN OUTLIER... 
EJECTING THE FULL LATITUDE TROUGH OUT TOO QUICKLY. THE 29.00Z 
ECMWF/GFS/CANADIAN IN ADDITION TO THE 29.00Z GFS ENSEMBLES ARE ALL 
IN GOOD AGREEMENT SHOWING A SLOWER EJECTION. THIS MAKES SENSE GIVEN 
THAT THE TROUGH IS FULL LATITUDE. THEREFORE...THE WEEKEND MAY END UP 
BELOW NORMAL TEMPERATURE-WISE AS WELL. THE 29.00Z ECMWF HOLDS 850MB 
TEMPS THE SAME FROM FRIDAY THROUGH SUNDAY...BUT ALSO INDICATES VERY 
LITTLE PRECIPITATION GIVEN LACK OF MOISTURE AND DYNAMICS. LATER 
FORECASTS MAY NEED TO LOWER TEMPERATURES.

&&

.AVIATION...TODAY AND TONIGHT

MID-LEVEL TROUGH OF LOW PRESSURE CURRENTLY MOVING ACROSS THE DAKOTAS 
INTO NORTHERN MN. THIS FEATURE WAS PRODUCING MID-LEVEL FRONTOGENESIS 
AND BAND OF MAINLY -SN EXTENDING FROM NORTH CENTRAL WI INTO 
EAST-CENTRAL MN. VIS IN THIS SNOW GENERALLY 3-5SM WITH POCKETS OF 
VIS DIPPING BELOW 2SM ACROSS PORTIONS OF NORTHWEST WI UNDER THE 
STRONGEST ATMOSPHERIC FORCING. OTHERWISE...CLOUD CIGS WITHIN THIS 
FORCING/PRECIPITATION BAND IN THE MVFR RANGE. SO...WILL BE WATCHING 
THIS TROUGH AND ASSOCIATED PRECIPITATION MOVE SOUTHEAST ACROSS THE 
AREA TODAY. CURRENTLY...KRST/KLSE TAF SITES CARRYING 5-6SM IN BR. AS 
THE TROUGH CONTINUES TO APPROACH/PASS THROUGH THE AREA...THE TAF 
SITES CAN EXPECT CLOUD CIGS TO LOWER INTO MVFR RANGE ALONG WITH VIS 
AFTER 11Z. JUDGING FROM CURRENT RADAR TRENDS AND LATEST MODEL 
OUTPUT...WILL LIKELY ALSO HAVE TO ADD -SN MENTION AT BOTH TAF SITES 
THIS MORNING THROUGH EARLY THIS AFTERNOON. LITTLE IF ANY SNOW 
ACCUMULATION IS EXPECTED AS THE GROUND IS RELATIVELY WARM. NEXT 
CONCERN WILL DEAL WITH STRATUS CLEARING TONIGHT. RIGHT NOW IT 
APPEARS KRST WILL CLEAR OUT AROUND 30.03Z AND KLSE AROUND 30.06Z. 
WILL CONTINUE TO ASSESS ALL THIS AND PROVIDE MORE DEFINITION WITH 
THE 29.12Z TAF ISSUANCE. 

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT/LONG TERM...AJ
AVIATION..........DAS