FXUS63 KARX 280919
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
319 AM CST SAT NOV 28 2009

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

MAIN FORECAST CONCERNS ARE POTENTIAL FOR FLURRIES TONIGHT INTO 
SUNDAY MORNING...AS WELL AS TEMPERATURES THROUGH THE PERIOD.

CURRENTLY AS OF 09Z...WATER VAPOR LOOP AND RUC 500MB HEIGHT ANALYSIS 
SHOWED RIDGING FROM THE SOUTHERN PLAINS INTO THE UPPER MISSISSIPPI 
VALLEY...A SPLIT TROUGH FROM SOUTHERN CALIFORNIA INTO SOUTHERN 
ALBERTA...AND RIDGING OVER THE EAST PACIFIC. PRESENT WITHIN THE 
SPLIT TROUGH INCLUDE AN UPPER LOW OVER CENTRAL CALIFORNIA...A 
SHORTWAVE IN SOUTHWEST SASKATCHEWAN AND A SHORTWAVE IN EASTERN 
BRITISH COLUMBIA. ALSO NOTED ON WATER VAPOR IS A STREAM OF UPPER 
LEVEL MOISTURE BETWEEN THE SPLIT TROUGH AND RIDGE...WHICH THEN RIDES 
UP ON TOP OF THE RIDGE INTO NORTHERN MINNESOTA. A FEW CIRRUS CLOUDS 
ARE CROSSING THE FORECAST AREA ASSOCIATED WITH THE UPPER LEVEL 
MOISTURE...THOUGH MOST OF THE CIRRUS IS CONFINED TO THE DAKOTAS. AT 
THE SURFACE...A TROUGH OF LOW PRESSURE EXTENDED FROM NORTHEAST 
MINNESOTA TO A LOW IN SOUTHWEST KANSAS. A WARM FRONT WAS ALSO 
PRESENT OVER SOUTHERN IOWA. 

TODAY AND TONIGHT...NORTHERN PORTION OF THE SPLIT TROUGH IS PROGGED 
TO DIG SOUTHEAST DURING THE PERIOD...COVERING MUCH OF THE DAKOTAS 
AND MINNESOTA BY 12Z SUNDAY. THIS UPPER TROUGH DIGGING SOUTHEAST 
WILL HELP TO PUSH THE SURFACE TROUGH CROSSING THROUGH MINNEAPOLIS 
EARLY THIS MORNING EASTWARD THROUGH THE AREA TODAY. IN ADDITION...IT 
APPEARS THE UPPER TROUGH SHOULD CAUSE THE SURFACE PRESSURE GRADIENT 
TO TIGHTEN UP TONIGHT...AS LOW PRESSURE IN SOUTHWEST KANSAS MOVES 
NORTHEAST ALONG THE SURFACE TROUGH AND HIGH PRESSURE BUILDS INTO THE 
DAKOTAS. THEREFORE AN INCREASE IN NORTHWESTERLY WINDS ARE LIKELY 
TONIGHT...HELPING TO DRIVE COLDER AIR INTO THE REGION. TODAY SHOULD 
REMAIN MILD...THOUGH...AS A DRY AIRMASS IN PLACE (SEE 00Z MPX AND 
DVN SOUNDINGS) ALLOWS FOR PLENTY OF SUNSHINE AND 850MB TEMPS HOVER 
BETWEEN 6-8C. LOW SUN ANGLE AND LACK OF WIND WILL PRECLUDE ANY DEEP 
MIXING...BUT A FEW SITES SUCH AS THOSE IN THE MISSISSIPPI AND 
WISCONSIN RIVER VALLEYS COULD REACH 50. CLOUDS LOOK TO INCREASE 
TONIGHT IN THE WAKE OF THE SURFACE TROUGH PASSAGE... AIDED BY 
MID-LEVEL HEIGHT FALLS AHEAD OF THE UPPER TROUGH (90 TO 110 METERS 
BETWEEN 00-12Z SUNDAY)...UPPER DIVERGENCE IN THE RIGHT ENTRANCE 
REGION OF A JET CROSSING NORTHERN WI AND UPPER MI...AS WELL AS A 
BAND OF MID LEVEL FRONTOGENESIS. THE FORCING OVERALL IS NOT THAT 
STRONG...AND MOISTURE IN THE MID-LEVELS IS MINIMAL AS 700MB RH PROGS 
FROM THE 28.00Z NAM/GFS SHOW. NONETHELESS...FEEL IT IS WORTHY TO AT 
LEAST MENTION SOME FLURRIES IN THE 06-12Z TIME WINDOW NORTH OF I-90 
WHERE A NARROW ZONE OF 700MB MOISTURE MOVES ACROSS. WITH THE 
INCREASE OF CLOUDS...TEMPERATURES SHOULD NOT FALL MUCH BELOW 
FREEZING...THOUGH THE INCREASING WIND WILL MAKE IT FEEL COOLER.

SUNDAY AND SUNDAY NIGHT...UPPER TROUGH LOOKS TO STAY FAIRLY 
PROGRESSIVE...BUT DOES CONTINUE ITS DIGGING NATURE...COVERING THE 
WESTERN GREAT LAKES REGION INTO THE OHIO VALLEY BY 12Z MONDAY. THE 
PROGRESSION WILL HELP TO KEEP THE AREA MOSTLY DRY THROUGH THE 
PERIOD...DUE TO DRIER CANADIAN AIR POURING IN WITH THE COLD 
ADVECTION. ONLY IN THE MORNING DOES IT LOOK LIKE A FEW FLURRIES 
COULD OCCUR ASSOCIATED WITH THE FEATURES DISCUSSED IN THE TONIGHT 
PERIOD...AND THESE SHOULD BE CONFINED TO NORTH AND EAST OF I-94. 
REGARDING THE COLD ADVECTION...850MB TEMPS DURING THE DAY SUNDAY 
FALL FROM 0 TO -4C AT 12Z TO -6 TO -8C BY 00Z. WITH THIS COLD 
ADVECTION...AS WELL AS THE LIKELIHOOD TO HAVE SOME LOW STRATUS 
AROUND...WILL RESULT IN A MUCH COOLER DAY COMPARED TO TODAY. BREEZY 
NORTHWEST WINDS ARE EXPECTED TO PERSIST TOO AS THE PRESSURE GRADIENT 
NEVER REALLY RELAXES...EVEN INTO SUNDAY NIGHT. THIS WIND SHOULD HELP 
KEEP READINGS FROM FALLING INTO THE TEENS SUNDAY NIGHT...SINCE A DRY 
AIRMASS WOULD BE IN PLACE AND THE ANTICIPATION OF SOME CLEARING. 
NONETHELESS...NIGHT TIME COOLING AND COLD ADVECTION SHOULD STILL 
RESULT IN LOWS IN THE 20S.

MONDAY AND MONDAY NIGHT...RIDGING CURRENTLY OVER THE EASTERN PACIFIC 
SHOULD HAVE BUILT EASTWARD ACROSS THE NORTHERN U.S. ROCKIES BY 12Z 
MONDAY. THIS RIDGING IS FORECAST TO PUSH EASTWARD TOWARDS THE AREA 
DURING THIS PERIOD...IN RESPONSE TO A POTENT TROUGH DROPPING SOUTH 
THROUGH ALBERTA TOWARDS THE MONTANA BORDER. THE BUILDING HEIGHTS 
ALOFT COMBINED WITH A NORTHWEST TO WEST LOW LEVEL FLOW BRINGING DRY 
AIR IN SHOULD KEEP THE AREA DRY DURING THIS PERIOD. IN ADDITION... 
CLOUDS SHOULD CONTINUE TO SLOWLY CLEAR AS LOW LEVEL FLOW TURNS 
WESTERLY. ALTHOUGH CLEARING IS ANTICIPATED...LOOK FOR TEMPERATURES 
ONLY A DEGREE OR TWO WARMER COMPARED TO SUNDAY AS 850MB TEMPS ARE 
STILL -4 TO -6C AT 18Z MONDAY. QUESTION MARK FOR MONDAY NIGHT IS IF 
WINDS CAN DECOUPLE...WHICH WILL DEPEND A LITTLE BIT ON THE TIMING OF 
THE TROUGH IN WESTERN CANADA. RIGHT NOW IT LOOKS LIKE ENOUGH OF A 
PRESSURE GRADIENT IS GOING TO BE IN PLACE TO PREVENT DECOUPLING. 
THEREFORE...HAVE KEPT LOWS IN THE 20S FOR MONDAY NIGHT. IF WINDS CAN 
DECOUPLE...SOME PLACES SHOULD DROP INTO THE TEENS. 

.LONG TERM...TUESDAY THROUGH SATURDAY

MODELS AND ENSEMBLES CONTINUE TO SHOW THE DEVELOPMENT OF CENTRAL 
U.S. TROUGH AROUND THE MIDDLE OF THE WEEK...BRINGING IN THE COLDEST 
AIR SEEN SO FAR THIS SEASON. THE DEVELOPMENT IS A RESULT OF THAT 
POTENT TROUGH IN WESTERN CANADA TUESDAY MORNING DIGGING SOUTHEAST... 
AND EVENTUALLY PHASING WITH THE CURRENT UPPER LOW IN CALIFORNIA. THE 
PHASING TAKES PLACE WEDNESDAY NIGHT WELL EAST OF OUR AREA...TOWARDS 
THE MID-ATLANTIC ACCORDING TO THE 28.00Z ECMWF/GFS/CANADIAN. THE 
BIGGEST ISSUE DURING THIS PERIOD IS THE TIMING OF A COLD FRONT 
ASSOCIATED WITH THE POTENT TROUGH...WHERE THE 28.00Z GFS IS QUITE A 
BIT FASTER THAN THE ECMWF. PREFERRED A COMPROMISE SOLUTION FOR NOW 
WHICH IS THE CANADIAN...SHOWING THE FRONTAL PASSAGE ON TUESDAY. AS 
TO BE EXPECTED WITH COLD FRONTS THIS TIME OF YEAR...A DRY FRONTAL 
PASSAGE IS PLANNED. EVEN IN THE WAKE OF THE FRONT...THE MOISTURE IS 
JUST NOT THERE DESPITE HEIGHT FALLS AND PROBABLY THE PRESENCE OF 
SOME MID-LEVEL FRONTOGENESIS. THEREFORE THE GOING DRY FORECAST FOR 
TUESDAY THROUGH WEDNESDAY IS REASONABLE...AND MAY REMAIN DRY INTO 
WEDNESDAY NIGHT. ADJUSTMENTS WERE NEEDED TO THE TEMPERATURE 
FORECASTS WITH THE FASTER FRONT THAN PROGGED YESTERDAY...AND BOTH 
HIGHS AND LOWS FROM TUESDAY NIGHT INTO THURSDAY WERE LOWERED CLOSER 
TO MEX GUIDANCE. FURTHER LOWERING MAY BE REQUIRED...AS 28.00Z 
GFS/ECMWF DEPICT 850MB TEMPS OF -12C TO -14C ON THURSDAY. 

LOOKING TOWARDS NEXT WEEKEND...INDICATIONS ARE OF A POTENT TROUGH 
ENTERING THE PACIFIC NORTHWEST...WHICH SHOULD HELP RAISE MID LEVEL 
HEIGHTS OVER THE NORTHERN PLAINS. THEREFORE...THE CENTRAL U.S. 
TROUGH WOULD END UP MORE PROGRESSIVE THAN SOME MODELS SHOWED 
YESTERDAY. IN ADDITION...WOULD ANTICIPATE A SLOW WARMING TREND. AT 
THIS TIME...PLENTY OF UNCERTAINTY EXISTS AND NO MODIFICATIONS WERE 
MADE. 

&&

.AVIATION...TODAY AND TONIGHT

A COLD FRONT CURRENTLY ACROSS CENTRAL MN THIS MORNING WILL MOVE EAST 
TODAY... MAKING PASSAGE AT KRST AROUND 18Z AND KLSE AROUND 20Z. THIS 
WILL SWING LIGHT SOUTHERLY WINDS AROUND TO THE NORTHWEST. DUE TO THE 
RELATIVELY WEAK PRESSURE GRADIENT...WINDS WILL REMAIN LIGHT WITH THE 
FRONTAL PASSAGE...GENERALLY LESS THAN 10KT. OTHERWISE...VFR 
CONDITIONS WILL PREVAIL TODAY WITH ONLY SCATTERED CIRRUS CLOUDS 
EXPECTED. MODELS CONTINUING TO INDICATE A MID-LEVEL TROUGH OF LOW 
PRESSURE MOVING ACROSS NORTHERN MN INTO NORTHERN WI LATER TONIGHT. 
ANY PRECIPITATION WITH THIS FEATURE IS EXPECTED TO REMAIN NORTH OF 
THE KRST/KLSE TAF SITES. HOWEVER...MODELS ARE SHOWING AN INCREASE IN 
STRATUS...ADVECTING INTO THE AREA AFTER 29.09Z. APPEARS RIGHT NOW 
THIS STRATUS SHOULD BE IN THE MVFR CEILING RANGE. PLAN TO ADD THIS 
DETAIL WITH THE 28.12Z TAF ISSUANCE.   

&&

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

$$

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