FXUS63 KARX 020944
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
344 AM CST WED DEC 2 2009

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

FORECAST FOCUS IN THE SHORT TERM PERIOD IS SQUARELY ON COOLING
TEMPERATURE TREND AND PERIODIC LIGHT SNOW OR FLURRIES.

09Z SURFACE ANALYSIS SHOWS A LOW PRESSURE AREA OVER THE UPPER
PENINSULA OF MICHIGAN...TRACKING QUICKLY EASTWARD. A COLD FRONT
REACHED FROM THE LOW DOWN THROUGH EASTERN WI AND WESTERN IL...WITH
CRISP NORTHWEST WINDS ACROSS THE FORECAST AREA.  THIS MARKS THE START
OF THE COLD INVASION WHICH WILL DWELL ACROSS THE UPPER MIDWEST FOR
THE FORESEEABLE FUTURE. SATELLITE IMAGERY SHOWS PLENTY OF LOW CLOUD
BEHIND SYSTEM...BUT THERE ARE SOME HOLES IN THE CLOUD SHIELD. LIGHT
SNOW AND FLURRIES ARE SHOWN BY SEVERAL SURFACE OBSERVING SITES
UPSTREAM...BUT NOT MUCH SEEN ON REGIONAL RADAR LOOPS.

PERUSAL OF VARIOUS SHORT TERM MODEL SOLUTIONS SHOW ALL IN PRETTY
REASONABLE AGREEMENT AGAIN TODAY WITH THE PROGRESSION OF FEATURES
ACROSS THE REGION THROUGH THE END OF THE WEEK. THE TRANSITION TO MORE
WINTER-LIKE CONDITIONS IS UNDERWAY. 850MB TEMPERATURES IN THE TEENS
BELOW ZERO CELSIUS ARE ALREADY IN PLACE ACROSS SOUTHERN CANADA...
AND WILL PARADE INTO THE REGION FOR THE REST OF THE WEEK. THE CENTER
OF THE COLD POOL WILL BE OVER THE AREA FRIDAY AND SATURDAY...
SOMEWHERE AROUND -15 DEG C.  HELLO DECEMBER...

THE LOW AND ASSOCIATED SURFACE COLD FRONT WILL CONTINUE TO PUSH EAST
OF THE REGION TODAY...WITH BRISK NORTHWEST WINDS USHERING IN THE
COLD SURGE. WITH MODERATE COLD ADVECTION THROUGH THE DAY...DO NOT
ANTICIPATE MUCH OF A TEMPERATURE RISE. THIS IS ESPECIALLY TRUE IF
WE DON'T SEE ANY SUNSHINE. IF WE DO GET A FEW HOLES...EXPECT THEM TO
FILL WITH CUMULUS QUICKLY WITH AN INCREASINGLY STEEP LAPSE RATE.

THIS FIRST WINTER COLD SNAP IS THANKS TO A DEEPENING BROAD UPPER
TROUGH REACHING FROM HUDSON BAY SOUTHWARD INTO THE WESTERN GREAT
LAKES STATES.  THIS TROUGH IS RETROGRADING SOUTHWEST WITH TIME INTO
OUR AREA DUE TO A BLOCKING RIDGE OFF THE CANADIAN MARITIMES AND
GREENLAND. WITH ADDITIONAL SHORT WAVE ENERGY ROTATING ABOUT THE
CLOSED CIRCULATION WITHIN THE MEAN TROUGH...EXPECT THE COLD TO
CONTINUE THROUGH THE REST OF THE WEEK AND INTO THE FIRST PART OF
THE WEEKEND. ALTHOUGH SKIES WILL REMAIN MAINLY CLOUDY THROUGH THE
REST OF THE WEEK...MOISTURE WILL NOT BE PARTICULARLY DEEP.
ANTICIPATED THAT THE COLD ADVECTION AND PASSING FORCING MECHANISMS
FROM TIME TO TIME WILL PROVIDE FOR A CHANCE FOR SOME LIGHT SNOW OR
FLURRIES OFF AND ON. HOWEVER DO NOT ANTICIPATE ANY ACCUMULATION.

.LONG TERM...SATURDAY THROUGH TUESDAY

THE MEDIUM RANGE MODEL SUITE SHOWS THAT A BROAD TROUGH WILL COVER
MOST OF NORTH AMERICA INTO THE MIDDLE OF NEXT WEEK. THE LARGE LOW
WHICH IS PROVIDING OUR FIRST REAL TASTE OF WINTER THIS WEEK WILL
BEGIN TO SHIFT EAST OF THE REGION BY SATURDAY...ALLOWING FOR A BRIEF
PERIOD OF HIGH PRESSURE. HOWEVER...THERE IS ANOTHER TROUGH WHICH IS
DIGGING INTO THE PACIFIC NORTHWEST AS WE SPEAK. THIS ONE IS ALSO
EXPECTED TO CLOSE OFF AND STALL ALONG THE WESTERN U.S. COAST FOR THE
REST OF THE WEEK. THE VARIOUS MODEL SOLUTIONS AND INDIVIDUAL ENSEMBLE
MEMBERS ARE ALL STRUGGLING WITH EXACTLY HOW THIS TROUGH WILL EVOLVE
AND TRANSLATE EASTWARD NEXT WEEK. MODEL CONTINUITY FROM RUN TO RUN
IS POOR...SO CONFIDENCE IN THE OUTCOME IS LIKEWISE LOWER THAN
NORMAL. AT THIS TIME...IT DOES APPEAR THAT THE FIRST PIECE OF SHORT
WAVE ENERGY WILL EJECT EAST FROM THE TROUGH AND INTO OUR PART OF
THE COUNTRY SUNDAY NIGHT INTO MONDAY. NOT SURE EXACTLY WHERE IT WILL
TRACK...OR IF THERE WILL BE MUCH IN THE WAY OF MOISTURE AVAILABLE
FOR ANY SNOW...BUT AFTER COORDINATION WITH SURROUNDING OFFICES DID
INTRODUCE A LOW CHANCE FOR SNOW FOR THIS TIMEFRAME.  WE WILL LIKELY
NEED TO ADD ADDITIONAL CHANCES SOMETIME DURING THE WEEK AS THE
TROUGH FINALLY BREAKS DOWN AND MOVES EAST. BUT AS THIS OCCURS...THE
VERY LONG RANGE IS SHOWING ANOTHER SURGE OF COLD AIR POISED TO
FOLLOW IT FOR THE END OF NEXT WEEK. LOOKS LIKE THE COLD IS HERE TO
STAY...

&&

.AVIATION...TODAY AND TONIGHT

BIGGEST ISSUE WITH THE FORECAST THROUGH TONIGHT IS THE STRATUS DECK
SITUATED OVER THE EASTERN DAKOTAS AND MUCH OF MINNESOTA EARLY THIS
MORNING. ALL OF THE STRATUS LIES IN A LOW LEVEL NORTHWEST FLOW COLD
ADVECTION REGIME...BEHIND A COLD FRONT THAT MOVED THROUGH LAST
EVENING. THE PROBLEM IS THAT THE STRATUS DECK...WHICH HAS MOSTLY
MVFR CEILINGS...CONTAINS HOLES WHERE SKIES CLEAR OUT. THIS HAS
ALREADY BEEN SEEN AT KRST. DAYTIME HEATING TODAY INCREASES THE
CONCERN FOR THE DECK TO CONTINUE DEVELOPING HOLES...DUE TO MIXING.
MODELS INDICATE THIS AS WELL...WITH EVEN A LOCAL MODEL SUGGESTING
TONIGHT COULD END UP CLEAR. THEREFORE...BOTH TAF SITES HAVE BEEN
HELD AT PREDOMINANTLY VFR WITH MENTIONS OF THE STRATUS DECK BY
SCATTERED 1500-2500 FT BASES. TEMPO GROUPS HAVE BEEN INCLUDED IN THE
EARLY MORNING HOURS TO ACCOUNT FOR THE IN AND OUT FLUCTUATIONS OF
MVFR CEILINGS...AND MORE TEMPO GROUPS MAY BE NEEDED IN LATER TAF
ISSUANCES. NO OBSCURATIONS ARE EXPECTED TO VISIBILITY THROUGH
TONIGHT...AND THEREFORE VISIBILITIES ARE HELD AT VFR.

&&

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

$$

SHORT/LONG TERM...MW
AVIATION..........AJ