FXUS63 KARX 022146
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
346 PM CST WED DEC 2 2009

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT

WEATHER CONCERNS THROUGH THIS PERIOD MAINLY DEAL WITH SNOW CHANCES
THURSDAY THROUGH FRIDAY...AS WELL AS TEMPERATURES THROUGHOUT THE
PERIOD. 

AT 20Z WEDNESDAY...SURFACE ANALYSIS SHOWED A CLOSED LOW PRESSURE
SYSTEM OVER THE TENNESSEE VALLEY...WHICH EXTENDED A CIRRUS SHIELD
NORTHWARD INTO THE FORECAST AREA. ALSO...IN THE UPPER LEVELS...A
RATHER AMPLIFIED RIDGE WAS OBSERVED OVER THE WEST COAST...WHILE A
SHORTWAVE TROUGH WAS ROTATING FROM CANADA INTO THE NORTHERN
PLAINS. RADAR ALSO INDICATED SOME LIGHT SNOW/FLURRIES NORTH AND
WEST OF THE FORECAST AREA JUST AHEAD OF THE MAIN SHORTWAVE ENERGY.

AN AREA OF LOW LEVEL MOISTURE/STRATUS DECK SEEN OVER CENTRAL
MINNESOTA WILL MOVE SOUTH IN THE LOW LEVEL FLOW...BUT WILL MAINLY
STAY WEST OF THE FORECAST AREA TONIGHT. THERE HAVE BEEN A FEW
FLURRIES REPORTED FROM THIS CLOUD LAYER...BUT AS THESE CLOUDS MAY
JUST EDGE INTO THE THE WESTERN PORTIONS OF THE AREA...HELD OFF ON
ANY FLURRIES IN THESE AREAS UNTIL AFTER MIDNIGHT.

WITH THE UPPER LEVEL RIDGE OVER THE WEST STAYING PUT FOR THE NEXT
SEVERAL DAYS...THE REGION WILL REMAIN UNDER NORTH/NORTHWEST FLOW.
THIS WILL ALLOW FOR THE THE UPPER LEVEL SHORTWAVE TROUGH OVER THE
NORTHERN PLAINS TO MOVE SOUTHEAST OVER THE FORECAST AREA ON
THURSDAY. DECENT LARGE SCALE QG FORCING WITH OMEGA SIGNAL
INDICATED FROM CROSS SECTIONS THROUGH THE LAYER OF SATURATION.
ALSO...ISENTROPIC UPGLIDE INDICATED ON THE 280K SURFACE DURING THE
DAY. IS ALSO SOME WEAK FRONTOGENESIS...MAINLY WEST OF THE
MISSISSIPPI RIVER. THESE FORCING SIGNALS WOULD INDICATE THAT SNOW
CHANCES ARE CERTAINLY WARRANTED FOR THE THURSDAY TIME PERIOD...AND
02.15Z SREF GIVING PROBABILITY OF 60 FOR MEASURABLE PRECIPITATION
OVER THE WESTERN AREAS. DETERMINISTIC MODELS ARE QUITE LIGHT WITH
QPF VALUES THOUGH...AND WITH PRECIPITABLE WATER VALUES AT 0.20
INCHES OR LESS...REALLY NOT EXPECTING MUCH FOR ACCUMULATIONS.
OPTED TO GO WITH FLURRIES THROUGH THE DAY...AS WELL AS CHANCES FOR
LIGHT SNOW AS WOULD NOT BE SURPRISED TO SEE LOCALIZED ACCUMULATIONS
UP TO A HALF INCH OR SO IN AREAS WHERE FRONTOGENESIS MAY ENCOURAGE
SOME BANDS TO FORM.

THE UPPER LEVEL SHORTWAVE TROUGH WILL PROGRESS EAST THURSDAY
NIGHT...WITH THE AFOREMENTIONED FORCING SIGNALS WEAKENING.
HOWEVER...DETERMINISTIC AND ENSEMBLE MODELS WOULD CONTINUE SOME
LIGHT PRECIPITATION INTO THE EVENING...SO LEFT SMALL CHANCES FOR
SNOW/FLURRIES IN THE FORECAST...WITH CHANCES FOR ANYTHING
MEASURING MAINLY ALONG AND EAST OF THE MISSISSIPPI RIVER.

SEVERAL MORE WEAK IMPULSES OF UPPER LEVEL SHORTWAVE ENERGY WILL
PUSH ACROSS THE AREA THROUGH FRIDAY NIGHT...BUT WITH LOW MOISTURE
VALUES IN THE ATMOSPHERE...LIMITED SATURATION...AND LITTLE UPWARD
MOTION...DON/T EXPECT ANYTHING MORE THAN FLURRIES.

TEMPERATURES LOOK TO BE NEAR OR BELOW NORMAL THROUGH THIS TIME
PERIOD. SUNSHINE WILL BE VERY LIMITED IF ANY IS SEEN...AND WITH
COLD AIR ADVECTION INTO THE REGION BEHIND THE SUBSEQUENT SHORT
WAVE TROUGHS...WON/T SEE SIGNIFICANT RISES IN DAYTIME HIGHS. LOWS
MAY BE A BIT MORE PROBLEMATIC...DUE TO CLOUD COVER
INSULATION...BUT STILL FEEL THAT LOWS IN THE TEENS/LOW 20S ARE A
GOOD BET...AS TEMPERATURES UPSTREAM IN THE COLDER AIRMASS WERE IN
THE SINGLE DIGITS/TEENS WEDNESDAY MORNING.

.LONG TERM...SUNDAY THROUGH WEDNESDAY

WILL BE A RATHER PERSISTENT UPPER LEVEL RIDGE OVER ALASKA THROUGH
THIS PERIOD...WITH TROUGHING SITUATED OVER NORTH CENTRAL CANADA.
COLD AIR WILL POOL UNDER THIS TROUGH BY TUESDAY NIGHT AND WEDNESDAY...WITH
850MB TEMPERATURES OVER THE NORTHERN PARTS OF SASKATCHEWAN AND
MANITOBA APPROACHING -35C ACCORDING TO THE 02.00Z ECMWF. GFS IS A
BIT WARMER WITH 850MB TEMPS FROM -20C TO -30C. EITHER WAY...COLDER
AIR WILL BE SITUATED TO THE NORTH...AND BY THE TUESDAY NIGHT/WEDNESDAY
PERIOD...THE COLDER AIR /DOWN TO -15C AT 850MB/ MAY COME SOUTH
INTO THE LOCAL AREA.

02.00Z RUN OF THE DETERMINISTIC ECMWF IS A BIT FASTER WITH AN
UPPER LEVEL SHORTWAVE TROUGH EJECTING EASTWARD...AWAY FROM THE
WEST COAST. 01.12Z RUN MORE IN LINE WITH THE 02.00Z CANADIAN AND
PAST FEW DETERMINISTIC GFS RUNS /02.06Z AND 02.00Z/ WHICH DIGS THE
TROUGH FURTHER SOUTH ACROSS THE ROCKIES AND HOLDS IT WEST OF THE
AREA THROUGH TUESDAY. THE SLOWER SOLUTION WOULD BRING WEAK RIDGING INTO
THE REGION AND WITH DEPARTING SURFACE HIGH PRESSURE THERE WILL BE
SOME WEAK WARM AIR ADVECTION ACROSS THE FORECAST AREA THROUGH
SUNDAY. GOOD AGREEMENT WITHIN THE MODEL SUITE WITH A SHORTWAVE
TROUGH MOVING THROUGH THE REGION SUNDAY NIGHT/MONDAY. THUS...COLD
AIR ADVECTION/COLDER AIR WILL MOVE SOUTH. EVEN COLDER PUSH...WITH
UPPER LEVEL SHORTWAVE AND SURFACE COLD FRONTAL PASSAGE WILL MOVE
THROUGH WEDNESDAY. BY THE ENDS OF THIS PERIOD...LOOKING AT NEAR TO
BELOW NORMAL TEMPERATURES.

&&

.AVIATION...

CEILINGS WILL BE PROBLEMATIC FOR THE TAF SITES...WITH THE CURRENT 
LOW CLOUD SHIELD ACROSS NORTHERN PARTS OF THE UPPER MISSISSIPPI 
RIVER VALLEY HOVERING BETWEEN MVFR/VFR. MODELS HAVING A DIFFICULT 
TIME CAPTURING THESE CLOUDS...WITH THE LATEST RUC 850-925 RH FIELDS 
PROBABLY DOING THE BEST. KLSE HAD CEILINGS AROUND 2500 FT THIS  
MORNING...BUT SOME DIURNAL RISE HAS ALLOWED CEILINGS TO CLIMB INTO 
THE VFR RANGE. THE RUC THEN BRINGS SOUTH THE DEEPER LOW LEVEL 
SATURATION ACROSS KRST/KLSE AROUND 03Z. WILL PLAY THIS AS A VFR 
CEILING FOR NOW...DROPPING TO MVFR TOWARD 12Z THU. LOWER CEILINGS 
COULD BE REALIZED SOONER HOWEVER...AND TRENDS WILL HAVE TO BE 
MONITORED. DECENT ISENTROPIC LIFT ON THE 280-295 K SFCS...COUPLED 
WITH QG CONVERGENCE ASSOCIATED WITH AN UPPER LEVEL LOW/SHORTWAVE 
ENERGY...COULD SQUEEZE OUT SOME -SN/-SHSN BY WED MORNING. WILL ADD 
-SN MENTION...BUT NO VSBY REDUCTIONS AT THIS TIME. SOME SNOW BANDS 
DO LOOK POSSIBLE ON WED THOUGH...AND SOME -SN VSBY REDUCTIONS TO 2SM 
COULD OCCUR. TOO FAR OUT...AND ENOUGH UNCERTAINTY ON 
WHERE/WHEN...SO WILL NOT ADD TO TAFS AT THIS TIME. THESE TRENDS WILL 
ALSO HAVE TO BE MONITORED. 

&&

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

$$

SHORT/LONG TERM...BROOKS
AVIATION...RIECK