FXUS63 KARX 302056
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
256 PM CST MON NOV 30 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT

FORECAST CONCERNS THIS PACKAGE...LIGHT SNOW/FLURRY CHANCES WED
THROUGH THU NIGHT...TEMPERATURES THRU THE PERIOD.

SURFACE MAP AT 18Z HAD LOW PRESSURE OVER SOUTHWEST ONT. A BROAD
AREA OF HIGH PRESSURE WAS CENTERED OVER OK/NORTHERN TX WITH RIDGING
INTO IL AND MI. WV IMAGERY DEPICTED A SHORTWAVE MOVING SOUTHEAST
FROM NEAR LK WINNIPEG INTO FAR SOUTHWEST ONT. LIFT AHEAD OF THIS
FEATURE COUPLED WITH LEFT EXIT REGION OF 130KT JET MAX AND 850-700MB
WARM ADVECTION/ISENTROPIC LIFT RESPONSIBLE FOR BAND OF SNOW MOVING
SOUTHEAST ACROSS MN ARROWHEAD REGION. AREA RADARS SHOWING RETURNS
OVER PARTS OF EAST-CENTRAL MN AND NORTHWEST WI...BUT LOWER LEVEL
AIRMASS STRUGGLING TO SATURATE OVER THESE AREAS WITH ANY PRECIP
REMAINING ALOFT. WITH SUNSHINE ACROSS THE FCST AREA SO FAR TODAY...
TEMPS WARMING INTO THE UPPER 30S-LOW 40S.

NO BIG ERRORS NOTED WITH 30.12Z NAM/GFS INITIALIZATIONS...WITH
MODELS PRESENTING RATHER SIMILAR SOLUTIONS TO EACH OTHER FOR TONIGHT
INTO THU NIGHT. SOLUTIONS WELL SUPPORTED BY 30.12Z CAN-GEM/UKMET/
ECMWF AS A LONGWAVE TROUGH/UPPER LOW AND A COLDER...MORE WINTER-LIKE
AIRMASS SETTLES INTO THE REGION. DPROG/DT OF 500MB HGTS AT 30.12Z
SHOWED NAM/GFS/ECMWF RUNS OF 28.12Z AND 29.12Z VERIFIED QUITE WELL
ACROSS SOUTHERN AND EASTERN NOAM...BUT STRUGGLING A BIT WITH THE
DETAILS OF THE SHORTWAVE ENERGY OVER BC AND THE UPPER LOW NEAR 35N
135W. GFS WITH THE BETTER RUN-TO-RUN CONSISTENCY ON THE PAC UPPER
LOW...ECMWF BETTER OVER BC. THRU 36HRS...TREND IS FASTER LIFTING THE
EASTERN CONUS TROUGH/ENERGY INTO THE CAN MARITIMES AND STRONGER WITH
THE TROUGHING/ENERGY INTO THE NORTHERN PLAINS/MAN/ONT. GFS WITH A
BIT BETTER RUN-TO-RUN CONSISTENCY FOR THIS PERIOD. THE STRONGER
TREND CONTINUES FOR 36-84HRS AS A LARGE TROUGH IS CARVED OUT OVER
THE NORTH-CENTRAL CONUS AND AN UPPER LOW SETTLES ACROSS MN/IA/WI.
TREND IS ALSO FASTER WITH THE SOUTHERN PLAINS UPPER LOW/SHORTWAVE
BEING PICKED UP AND EJECTED EAST AND EVENTUALLY NORTHEAST. GFS
CONTINUES TO SHOW THE BETTER RUN-TO-RUN CONSISTENCY THRU 60HRS WITH
ECMWF THEN BETTER AT 72 AND 84HRS. CHECK OF OBS VS. MODEL DATA AT
18Z SHOWED NAM/GFS WITH GOOD DEPICTIONS OF THE SFC MASS FIELDS
ACROSS THE CENTRAL CONUS. PER WV IMAGERY MODELS LOOKED GOOD WITH THE
SHORTWAVE FEATURES ACROSS NOAM/EASTERN PAC...WITH PERHAPS GFS
SLIGHTLY BETTER. GFS ALSO BETTER WITH THE 12Z-18Z PRECIP ACROSS THE
REGION...NAM WAS TOO FAR WEST WITH PRECIP ACROSS CENTRAL MN. SEVERAL
POINTS TO FAVOR GFS THIS CYCLE...BUT WITH ALL MODELS SHOWING TREND
TOWARD STRONGER TROUGHING OVER THE REGION BY MIDWEST AND REMAINING
RATHER TIGHTLY GROUPED WITH THEIR SOLUTIONS...PREFER TO FAVOR THE
MODEL/ENSEMBLE CONSENSUS...LEAD BY GFS/ECMWF. FORECAST CONFIDENCE
FOR THE SHORT TERM GOOD THIS CYCLE.

FOR THE SHORT TERM...BASED ON RADAR/SATELLITE TRENDS AND MODEL
DIAGNOSTICS...FORCING/LIFT/PRECIP THREAT FROM THE PASSING SHORTWAVE
THIS AFTERNOON WILL PASS NORTH/EAST OF THE FCST AREA AND BE WELL
EAST OF THE FCST AREA BY 00Z THIS EVENING. WEAK RIDGE OF HIGH
PRESSURE BUILDS ACROSS THE AREA TONIGHT. 850-700MB WARM ADVECTION/
WEST/SOUTHWEST FLOW CONTINUES ACROSS THE AREA TONIGHT THRU ABOUT
MID-DAY TUE. WITH SOURCE REGION OF THIS AIRMASS THE CENTRAL/NORTHERN
PLAINS...CLOUDS FOR MUCH OF TONIGHT/TUE LOOK LIMITED TO CIRRUS
IN THE NORTHWEST FLOW ALOFT AHEAD OF THE SHORTWAVE MOVING ALONG THE
US/CAN BORDER. THIS WAVE TRACKS TO NORTH OF LK SUPERIOR BY LATE WED.
ASSOCIATED SFC LOW TRACKS ACROSS NORTHERN MN TUE AND TO EASTERN LK
SUPERIOR BY WED MORNING...DRIVING A STRONG COLD FRONT SOUTHEAST THRU
THE REGION. MODEL SOUNDINGS AND X-SECTIONS INDICATE SFC-600MB
AIRMASS REMAINS QUITE DRY AHEAD OF/WITH/BEHIND THIS FRONT TUE/TUE
NIGHT. SOME STRONGER 850-500MB FN CONVERGENCE SIGNALS AND NEAR
NEUTRAL MID LEVEL STABILITY SEEN WITH/BEHIND THE FRONTAL PASSAGE...
BUT WITH THE RATHER DRY AIRMASS...LEFT TUE/TUE NIGHT DRY. 925-850MB
TEMPS WARM INTO THE +2C TO +6C RANGE AHEAD OF THE FRONT TUE...THEN
FALL TO THE -2C TO -6C RANGE BY 12Z WED. WITH PRESENT TIMING OF THE
FRONT ACROSS THE AREA CENTERED ON 00Z WED...OPTED NOT TO ADD A NON-
DIURNAL TEMP TREND TO TUE/TUE NIGHT GRIDSET. TEMP WOULD BEGIN
FALLING BEHIND THE FRONT LATE TUE AFTERNOON...ABOUT WHEN THEY WOULD
UNDER NORMAL CONDITIONS. THERE WILL JUST BE A LARGE TEMP CHANGE FROM
THE TUE HIGHS SOME 10-15 DEGREES ABOVE NORMAL TO THE LOWS WED
MORNING...WITH MUCH OF THE COOLING COMING WITH THE STRONGER LOW
LEVEL COLD ADVECTION BEHIND THE FRONT TUE NIGHT. NOT MUCH FOR TEMP
RECOVERY WED WITH HIGHS MUCH CLOSER TO NORMAL AS LOW LEVEL COLD
ADVECTION CONTINUES...WINDS BECOME MORE NORTHERLY AND INCREASING
925-800MB MOISTURE/CLOUDS SPREAD SOUTHEAST ACROSS THE AREA. LOW
LEVEL COLD ADVECTION DOMINATES ON WED WITH LITTLE FORCING FOR UPWARD
MOTION. LEFT WED DRY BUT FOR A SMALL -SW CHANCE NORTH OF HIGHWAY 29
ACROSS CENTRAL WI WED AFTERNOON. MOISTURE CONTINUES TO INCREASE/
DEEPEN FOR WED NIGHT INTO THU NIGHT...ESPECIALLY IN THE 925-700MB
LAYER. CYCLONIC FLOW/CONVERGENCE INCREASES/DEEPENS OVER THE AREA AS
WELL WED NIGHT INTO THU NIGHT AS THE COLD-CORE 500MB LOW SETTLES
ACROSS THE REGION. ADDED SMALL -SW CHANCE TO ENTIRE FCST AREA FOR
WED NIGHT. WITH MODEL SOUNDINGS SHOWING STEEP LOW LEVEL LAPSE AND
THE SATURATION TO 700MB OR HIGHER...RAISED -SW CHANCE TOWARD 30
PERCENT ON THU. WITH THE UPPER LOW OVERHEAD...SMALL -SW CHANCE THU
NIGHT CONTINUES TO LOOK REASONABLE.

WITH LIGHTER WINDS TONIGHT UNDER THE WEAK RIDGE AXIS FAVORED COOLER
OF GUIDANCE LOWS. GUIDANCE HIGHS TUE GENERALLY SIMILAR AND APPEAR
REASONABLE. WITH THE STRONG COLD ADVECTION AND PARTLY CLOUDY SKIES
TUE NIGHT...FAVORED COOLER OF GUIDANCE LOWS. WITH INCREASING CLOUDS
AND CONTINUED COLD ADVECTION WED TRENDED TOWARD COOLER OF GUIDANCE
HIGHS. GUIDANCE LOWS SIMILAR AND LOOK GOOD FOR WED NIGHT. TRENDED
TOWARD A BLEND OF GFS MEX-MOS AND HPC GUIDANCE HIGHS/LOWS FOR
THU/THU NIGHT.

.LONG TERM...FRIDAY THROUGH MONDAY

30.00Z MEDIUM RANGE MODELS IN MODEST AGREEMENT WITH THE EASTERN
CONUS TROUGH FRI AND WITH THE AMPLIFYING...BLOCKY-LOOKING RIDGING
DEVELOPING INTO AK. HOWEVER MODELS SHOW RATHER POOR AGREEMENT WITH
THE SHORTWAVE TROUGHING IN BETWEEN ACROSS WESTERN CAN/NORTHWEST
CONUS. AT LEAST CAN-GEM/ECMWF/GFS REASONABLY TRUE TO THEIR 29.00Z
RUNS WITH POSITION OF THE TROUGH/UPPER LOW OVER/NEAR THE NORTHWEST
CONUS AT 00Z SAT. ECMWF LOOKS SLOW...GFS FAST WITH THIS FEATURE...
WITH UKMET/CAN-GEM/GFS ENSEMBLE MEAN MORE MIDDLE-OF-THE-ROAD WITH
THIS FEATURE OVER OR/WA/ID. 29.06Z GFS DID TREND SLOWER AND TOWARD
THE MODEL CONSENSUS. THE SIGNIFICANT DIFFERENCES AT DAY 4 TRANSLATE/
CONTINUE AS SIGNIFICANT DIFFERENCES THRU DAYS 5-7. MODEL/ENSEMBLE
CONSENSUS TRENDS TOWARD RIDGING CONTINUING TO AMPLIFY IN TO AK...
DEVELOPING AN OMEGA-BLOCK LOOKING PATTERN BY SUN/MON WITH DOWNSTREAM
TROUGHING OVER THE WESTERN CONUS AND A BROAD WESTERLY FLOW OVER THE
CENTRAL CONUS. POOR BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY
PRECLUDES MUCH IN THE WAY OF CONFIDENCE IN ANY SMALLER SCALE/
SHORTWAVE DETAILS IN THE FLOW BEYOND FRI. FORECAST CONFIDENCE FOR
THE LONG-TERM ON THE POOR SIDE. COLD UPPER TROUGH SWINGS EAST OF THE
AREA BY LATE FRI...BUT NOT BEFORE UKMET/ECMWF/CAN-GEM ROTATE A
STRONGER SHORTWAVE AND THE TROUGH AXIS ACROSS THE REGION. DEEP
CYCLONIC FLOW AND MODEST MOISTURE IN THE SFC-700MB LAYER REMAINS
OVER THE AREA AND CONTINUED THE SMALL -SW CHANCE FRI. MID LEVEL HGTS
RISE OVER THE AREA SAT/SUN WITH SOME NON-GFS MODEL CONSENSUS FOR A
DRIER AIRMASS TO SPREAD ACROSS THE AREA THRU THE WEEKEND INTO EARLY
NEXT WEEK. GIVEN THIS AND NO CONFIDENCE IN ANY SHORTWAVE DETAILS BY
SAT...LEFT SAT-MON DRY FOR NOW BUT MAY YET NEED A SMALL -SN CHANCE
SUN/MON AT SOME POINT. EVEN AS MID LEVEL HGTS RISE FOR SAT AND
BEYOND...SEASONABLY COLD LOWER LEVEL AIRMASS LOOKS TO STAY
ENTRENCHED OVER THE REGION INTO EARLY NEXT WEEK WITH 850MB TEMPS
REMAINING IN THE -10C TO -12C RANGE INTO MON. FAVORED A BLEND OF GFS
MEX-MOS AND HPC GUIDANCE FOR HIGHS/LOWS THRU THE PERIOD...WITH TEMPS
NEAR TO BELOW NORMAL.

&&

.AVIATION...TONIGHT THROUGH TUESDAY

A SHORT WAVE TROUGH WILL MOVE SOUTHEAST ACROSS ONTARIO TONIGHT. THIS
SYSTEM WILL PRODUCE A BROKEN DECK OF 70-10K CLOUDS ACROSS THE
NORTHERN TWO THIRDS OF MINNESOTA AND WISCONSIN. ANOTHER BAND OF MID
CLOUDS WILL MOVE INTO THESE SAME AREAS ON TUESDAY AFTERNOON AS YET
ANOTHER SHORT WAVE MOVES ACROSS NORTHERN MINNESOTA...WITH CONDITIONS
AT THE TAF SITES REMAINING VFR THROUGH TUESDAY.

&&

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

$$

SHORT/LONG TERM...RRS
AVIATION..........BOYNE