FXUS63 KARX 292048
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
248 PM CST SUN NOV 29 2009

.SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT

MAIN FORECAST CONCERNS THIS PACKAGE...PRECIP CHANCES MON AFTERNOON
LIGHT SNOW CHANCES WED/WED NIGHT...TEMPERATURES THRU THE PERIOD.

DATA ANALYSIS AT 18Z HAD LOW PRESSURE NEAR DETROIT AND BROAD HIGH
PRESSURE OVER MUCH OF THE CENTRAL CONUS. WV IMAGERY SHOWED THE MID
LEVEL TROUGH MAKING STEADY PROGRESS EAST ACROSS MN WITH THE DEEPER
MOISTURE PUSHED OFF TO THE EAST OF WI. BAND OF -SN THAT MOVED
ACROSS THE NORTH HALF OF THE FCST AREA EARLIER THIS MORNING
WEAKENED/MOVED EAST OF THE AREA QUICKLY AS THE LIFT/DEEPER MOISTURE
MOVED OUT. VIS IMAGERY SHOWED CONSIDERABLE STRATUS/STRATO-CU CLOUDS
OVER MN/IA/WI...WITH A HOLE IN THE CLOUDS OVER WESTERN WI...
DRIFTING SOUTH ACROSS THE FCST AREA. EVEN UNDER THE CLOUDS AND LOW
LEVEL COLD ADVECTION/NORTHWEST FLOW...EARLY AFTERNOON TEMPS STILL
ABOVE NORMAL FOR THE END OF NOV.

NAM/GFS RUNS OF 29.12Z LOOK TO HAVE INITIALIZED WITHOUT BIG ERRORS
AND OFFER QUITE SIMILAR SOLUTIONS FOR TONIGHT INTO WED NIGHT.
SOLUTIONS AGAIN WELL SUPPORTED BY UKMET/ECMWF/CAN-GEM...WITH MODELS
CONVERGING TOWARD A SOLUTION OF A STRONGER SHORTWAVE TO MOVE ACROSS
THE REGION MON. DPROG/DT OF 500MB HGTS AT 29.12Z SHOWED NAM/GFS/
ECMWF RUNS OF 27.12Z AND 28.12Z VERIFIED WELL ACROSS NOAM/EASTERN
PAC WITH BETTER RUN-TO-RUN CONSISTENCY TO ECMWF. THRU 36HRS MODELS
CONVERGING ON A SOLUTION MOST SIMILAR TO EARLIER ECMWF RUNS...
FAVORING FASTER PROGRESSION OF THE TROUGH AXIS INTO THE EASTERN
CONUS AND FLATTER WITH THE SHORTWAVE RIDGING ACROSS SOUTH-CENTRAL
CAN. FOR 36-60HRS TREND IS STRONGER WITH THE NEXT SHORTWAVE TROUGH
INTO THE REGION AND TOWARD A COMPROMISE OF THE EARLIER RUNS WITH ITS
SPEED. FOR 60-84HRS TREND IS A BIT SLOWER/STRONGER WITH THIS
TROUGHING OVER THE REGION...SLOWER WITH THE SOUTHERN MS VALLEY
SHORTWAVE AS WELL. ECMWF WITH THE BETTER RUN-TO-RUN CONSISTENCY FOR
36-84HRS. CHECK OF OBS VS. MODEL DATA SHOWED NAM/GFS QUITE
REASONABLE WITH THE SFC MASS FIELDS ACROSS THE CENTRAL CONUS. PER WV
IMAGERY...BOTH MODELS LOOKED GOOD WITH THE SHORTWAVE DETAILS ACROSS
NOAM. NO CLEAR REASON TO FAVOR ANY ONE PARTICULAR DETERMINISTIC RUN
THIS CYCLE...NAM WITH GOOD DETAIL...ECMWF WITH THE BETTER RUN-TO-RUN
CONSISTENCY...GFS THE FIRST TO PICK UP ON THE STRONGER SHORTWAVE FOR
MON. WITH TREND TOWARD THE COMMON SOLUTION...FAVORED THE MODEL/
ENSEMBLE COMPROMISE. SHORT-TERM FORECAST CONFIDENCE AVERAGE TO GOOD
THIS CYCLE.

IN THE SHORT TERM...STRATUS CLOUDS PROBLEMATIC TONIGHT...WITH
ABUNDANT MOISTURE CENTERED ON 900MB REMAINING TRAPPED UNDER AN
INVERSION BETWEEN 900-850MB. 850MB WARM ADVECTION AHEAD OF THE NEXT
WAVE ALREADY SPREADS INTO THE AREA AFTER MIDNIGHT. TRENDED TOWARD
THE PESSIMISTIC SIDE TONIGHT WITH SKIES ONLY BECOMING PARTLY CLOUDY
AT THE LEAST TONIGHT. MODELS HAVE ALL TRENDED TOWARD A STRONGER
SHORTWAVE TO DROP SOUTHEAST ACROSS WI ON MON...SEEN IN 28.12Z GFS
FIRST. SHORTWAVE APPEARS DIFFUSE EARLY THIS AFTERNOON...TOPPING THE
RIDGE OVER NORTHERN BC. WAVE COMES ACROSS MONDAY ALONG WITH 300MB
DIVERGENCE IN LEFT EXIT REGION OF 130+KT JET. 280-290K ISENTROPIC
LIFT SPREADS ACROSS THE AREA MON...IN STRONG 850-700MB WARM
ADVECTION. INITIAL FORCING/LIFT GOES INTO SATURATION...AND CONFINED
SMALL MORNING -SN CHANCE TO FAR NORTH END OF FCST AREA. PER MODEL
SOUNDINGS AND X-SECTIONS...SFC-600MB LAYER SATURATES DURING THE
AFTERNOON OVER THE NORTHEAST THIRD OF THE FCST AREA...AND RAISED
PRECIP CHANCE THERE. 925MB TEMPS WARM TO AROUND 0C BY 00Z TUE...WITH
SFC/BOUNDARY LAYER TEMPS EXPECTED TO WARM TO AROUND 40F. INCLUDED
MENTION OF SPRINKLES ON SOUTHWEST SIDE OF PRECIP CHANCE. AREAS
NORTH/EAST OF I-94 WILL HAVE TO BE WATCHED FOR NEED OF -RA MENTION
THERE AS WELL MON AFTERNOON. FORCING/LIFT/DEEPER MOISTURE EXIT
QUICKLY BY MON EVENING. LOW LEVEL WARM ADVECTION CONTINUES MON NIGHT
WITH WEST/SOUTHWEST FLOW PULLING A DRIER AIRMASS INTO THE REGION
FROM THE CENTRAL/NORTHERN PLAINS. LOW WITH NEXT TROUGH/SHORTWAVE
TRACKS NEAR THE MN/CAN BORDER TUE. COLD FRONT SOUTH OF THE LOW
PUSHES INTO/ACROSS THE TUE AFTERNOON. 925MB TEMPS AHEAD OF THE FRONT
RISE INTO THE +2C TO +7C RANGE TUE AFTERNOON...FOR ONE LAST
UNSEASONABLY WARM DAY. AIRMASS WITH/BEHIND THE FRONT REMAINS DRY AND
LEFT TUE/TUE NIGHT PERIODS DRY. RATHER STRONG 925MB COLD ADVECTION
SPREADS ACROSS THE AREA BEHIND THE FRONT LATE TUE AND DEPENDING ON
TIMING OF THE FRONT MAY YET NEED A NON-DIURNAL TEMP TREND FOR TUE
AFTERNOON. INCREASING SFC-700MB MOISTURE SPREADS SOUTH ACROSS THE
AREA WED...AHEAD OF THE APPROACHING MID LEVEL TROUGH AXIS. ADDED A
SMALL -SW CHANCE TO FAR NORTH END OF FCST AREA FOR WED. MOISTURE
CONTINUES TO INCREASE/DEEPEN AHEAD OF THE MID LEVEL TROUGH AXIS WED
NIGHT. ADDED A SMALL -SW CHANCE TO THE ENTIRE FCST AREA AS
INCREASING CYCLONIC FLOW AND COOLING 850-700MB AIRMASS MAY SQUEEZE
OUT A FEW -SW/FLURRIES.

GENERALLY FAVORED A BLEND OF GUIDANCE LOWS/HIGHS FOR TONIGHT THRU
MON NIGHT. WITH STRONG LOW LEVEL WARM ADVECTION AHEAD OF THE FRONT
TUE AND PARTLY-MOSTLY SUNNY SKIES AND NO SNOW COVER...GUIDANCE HIGHS
FIR TUE LOOKED ABOUT A CATEGORY TOO COOL MOST AREAS. TRENDED TOWARD
A BLEND OF GUIDANCE LOWS TUE NIGHT. WITH COLD ADVECTION AND
INCREASING/ THICKENING CLOUDS WED...LEANED TOWARD COOLER OF GUIDANCE
HIGHS. GUIDANCE LOWS WED NIGHT ALL QUITE SIMILAR AND APPEAR
REASONABLE AT THIS TIME.

.LONG TERM...THURSDAY THROUGH SUNDAY

29.00Z MEDIUM RANGE MODELS IN MODEST AGREEMENT WITH EACH OTHER AND
THEIR PREVIOUS RUNS ON THU...AT LEAST WITH THE LONGWAVE TROUGHING
OVER CENTRAL/EASTERN NOAM. TREND IS A BIT SLOWER/DEEPER WITH THIS
TROUGH/UPPER LOW OVER THE GREAT LKS/ONT. CONSIDERABLE DIFFERENCES
EXIST WITH THE FLOW PATTERN/ENERGY APPROACHING THE WEST COAST AT 00Z
FRI. THESE DIFFERENCES CONTINUE THRU THE REMAINDER OF THE LONG-
TERM PERIOD AS ENERGY/TROUGHING PROGRESSES EAST...WITH POOR BETWEEN
MODEL AND RUN-TO-RUN CONSISTENCY FOR FRI-SUN. FCST CONFIDENCE
AVERAGE THU...THEN POOR FOR FRI-SUN UNTIL MODELS SETTLE DOWN AND
CONVERGE TOWARD A COMMON SOLUTION. GIVEN ALL THE VARIABILITY...
LIKED HPC IDEA /PMDEPD/ OF TRENDING TOWARD GFS/ECMWF ENSEMBLE
MEANS...WHICH PROVIDES SOME STABILITY TO THE DAY 4-7 FCST AT THIS
TIME. MID-WEEK SOUTHERN STREAM SYSTEM REMAINS UN-PHASED WITH THE
NORTHERN STREAM AND WELL EAST/SOUTH OF THE AREA ON THU. COLD CORE OF
850-700MB AIRMASS DROPS ACROSS THE REGION THU/FRI...700MB TEMPS
AROUND -20C. THIS COUPLED WITH PASSAGE OF DEEPER MOISTURE AND MID
LEVEL TROUGH AXIS...SMALL -SW CHANCE THU REASONABLE. WITH COLD AIR
LOOKING TO STILL BE IN PLACE FRI...ADDED A SMALL -SW CHANCE TO FRI.
LITTLE CONFIDENCE IN DETAILS OF ANY FEATURES FOR SAT/SUN...OTHER
THAN A COLDER AIRMASS LOOKS TO REMAIN IN PLACE ACROSS THE REGION.
LEFT SAT/SUN DRY FOR NOW...BUT DEPENDING ON WHICH...IF ANY...MODEL
SOLUTION THE MODELS CONVERGE TOWARD...MAY YET NEED SOME SMALL -SN
OR -SW CHANCES EITHER OR BOTH DAYS. IN FACT 29.12Z GFS SOLUTION
TRACKS A SIGNIFICANT SFC LOW/PRECIP ACROSS THE REGION SUN WHILE
ECMWF HAS HIGH PRESSURE AND SHORTWAVE RIDGING OVER THE REGION...SO
APPEARS ALMOST ANYTHING POSSIBLE BY DAY 7. GENERALLY FAVORED A BLEND
OF GFS ENSEMBLE MOS AND HPC GUIDANCE FOR HIGHS/LOWS THRU THE PERIOD.

&&

.AVIATION...TONIGHT AND MONDAY

BIGGEST CHALLENGE IS ON CEILING HEIGHTS AND POTENTIAL CLEARING TREND
TONIGHT/MONDAY.

MID-LEVEL TROUGH PUSHING ACROSS THE UPPER MISSISSIPPI RIVER VALLEY
EARLY THIS AFTERNOON. THE ASSOCIATED PRECIPITATION HAS MOVES WELL
EAST OF THE TAF SITES LEAVING BEHIND MAINLY CLOUDY SKIES. SATELLITE
SHOWING SOME BREAKS IN THE CLOUDS...WITH ONE HOLE OVER WESTERN
WISCONSIN AFFECTING THE KLSE TAF SITE. OTHERWISE LARGE SHIELD OF
CLOUDS FOUND ALL THE WAY BACK INTO WESTERN MINNESOTA. SURFACE
OBSERVATIONS SHOW CEILINGS MAINLY HAVE RISEN INTO THE MVFR TO VFR
CATEGORIES OVER MOST SECTIONS. MODELS HOLD ON TO LOW LEVEL MOISTURE
THROUGH MUCH OF THE OVERNIGHT HOURS BUT BEGIN TO THIN AS THE NIGHT
WEARS ON...THUS EXPECT A SLOW CLEARING TREND...WITH JUST TEMPORARY
HOLES IN CLOUDS THROUGH THE EARLY EVENING HOURS. WITH SUBSIDENCE
BEHIND THE WAVE EXPECT MVFR/VFR CEILINGS INTO THE EVENING HOURS WITH
A CLEARING TREND AFTER ABOUT 03Z-06Z. CONFIDENCE NOT HIGH ON THIS
SCENARIO AND CLOUD TRENDS WILL CERTAINLY HAVE BE ADDRESSED WITH THE
00Z TAF ISSUANCE.

&&

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

$$

SHORT/LONG TERM...RRS
AVIATION..........RABERDING