FXUS63 KARX 282030
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
230 PM CST SAT NOV 28 2009

.SHORT TERM...TONIGHT THROUGH TUESDAY NIGHT

MAIN FORECAST CONCERNS THIS PACKAGE...-SN/FLURRY CHANCES LATE
TONIGHT/SUN MORNING...TEMPERATURES THROUGH THE PERIOD.

18Z DATA ANALYSIS HAD A WEAK AREA OF LOW PRESSURE OVER THE U.P OF
MI WITH A WEAK TROUGH/COLD FRONT SOUTHWEST ACROSS THE AREA TO A
ANOTHER LOW NEAR/OVER THE OK PANHANDLE. TROUGH/FRONT ACROSS THE
AREA NOT RESPONSIBLE FOR MUCH IN THE WAY OF WEATHER TODAY...OTHER
THAN A WIND SHIFT AND PATCHY LOWER STRATUS BEHIND IT ACROSS PARTS
OF WESTERN MN AND NORTHERN WI. VIS IMAGERY SHOWED GENERALLY THIN
CIRRUS ACROSS THE REGION...ALLOWING FOR PLENTIFUL SUNSHINE AND
TEMPS WARMING INTO THE 40S...SOME 10F OR SO ABOVE NORMAL.

28.12Z NAM/GFS INITIALIZED WELL...OFFER QUITE SIMILAR SOLUTIONS FOR
TONIGHT INTO TUE NIGHT...AND APPEAR WELL SUPPORTED BY UKMET/ECMWF/
CAN-GEM. DPROG/DT OF 500MB HGTS AT 28.12Z SHOWED NAM/GFS/ECMWF RUNS
OF 26.12Z AND 27.12Z VERIFIED WELL ACROSS NOAM/EASTERN PAC...WITH
BETTER RUN-TO-RUN CONSISTENCY TO GFS AND ECMWF. THRU 36HRS MODELS
HAVE CONVERGED TOWARD THE FASTER OF THE SOLUTIONS WITH THE TROUGH
MOVING ACROSS THE REGION AND FLATTER WITH THE RIDGING BEHIND IT INTO
ALB/SASKAT. FOR 36-60HRS MODELS TRENDING TOWARD A COMMON SOLUTION
OF THE EARLIER RUNS AND OVERALL TREND IS TOWARD SLIGHTLY FASTER WITH
THE NORTHERN STREAM FEATURES. FOR 60-84HRS MODELS TRENDING A BIT
SLOWER WITH THE NEXT TROUGH INTO THE NORTHERN PLAINS...WITH EARLIER
ECMWF RUNS FAVORED. THESE TRENDS WELL SUPPORTED BY GFS ENSEMBLE
MEAN. CHECK OF OBS VS. MODEL DATA AT 18Z SHOWED NAM/GFS QUITE
REASONABLE WITH THE SFC MASS FIELDS ACROSS THE CENTRAL CONUS. PER WV
IMAGERY...BOTH LOOKED GOOD WITH THE SHORTWAVE DETAILS ACROSS
NOAM/EASTERN PAC WITH PERHAPS SLIGHT EDGE TO GFS. AS USUAL...NO
CLEAR DETERMINISTIC MODEL FAVORITE. WITH MODELS TRENDING TOWARD A
COMMON SOLUTION OF THEIR EARLIER RUNS...FAVORED THE MODEL BLEND/
COMPROMISE THIS CYCLE. WITH RATHER GOOD CONSISTENCY AMONG THE
MODELS...SHORT TERM FORECAST CONFIDENCE GOOD THIS CYCLE.

FOR THE SHORT TERM...SFC TROUGH/FRONT WILL SAG SOUTH OF THE AREA
TONIGHT. SFC-700MB COLD ADVECTION BEHIND IT WILL ERODE THE SFC-800MB
WARM LAYER OVERNIGHT...WITH COLUMN OVER THE NORTHWEST 2/3 OF THE
FCST AREA AT OR BELOW 0C BY 12Z SUN. WITH MODELS TRENDING TOWARD A
FASTER SOLUTION THRU 00Z MON...MAIN SHOT OF 300MB AGEOSTROPHIC
FLOW/DIVERGENCE IN RIGHT ENTRANCE REGION OF 100-120KT JET MOVES
ACROSS THE AREA LATE TONIGHT/SUN MORNING. THIS DIVERGENCE ALOFT IN
CONJUNCTION WITH SOME 700-500MB FN CONVERGENCE AND NEAR NEUTRAL
STABILITY AHEAD OF THE MID LEVEL TROUGH AXIS. EARLIER MODEL RUNS
HAVE STRUGGLED WITH SATURATION OF THE COLUMN WITH THIS SHOT OF
FORCING/LIFT...WITH MODELS GENERALLY KEEPING THE 850-700MB LAYER ON
THE DRY SIDE WITH ANY PRECIP PRODUCED ABOVE 700MB NOT MAKING IT THRU
TO THE GROUND. 28.12Z MODELS A BIT MORE ROBUST WITH THE MOISTURE...
AND TREND TOWARD SATURATING THE 850-700MB LAYER WITH THE STRONGER OF
THE LIFT LATE TONIGHT/SUN MORNING...ESPECIALLY OVER THE NORTHEAST
2/3 OF THE FCST AREA. WITH A GOOD MODEL CONSENSUS FOR THIS...RAISED
PRECIP CHANCE LATE TONIGHT/SUN MORNING OVER NORTH/NORTHEAST PORTIONS
OF THE FCST AREA WITH MENTION OF -SN OR FLURRIES. DEEPER MOISTURE/
LIFT EXIT QUICKLY BY/AFTER 18Z SUN...HOWEVER MODELS TREND TOWARD
LINGERING CONSIDERABLE 925-875MB MOISTURE OVER THE AREA THRU SUN
NIGHT. HOW THIS WILL MANIFEST ITSELF AS FAR AS LOW CLOUDS IS
QUESTIONABLE. MOISTURE IS ON THE SHALLOW SIDE...925-850MB FLOW IS
ANTI-CYCLONIC WITH WEAK SHORTWAVE RIDGING AND WEAK LOW LEVEL COLD
ADVECTION CONTINUING OVER THE AREA. PREVIOUS GRIDS HELD MOSTLY
CLOUDY SKIES THRU SUNDAY WITH A SLOW DECREASE OF CLOUDS FROM WEST TO
EAST SUN NIGHT. LEFT THIS TREND ALONE FOR NOW. QUIET WEATHER FOR MON
THRU TUE AS SHORTWAVE RIDGING ALOFT AND SFC HIGH PRESSURE BUILD
ACROSS THE REGION. GFS DROPS A STRONGER SHORTWAVE/PRECIP CHANCE
ACROSS THE NORTHEAST HALF OF WI MON...BUT THIS GOES AGAINST MODEL
CONSENSUS AND LEFT MON DRY. AFTER A COOL-DOWN FOR SUN/SUN NIGHT...
MODERATING TEMPERATURES EXPECTED MON-TUE WITH WEST-SOUTHWEST FLOW
AND MODEST/ROBUST 925-850MB WARM ADVECTION ACROSS THE AREA. SOME
DIFFERENCES AS TO HOW MUCH 925-850MB WARMING OCCURS AHEAD OF THE
TROUGH/FRONT ON TUE...NAM/ECMWF WARMER THAN GFS...SO NOT A LOT OF
CERTAINTY ON TUE HIGHS. WITH TREND TOWARD SLOWER WITH THIS TROUGH
INTO THE REGION...WARMER APPEARS BETTER AT THIS TIME. COLD FRONT
MOVES THRU LATE TUE/TUE NIGHT WITH ANOTHER SHOT OF LOW LEVEL COLD
ADVECTION FOR TUE NIGHT. SFC-700MB MOISTURE WITH/BEHIND THIS FEATURE
APPEARS QUITE LIMITED AND LEFT TUE NIGHT DRY.

GUIDANCE LOWS TONIGHT SIMILAR AND LOOK GOOD. WITH LOW LEVEL COLD
ADVECTION AND CLOUDS SUN...GUIDANCE HIGHS LOOK ABOUT A CATEGORY TOO
WARM MOST LOCATIONS. FAVORED A BLEND OF GUIDANCE LOWS SUN NIGHT.
GUIDANCE HIGHS FOR MON SIMILAR AND LOOK REASONABLE. WITH SOME
WESTERLY WINDS AND WARM ADVECTION MON NIGHT...RAISED LOWS TOWARD
WARMER OF GUIDANCE VALUES. TRENDED TOWARD WARMER OF GUIDANCE HIGHS
ON TUE WITH FRONTAL PASSAGE LATE IN THE DAY. FAVORED A BLEND OF GFS
MEX MOS AND HPC GUIDANCE LOWS TUE NIGHT.

.LONG TERM...WEDNESDAY THROUGH SATURDAY

MEDIUM RANGE MODEL RUNS OF 28.00Z IN REASONABLY GOOD AGREEMENT
WED...WITH BOTH BETWEEN MODEL AND RUN-TO-RUN CONSISTENCY THEN
STEADILY DECREASING THRU SAT. BY FRI/SAT ECMWF IS MORE SIMILAR TO
GFS ENSEMBLE MEAN THAN GFS...AT LEAST WITH THE TROUGHING/FLOW OVER
NOAM. WITH THE MODEST/DECENT AGREEMENT WED...FORECAST CONFIDENCE
AVERAGE ON DAY 4...BUT QUICKLY TAILS TO POOR BY FRI/SAT WITH THE
POOR RUN-TO-RUN CONSISTENCY. MODEL/ENSEMBLE CONSENSUS MAINTAINS A
SPLIT FLOW/LIMITED PHASING OF THE NORTHERN/SOUTHERN STREAM PIECES OF
ENERGY MID-WEEK...WITH SOUTHERN STREAM PIECE AND ITS ASSOCIATED SFC
LOW REMAINING WELL SOUTH/EAST OF THE AREA WED INTO THU. GOOD
CONSISTENCY FOR A PIECE OF CANADIAN/ARCTIC AIR TO DROP SOUTHEAST
ACROSS THE REGION BEHIND THE PASSING LOW/TROUGH FOR WED NIGHT INTO
THU NIGHT. WITH ALL THE UNCERTAINTY BY FRI/SAT...HPC GUIDANCE
/PMDEPD/ FAVORING A BLEND OF GFS/ECMWF ENSEMBLE MEANS AND OVERALL
SLOWER EVOLUTION OF THE PATTERN APPEARS TO BE A REASONABLE SOLUTION
AT THIS TIME. HIGH PRESSURE BUILDS INTO THE REGION WED/THU...WITH
CORE OF THE ARCTIC AIRMASS TO MOVE ACROSS THE REGION THU/THU NIGHT.
DEPENDING ON DETAILS OF MOISTURE WITH THIS AIRMASS...MAY BE ABLE TO
SQUEEZE A FEW FLURRIES OUT OF IT ON THU AS A MID LEVEL TROUGH
PASSES...AND LEFT THE SMALL -SW CHANCE FOR MUCH OF THE AREA WED
NIGHT INTO THU NIGHT. HIGH DROPS INTO THE SOUTHEAST CONUS FOR
FRI/SAT...WITH SOME MODERATION OF AT LEAST THE MID LEVEL TEMPS.
FAVORING THE SLOWER MODEL/ENSEMBLE SOLUTION BY SAT...NEXT SYSTEM
REMAINS WEST OF THE AREA THRU SAT AND LEFT FRI/SAT DRY. FAVORING THE
ENSEMBLE MEANS OVER THE DETERMINISTIC RUNS...USED A BLEND OF THE GFS
ENSEMBLE MOS AND HPC GUIDANCE FOR HIGHS/LOWS THRU THE PERIOD.

&&

.AVIATION...TONIGHT AND SUNDAY

WEAK COLD FRONT MOVING SLOWLY THROUGH THE AREA TODAY WITH QUIET VFR
CONDITIONS. MAIN FOCUS IS APPROACH OF NEXT SHORT WAVE TROUGH IN
PROGRESSIVE NORTHERN STREAM TONIGHT. ALTHOUGH PRECIPITATION LIKELY
TO REMAIN NORTH OF TAF SITES...COLD AIR ADVECTION AND INCREASE IN
LOW LEVEL MOISTURE LEVELS COULD SPREAD BROKEN LOW STRATUS DECK IN
WITH IT. ALTHOUGH CONFIDENCE IS NOT OVERLY HIGH...WILL KEEP TREND OF
SPREADING MVFR CEILINGS IN DURING OVERNIGHT HOURS AND FOR BULK OF
SUNDAY. WOULD EXPECT IMPROVING CONDITIONS BY LATE SUNDAY THOUGH WITH
SHORT TERM RIDGE BUILDING BACK IN.

&&

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

$$

SHORT/LONG TERM...RRS
AVIATION..........SHEA