FXUS63 KARX 252041
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
240 PM CST WED NOV 25 2009

.SHORT TERM...TONIGHT THRU SAT NIGHT

MAIN FORECAST CONCERNS THIS PACKAGE...PRECIP TYPE AND ANY POTENTIAL
SNOW AMOUNTS TONIGHT...CLOUDS/TEMPERATURES THROUGH THE PERIOD.

18Z DATA ANALYSIS HAD A BROAD AREA OF LOW PRESSURE CENTERED OVER
NORTHERN LAKE MI. CIRCULATION AROUND THIS LOW ENCOMPASSED MUCH OF
THE EASTERN HALF OF NOAM. WV IMAGERY SHOWED A MID LEVEL LOW NEAR
KMCW...WITH ONE SHORTWAVE ROTATING AROUND THE EAST SIDE OF THIS LOW
AND A SECOND STRONGER WAVE ROUNDING THE BASE OF THE TROUGH OVER
EASTERN KS/NORTHWEST MO. AREAS RADARS SHOWED LIGHT PRECIP WRAPPED
AROUND THE CIRCULATION OF THE MID LEVEL LOW. PRECIP -RA EAST OF THE
MID LEVEL TROUGH AXIS...-SN TO THE WEST OF IT. SOME -SN OR -RASN AS
CLOSE AS KAEL AS OF NOON. VSBYS IN MUCH OF THE -SN OVER WEST
CENTRAL/SOUTHWEST MN MOSTLY IN THE 1.5 TO 5SM RANGE...WITH TEMPS IN
THE LOWER-MID 30S.

25.12Z NAM/GFS LOOK TO HAVE INITIALIZED WELL...OFFER QUITE SIMILAR
SOLUTIONS AND ARE WELL SUPPORTED BY ECMWF/CAN-GEM/UKMET FOR TONIGHT
INTO SAT NIGHT. PER RA-OBS...BOTH DID INITIALIZE 850MB TEMPS AT
KOMA/KMSP 1C TO 2C TOO COOL. DPROG/DT OF 500MB HGTS AT 25.12Z
SHOWED NAM/GFS/ECMWF RUNS OF 23.12Z AND 24.12Z VERIFIED RATHER WELL
ACROSS NOAM WITH BETTER RUN-TO-RUN CONSISTENCY TO NAM/ECMWF. THRU
36HRS...MODELS CONVERGE ON A COMMON SOLUTION OF THEIR EARLIER
RUNS...WITH NAM SHOWING THE BETTER RUN-TO-RUN CONSISTENCY AS THE
TROUGH SWINGS INTO THE OH VALLEY. FOR 36-60HRS MODELS CONVERGING
TOWARD EARLIER ECMWF RUNS WITH MORE RIDGING ALOFT OVER THE NORTH-
CENTRAL CONUS AND SLOWER WITH THE NEXT TROUGH/ENERGY INTO THE
WESTERN CONUS. THIS SLOWER TREND FAVORING EARLIER ECMWF RUNS
CONTINUES IN THE 60-84HR TIME-FRAME...WITH A TREND TOWARD A MORE
POSITIVE TILT NORTHERN STREAM TROUGH INTO THE NORTHERN PLAINS SAT
AND MORE OF A SPLIT/ STRONGER/CLOSED LOW IN THE SOUTHERN STREAM OVER
THE SOUTHWEST CONUS. CHECK OF OBS VS. MODEL DATA AT 18Z SHOWED
NAM/GFS WITH GOOD DEPICTIONS OF THE SFC MASS FIELDS ACROSS THE
REGION. PER WV IMAGERY...AS BLEND OF NAM/GFS APPEARED BEST WITH THE
SHORTWAVE DETAILS AROUND THE MN/IA MID LEVEL LOW. GFS APPEARED A BIT
BETTER WITH THE 12Z-18Z PRECIP ACROSS THE REGION. WITH NO CLEAR
MODEL FAVORITE BASED ON DPROG/DT AND 18Z TRENDS AND MODELS TRENDING
TOWARD A COMMON SOLUTION OF THEIR EARLIER RUNS...AT LEAST THRU THE
FIRST 36-48HRS...FAVORED THE MODEL/ENSEMBLE COMPROMISE. WITH
SOLUTIONS QUITE SIMILAR...SHORT TERM FORECAST CONFIDENCE GOOD THIS
CYCLE.

FOR THE SHORT TERM...MID LEVEL LOW WILL TRACK SOUTHEAST ACROSS IA
THIS AFTERNOON/EVENING THE EAST ACROSS NORTHERN IL TONIGHT. 700-
500MB DIFFLUENCE AND WARM ADVECTION NORTH OF THE MID LEVEL
CIRCULATION WRAP ACROSS THE AREA CENTERED ON THIS EVENING...ALONG
WITH 700-500MB QG DIVERGENCE. SFC-850MB COLD ADVECTION CONTINUES
OVER THE AREA ON THE WEST/BACK SIDE OF THE LOW LEVEL CIRCULATION
TONIGHT...WITH SFC-925MB TEMPS AND MAXIMUM WET-BULB ZEROS CONTINUING
TO COOL TO THE POINT WHERE PRECIP WOULD MIX WITH/EVENTUALLY CHANGE
OVER TO ALL -SN ACROSS THE FCST AREA. SFC TEMPS OVER THE AREA INTO
SOUTHWEST/WEST-CENTRAL MN ARE PROBLEMATIC...WITH MOST IN THE 33F TO
43F RANGE...UNDER A CLOUD BLANKET AND TEMPS UPSTREAM OF THIS ONLY IN
THE LOWER 30S. PER MODEL SOUNDINGS...SFC-925MB TEMPS AND WET BULB
ZEROS REMAIN AT OR ABOVE 0C OVER THE CENTRAL/EAST PARTS OF THE FCST
AREA UNTIL ABOUT THE TIME THE DEEPER FORCING/LIFT EXITS AND PRECIP
TAPERS OFF/ENDS ACROSS THE AREA LATER TONIGHT. WITH LACK OF A STRONG
BANDING /FN FORCING/ SIGNAL...APPEARS PRECIP RATES WILL REMAIN ON
THE LIGHT SIDE FOR THE MOST PART TONIGHT. GIVEN THIS AND GENERALLY
WARM GROUND...BELIEVE ANY -SN TONIGHT WILL STRUGGLE TO ACCUMULATE...
ESPECIALLY IN THE THE RIVER VALLEYS/LOWER ELEVATIONS. LEFT BULK OF
PRECIP TONIGHT AS -RASN MIX OVER CENTRAL/EAST PARTS OF THE FCST
AREA...WITH PREDOMINANTLY -SN OVER WEST THIRD TO HALF OF FCST AREA
AFTER MIDNIGHT. ANY SNOW ACCUMULATIONS GENERALLY LESS THAN AN
INCH AND MAINLY ON GRASSY AREAS/RIDGE TOPS. WITH GOOD MODEL SIGNAL
FOR THE FORCING SIGNAL TO BLOSSOM LIGHT PRECIP ACROSS THE FCST AREA
LATE THIS AFTERNOON/EVENING...DID RAISE PRECIP CHANCE TO 80-100
PERCENT ACROSS MUCH OF THE FCST AREA THIS EVENING...TAPERING DOWN
AFTER MIDNIGHT AS THE MID LEVEL LOW PASSES AND LIFT MOVES EAST OF
THE AREA. LINGERED A SMALL -SN CHANCE OVER THE FAR SOUTHEAST END OF
THE FCST AREA EARLY THU MORNING. WEATHER PATTERN FOR MUCH OF THU
THRU SAT DOMINATED BY SHORTWAVE RIDGING ALOFT. SFC-850MB SUBSIDENCE/
DRYING SPREAD ACROSS THE AREA DURING THE DAY THU...WITH CLOUDS
LOOKING TO DECREASE/CLEAR. SFC HIGH PRESSURE BUILDS IN/MOVES ACROSS
THE REGION FOR THU THRU FRI. FLATTENING OF THE RIDGE BY WEAK PIECES
OF SHORTWAVE ENERGY FRI/FRI NIGHT DEVELOPS A LOW IN THE NORTHERN
PLAINS. AS WEAK PIECE OF ENERGY CONTINUE TO RIPPLE THRU THE RIDGE
SAT/SAT NIGHT...THE SFC LOW/TROUGH/FRONT PUSHES INTO/ACROSS THE
AREA. MODEL SOUNDINGS/RH FIELDS AND X-SECTIONS INDICATE THE SFC-
700MB AIRMASS REMAINS QUITE DRY AS THE SFC LOW/TROUGH MOVES ACROSS
THE AREA...AND LEFT SAT/SAT NIGHT DRY FOR NOW.

WITH CLOUD BLANKET AND PRECIP TONIGHT...FAVORED WARMER OF GUIDANCE
LOWS AND THESE MAY STILL BE A BIT COOL. WITH SOME CLOUDS...AT LEAST
THU MORNING...AND CONTINUED BRISK NORTHWEST WINDS/COLD ADVECTION...
FAVORED COOLER OF GUIDANCE HIGHS. GENERALLY FAVORED A BLEND OF
GUIDANCE LOWS/HIGHS THU NIGHT NIGHT THRU FRI NIGHT. WITH THE
RETREATING HIGH AND INCREASING LOW LEVEL WARM ADVECTION SAT/SAT
NIGHT...FAVORED A BLEND OF HPC GUIDANCE AND WARMER 25.12Z GFS MEX
MOS HIGHS/LOWS.

.LONG TERM...SUNDAY THROUGH WEDNESDAY

MEDIUM RANGE MODEL RUNS OF 25.00Z IN RATHER GOOD AGREEMENT WITH EACH
OTHER SUN/MON AS THE NEXT TROUGH MOVES ACROSS THE UPPER MIDWEST...
MORE SO THAN THEIR RUNS OF 24.00Z. MODELS CONVERGING ON A TIMING OF
THE MID LEVEL TROUGH AXIS PASSING SUN NIGHT/MON WITH SHORTWAVE
RIDGING BUILDING IN MON NIGHT. BETWEEN MODEL AND RUN-T0-RUN
CONSISTENCY LEAVES A BIT TO BE DESIRED TUE/WED AS LONGWAVE TROUGHING
DEEPENS INTO CENTRAL NOAM. WITH THE INCREASING MODEL AGREEMENT SUN/
MON...FORECAST CONFIDENCE AVERAGE EARLY IN THE LONG TERM PERIOD...
TAILING OFF TO POOR BY WED WITH THE LESSER MODEL/RUN-TO-RUN
CONSISTENCY. ECMWF APPEARS AS A MEDIAN/BLEND OF GFS/GFS ENSEMBLE
MEAN/CAN-GEM/UKMET SUN/MON AS THE SFC LOW EXITS THE REGION AND HIGH
PRESSURE BUILDS IN FROM THE CENTRAL/NORTHERN PLAINS. COLDER...MORE
SEASONABLE AIRMASS SLIDES INTO THE REGION BEHIND THE DEPARTING LOW
SUN...PERHAPS ABLE TO SQUEEZE SOME SPRINKLES/FLURRIES OUT OF
THE AIRMASS SATURATED OR NEARLY SO BELOW 800MB...AND CARRIED A SMALL
-RA/-SN CHANCE SUN...SMALL -SN CHANCE SUN NIGHT. SUBSIDENCE/DRYER
AIRMASS SPREADS IN FOR MON INTO TUE WITH DRY CONDITIONS EXPECTED.
DEEPENING CENTRAL NOAM TROUGH AND SHORTWAVE ENERGY ROTATING THRU IT
DRIVES A COLD FRONT ACROSS THE REGION TUE NIGHT/WED. HOWEVER GIVEN
THE MODEL DIFFERENCES BY WED...NOT MUCH FOR CONFIDENCE IN ANY
TIMING/STRENGTH/MOISTURE DETAILS WITH THIS SYSTEM AND LEFT THESE
PERIODS DRY FOR NOW. HPC MODEL/ENSEMBLE BLEND GUIDANCE FOR DAYS 6/7
REASONABLE FOR NOW UNTIL BETTER MODEL CONSISTENCY DEVELOPS. DOES
APPEAR A CHUNK OF ARCTIC AIR WILL PULLED SOUTH INTO THE REGION
BEHIND THIS SYSTEM FOR LATE NEXT WEEK. HPC MAX/MIN TEMP GUIDANCE FOR
SUN-WED GENERALLY A BLEND OF GFS MEX/ENSEMBLE MOS GUIDANCE AND
APPEARS WELL TRENDED AT THIS TIME.

&&

.AVIATION...TONIGHT AND THURSDAY

SHORT WAVE TROUGH ROTATING ACROSS AREA WILL MAKE FOR COMPLEX WEATHER
NEXT 24 HOURS...INCLUDING MIX OF IFR AND MVFR FLIGHT CATEGORIES.
EVEN WITH RAIN SHIELD AHEAD OF WAVE...CONDITIONS HAVE IMPROVED AS
NORTHWEST WINDS HAVE INCREASED BRINGING MANY AREAS INTO VFR
CONDITIONS AT LEAST TEMPORARILY. WRAP AROUND PRECIPITATION IN
DEFORMATION AREA WILL ROTATE ACROSS SOUTHERN MINNESOTA AND NORTHERN
IOWA HEADING INTO THIS EVENING...EVENTUALLY ACROSS SOUTHERN
WISCONSIN. PRECIPITATION LIKELY TO START OFF AS SNOW OR A MIX OF
RAIN AND SNOW IN SOUTHEAST MINNESOTA BUT GRADUALLY TRANSITION FROM
WEST TO EAST HEADING INTO THE EVENING. AS THIS HAPPENS EXPECT
CEILINGS AND VISIBILITIES TO DROP BACK INTO IFR CATEGORIES MOST
AREAS BUT QUICKLY END AND IMPROVE EARLY THURSDAY AS WAVE EXITS TO
THE EAST. CLOUDS SHOULD BREAK UP BUT WINDS WILL INCREASE OUT OF THE
NORTHWEST GOING INTO DAYBREAK ON THANKSGIVING.

&&

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

$$

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