National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KARX 041150
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
550 AM CST WED DEC 4 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 402 AM CST WED DEC 4 2013

MAIN FORECAST CONCERNS THIS PACKAGE...FOG THIS MORNING...PRECIP
TODAY INTO THIS EVENING...TEMPERATURES TONIGHT.

DATA ANALYSIS AT 06Z HAD A 996MB LOW OVER THE OK/TX PANHANDLE AREA
WITH AN INVERTED TROUGH NORTHEAST THRU IA/WESTERN MN. WV IMAGERY
DEPICTED PLENTY OF SHORTWAVE ENERGY ROTATING THRU THE CENTRAL/
SOUTHERN ROCKIES. DEFORMATION BAND OF SNOW ASSOCIATED WITH 850-700MB
WARM ADVECTION/ISENTROPIC LIFT AND DIVERGENCE ALOFT AHEAD OF THE
LEAD PIECE OF SHORTWAVE ENERGY WAS SPREADING NORTHEAST ACROSS NEB/
SOUTHEAST SD/SOUTHWEST MN. FURTHER EAST...FORCING/LIFT WAS WEAKER...
WITH MAINLY PATCHY -DZ OR -FZDZ ACROSS THE FCST AREA. ABUNDANT AND
INCREASING LOW LEVEL MOISTURE COUPLED WITH COLD GROUND CONTINUED TO
RESULT IN WIDESPREAD MDT TO DENSE FOG.

04.00Z MODEL RUNS HAVE INITIALIZED WELL AND OFFER A CONTINUED
TIGHTENING CONSENSUS FOR TODAY/TONIGHT AS THE RATHER VIGOROUS SFC
THRU MID LEVEL TROUGH AXIS LIFTS THRU THE UPPER MIDWEST. ECMWF
REMAINS THE MODEL WITH THE BETTER RUN-TO-RUN CONSISTENCY IN THIS
TIME-FRAME...WITH RATHER GOOD CONSISTENCY BACK TO ITS 02.00Z RUN AND
CONSENSUS TIGHTENING TOWARD IT. CHECK OF OBS VS. MODEL DATA AT 06Z
SHOWED ALL TO BE QUITE REASONABLE WITH SFC LOW/TROUGH STRENGTH/
POSITION. PER WV IMAGERY...ALL LOOKED GOOD ON THE SHORTWAVE DETAILS
IN THE WESTERN CONUS TROUGH. MODELS/MODEL CONSENSUS ALL LOOK TO BE
DOING A DECENT JOB ON THE PRECIP ACROSS THE REGION EARLY THIS
MORNING. GIVEN THE TIGHT MODEL CONSENSUS THIS CYCLE AND SEEMINGLY
GOOD PERFORMANCE EARLY THIS MORNING...SHORT TERM FCST CONFIDENCE IS
GOOD THIS CYCLE. FAVORED THE MODEL/ENSEMBLE CONSENSUS.

FOR THE SHORT TERM...SHORT-TERM FORECASTER HAS ALREADY UPDATED FCSTS
FOR WINTER WEATHER ADVISORY FOR -FZDZ THRU 15Z GENERALLY ALONG/NORTH
OF I-90...WHERE SFC TEMPS ARE HOVERING NEAR OR JUST BELOW 32F. SFC
LOW LIFTING RAPIDLY TOWARD THE AREA THIS MORNING WITH A SHIFT TO
MORE SOUTHEAST BOUNDARY LAYER FLOW SHOULD HELP SFC TEMPS WARM ABOVE
32F BY MID MORNING.

SFC LOW TRACK TO NEAR KLSE BY 18Z...THEN TO NORTHEAST WI BY 00Z.
850MB LOW TRACKS FROM NORTHWEST IA AT 12Z TO NEAR KDLH BY 00Z. MAIN
BAND OF LOWER LEVEL THERMO-DYNAMIC FORCING FOLLOWS THE 850MB LOW
TRACK TODAY. TEMPS IN THE SFC-850MB AIRMASS SOUTHEAST OF THE 850MB
LOW TRACK GENERALLY ABOVE 0C...WITH THE BULK OF WHAT PRECIP FALLS
ACROSS THE FCST AREA TODAY AS -RA/-DZ. STILL POTENTIAL FOR A WINTRY
MIX/SOME ACCUMULATING SNOW ALONG/NORTH OF HWY 29 IN CLARK/TAYLOR
COUNTIES. MAIN LOWER LEVEL FORCING/LIFT PASSES NORTH OF THE FCST
AREA WITH PASSAGE OF THE SFC-850MB LOWS THIS AFTERNOON. WEST/
NORTHWEST FLOW BEHIND THESE LOWS PULLS IN THE COLDER AIR...CHANGING
PRECIP TYPE FROM LIQUID TO FROZEN...BUT BY THE TIME THE COLDER AIR
ARRIVES...LITTLE LIFT REMAINS. THUS SNOW AMOUNTS FOR ALL BUT THE FAR
NORTH END OF THE FCST AREA LOOKING QUITE MINOR. EVEN ACROSS THE FAR
NORTH END...THE 925-850MB WARM AIR INTRUSION IS LIKELY TO LIMIT SNOW
FALL THIS AFTERNOON. FORCING/LIFT EXIT RATHER QUICKLY THIS
EVENING...WITH THE AREA DOMINATED BY LOW LEVEL COLD ADVECTION
TONIGHT. CARRIED RATHER HIGH -RA/-DZ/-SN CHANCES ACROSS THE CENTRAL
AND NORTH PARTS OF THE FCST AREA TODAY...TAPERING OFF RATHER QUICKLY
LATE THIS AFTERNOON/EARLY THIS EVENING AS THE LOW/TROUGH AXIS PASS.
WINTER WEATHER ADVISORY FOR CLARK/TAYLOR NOT LIKELY TO BE NEEDED
MUCH PAST MID EVENING...BUT WILL NOT GET CUTE WITH EXPIRATION AT
THIS TIME. EVENING CREW CAN COORDINATE WITH NEIGHBORS ON EXPIRING/
CANCELING ANY HEADLINES AS NEEDED FOR TONIGHT. CONSIDERABLE 925-
850MB MOISTURE WRAPS AROUND THE DEPARTING LOW...FOR CONTINUED CLOUDY
SKIES TONIGHT. ARCTIC AIR POURS IN TONIGHT BEHIND THE PASSING
LOW/TROUGH...WITH 925MB TEMPS ALREADY IN THE -10C TO -16C RANGE BY
12Z THU. MDT/STRONG PRESSURE GRADIENT SPREADS ACROSS THE AREA
TONIGHT...WITH WEST TO NORTHWEST WINDS OF 10-20MPH AND GUSTY ALREADY
PRODUCING WIND CHILLS OF -5 TO +10 BY 12Z THU. WITH PLENTY OF
CLOUDS/PRECIP TODAY AND WINDS FOR MIXING TONIGHT...USED A BLEND OF
THE GUIDANCE HIGHS/LOWS.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 402 AM CST WED DEC 4 2013

MAIN FORECAST CONCERNS FOR THURSDAY THROUGH FRIDAY NIGHT...ARCTIC
HIGH PRESSURE AND TEMPERATURES THRU THE PERIOD.

04.00Z MODELS REMAIN IN GOOD AND IMPROVING AGREEMENT FOR THU THRU
FRI NIGHT AS THE SFC-MID LEVEL LOW CONTINUE QUICKLY NORTHEAST OF THE
REGION AND LONGWAVE TROUGHING/ARCTIC HIGH PRESSURE SET UP SHOP OVER
CENTRAL NOAM. THU THRU FRI NIGHT REMAIN TRENDED TOWARD A QUIET/COLD
WEATHER PERIOD AND FCST CONFIDENCE IS GOOD.

SFC THRU MID LEVEL LOW CONTINUE TO EXIT QUICKLY NORTHEAST OF THE
AREA THU. QUESTION BECOMES HOW LONG WITH THE LOWER STRATUS DECKS
HANG AROUND. RATHER STRONG CYCLONIC LOWER LEVEL FLOW REMAINS OVER
THE AREA THU...WITH MDT 925-850MB MOISTURE IN THE WRAP-AROUND FLOW.
WITH STEEP LOW LEVEL LAPSE RATES AND THE COLD AIR ALOFT...APPEARS
CLOUDS WILL BE TOUGH TO GET RID OF ON THU EVEN UNDER DEEPER LAYERED
SUBSIDENCE. 925-850MB CYCLONIC FLOW RELAXES THU NIGHT/FRI WITH
BETTER MODEL CONSENSUS FOR SOME DRYING IN THIS LAYER. PARTLY CLOUDY/
MOSTLY CLEAR SKIES EXPECTED THU NIGHT THRU FRI NIGHT. LOWER LEVEL
COLD ADVECTION CONTINUES THU THRU FRI NIGHT AS THE ARCTIC HIGH
BUILDS INTO THE NORTH-CENTRAL CONUS WITH 925MB TEMPS BOTTOMING OUT
IN THE -16C TO -20C RANGE. PRESSURE GRADIENT OVER THE AREA ONLY
SLOWLY RELAXES THRU THE THU TO FRI NIGHT PERIOD. WEST-NORTHWEST
WINDS WINDS ONLY DROP OFF INTO THE 5-10MPH RANGE FRI NIGHT. WINDS
FOR BOUNDARY LAYER MIXING OVER WHAT SHOULD BE SNOW-FREE GROUND
ACROSS MUCH OF THE FCST AREA SHOULD KEEP LOWS FROM BOTTOMING OUT
WELL BELOW ZERO. MIXED 925MB TEMPS BOTH THU/FRI NIGHTS INDICATE MANY
LOWS IN THE ZERO TO 10 ABOVE RANGE ACROSS THE FCST AREA. WITH EITHER
CLOUDS OR WINDS FOR MIXING...USED A BLEND OF THE GUIDANCE HIGHS/LOWS
FOR THU THRU FRI NIGHT.

FOR SATURDAY THROUGH TUESDAY.../DAYS 4 TO 7/...

04.00Z MEDIUM RANGE MODELS IN QUITE GOOD AGREEMENT SAT/SUN AS THE
FLOW TURNS BACK TO THE SOUTHWEST OVER THE REGION AND NEW ENERGY/
TROUGHING DIGS INTO THE ROCKIES. ECMWF AGAIN THE MODEL WITH THE
BETTER RUN-TO-RUN CONSISTENCY AND GFS/CAN MODELS TRENDING TOWARD IT.
SURPRISINGLY GOOD CONSISTENCY FOR SOME NORTHERN/SOUTHERN STREAM
SHORTWAVE INTERACTION/PHASING OVER THE CENTRAL CONUS SUN AND A
STRONGER PIECE OF SHORTWAVE ENERGY EJECTING ACROSS THE MID/UPPER MS
VALLEY SUN NIGHT. MODELS REMAIN IN GOOD AGREEMENT MON/TUE AS
LONGWAVE TROUGHING SLOWLY MOVES EAST ACROSS THE UPPER MIDWEST. FCST
CONFIDENCE IN THE DAY 4 TO 7 PERIOD IS ALSO GOOD THIS CYCLE.

CENTER OF THE ARCTIC HIGH MOVES ACROSS THE REGION SAT/SAT NIGHT.
COLDEST LOWS EXPECTED SAT NIGHT WITH LIGHT WINDS UNDER THE CENTER OF
THE HIGH. HIGH DRIFTS EAST RATHER QUICKLY SUN...WITH FALLING
PRESSURES AND INCREASING SOUTHWEST FLOW ACROSS THE CENTRAL
PLAINS/UPPER MIDWEST. THIS FLOW AND THE SHORTWAVE LIFTING OUT OF THE
ROCKIES SENDS A ROUND OF INCREASING 925-500MB MOISTURE AND 275-290K
ISENTROPIC LIFT ACROSS THE REGION CENTERED ON SUNDAY NIGHT...ALONG
WITH PV ADVECTION/DIVERGENCE ALOFT. CONSISTENT/IMPROVING SIGNAL FOR
THIS FORCING/LIFT TO PRODUCE A SNOW EVENT ACROSS THE FCST AREA
CENTERED ON SUN NIGHT. DID RAISE SNOW CHANCES FOR SUN NIGHT INTO THE
40 TO 55 PERCENT RANGE. AFTER A BIT OF A WARM-UP SUN/SUN NIGHT/MON
UNDER THE SOUTHWEST FLOW ALOFT/WARM ADVECTION/MORE CLOUDS...LOW
LEVEL COLD ADVECTION SENDS 925MB TEMPS INTO THE -20C TO -24C RANGE
FOR MON NIGHT. LOW LEVEL MOISTURE/CLOUDS APPEAR TO LINGER THRU MON
NIGHT...ALONG WITH MDT WEST TO NORTHWEST BOUNDARY LAYER WINDS FOR
MIXING. EVEN SO...APPEARS MOST LOCATIONS LOOKING AT SUB-ZERO LOWS BY
TUE MORNING. OTHER THAN SUN NIGHT SNOW CHANCES...MODEL/ENSEMBLE
CONSENSUS OF PRECIP CHANCES AND HIGHS/LOWS FOR SAT THRU TUE LOOKED
WELL TRENDED.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 550 AM CST WED DEC 4 2013

LOW FLIGHT CONDITIONS TO CONTINUE INTO TONIGHT AS A LOW PRESSURE
SYSTEM MOVES UP INTO THE REGION. CEILINGS IN THE 200-600FT RANGE
WITH VISIBILITIES IN THE 1/2SM-3SM RANGE WILL PERSIST THROUGH THE
MORNING AND AFTERNOON HOURS BEFORE A COLD FRONT MOVES THROUGH BY
THIS EVENING. CONDITIONS ARE EXPECTED TO GRADUALLY IMPROVE...BUT
IFR CEILINGS WILL LIKELY HOLD ON INTO TOMORROW MORNING.
PRECIPITATION IS MAINLY EXPECTED TO BE IN THE FORM OF DRIZZLE OR
FREEZING DRIZZLE BEFORE SOME MORE WIDESPREAD SHOWERS MOVE IN THIS
AFTERNOON. WINDS WILL SWING AROUND FROM THE EAST TO THE SOUTHEAST
THIS MORNING AND THEN TO THE WEST AFTER THE COLD FRONT COMES
THROUGH. WINDS WILL BECOME GUSTY LATE THIS AFTERNOON INTO TONIGHT
WITH SOME GUSTS IN THE 20-30KT RANGE.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR WIZ032>034-041>044-
     053>055-061.

     WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR
     WIZ032>034-041>044.

     WINTER WEATHER ADVISORY UNTIL 6 AM CST THURSDAY FOR WIZ017-029.

MN...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR MNZ079-086>088-
     094>096.

     WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR MNZ079-
     086>088.

IA...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR IAZ008>011-018-019-
     029-030.

&&

$$

SHORT TERM...RRS
LONG TERM....RRS
AVIATION...HALBACH