Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 192115
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
315 PM CST WED NOV 19 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 315 PM CST WED NOV 19 2014

THE MAIN FOCUS INTO TOMORROW IS WITH CLOUD COVER/FLURRIES
POTENTIAL AND HOW LONG IT WILL LINGER INTO TONIGHT/TOMORROW.

CURRENTLY...THE REGION IS IN THE CYCLONIC NORTHWEST FLOW SIDE OF A
LONG WAVE MID LEVEL TROUGH THAT COVERS THE EASTERN HALF OF THE US.
A SURGE OF COLDER LOW LEVEL AIR HAS BEEN ADVECTED INTO THE REGION
FROM SOUTH CENTRAL CANADA WHICH HAS SET UP SOME STEEP LOW LEVEL
LAPSE RATES. THIS HAS PROVIDED ENOUGH LIFT TO PRODUCE SOME
STRATOCUMULUS AND SNOW SHOWERS AS THIS WAVE MOVED IN. LAPSE RATES
LOOK LIKE THEY STAY ABOUT THE SAME INTO TONIGHT...BUT THE OVERALL
LIFT IS NOT AS STRONG WITH THE LOW LEVEL TEMPS STAYING ABOUT THE
SAME. DUE TO THE TIGHT PRESSURE GRADIENT...WINDS WILL REMAIN GUSTY
OUT THE WEST-NORTHWEST AS WELL AND KEEP SOME MINOR
BLOWING/DRIFTING OF SNOW GOING IN OPEN AREA. SOME MINOR
ACCUMULATIONS OF UP TO A HALF INCH WILL BE POSSIBLE WITH THE SNOW
SHOWERS LATE THIS AFTERNOON INTO THE EARLY EVENING.

CLOUD COVER IS GOING TO BE TRICKY OVERNIGHT INTO TOMORROW AND HAVE
PLAYED IT ON THE PESSIMISTIC SIDE AS FORECAST SOUNDINGS FROM THE
RAP/NAM/GFS ALL KEEP SOME HIGHER RH IN THE LOW LEVELS. THINKING
THAT WHILE THERE WILL BE SOME POCKETS OF CLEARING...THE WIDESPREAD
CLEARING LIKELY WILL NOT MAKE IT IN UNTIL THE SURFACE RIDGE AXIS
MOVES IN THURSDAY NIGHT. DUE TO THIS EXTRA CLOUD COVER...BUMPED
UP LOW TEMPERATURES TONIGHT A FEW DEGREES.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 315 PM CST WED NOV 19 2014

THE MAIN FOCUS IN THE EXTENDED PERIOD IS WITH THE NEXT SYSTEM THAT
WILL MOVE IN THIS WEEKEND AND BRING WARMER AIR IN WITH IT ALONG
WITH A CHANCE FOR FREEZING DRIZZLE.

AS THE RIDGE AXIS MOVES THROUGH THURSDAY NIGHT...WARMER LOW LEVEL
AIR WILL MOVE IN FROM THE SOUTHWEST AS THE FLOW BECOMES MORE
SOUTHWESTERLY FRIDAY. 850MB TEMPERATURES WILL IMPROVE FROM -20C
THURSDAY TO +5 BY LATE FRIDAY NIGHT/SATURDAY. WHILE THIS WARMER
AIR ALOFT TWILL BE MOVING IN FRIDAY NIGHT...SURFACE TEMPERATURES
WILL STILL BE WELL BELOW FREEZING. FORECAST SOUNDINGS FROM THE
GFS/NAM HAVE BEEN VERY CONSISTENT OVER THE PAST NUMBER OF RUNS
SHOWING THE LOW LEVELS SATURATING OUT FROM THE SOUTH AROUND
MIDNIGHT FRIDAY ON INTO SATURDAY MORNING. WITH THE WEAK...SHALLOW
LIFT...SATURATION DOES NOT OCCUR ALOFT SO THERE IS NO ICE
INTRODUCED INTO THE COLUMN. USING THE TOP-DOWN METHOD...IT WOULD
SUGGEST THAT WHATEVER MAKES IT TO THE GROUND WOULD BE IN THE FORM
OF A LIQUID. THE SHALLOW SUB-FREEZING LAYER IS UNDER 1KFT AND
JUST BARELY GETS TO -6C FOR A VERY BRIEF PERIOD OVERNIGHT BEFORE
WARMER AIR MOVES IN...SO DO NOT THINK THAT IT WILL BE COLD ENOUGH
TO REFREEZE BACK INTO SLEET. OVERALL...THIS LOOKS TO BE A DRIZZLE
SOUNDING LATE FRIDAY NIGHT THROUGH SATURDAY NIGHT WITH THE WEAK
LIFT AND SATURATED LOW LEVEL INVERSION. THE MAIN PERIOD OF CONCERN
IS SATURDAY MORNING WHEN THOSE SURFACE TEMPERATURES WILL BE WELL
BELOW FREEZING AND SOME ICING IS POSSIBLE. ANOTHER POTENTIAL
HAZARD IS WITH DENSE FOG SATURDAY NIGHT AS THE WARMER AIR AND
DRIZZLE HELPS TO ERODE THE SNOWPACK UNDER THE STRONG SHALLOW
INVERSION.

A PAIR OF MID LEVEL SHORTWAVE TROUGHS WILL CONVERGE ON THE AREA
SUNDAY AND PRODUCE SOME MUCH DEEPER LIFT AND WIDESPREAD
RAIN...PARTICULARLY IN WISCONSIN PER THE 19.12Z GFS/GEM. THE
19.12Z ECMWF IS A TAD FURTHER WEST AND WOULD PRODUCE SOME HEAVIER
RAINS FURTHER WEST ON SUNDAY. FAIRLY CONFIDENT THAT THIS WILL ALL
BE IN THE FORM OF RAIN AS THE WARM LAYER IS WELL ABOVE FREEZING
UNTIL SUNDAY NIGHT INTO MONDAY WHEN THE COLDER AIR MOVES IN. A
SECONDARY COLD FRONT WILL ROUND THE SOUTHWESTERN PERIPHERY OF THE
SURFACE LOW SUNDAY NIGHT INTO MONDAY AND MARK THE BEGINNING OF
ANOTHER LONG PERIOD OF COLD AIR THAT WILL LIKELY RESIDE ACROSS THE
REGION INTO THANKSGIVING.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1154 AM CST WED NOV 19 2014

SNOW SHOWERS WILL CONTINUE AT THE TAF SITES THROUGH THIS AFTERNOON
REDUCING THE VISIBILITIES TO AROUND 5 SM AT TIMES.
ALSO...NORTHWEST  WINDS OF 17 TO 20 KTS...GUSTING TO AROUND 30
KTS AT TIMES...WILL CREATE AREAS OF BLOWING SNOW AT KRST. PLAN ON
VISIBILITIES BEING REDUCED TO AROUND 4 MILES AT TIMES...AND
POSSIBLY AS LOW AS 2 MILES BRIEFLY. WINDS WILL SUBSIDE INTO THE
10 TO 12 KT RANGE LATE THIS AFTERNOON INTO EARLY THIS EVENING AND
THE SNOW SHOWERS ARE EXPECTED TO TAPER OFF TO FLURRIES. PLAN ON
MVFR CONDITIONS DURING THE OVERNIGHT HOURS WITH STRATUS IN PLACE.
LOOK FOR CEILINGS IN THE 2500 TO 3500 FT RANGE.


&&

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

$$

SHORT TERM...HALBACH
LONG TERM...HALBACH
AVIATION...WETENKAMP



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