Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 232318
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
520 PM CST TUE DEC 23 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 202 PM CST TUE DEC 23 2014

FORECAST CHALLENGES INCLUDE LINGERING LIGHT PRECIPITATION TONIGHT
INTO WEDNESDAY AND THEN LOW-END PRECIPITATION CHANCES AGAIN
FRIDAY/FRIDAY NIGHT. 23.12Z GFS/NAM/ECMWF/GEM ARE IN GOOD
AGREEMENT THROUGH 26.12Z...DIVERGING SOMEWHAT THEREAFTER WITH THE
LATE WEEK SYSTEM. WILL USE A BLENDED MODEL SOLUTION.

FOR TONIGHT...SURFACE LOW CURRENTLY ACROSS CENTRAL WI WILL QUICKLY
EJECT INTO SOUTHEAST ONTARIO. DEFORMATION PRECIPITATION AXIS WILL
CONTINUE TO DISSIPATE ACROSS THE FORECAST AREA...BUT WITH MODEL
SOUNDINGS SUGGESTING A LOSS OF ICE IN THE CLOUD...WILL TRANSITION
FROM RAIN/SNOW THIS EVENING TO MAINLY DRIZZLE AFTER MIDNIGHT.
SURFACE TEMPERATURES WILL HOVER RIGHT AROUND THE FREEZING
MARK...SO THERE COULD BE SOME PATCHY ICING FOR ANY AREA THAT
EXPERIENCES MORE CONTINUOUS DRIZZLE. OTHERWISE...CONDITIONS SHOULD
GRADUALLY IMPROVE WITH ONLY MINOR ADDITIONAL SNOW ACCUMULATION.

A STRONG SECONDARY SURFACE LOW WILL SURGE NORTHWARD AND ACROSS
MICHIGAN ON WEDNESDAY AS THE PRIMARY TROUGH ALOFT LIFTS INTO THE
GREAT LAKES REGION. THE PRECIPITATION SHIELD WITH THIS SYSTEM
WILL PRIMARILY IMPACT IL/EASTERN WI AND INTO IN/MI...BUT ITS
WESTERN FLANK COULD CLIP THE EASTERN FORECAST AREA. MOST OF
WEDNESDAY WILL BE DRY...BUT KEPT 20 POPS EAST OF THE MISSISSIPPI
RIVER FOR SOME LIGHT SNOW AND POSSIBLE ACCUMULATIONS AROUND A
TENTH OR TWO. OTHERWISE...WEDNESDAY WILL BE CLOUDY WITH A MODEST
NORTHWEST BREEZE AND TEMPERATURES TOPPING OUT IN THE MID 30S.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 202 PM CST TUE DEC 23 2014

CHRISTMAS DAY WILL BE MOSTLY CLOUDY...BUT DRY AS A SURFACE RIDGE
MOVES ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. NO REAL CHANGE IN
AIR MASS...SO TEMPERATURES WILL REMAIN STEADY IN THE 30S.

THE NEXT PACIFIC TROUGH DIGS INTO THE SOUTHERN ROCKIES CHRISTMAS
NIGHT INTO FRIDAY WITH ITS SURFACE LOW MOVING FROM THE LEE OF THE
ROCKIES INTO THE UPPER MIDWEST. PRECIPITATION EXPECTED ALONG THE
850 TO 700 HPA THERMAL GRADIENT...BUT DIFFERENCES ARISE CONCERNING
ITS PLACEMENT. 23.12Z ECMWF/GEM KEEP MAJORITY OF PRECIPITATION
NORTH OF THE FORECAST AREA...WHERES THE GFS/NAM ARE A BIT MORE
BULLISH ON LIGHT QPF...ESPECIALLY FRIDAY AFTERNOON AND EVENING.
TRIMMED POPS ACROSS THE SOUTH ON FRIDAY...BUT KEPT 20-30 POPS
REGION-WIDE FRIDAY NIGHT FOR SOME LIGHT SNOW.

SATURDAY THROUGH TUESDAY WILL BE MOSTLY DRY AS A NORTHWEST FLOW
SYNOPTIC REGIME SETS-UP ACROSS THE UPPER MIDWEST. A COUPLE LIGHT
SNOW EPISODES ARE POSSIBLE...BUT DIFFERENCES IN TIMING AND
STRENGTH OF SHORT-WAVES ROTATING AROUND THE PARENT HUDSON BAY
TROUGH LENDS ITSELF TO LOW CONFIDENCE AND ONLY 20 POPS MONDAY/
MONDAY NIGHT. BIGGER STORY WILL BE MUCH COOLER TEMPERATURES WITH
DAILY HIGHS IN THE UPPER TEENS AND 20S AND NIGHTTIME LOWS IN THE
SINGLE DIGITS TO TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 520 PM CST TUE DEC 23 2014

LOW MVFR/IFR CIGS EXTENDED WELL WEST INTO THE DAKOTAS AND CENTRAL
PLAINS EARLY THIS EVENING...PER LATEST SFC OBS AND FOG/STRATUS
SATELLITE IMAGERY. NAM RH FIELDS/BUFKIT SOUNDINGS SUGGEST NO CHANGE
IN THE LOW CIGS UNTIL CHRISTMAS NIGHT...WHILE THE GFS POINTS TO A
POSSIBLE BREAK BY XMAS MORNING. GOING TO STAY ON THE PESSIMISTIC
SIDE.

WITH THE AMPLE LOW LEVEL MOISTURE HOLDING FAST UNDER THE
INVERSION...COULD HAVE SOME VSBY REDUCTIONS FROM BR AND POTENTIALLY
-DZ. RAP POINTS TO SOME ISENTROPIC LIFT THROUGH THE SATURATED LAYER
THROUGH THE NIGHT...WHILE THE NAM HINTS AT WEAK FRONTOGENETIC LIFT
AROUND A SFC BOUNDARY. BUFKIT SOUNDINGS FAVORING NO ICE IN THE
CLOUD...AND THUS -DZ FOR ANY PCPN TYPE. SFC TEMPS STAYING ABOVE
FREEZING FOR THE MOST PART. WILL NOT ADD PCPN TO THE FORECAST RIGHT
NOW...BUT IT NEEDS WATCHING. WILL ADD IN SOME MVFR BR.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...

WI...NONE.
MN...NONE.
IA...NONE.

&&

$$

SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION.....RIECK



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