Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191140
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
540 AM CST FRI DEC 19 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 333 AM CST FRI DEC 19 2014

THE MAIN FORECAST CHALLENGE INTO TONIGHT IS WITH THE LOW LEVEL
MOISTURE AND WHETHER IT WILL BE ENOUGH TO PRODUCE SOME FREEZING
DRIZZLE OR FLURRIES.

CURRENTLY...A BAND OF 1-2KFT STRATUS THAT EXTENDS FROM NORTHWEST
WISCONSIN DOWN THROUGH SOUTHERN WISCONSIN HAS BEEN PRODUCING SOME
FLURRIES DUE TO SOME WEAK LIFT ASSOCIATED WITH A COLD FRONT THAT
EXTENDS FROM SOUTHERN MICHIGAN WEST-NORTHWEST INTO WESTERN
WISCONSIN. THIS FEATURE WILL PULL EASTWARD THIS MORNING/AFTERNOON
AND SHOULD TAKE THESE FLURRIES EAST AS WELL. TO THE SOUTHWEST
TOWARD DES MOINES...ANOTHER BAND OF LOW LEVEL MOISTURE ASSOCIATED
WITH SOME RETURN SOUTHERLY FLOW/WARM AIR ADVECTION HAS FORMED SOME
FREEZING DRIZZLE AND FLURRIES IN THAT REGION. THE QUESTION FOR
TODAY/TONIGHT IS WHETHER THAT FREEZING DRIZZLE/FLURRIES HOLDS
TOGETHER.

19.00Z NAM/GFS AND 19.06Z RAP SOUNDINGS CERTAINLY SHOW THE SURFACE
TO 800MB LAYER MOISTENING UP THROUGH TONIGHT...ITS JUST A MATTER
OF WHETHER THERE IS ANY LIFT THERE. GIVEN THAT THERE CURRENTLY IS
SOME PRECIPITATION OCCURRING UPSTREAM...THERE DOES APPEAR TO BE
ENOUGH LIFT AND HAVE GONE AHEAD AND ADDED A MENTION OF SOME
PATCHY FREEZING DRIZZLE IN FOR TODAY IN SE MN/NE IA WITH IT
SPREADING EASTWARD OVERNIGHT AS THE MOISTURE SHIFTS EAST. DMX HAS
REPORTED SOME FLURRIES OCCURRING AS WELL AT THE MOMENT MEANING
THAT THERE IS SOME ICE BEING INTRODUCED IN THE LOW LEVELS THOUGH
MOST OF THE FORECAST SOUNDINGS SHOW THAT SATURATED LAYER BEING TOO
WARM TONIGHT TO PRODUCE ANY FLURRIES LOCALLY. NOT SURE WHETHER
THIS FREEZING DRIZZLE IS GOING TO BE ADVISORY WORTHY GIVEN THAT
THERE IS NOT MUCH FOCUS FOR LOW LEVEL LIFT...BUT CONDITIONS WILL
HAVE TO BE MONITORED SINCE AIR/ROAD TEMPERATURES WILL BE BELOW
FREEZING.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 333 AM CST FRI DEC 19 2014

THE PATTERN BECOMES MORE ACTIVE GOING INTO THE LATER PORTION OF
THE WEEKEND ON INTO EARLY NEXT WEEK AS A SERIES OF MID LEVEL SHORT
WAVE TROUGHS PROPAGATE ON THROUGH. THE NEXT DECENT CHANCE FOR
PRECIPITATION APPEARS TO COME IN ON SUNDAY AS LOW LEVEL WARM AIR
ADVECTION WILL COMBING WITH SOME WEAK 700MB TROUGHING TO DEVELOP
SOME PRECIPITATION. PRECIPITATION TYPE IS TRICKY WITH THIS SYSTEM
AS THERE IS A WEAK WARM LAYER THAT REACHES +1 TO +2C AND WOULD
MELT SOME OF THE SNOW THAT FALLS THROUGH IT. THERE ALSO APPEARS
TO BE A DRY LAYER BETWEEN THE 700MB MOISTURE AND SURFACE/LOW LEVEL
MOISTURE WHICH BRINGS INTO QUESTION HOW DEEP THE LIFT REALLY WILL
BE. SURFACE TEMPERATURES WILL ALSO BE CLIMBING TOWARD AND ABOVE
FREEZING WHICH COMPLICATES HOW MUCH SNOW COULD ACCUMULATE. KEPT
SNOW ACCUMULATIONS ON THE LOW SIDE...HALF INCH OR LESS...GIVEN ALL
OF THE QUESTIONS WITH THIS ROUND OF PRECIP.

A DEEPER TROUGH DEVELOPS ACROSS THE DAKOTAS SUNDAY NIGHT INTO
TUESDAY AND WILL BRING A MORE WIDESPREAD SHOT OF
PRECIPITATION...MAINLY RAIN BEFORE CHANGING OVER TO SNOW ON THE
BACKSIDE TUESDAY. THE 19.00Z GFS/ECMWF ARE IN DECENT AGREEMENT
WITH THIS SYSTEM IN REGARD TO TIMING BUT ARE DIFFERENT WITH THEIR
PROGRESSION OF THE SURFACE LOW WITH THE GFS DIGGING DEEPER EARLIER
WITH THE ECMWF KEEPING PRECIPITATION AROUND A TAD LONGER. BOTH
MODELS HAVE THE SNOW OFF TO THE EAST BY CHRISTMAS DAY WITH JUST
SOME WEST TO NORTHWEST WINDS IN THE WAKE OF THE SYSTEM.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 540 AM CST FRI DEC 19 2014

EXTENSIVE DECK OF MVFR CLOUD COVER IN PLACE ACROSS THE REGION.
THERE IS A THIN SLIVER OF VFR CLOUD CIGS EXTENDING FROM VCNTY KRST
SOUTHEASTWARD INTO NORTHEAST IA...BUT THINKING THIS WILL QUICKLY
FILL IN WITH MVFR CLOUD AS WELL THIS MORNING. IN ADDITION...SOME
PATCHY FREEZING DRIZZLE MAY SEEN ACROSS PORTIONS OF NORTHEAST IA
INTO SOUTHEAST MN BY MID-MORNING INTO THIS AFTERNOON AS SOUTHERLY
FLOW BRINGS MORE MOISTURE INTO THE AREA AHEAD OF A TROUGH OF LOW
PRESSURE MOVING OUT OF THE PLAINS.EXPECTING PATCHY FREEZING
DRIZZLE TO SPREAD EAST OF THE MISSISSIPPI LATER TONIGHT INTO
SATURDAY MORNING AS THE TROUGH MOVES INTO THE REGION. SINCE THIS
FREEZING DRIZZLE IS EXPECTED TO BE PATCHY IN NATURE...DECIDED TO
KEEP OUT OF THE BODY OF THE TAF FOR NOW...BUT WILL CONTINUE TO
MONITOR CLOSELY. OTHERWISE...LOOK FOR KRST CIGS TO SLIP FROM MVFR
TODAY INTO IFR AFTER 04Z.

&&

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

$$

SHORT TERM...HALBACH
LONG TERM...HALBACH
AVIATION...DAS


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