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000
FXUS63 KARX 102058
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
258 PM CST TUE DEC 10 2013

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 258 PM CST TUE DEC 10 2013

FOCUS OF THE FORECAST IS ON THE SNOW CHANCES TONIGHT FOLLOWED BY
AN INCREASE IN THE WINDS THAT WILL CREATE WIND CHILLS IN THE
ADVISORY RANGE AND POSSIBLY SOME BLOWING SNOW.

WATER VAPOR SATELLITE SHOWS TWO SHORT WAVE TROUGHS DROPPING OUT OF
SOUTHERN CANADA THIS AFTERNOON. THESE TWO WAVES WILL MOVE ACROSS
THE UPPER MIDWEST TONIGHT PRODUCING SOME WEAK TO MODERATE PV
ADVECTION IN THE 500-300 MB LAYER OVERNIGHT. THE WAVES ARE
EXPECTED TO PRODUCE MODERATE TO STRONG QG CONVERGENCE IN THE
1000-700 MB LAYER WITH WEAK CONVERGENCE UP THROUGH 500 MB. GOOD
ISENTROPIC UP GLIDE AHEAD OF THE WAVE SHOULD OCCUR WITH BETWEEN 2
AND 4 UBAR/S EXPECTED ON THE 270K SURFACE. THIS FORCING WILL BE
ENOUGH FOR SATURATION TO OCCUR AND A QUICK MOVING BAND OF SNOW TO
FALL MAINLY SOUTH OF A KAUM TO KOVS LINE. SNOWFALL AMOUNTS IN THE
AREA SHOULD BE 1 TO 2 INCHES WITH SOME ISOLATED 3 INCH AMOUNTS.
ONCE THE SURFACE LOW GOES BY WITH THIS SYSTEM...THE WINDS WILL
SWITCH AROUND TO THE NORTHWEST AND INCREASE TO SUSTAINED SPEEDS OF
15 TO 20 MPH WITH GUSTS APPROACHING 30 MPH FOR A SHORT PERIOD
BETWEEN 09Z AND 15Z. THESE WINDS WILL BE ENOUGH TO PUSH THE
APPARENT TEMPERATURE DOWN INTO ADVISORY CRITERIA AND POSSIBLY KICK
UP SOME OF THE FRESH SNOW. PLAN TO ISSUE A WINTER WEATHER ADVISORY
ACROSS NORTHEAST IOWA INTO SOUTHWEST WISCONSIN TO HANDLE THE
FALLING SNOW...WIND CHILLS AND POTENTIAL FOR SOME BLOWING SNOW.
EXPECT THAT THIS WILL NEED TO BE SWITCHED OVER TO A WIND CHILL
ADVISORY WEDNESDAY MORNING AS THE WINDS START TO DIE DOWN AND THE
BLOWING/DRIFTING SNOW ENDS. NO CHANGES PLANNED TO THE OTHER
EXISTING ADVISORIES AS WIND CHILLS WILL STILL EXPECTED TO DROP
INTO THE 20 TO 35 BELOW RANGE WEDNESDAY MORNING.

THE WIND CHILL ADVISORY FOR LATE WEDNESDAY AFTERNOON AND NIGHT
WILL LIKELY NEED TO BE EXPANDED TO COVER A GOOD SHARE OF THE AREA.
WIND CHILLS OF 20 TO 30 BELOW SHOULD OCCUR FOR ALL BUT SOUTHWEST
WISCONSIN AND A SMALL PART OF NORTHEAST IOWA. BUT WILL LET THESE
HEADLINES BE CHANGED LATER ONCE THE AREA IS PAST THE WINTER
WEATHER ADVISORY. TEMPERATURES SHOULD START TO RISE OVERNIGHT
WEDNESDAY AHEAD OF THE NEXT SYSTEM. THE NEXT FAST MOVING SHORT
WAVE TROUGH WILL MOVE OUT OF CANADA ON THE NORTHWEST FLOW ALOFT.
RIGHT NOW...THE FORCING DOES NOT LOOK THAT IMPRESSIVE WITH THIS
WAVE. ONLY WEAK QG CONVERGENCE IS EXPECTED IN THE 1000-850 MB
LAYER WITH 1 TO 2 UBAR/S OF UP GLIDE ON THE 270K ISENTROPIC
SURFACE. CONCERNED THAT THIS MAY NOT BE ENOUGH FOR SATURATION...
SO HELD THE SNOW CHANCES IN THE 20 TO 30 PERCENT RANGE FOR LATE
WEDNESDAY NIGHT INTO THURSDAY MORNING.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 258 PM CST TUE DEC 10 2013

THE CHANCES FOR PRECIPITATION IN THE EXTENDED WILL BE CENTERED
AROUND FRIDAY NIGHT THROUGH SATURDAY NIGHT. STILL SOME UNCERTAINTY
ON HOW THIS WILL PLAY OUT AS IT DEPENDS ON HOW MUCH INTERACTION
THERE WILL BE BETWEEN THE NORTHERN AND SOUTHERN STREAMS. RIGHT NOW
THE MODELS ARE IN FAIRLY GOOD AGREEMENT THAT A SOUTHERN STREAM
SHORT WAVE TROUGH WILL EJECT OUT OF THE DESERT SOUTHWEST AND MOVE
TOWARD THE OHIO RIVER VALLEY AHEAD OF STRONG NORTHERN STREAM SHORT
WAVE TROUGH AND UPPER LEVEL LOW COMING DOWN FROM HUDSONS BAY.
INITIALLY AT THE SURFACE...A LOW WILL BE ASSOCIATED WITH THE
SOUTHERN STREAM WAVE AND MOVE TOWARD THE OHIO RIVER VALLEY. AN
INVERTED TROUGH OF LOW PRESSURE IS EXPECTED TO THEN DEVELOP NORTH
OF THIS LOW AS THE FORCING FROM THE NORTHERN STREAM SYSTEM MOVES
IN WITH A SURFACE LOW DEVELOPING OVER EASTERN LAKE SUPERIOR INTO
ONTARIO. IN COORDINATION WITH THE OFFICES TO THE EAST...RAISED THE
PRECIPITATION CHANCES OVER THE EASTERN HALF OF THE AREA BASED ON
THE EXPECTATION THAT SNOW WILL DEVELOP AS THE INVERTED SURFACE
TROUGH MOVES ACROSS THE REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY NOON)
ISSUED AT 1136 AM CST TUE DEC 10 2013

GENERALLY GOOD VFR CONDITIONS EXPECTED THIS AFTERNOON. AWOS/ASOS
UNITS ACROSS THE AREA CONTINUE TO REPORT MORE MVFR CIGS THAN
ACTUALLY EXIST. SATELLITE IMAGERY AND SERIES OF WEB/SKY CAMS ACROSS
THE AREA SHOW GENERALLY CLEAR SKIES OVER SOUTHEAST MN/WESTERN WI.
SUBSIDING WINDS HAVE ALLOWED THE BLOWING SNOW TO LAY DOWN TOO.
HOWEVER SOME DRIFTING LIKELY TO PERSIST AT SITES LIKE KRST UNTIL THE
WEST-NORTHWEST WINDS STOP GUSTING.

ANOTHER IN A FAST PARADE OF WEAK LOWS WILL TRACK ACROSS IA TONIGHT
AND SPREAD ANOTHER ROUND OF -SN ACROSS THE TAF SITES. MAINLY IN THE
02Z-08Z PERIOD AT KRST AND 04-10Z AT KLSE AND MAINLY WITH MVFR
CIGS/IFR VSBYS. BOTH SITES LOOK TO RECEIVE 1/2 TO 1 INCH OF FLUFFY
SNOW. WINDS AGAIN INCREASE ONCE THE WEAK LOW PASSES...WITH NORTHWEST
WINDS OF 10-20MPH AND GUSTY LATE TONIGHT/MUCH OF WED MORNING...TO
ONCE AGAIN BLOW THE FRESH SNOW AROUND FOR A FEW HOURS. LOW CLOUDS
EXPECTED TO DECREASE RATHER QUICKLY WED MORNING ONCE THE LOW
PASSES...WITH WINDS DECREASING THRU WED AS THE NEXT WEAK HIGH
BUILDS IN.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 9 AM CST
     WEDNESDAY FOR WIZ054-061.

     WIND CHILL ADVISORY FROM 4 AM TO NOON CST WEDNESDAY FOR
     WIZ032>034-041>044.

     WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM CST THURSDAY
     FOR WIZ017-029.

MN...WIND CHILL ADVISORY FROM 4 AM TO NOON CST WEDNESDAY FOR MNZ079-
     086>088-094>096.

IA...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 9 AM CST
     WEDNESDAY FOR IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...04
LONG TERM...04
AVIATION.....RRS