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000
FXUS63 KARX 121134
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
534 AM CST THU DEC 12 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 329 AM CST THU DEC 12 2013

CURRENTLY AS OF 09Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED RIDGING OVER THE WESTERN U.S. INTO SOUTHWEST CANADA...AND
TROUGHING OVER EASTERN CANADA INTO THE GREAT LAKES. IN THE NORTHWEST
FLOW BETWEEN THE RIDGE AND TROUGH...A SHORTWAVE WAS NOTED OVER
NORTHWEST WISCONSIN. DPVA FORCING FROM THE SHORTWAVE COMBINED WITH
ISENTROPIC LIFT ON THE 275-280K SURFACES AS SUGGESTED BY THE RAP HAS
SPREAD LIGHT SNOW ACROSS THE NORTHEAST HALF OF THE FORECAST AREA. IN
ADDITION...THE CLOUDS AND A WARM ADVECTION SOUTHWEST WIND IN THE LOW
LEVELS HAS CAUSED TEMPERATURES TO CLIMB OVERNIGHT. THE BREEZE...
HOWEVER...HAS HELD WIND CHILLS DOWN TO 10 TO 20 BELOW ZERO SOUTHWEST
OF I-94 TO 20 TO 25 BELOW ZERO TO THE NORTH. REGARDING THE WARM
ADVECTION HIGHER ABOVE THE SURFACE...FROM 00Z SOUNDINGS...850MB
TEMPS WERE AROUND -20C OVER THE FORECAST AREA COMPARED TO -7C AT
BIS AND AROUND -10C AT ABR AND OAX. FARTHER UPSTREAM...PLENTY OF
HIGH CLOUDS REFLECTING PACIFIC MOISTURE WERE STREAMING INTO NORTH
DAKOTA IN THE WAKE OF THE SHORTWAVE.

FIRST...WITH RESPECT TO THE WIND CHILL HAZARDS...WILL LET THEM
EXPIRE AT 12Z. ALTHOUGH WIND CHILLS ARE IMPROVING...THERE IS ONLY A
FEW HOURS LEFT TO THE ADVISORY...AND THEY ARE STILL CHILL AS
MENTIONED ABOVE.

ONGOING SNOW EARLY THIS MORNING REMAINS ON TRACK TO QUICKLY EXIT THE
FORECAST AREA...LIKELY BY 7 AM...AS THE SHORTWAVE HEADS OFF TO LAKE
MICHIGAN BY 12Z. OTHERWISE...THE REST OF THE SHORT TERM GENERALLY
LOOKS QUIET PRECIPITATION-WISE AS THE UPPER LEVEL FLOW BECOMES MORE
ZONAL OVER THE NORTHERN U.S.. THE 12.00Z GFS/CANADIAN AND 12.03Z
SREF ALL SHOW SOME LIGHT SNOW OR FLURRIES FALLING LATE THIS
AFTERNOON INTO EARLY THIS EVENING FROM TAYLOR COUNTY NORTHWARD. THIS
LIGHT PRECIPITATION IS ASSOCIATED WITH WEAK BUT MAINTAINED
ISENTROPIC LIFT AND MID-LEVEL FRONTOGENESIS. DECIDED TO ADD SOME LOW
CHANCES ON THE ORDER OF 20 PERCENT TO TAYLOR COUNTY. DESPITE MAINLY
DRY WEATHER FOR THE NEXT 24 HOURS...WE SHOULD SEE QUITE A BIT OF
CLOUD COVER...ESPECIALLY OVER THE NORTH HALF OF THE FORECAST AREA.
THESE CLOUDS OF THE MID/HIGH LEVEL VARIETY REFLECT BOTH THE PACIFIC
MOISTURE FLOWING IN BEHIND THE CURRENT SHORTWAVE AS WELL AS THE
GENERAL WARM ADVECTION PATTERN. ADDITIONALLY...LATE TONIGHT...THE
FORECAST AREA LIES IN THE RIGHT ENTRANCE REGION OF AN UPPER JET
STREAK OVER THE UPPER GREAT LAKES...FAVORING CLOUDS.

WARMER TEMPERATURES ARE ON TRACK TODAY AS SOUTHWEST WINDS BRING UP
WARMER AIR OUT OF NEBRASKA. THE 24 HOUR CHANGE AT 850MB IS FAIRLY
IMPRESSIVE...FROM THE -20C OBSERVED BACK AT 00Z YESTERDAY EVENING TO
-2C TO -10C FOR THIS EVENING. WE CERTAINLY WILL NOT MIX TO THESE
VALUES GIVEN TIME OF YEAR...CLOUDS AND SNOW COVER...BUT DEFINITELY
WARMER NONETHELESS. COLDEST READINGS WILL REMAIN IN THE CHIMNEY
AREA. AS THE UPPER FLOW TURNS ZONAL TONIGHT...A COLD FRONT CURRENTLY
OVER SOUTHERN SASKATCHEWAN IS PROGGED TO SLIDE SOUTH THROUGH THE
FORECAST AREA. THE COLD AIR IS SHALLOW BEHIND THIS FRONT AS MUCH OF
THE TEMPERATURE FALL TAKES PLACE AT 925MB AND BELOW. 925MB TEMPS
FALL 6C ON A NORTH TO NORTHEAST WIND...SO WE SHOULD SEE A DECENT
TEMPERATURE DROP TONIGHT DESPITE CLOUDS IN PLACE.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 329 AM CST THU DEC 12 2013

FOR FRIDAY THROUGH SATURDAY...ATTENTION TURNS TO AN UPPER LOW
CURRENTLY SITTING NEAR FAR SOUTHERN CALIFORNIA. 12.00Z MODELS
REMAIN CONSISTENT ON TRACKING THIS FEATURE INTO THE CENTRAL
PLAINS ON FRIDAY...THEN UP THROUGH THE OHIO VALLEY FRIDAY NIGHT
AND SATURDAY. THIS TRACK WOULD KEEP THE BULK OF THE SYSTEMS
PRECIPITATION... INCLUDING THE DEFORMATION SHIELD...SOUTHEAST OF
THE FORECAST AREA. 12.00Z ECMWF SHOWS A COMPLETELY DRY FORECAST
FOR THE AREA. HOWEVER...THE 12.00Z GFS/CANADIAN/NAM SUGGEST
POTENTIAL FOR LIGHT SNOW THROUGH THIS ENTIRE PERIOD. ALL
INDICATIONS FROM THESE MODELS SUGGEST THE OHIO VALLEY SHORTWAVE
TROUGH IS NOT THE CAUSE FOR THE PRECIPITATION...BUT ACTUALLY 2
NORTHERN STREAM SHORTWAVE TROUGHS DIGGING DOWN THROUGH THE AREA
AND LINGERING WEAK MID LEVEL FRONTOGENESIS FROM TONIGHT. HARD TO
SAY REALLY WHAT SOLUTION WILL END UP VERIFYING...THE DRY ECMWF OR
THE WETTER GFS/CANADIAN/NAM... BUT EVEN THE WETTER SOLUTION DOES
NOT LOOK TO AMOUNT TO MUCH ACCUMULATION. CONSENSUS WARRANTS
MAINTAINING AT LEAST A 20 PERCENT CHANCE OVER TAYLOR/CLARK
COUNTIES ON FRIDAY...INCREASING CHANCES TO 30-40 PERCENT FRIDAY
NIGHT...THEN DECREASING TOWARDS 20-30 PERCENT BY SATURDAY
AFTERNOON. ALSO BELIEVE THE CHANCES ARE NEEDED AS EVEN THE ECMWF
SHOWS THE 2 NORTHERN STREAM SHORTWAVE TROUGHS. WHETHER WE GET
PRECIPITATION OR NOT...ALL MODELS AGREE ON PLENTY OF CLOUD COVER.
DESPITE THESE CLOUDS...CONSENSUS OF GUIDANCE SUGGESTS TEMPERATURES
WILL BE WARMER THAN WHAT HAS BEEN SEEN RECENTLY. SOME OF THIS IS
DUE TO SLIGHTLY WARMER AIR GETTING PULLED UP TOWARDS THE AREA
AROUND THE SYSTEM TRACKING INTO THE OHIO VALLEY.

OF THE TWO AFOREMENTIONED SHORTWAVE TROUGHS...THE SECOND ONE IS
MUCH MORE POTENT...DIGGING INTO LAKE SUPERIOR AND UPPER MICHIGAN
SATURDAY NIGHT. SOME LIGHT SNOW COULD OCCUR ACROSS AT LEAST
WISCONSIN PORTIONS OF THE AREA SATURDAY NIGHT AS THIS TROUGH DIGS
SOUTH. MORE IMPORTANTLY IS THE COLD SHOT OF AIR FOLLOWING IN ITS
WAKE...WHICH LIKE THE ONE COMING IN TONIGHT IS SHALLOW AS SEEN IN
925MB VERSUS 850MB PROGS. THE 12.00Z ECMWF IS BY FAR THE COLDEST
BRINGING 925MB TEMPS DOWN TO -13 TO -20C AT 18Z SUNDAY. HIGHS AT A
MINIMUM ARE LIKELY IN THE LOW TO MID TEENS...AND IF THE ECMWF IS
RIGHT TAYLOR COUNTY DOES NOT REACH 10 ABOVE.

LOOKING AHEAD TO NEXT WEEK...12.00Z ECMWF/GFS/CANADIAN/GFS ENSEMBLES
AGREE ON A NORTHWEST FLOW PATTERN FOR EARLY IN THE WEEK WITH
TROUGHING OVER THE GREAT LAKES. DESPITE BEING IN THE TROUGH AND
NORTHWEST FLOW...ITS ACTUALLY A WARM ADVECTION PATTERN IN THE LOW
LEVELS. THUS...LOW PRECIPITATION CHANCES ARE NEEDED...ESPECIALLY
ACROSS WISCONSIN WHERE THE FORCING IS STRONGEST. SOME HINTS THAT THE
FORCING WEAKENS ON TUESDAY...ENOUGH SO THAT CHANCES ARE ONLY INCLUDE
UP AROUND TAYLOR COUNTY. AS WE HEAD TOWARDS WEDNESDAY A POTENT
TROUGH STARTS DIGGING INTO THE PACIFIC NORTHWEST...PRODUCING ZONAL
FLOW DOWNSTREAM. THAT IS IF YOU BELIEVE THE ECMWF...BECAUSE THE GFS
DIGS A SHORTWAVE TROUGH DOWN INTO THE OHIO VALLEY. BOTH MODELS
SUGGEST DRY CONDITIONS...BUT THERE ARE MASSIVE TEMPERATURE
DIFFERENCES. GIVEN A SIMILAR SPLIT IN THE GFS ENSEMBLES...HAVE SPLIT
THE DIFFERENCE FOR NOW ON TEMPS.

FARTHER OUT...IT APPEARS AFTER A BRIEF POSSIBLE WARM UP ON WEDNESDAY
AND THURSDAY...ANOTHER BIG SURGE OF ARCTIC AIR LOOKS POISED TO DROP
DOWN INTO THE NORTH CENTRAL U.S. HEADING INTO THE FIRST OFFICIAL
WEEKEND OF WINTER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 534 AM CST THU DEC 12 2013

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. CIRRUS WILL
SPREAD ACROSS THE REGION TODAY AHEAD OF A WEAK STORM SYSTEM
PUSHING SOUTHEAST FROM THE NORTHERN PLAINS. THE SYSTEM WILL SLIDE
OVER NORTHERN WISCONSIN LATE THIS AFTERNOON INTO TONIGHT BUT WILL
DO LITTLE MORE THAN DROP CEILINGS INTO THE 8 TO 10 KFT RANGE AT
BOTH KRST AND KSLE. WINDS WILL BE OUT OF THE WEST/SOUTHWEST TODAY
AT AROUND 8 KTS...THEN BECOMING LIGHT LATE THIS AFTERNOON INTO
THIS EVENING. WINDS WILL SWITCH TO THE EAST EARLY FRIDAY MORNING
AS A SYSTEM DEVELOPS OVER THE CENTRAL PLAINS AND EDGES EAST INTO
THE MID MISSISSIPPI RIVER VALLEY.

&&

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

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...WETENKAMP