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000
FXUS63 KARX 091142
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
542 AM CST MON DEC 9 2013

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 352 AM CST MON DEC 9 2013

MAIN SHORT TERM CONCERNS ARE ON TEMPERATURES...WIND CHILLS AND
POTENTIAL FOR MORE SNOW LATER TONIGHT.

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED A HIGHLY AMPLIFIED RIDGE OVER THE EASTERN PACIFIC...A DEEP
TROUGH FROM CENTRAL CANADA INTO THE FOUR CORNERS...AND RIDGING OVER
THE SOUTHEASTERN U.S.. WITHIN THE DEEP TROUGH THERE WERE 3
SHORTWAVES OF NOTE. THE FIRST WAS OVER SOUTHEAST WISCONSIN WHICH
HELPED BRING THE SNOW TO THE AREA YESTERDAY INTO THE EARLY MORNING
HOURS. MOST OF THE SNOW HAS PUSHED OFF TO THE EAST AS SHOWN BY RADAR
IMAGERY...IN RESPONSE TO SUBSIDENCE AND ISENTROPIC DESCENT IN THE
WAKE OF THE SHORTWAVE. THE SECOND SHORTWAVE OF NOTE WAS OVER THE
DAKOTAS. ALTHOUGH THIS SHORTWAVE WAS ONLY PRODUCING SOME ALTOSTRATUS
AHEAD OF IT...DUE TO DRY AIR SEEN ON THE 00Z BIS SOUNDING...THERE
WAS PLENTY OF COLD AIR WITH IT. 850MB TEMPS ACCORDING TO THE RAP ARE
-25C ACROSS NORTH DAKOTA...OR 2 STANDARD DEVIATIONS BELOW NORMAL.
FINALLY...THE THIRD SHORTWAVE WAS COMING DOWN THE BACK SIDE OF THE
TROUGH THROUGH CENTRAL ALBERTA. IMPRESSIVE 140KT JET AT THE
TROPOPAUSE ACCOMPANYING THE SHORTWAVE. ALREADY SOME LIGHT SNOW
FALLING JUST AHEAD OF THE SHORTWAVE.

A LOT OF RAPID MOTION FORECAST OVER THE NEXT 24 HOURS IN THE UPPER
LEVEL PATTERN...MOSTLY A RESULT FROM THAT STRONG UPPER JET CORE
COMING THROUGH ALBERTA. FIRST OFF...THE SHORTWAVE TROUGH OVER NORTH
DAKOTA IS PROGGED BY MODELS TO SLIDE THROUGH THE FORECAST AREA THIS
AFTERNOON. WE MAY SEE SOME MID OR HIGH CLOUDS PASS THROUGH AHEAD OF
THE SHORTWAVE...BUT THE BULK OF THE CLOUD COVER IS GOING TO BE THE
CURRENT STRATUS AFFECTING THE AREA. ANTICIPATING AS THE SHORTWAVE
PASSES...THE DRY ARCTIC AIR SEEN ACROSS NORTH DAKOTA CURRENTLY WILL
CLEAR OUT THE STRATUS. THIS MAY HAPPEN PRETTY QUICK WITH CLEARING
ALREADY COMING INTO THE FORECAST AREA. IN ADDITION...THAT SAME
ARCTIC AIR IS EXPECTED TO CAUSE TEMPERATURES TO FALL AS 850MB TEMPS
PLUMMET FROM THE CURRENT -14 TO -18C READINGS TO -18 TO -22C BY 21Z.
WINDS LOOK TO CRANK UP TOO AS THAT SHORTWAVE AND ASSOCIATED COLD AIR
COME IN. THESE WINDS...WITH GUSTS UPWARDS OF 20 TO 30 MPH...ARE
LIKELY TO CAUSE SOME BLOWING AND DRIFTING OF THE RECENT SNOW. AS
TEMPERATURES FALL THIS AFTERNOON...WIND CHILLS WILL BECOME MORE OF
AN ISSUE. TAYLOR/CLARK COUNTIES LOOK TO DROP INTO ADVISORY RANGE
AROUND 22Z AND DO NOT GET OUT UNTIL 12Z TUESDAY...THUS HAVE GONE
AHEAD AND ISSUED AN ADVISORY FOR THEM.

THE COLD AIR TONIGHT DOES NOT LAST LONG. MODELS ARE IN GOOD
AGREEMENT SHOWING THE ALBERTA SHORTWAVE DIGGING INTO THE DAKOTAS
THIS EVENING...THEN MOVING INTO THE FORECAST AREA TOWARDS 12Z. AS
THIS SHORTWAVE APPROACHES...WARM ADVECTION ENSUES...WITH 850MB TEMPS
CLIMBING UP TO -13 TO -17C BY 09Z. ALL INDICATIONS ARE THAT THE
ISENTROPIC LIFT AND SOME MOISTURE ADVECTION WILL CAUSE A MID CLOUD
DECK TO SPREAD ACROSS THE FORECAST AREA. THESE CLOUDS AND THE WARM
ADVECTION SHOULD RESULT IN RISING TEMPS LATE THIS EVENING INTO THE
OVERNIGHT...HELPING TO BRING WIND CHILLS UP. ADDITIONALLY...THE BEST
JUXTAPOSITION OF LOW LEVEL SATURATION AND ISENTROPIC LIFT OCCURS
NORTH OF INTERSTATE 90. GIVEN THE ARCTIC AIRMASS IN PLACE PRIOR TO
THE SHORTWAVE ARRIVAL...LIKELY WILL NOT TAKE MUCH TO SNOW. QPF MAY
NOT AMOUNT TO MUCH WITH THE COLD AIRMASS...MAYBE A COUPLE HUNDREDTHS
TOPS...BUT ENOUGH FORCING TO WARRANT HIGH PRECIPITATION CHANCES.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 352 AM CST MON DEC 9 2013

MAIN LONG TERM FORECAST CONCERNS ARE ON TEMPERATURES...AS WELL AS
THE OSCILLATING DIURNAL TRENDS WITH THEM...AND POTENTIAL FOR
PRECIPITATION THROUGHOUT.

SHORTWAVE TROUGH COMING INTO THE FORECAST AREA TONIGHT QUICKLY MOVES
THROUGH DURING THE TUESDAY MORNING HOURS. ANY SNOW LOOKS TO DEPART
OFF TO THE EAST PRETTY FAST IN THE MORNING...FOLLOWED BY CLEARING
AND BRISK WEST WINDS. THESE WINDS COULD RESULT IN MORE BLOWING
SNOW...ESPECIALLY IF WE CAN GET A FEW TENTHS OUT OF TONIGHT.
ADDITIONALLY...THE WINDS DRIVE IN A BRIEF SURGE OF ARCTIC AIR WITH
850MB TEMPS FALLING TO -16 TO -20C BY 18Z. 09.00Z
ECMWF/NAM/CANADIAN/GFS THEN ALL DEPICT YET ANOTHER SHORTWAVE TROUGH
DROPPING INTO THE DAKOTAS TUESDAY NIGHT. AHEAD OF THIS
FEATURE...INCREASING ISENTROPIC LIFT AND MID LEVEL FRONTOGENESIS
LOOKS TO DEVELOP A BAND OF SNOW. POSITION OF THIS BAND OF SNOW IS
PROBLEMATIC...WITH THE ECMWF/NAM FARTHER NORTH COMPARED TO THE
GFS/CANADIAN. CONSENSUS WOULD SUGGEST LOCATIONS SOUTH OF I-90 WOULD
STAND TO SEE THE BEST CHANCE OF SEEING SNOW...SO RAISED CHANCES
TOWARDS 60 IN THIS AREA. THE BAND DOES APPEAR TO BE QUICK MOVING...
SUCH THAT BY 12Z WEDNESDAY...ITS ALREADY SOUTHEAST OF THE AREA.
NONETHELESS...WITH SNOW TO WATER RATIOS APPROACH 20 TO 1...WE COULD
SQUEEZE OUT AN INCH OR SO OUT OF THIS BAND.

JUST LIKE IN THE WAKE OF THE EVERY SHORTWAVE TROUGH...ANOTHER SURGE
OF ARCTIC AIR IS PROGGED TO FLOW INTO THE AREA ON WEDNESDAY WHEN THE
TROUGH MOVES THROUGH. 850MB TEMPS DROP TO -20 TO -24C AT 18Z
WEDNESDAY. THUS...DESPITE THAT SKIES SHOULD CLEAR ON WEDNESDAY AS
THE TROUGH COMES IN...IT WILL BE TOUGH TO WARM UP MUCH. MOST
LOCATIONS ARE LIKELY TO NOT GET OUT OF THE SINGLE DIGITS ABOVE
ZERO...AND NORTH OF HIGHWAY 10 MAY NOT EVEN GET TO ZERO. WITH THE
COLD TEMPS AND A NORTHWEST BREEZE...WIND CHILLS ARE YET AGAIN A
FACTOR WITH ANOTHER ADVISORY LIKELY NEEDED. NORTH OF HIGHWAY 10
APPEARS TO BE THE MOST LIKELY AREA FOR AN ADVISORY...STARTING LATE
TUESDAY NIGHT AND RUNNING THROUGH WEDNESDAY NIGHT. WEDNESDAY NIGHT
IS INTERESTING TOO. ALL MODELS ARE SUGGESTING RISING 500MB HEIGHTS
ACROSS THE CENTRAL PART OF THE COUNTRY. WARM ADVECTION ASSOCIATED
WITH THESE RISING HEIGHTS SHOULD CAUSE TEMPERATURES TO RISE...AFTER
A RAPID DROP OFF IN THE EVENING ASSOCIATED WITH A SURFACE RIDGE
PASSAGE. THERE MAY EVEN BE SOME SNOW THAT TRIES TO GET GOING NORTH
OF I-94...AS SUGGESTED BY THE ECMWF/CANADIAN AND HAVE INCLUDED 20
PERCENT CHANCES FOR THIS. THESE CHANCES PERSIST INTO THURSDAY. MUCH
WARMER 850MB TEMPS ON THURSDAY...ON THE ORDER OF -2 TO -8C BY
00Z...WILL RESULT IN HIGHS 15-20 DEGREES WARMER COMPARED TO
WEDNESDAY.

FROM THURSDAY NIGHT THROUGH SUNDAY...09.00Z ECMWF/GFS/CANADIAN
SUGGEST A NORTHWEST FLOW PATTERN IN THE MEAN...STRETCHING FROM
BRITISH COLUMBIA INTO THE GREAT LAKES. AT THE MOMENT THURSDAY NIGHT
LOOKS DRY. AS WE HEAD INTO FRIDAY AND ESPECIALLY FRIDAY
NIGHT...THERE ARE SUGGESTIONS A SOUTHERN STREAM SHORTWAVE TROUGH
COMING OUT OF THE CENTRAL PLAINS AND HEADING INTO THE OHIO VALLEY
COULD SPREAD SOME LIGHT SNOW INTO THE FORECAST AREA. THE CANADIAN IS
THE FARTHEST NORTHWEST AND DID HONOR THE SOLUTION WITH A 20 PERCENT
CHANCE. HOWEVER...THE 09.00Z GFS/ECMWF SUGGEST IT COULD STAY TO THE
SOUTHEAST...THUS SOMETHING TO MONITOR. HEADING INTO THE WEEKEND...
THE ECMWF/GFS SUGGEST A POTENT UPPER TROUGH WILL BE DROPPING SOUTH
INTO MANITOBA AND ONTARIO. THE ECMWF IS VERY AGGRESSIVE DIGGING IT
INTO WISCONSIN ON SUNDAY. FOR NOW STAYED WITH THE CONSENSUS WHICH
YIELDS A GENERALLY DRY SOLUTION WITH TEMPERATURES HOVERING SLIGHTLY
BELOW NORMAL. HOWEVER...SHOULD THE 00Z ECMWF BE CORRECT...
TEMPERATURES MAY NEED SIGNIFICANT LOWERING FOR SUNDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 542 AM CST MON DEC 9 2013

VFR TO MVFR CONDITIONS ARE EXPECTED AT THE TAF SITES TODAY. GUSTY
WEST WINDS OF 14 TO 18 KTS WITH GUSTS AROUND 24KTS WILL LEAD TO
SOME PATCHY BLOWING SNOW...POSSIBLY REDUCING VISIBILITIES TO
AROUND 5SM AT TIMES. SOUTH/SOUTHWEST WINDS WILL INCREASE LATE
TONIGHT AHEAD OF A WEAK SYSTEM APPROACHING FROM THE NORTHERN
PLAINS. LOOK FOR WINDS TO INCREASE INTO THE 14 TO 18 KT RANGE
AGAIN WITH GUSTS AROUND 25 KTS POSSIBLE. SOME PATCHY BLOWING SNOW
MAY OCCUR AGAIN LATE TONIGHT AS THE WINDS INCREASE. LIGHT SNOW OR
FLURRIES WILL MOVE ACROSS THE TAF SITES MAINLY AFTER 10Z TONIGHT.
A BRIEF PERIOD OF MVFR OR POSSIBLY IFR CONDITIONS MAY OCCUR AS THE
SNOW MOVES THROUGH.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WIND CHILL ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM CST TUESDAY
     FOR WIZ017-029.

MN...NONE.
IA...NONE.
&&

$$

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