Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 250507
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1100 PM CST TUE FEB 24 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 318 PM CST TUE FEB 24 2015

THE MAIN FOCUS INTO TOMORROW IS ON THE INCREASING CHANCES FOR SNOW
ACROSS NORTHEAST IOWA...SOUTHEAST MINNESOTA AND FAR SOUTHWEST
WISCONSIN.

CURRENTLY...STRONG SUBSIDENCE IN THE WAKE OF A COLD FRONT HAS LEAD
TO SOME STRONG GUSTS IN THE 25 TO 40 MPH RANGE ACROSS THE REGION.
THESE GUSTS WILL GRADUALLY SUBSIDE INTO THE EVENING AS THE
PRESSURE GRADIENT WEAKENS WITH A RIDGE OF HIGH PRESSURE DROPS DOWN
INTO THE UPPER MISSISSIPPI RIVER VALLEY. CLEAR SKIES AND LIGHT
WINDS WILL LEAD TO IDEAL RADIATIONAL COOLING CONDITIONS TONIGHT
WITH THE FAVORED LOW SPOTS DROPPING WELL BELOW ZERO.

THE FOCUS THEN GOES TO A SURFACE LOW CURRENTLY IN SOUTHWEST
ALBERTA WHICH WILL PROPAGATE SOUTHEAST THROUGH NEBRASKA AND
MISSOURI TOMORROW. THE 24.12Z GFS/NAM HAVE COME AROUND TO WHAT THE
ECMWF HAS ADVERTISING THE PAST FEW DAYS WITH THE SNOW BAND GOING A
BIT FURTHER TO THE NORTHEAST THAN WHAT THE OTHER MODELS HAD BEEN
SHOWING. THE 24.12Z NAM APPEARS TO BE THE DRY OUTLIER AND DOES NOT
BRING THE SNOW EAST OF THE MISSISSIPPI RIVER WHILE ALL OF THE
OTHER GUIDANCE DOES BRING IT INTO SOUTHWEST WISCONSIN. BASED ON
FORECAST THERMAL PROFILES OFF OF THE 24.12Z GFS...A SIGNIFICANT
PORTION OF THE SATURATED/LIFT REGION IS WITHIN THE DENDRITIC
GROWTH ZONE WITH RELATIVELY LIGHT WINDS THROUGH THAT COLUMN.
SO...SNOWFALL RATIOS SHOULD BE ON THE HIGHER SIDE AROUND 17-20:1.
THE HIGHER QPF STILL LOOKS LIKE IT GOES MORE SO THROUGH CENTRAL
IOWA WHERE IT WILL BE CLOSER TO THE SURFACE LOW. BASED ON THESE
FORECASTS...CAME UP WITH ABOUT 1-3 INCHES ACROSS FLOYD COUNTY WITH
2 INCHES OR LESS ACROSS THE REST OF NORTHEAST IOWA...SOUTHEAST
MINNESOTA AND GRANT COUNTY WISCONSIN. BASED ON THIS...HAVE NOT
ISSUED A WINTER WEATHER ADVISORY BUT TRENDS WILL HAVE TO BE
MONITORED OVERNIGHT TO SEE IF THERE IS AN ADDITIONAL SHIFT TO THE
NORTHEAST.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 318 PM CST TUE FEB 24 2015

THE AFOREMENTIONED SYSTEM WILL BRING THE NEXT OUTBREAK OF COLD AIR
DOWN INTO THE REGION FOR THE LATER PART OF THE WEEK. 850MB
TEMPERATURES ARE FORECAST TO GO FROM AROUND -10C ON WEDNESDAY DOWN
TO AROUND -22C BY MID DAY THURSDAY. THIS WILL LEAD TO WIND CHILLS
DROPPING DOWN INTO THE 10 TO 25 DEGREE BELOW ZERO RANGE THURSDAY
AND FRIDAY MORNINGS...SO SOME WIND CHILL ADVISORIES MAY BE NEEDED
THESE MORNINGS.

GOING INTO THIS WEEKEND...THE FOCUS HAS BEEN ON THE POTENTIAL FOR
AN ACCUMULATING SNOW AS A BROAD MID LEVEL TROUGH DIGS ACROSS THE
WESTERN CONUS AND SOUTHWESTERLY FLOW SETS UP ACROSS THE REGION.
THE TRENDS WITH THE 24.12Z GFS/ECMWF ARE TO TAKE THE BULK OF THIS
SYSTEM TO THE SOUTH OF THE REGION WITH MAINLY JUST SOME LIGHT SNOW
FALLING LOCALLY. THE SAME GOES FOR ANOTHER SYSTEM ON TUESDAY WHICH
MAINLY LOOKS TO TRACK WELL EAST OF THE REGION. QUITE A BIT OF
UNCERTAINTY THROUGH THIS PERIOD...THOUGH THE CHANCES OF A HEAVY
SNOW SEEM TO HAVE GONE DOWN SIGNIFICANTLY WITH THIS MODEL RUN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1100 PM CST TUE FEB 24 2015

MID-LEVEL CLOUD DECK MOVING IN FROM THE WEST...MOSTLY IN THE 8-10
KFT RANGE...IN ADVANCE OF AN UPPER LEVEL SHORTWAVE THAT WILL TRACK
ACROSS IA. THE SHORTWAVE WILL BRING SEVERAL INCHES OF SNOW TO
IOWA...BUT FARTHER NORTH TO THE I-90 CORRIDOR AND THE TAF
SITES...MUCH LESS IS EXPECTED - UP TO 1/2 INCH. THAT SAID...MODELS
ARE AT ODDS WITH HOW LOW CIGS WILL GO...WITH SOME FAVORING VFR WHILE
OTHERS SUGGEST AT LEAST MVFR. TRENDS DO SEEM TO POINT TO KRST HAVING
THE WORST OF ANY CIG/VSBY RESTRICTIONS...AND WILL KEEP FORECAST
TRENDS THIS WAY. WHATEVER FALLS LOOKS TO MOVE IN TOWARD 18Z AND EXIT
BY 00Z. EXPECTING SOME CIG IMPROVEMENT WED EVENING DESPITE WHAT THE
MODELS ARE SUGGESTING. CURRENT SATELLITE IMAGERY DOESN/T SUPPORT
MODELS/ LOW LEVEL RH...SO WILL TREND TOWARD VFR RATHER THAN MVFR FOR
THE MOMENT.

&&

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

$$

SHORT TERM...HALBACH
LONG TERM....HALBACH
AVIATION.....RIECK



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