Area Forecast Discussion
Issued by NWS La Crosse, WI

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824
FXUS63 KARX 171745
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1245 PM CDT SUN MAY 17 2015

.UPDATE...THIS AFTERNOON AND EVENING
ISSUED AT 1245 PM CDT SUN MAY 17 2015

CLOUD COVER IS REALLY IMPACTING THE OVERALL SEVERE THREAT FOR THIS
AFTERNOON INTO THIS EVENING. SCATTERED SHOWERS AND THUNDERSTORMS
ARE ONGOING ACROSS THE FORECAST AREA BUT WE HAVE NOT BUILT ENOUGH
CAPE FOR THESE STORMS TO BECOME SEVERE. WE WILL CONTINUE TO
DESTABILIZE THIS AFTERNOON AS A VIGOUS TROUGH MOVES INTO THE AREA
SO WE ARE STILL LOOKING AT THE POTENTIAL FOR A FEW SEVERE STORMS
WITH LARGE HAIL AND DAMAGING WINDS. AN ISOLATED TORNADO OR TWO
CANNOT BE RULED OUT.

LATEST MESOANALYSIS SHOWS CAPE VALUES INCREASING ALONG AND WEST
OF THE INTERSTATE 35 CORRIDOR AHEAD OF THE MAIN FRONTAL BOUNDARY.
WE WILL BE WATCHING THIS FRONT VERY CLOSELY THIS AFTERNOON FOR
SEVERE STORM DEVELOPMENT. ALSO...WE ARE WATCHING AN MCV LIFTING
INTO NORTHEAST IOWA THIS EARLY THIS AFTERNOON WITH A FEW BREAKS
IN THE CLOUD COVER AHEAD OF IT. IF A SURFACE BASED STORM CAN GET
GOING IN THIS AREA IT COULD BECOME SEVERE. MANY FEATURES TO KEEP
AN EYE ON THIS AFTERNOON SO STAY UP TO DATE ON THE LATEST FORECAST
AND STATEMENTS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 350 AM CDT SUN MAY 17 2015

AT 3 AM...WATER VAPOR AND RADAR SHOWED AN MCV JUST NORTHWEST OF
DES MOINES. THE 17.00Z MODELS ARE IN FAIRLY GOOD AGREEMENT THAT
THIS SYSTEM WILL MOVE NORTH NORTHEAST THROUGH THE AREA THIS
MORNING. MANY OF THE MESO MODELS SHOW THAT A WEAKENING LINE OF
CONVECTION WILL MOVE ACROSS THE AREA THIS MORNING. WITH MOST
UNSTABLE CAPES RUNNING BETWEEN 500 AND 1000 J/KG AND EFFECTIVE
SHEAR LESS THAN 40 KNOTS ALONG AND AHEAD OF THIS BAND... NOT
ANTICIPATING ANY SEVERE WEATHER WITH THIS INITIAL BAND OF
CONVECTION.

FOR THIS AFTERNOON AND EARLY EVENING...THERE IS QUITE A BIT OF
UNCERTAINTY AS MESO MODELS ARE SHOWING A VARIETY OF SOLUTIONS AND
THEY ARE ALL EQUALLY PLAUSIBLE. SOME OF THIS HAS TO DEAL WITH HOW
MUCH THE DEBRIS CLOUDS WILL LIMIT INSTABILITY. THE 17.03Z SUGGEST
THAT MOST UNSTABLE CAPES SHOULD BE ABLE TO RECOVER INTO THE 1500
TO 2000 J/KG RANGE. IN ADDITION...SOUNDINGS SHOW AN UNCAPPED
ATMOSPHERE WHICH WILL ALLOW ANY CONVERGENT AREA TO GENERATE
SHOWERS AND STORMS. THESE COULD USE UP THE AVAILABLE CAPE PRIOR TO
THE ARRIVAL OF A MESOSCALE CONVECTIVE COMPLEX FROM NORTHWEST
OKLAHOMA LATE IN THE AFTERNOON AND EVENING. WITH THE 0-6 KM
EFFECTIVE SHEAR GREATER THAN 40 KNOTS...ANY STORM WILL HAVE THE
POTENTIAL BECOME SUPER CELLULAR. WITH A MAJORITY OF THE SHEAR
BEING LOCATED IN THE 0-3 KM LAYER...STILL THINKING THAT THERE
COULD BE SEVERAL BROKEN LINES THAT MOVE QUICKLY ACROSS THE AREA.
WILL HAVE TO WATCH OUT FOR DAMAGING WIND POTENTIAL DESPITE THE
LACK OF DRY AIR IN THE SUB CLOUD LAYER. SOUNDINGS /ESPECIALLY
NAM/ SUGGEST THAT THERE COULD BE FAT CAPE WHICH COULD AID IN THE
DEVELOPMENT OF LARGE HAIL. WITH 0-1 KM SHEAR GREATER THAN 20 KNOTS
AND HELICITY CLIMBING INTO THE 200 TO 400 J/KG...THERE IS A
CONCERN FOR ISOLATED TORNADOES ESPECIALLY NORTH OF INTERSTATE 94.
AT THIS TIME...THINKING THE GREATEST RISK OF SEVERE WEATHER WILL
BE ACROSS SOUTHEAST MINNESOTA AND NORTHEAST IOWA THIS AFTERNOON...
AND FROM THIS AFTERNOON THROUGH EARLY EVENING FOR WESTERN
WISCONSIN.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 350 AM CDT SUN MAY 17 2015

ON MONDAY NIGHT...LOW TEMPERATURES WILL FALL INTO THE MID AND
UPPER 30S ACROSS THE AREA. HOWEVER WITH CLOUDS...NORTHWEST WINDS
AROUND 10 MPH...AND LARGE TEMPERATURE/DEW POINT DEPARTURES...NOT
ANTICIPATING ANY FROST ON THIS NIGHT.

ON TUESDAY NIGHT...HIGH PRESSURE WILL BUILD ACROSS THE AREA. THIS
HIGH WILL KEEP SKIES MOSTLY CLEAR AND THE SURFACE WINDS LESS THAN
5 MPH. THIS WILL ALLOW TEMPERATURES TO FALL INTO THE LOWER AND MID
30S ACROSS MUCH OF WEST-CENTRAL...CENTRAL...AND NORTH-CENTRAL
WISCONSIN. IF THIS TREND CONTINUES...MAY HAVE TO ISSUE A FROST
ADVISORY FOR THIS TIME PERIOD.

ON WEDNESDAY...BOTH THE GFS AND GEM HAVE A SHORT WAVE MOVING
THROUGH THE CENTRAL PLAINS AND MID MISSISSIPPI RIVER VALLEY. WITH
THIS TRACK...ANY PRECIPITATION WOULD REMAIN SOUTH OF OUR AREA.
MEANWHILE THE ECMWF HAS STARTED TO TREND FURTHER NORTH WITH SYSTEM
AND IT NOW HAS PRECIPITATION AS FAR NORTH INTERSTATE 90. WITH THIS
BEING A NEW TREND...JUST KEPT THE FORECAST DRY FOR NOW.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1245 PM CDT SUN MAY 17 2015

LOW PRESSURE LIFTING THROUGH THE REGION WILL PRODUCE SCATTERED
SHOWERS AND THUNDERSTORMS AND MVFR TO IFR CONTIONS AT TIMES. LOOK
FOR A COLD FRONT TO SWEEP ACROSS THE TAF SITES THIS EVENING WITH
SOUTHWEST WINDS INCREASING TO 15 TO 17 KTS WITH GUSTS OF 25 TO 30
KTS POSSIBLE.

&&

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

$$

UPDATE...WETENKAMP
SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...WETENKAMP



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