Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 031724
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1224 PM CDT SUN MAY 3 2015

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 321 AM CDT SUN MAY 3 2015

REGIONAL RADARS THIS MORNING SHOWING SOME CONVECTIVE ACTIVITY OVER
CENTRAL AND WESTERN IOWA. THIS IS OCCURRING ON THE NOSE OF THE LOW
LEVEL JET AND AHEAD OF A SHORT WAVE TROUGH MOVING ACROSS NORTHERN
NEBRASKA. THE 03.03Z RAP INDICATES THIS WAVE WILL CONTINUE TO
TRACK EASTWARD ACROSS NORTHERN IOWA THROUGH THE MORNING WITH THE
LOW LEVEL JET VEERING TO THE EAST TO REMAIN AHEAD OF THE WAVE. THE
RAP...03.04Z HRRR AND THE 03.00Z HI-RES ARW AND NMM ALL SUGGEST
THERE IS A CHANCE THAT SOME OF THE ACTIVITY WITH THIS WAVE COULD
GET INTO NORTHEAST IOWA AND SOUTHWEST WISCONSIN AND HAVE ADDED IN
A SMALL CHANCE FOR THIS THROUGH ABOUT THE MIDDLE OF THE MORNING.

THE MAIN CONVECTIVE SHOW WILL COME LATE THIS AFTERNOON INTO THE
EVENING. THE 03.00Z MODELS HAVE REMAIN FAIRLY CONSISTENT TAKING
THE MAIN SHORT WAVE TROUGH...CURRENTLY OVER SASKATCHEWAN...ALMOST
DUE EAST WITH A SLIGHT POSITIVE TILT AND THE PV ADVECTION IN THE
500-300 MB LAYER REMAINING NORTH OF THE AREA. AS THIS WAVE MOVES
EAST...IT WILL PUSH A COLD FRONT INTO THE AREA LATE THIS AFTERNOON
AND THEN ACROSS THE REGION TONIGHT. BUFKIT SOUNDINGS FROM THE
03.00Z NAM INDICATE A PRETTY DEEP MIXED LAYER...UP TO ABOUT 850
MB...AHEAD OF THE FRONT THAT COULD BRING DOWN SOME DRIER AIR AND
KEEP THE DEW POINTS CAPPED IN THE MID 50S. WITH 925 MB
TEMPERATURES RISING ABOUT 2 TO 3C OVER SATURDAY...EXPECT THE
SURFACE TEMPERATURES TO BE WARMER THAN SATURDAY WITH MIDDLE 80S
FOR MUCH OF THE AREA. THE COMBINATION OF THESE TEMPS AND DEW
POINTS SHOULD YIELD ML CAPES AROUND 1500 J/KG OR SO ALONG AND
AHEAD OF THE FRONT. THE FORECAST SOUNDINGS ALSO SHOW A WEAK CAP
IN THE WARM SECTOR AHEAD OF THE FRONT AND WITH MINIMAL HEIGHT
FALLS...IT WILL TAKE THE THERMODYNAMIC FORCING WITH THE FRONT TO
BREAK THE CAP. THE FRONTOGENESIS WITH THE FRONT LOOKS TO BE
MODERATE IN STRENGTH IN THE 1000-850 MB AND THEN WEAK FROM 850 MB
UP THROUGH 500 MB. THIS SHOULD BE ENOUGH TO BREAK THE WEAK CAP AND
ALLOW CONVECTION TO FORM ALONG THE FRONT. THERE IS GOOD CLUSTERING
AMONG THE HI-RES MESO MODELS...THE 03.00Z NAM12 AND 03.00Z NESTED
NAM THAT THE FRONT SHOULD START TO APPROACH LATE THIS AFTERNOON
WITH THE CONVECTION FIRST IMPACTING THE NORTHERN PARTS OF THE AREA
IN THE 21Z-24Z WINDOW AND THEN DEVELOPING SOUTHWEST ALONG THE
FRONT VERY LATE IN THE AFTERNOON INTO THE EARLY EVENING. THIS
ACTIVITY SHOULD REMAIN STRONG INTO THE MIDDLE OF THE EVENING
BEFORE THE CAPE QUICKLY DWINDLES WITH JUST GENERAL CONVECTION
EXPECTED FOR CENTRAL AND SOUTHWEST WISCONSIN. THE SEVERE THREAT IS
STILL PRESENT FROM ABOUT 4 PM THROUGH 10 PM WITH LARGE HAIL
LOOKING TO BE THE MAIN THREAT AS GOOD MID LEVEL LAPSE RATES SHOULD
AID IN THE HAIL PRODUCTION. NOT EXPECTING THE HAIL TO BE OVERLY
LARGE AS A GENERAL LACK OF SHEAR WILL KEEP THE UPDRAFT ROTATION
SUBDUED. WHAT SHEAR THERE IS WILL BE IN THE 0-3KM LAYER AND IS
EXPECTED TO BE ON THE ORDER OF 25 TO 30 KNOTS...WHICH SHOULD BE
ENOUGH TO PRODUCE SOME WIND GUSTS BUT MAY NOT BE ENOUGH TO KEEP
THE GUST FRONTS CLOSE TO THE STORMS.

THE MODELS NOW SUGGEST THE FRONT MAY NOT PUSH AS FAR SOUTH AS
PREVIOUSLY INDICATED BEFORE STALLING OUT MONDAY. THE GENERAL MODEL
CONSENSUS NOW SHOWS THE FRONT STALLING OVER SOUTHERN IOWA INSTEAD
OF NORTHERN MISSOURI. THIS CLOSER PROXIMITY TO THE AREA COULD
ALLOW SOME OF THE SHOWERS AND STORMS EXPECTED TO OCCUR NORTH OF
THE FRONT TO CONTINUE OVER NORTHEAST IOWA INTO SOUTHWEST WISCONSIN
MONDAY AFTERNOON AND EVENING. THE UPPER LEVEL PATTERN WILL START
TO SHIFT TO MORE OF A SOUTHWEST FLOW AND BEGIN TO PUSH THE FRONT
BACK TO THE NORTH LATE MONDAY NIGHT RESULTING IN A NORTHWARD
EXPANSION OF THE RAIN CHANCES OVER ALL OF SOUTHEAST MINNESOTA AND
MUCH OF WESTERN AND CENTRAL WISCONSIN. MOST OF THE AREA WILL THEN
HAVE A CHANCE FOR RAIN TUESDAY AS THE FRONT MOVES BACK INTO
THE AREA AND COULD POSSIBLY BE ACCOMPANIED BY A SHORT WAVE TROUGH
ALOFT IN THE SOUTHWEST FLOW.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 321 AM CDT SUN MAY 3 2015

THE SOUTHWEST FLOW ALOFT LOOKS TO CONTINUE THROUGH THE PERIOD AS
THE MAIN RIDGE REMAINS OVER THE EASTERN CONUS AND A LARGE UPPER
LEVEL LOW SINKS SLOWLY SOUTH OVER THE WESTERN CONUS. WITH THIS
FLOW PATTERN...SEVERAL PIECES OF ENERGY ARE EXPECTED TO COME OUT
AND ACROSS THE UPPER MIDWEST. IT LOOKS AS IF IT WILL TAKE UNTIL
SOMETIME WEDNESDAY OR WEDNESDAY NIGHT FOR THE RETREATING FRONT TO
GET NORTH OF THE AREA. ONCE THIS HAPPENS...A COLD FRONT AND
SURFACE LOW PRESSURE WILL START TO APPROACH FROM THE WEST WITH
WHAT SHOULD BE A STRONGER SHORT WAVE TROUGH ALOFT. THIS FRONT WILL
THEN MOVE ACROSS THE AREA IN THE END OF THE WORK WEEK WITH IT
POSSIBLY BECOME STALLED OUT JUST TO THE SOUTH OF THE AREA INTO THE
START OF THE WEEKEND. WITH THIS MESSY PATTERN...WILL CARRY RAIN
CHANCES EACH DAY...ALTHOUGH WOULD NOT BE SURPRISED TO SEE A DRY
PERIOD OR TWO...ESPECIALLY ONCE THE RETURNING FRONT GETS PAST THE
AREA. HOWEVER...CONFIDENCE ON THIS IS TOO LOW TO WORK INTO THE
FORECAST AT THIS TIME.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1224 PM CDT SUN MAY 3 2015

VFR CONDITIONS EXPECTED THROUGH THIS AFTERNOON BEFORE A COLD FRONT
ENTERS THE AREA EARLY THIS EVENING. EXPECTING A LINE OF
THUNDERSTORMS TO ACCOMPANY THE FRONT...MAKING PASSAGE THROUGH KRST
IN THE 23Z-03Z TIME FRAME...AND IN THE 01Z-05Z TIME FRAME AT KLSE.
EXPECT DETERIORATING CONDITIONS WITH THE SHRA/TS ACTIVITY WITH
CIGS/VSBY TEMPORARILY DIPPING INTO THE MVFR/IFR RANGE. THERE
REMAINS THE POSSIBILITY THAT A FEW OF THE STORMS WILL BE CAPABLE
OF PRODUCING STRONG GUSTY WINDS IN EXCESS OF 50KT AND HAIL TO THE
SIZE OF QUARTERS. LOOK FOR THE FRONT AND SHRA/TS ACTIVITY TO CLEAR
SOUTHEAST OF THE AREA IN THE 07-09Z TIME FRAME WITH A RETURN TO
VFR CONDITIONS.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...DAS



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