Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 041140
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
640 AM CDT FRI SEP 4 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM CDT FRI SEP 4 2015

FORECAST FOCUS IS ON SMALL RAIN CHANCES TODAY AND INTO TONIGHT.
CONVERGENT AREA SEEN IN SURFACE ANALYSIS AT 08Z FROM NORTHERN
IL...NORTHWEST THROUGH NORTHEAST IA AND INTO MN. OVERRUNNING THIS
AREA RESULTING IN NORTHWEST TO SOUTHEAST BANDS OF CLOUD COVER.
SOME CONVECTION OVER SOUTHWEST WI LAST NIGHT...BUT NOTHING
RECENTLY. BUT SATELLITE IMAGERY SHOWS CASTELLANUS ACROSS IA WITH
ISOLATED SLOW-MOVING -TSRA...WHICH HAS BEEN PERCOLATING ALL NIGHT.
WATER VAPOR IMAGERY CLEARLY SHOWS THE SHORT WAVE DROPPING SLOWLY
ACROSS WI AND INTO IL. MEANWHILE A WEAK RIPPLE WAS MOVING
NORTHEAST ACROSS THE DAKOTAS. THUS WITH THE MAIN FORCINGS JUST
OUTSIDE OUR FORECAST AREA...THE RAIN CHANCES ARE LIMITED. MODELS
ALL HAVE VARYING DEGREES OF RAIN CHANCES...WITH GFS MOST ROBUST
AND NAM MOST PALTRY. DESPITE WEAK FORCING...DEGREE OF AVAILABLE
MOISTURE AND INSTABILITY SHOULD AT LEAST ALLOW FOR SOME
POSSIBILITY FOR RAIN.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 400 AM CDT FRI SEP 4 2015

AREA TO REMAIN IN THE HOT AND STICKY RIDGE UNTIL LATE SUNDAY.
CLOSED CIRCULATION OVER THE PACIFIC NORTHWEST WILL EVENTUALLY
SHIFT FAR ENOUGH EAST INTO MANITOBA BY MONDAY. THIS WILL SEND A
COLD FRONT THROUGH THE REGION SUNDAY NIGHT. THERE IS A VERY GOOD
CHANCE FOR THUNDERSTORMS ALONG THIS BOUNDARY...ESPECIALLY GIVEN
THE SIGNIFICANT AIRMASS CHANGE AND THE AMOUNT OF MOISTURE AND
INSTABILITY AHEAD OF IT. AT FIRST BLUSH IT APPEARS THERE WOULD BE
A RISK FOR STRONG OR EVEN SEVERE STORMS AS THE FRONT PASSES. BUT
WITH THE FRONT PASSING AFTER THE PEAK DIURNAL TIMEFRAME...AND WITH
THE BEST SHEAR LAGGING IT...NOT OVERLY IMPRESSED. STILL...IT BEARS
WATCHING. COOLER WEATHER THEN ON TAP FOR THE REMAINDER OF THE
WEEK...MORE TYPICAL OF SEPTEMBER. ANOTHER CHANCE FOR SHOWERS
MONDAY NIGHT INTO TUESDAY THE TROUGH MOVES EAST ACROSS ONTARIO.
ZONAL TO SLIGHTLY NORTHWEST FLOW THEN PREVAILS THROUGH NEXT
WEEKEND.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 640 AM CDT FRI SEP 4 2015

SOME LOW CLOUDS/BR PROBLEMATIC EARLY THIS MORNING. DIURNAL WARMING/
MIXING AND INCREASE OF SOUTH TO SOUTHWEST SFC-850MB WINDS SHOULD
CLEAR THIS OUT OF THE KRST AREA BY 14Z. MVFR DECK EAST OF KLSE
SHOULD ADVECT EAST/BREAK UP THRU THE MORNING AS WELL. SCT DIURNAL
CUMULUS IN THE 3K-4K FT RANGE EXPECTED THIS AFTERNOON...WITH
GENERALLY GOOD VFR TONIGHT WITH THE STRONGER SOUTHWEST 925-850MB
FLOW AND AN INCREASE OF MOISTURE/CLOUDS IN THE 10K-15K FT RANGE.
SOME SIGNALS FOR FORCING/LIFT AROUND 700MB WITH MODEL SOUNDINGS
SHOWING SHOWING SOME WEAK INSTABILITY AND NO CAPPING WHEN LIFTING
PARCELS IN THE 700-650MB LAYER. MAY YET BE SOME HIGH-BASED SHRA/
TSRA AROUND THE TAF SITES AFTER MIDNIGHT TONIGHT. GIVEN LOWER
CONFIDENCE IN THESE DETAILS...LEFT ANY SHRA/TSRA MENTIONS AFTER 06Z
OUT OF THE TAFS FOR NOW.

&&

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

$$

SHORT TERM...MW
LONG TERM....MW
AVIATION.....RRS


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