Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 040448
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1148 PM CDT THU SEP 3 2015

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 336 PM CDT THU SEP 3 2015

MAIN FORECAST CONCERNS FOR THIS EVENING INTO TONIGHT ARE ON SLIGHT
CHANCES FOR SHOWERS AND STORMS OVER EXTREME SOUTHWEST WISCONSIN.
FOCUS THEN TURNS TO THE POSSIBILITY OF AN ISOLATED SHOWER OR
THUNDERSTORM TONIGHT ALONG WITH THE POTENTIAL FOR PATCHY DENSE FOG.

LATEST SURFACE OBSERVATIONS THIS AFTERNOON SHOW A BOUNDARY EXTENDING
FROM NEAR MINNEAPOLIS SOUTHEAST ALONG THE MISSISSIPPI RIVER
THROUGH SOUTHERN WISCONSIN. GIVEN STRONG SURFACE HEATING ACROSS
FAR SOUTHWEST WISCONSIN NEAR THIS FRONT...WE CANNOT RULE OUT AN
ISOLATED SHOWER OR THUNDERSTORM DEVELOPING ALONG IT LATE THIS
AFTERNOON INTO EARLY THIS EVENING. A SHORTWAVE DRIFTING SOUTH
ACROSS WISCONSIN...EVIDENT ON WATER VAPOR...MAY PROVIDE JUST
ENOUGH LIFT TO FOR THE ISOLATED SHOWERS OR STORMS. THE CUMULUS
FIELD ALONG THE FRONT HAS NOT SHOWED SIGNIFICANT DEVELOPMENT NOR
ARE WE SEEING ANY RADAR RETURNS YET. SPC MESOSCALE ANALYSIS SHOWS
3500 TO 5000 J/KG CAPE ACROSS NORTHEAST IOWA INTO FAR SOUTHWEST
WISCONSIN...SO THERE IS PLENTY TO WORK WITH. HOWEVER...A LACK OF
SIGNIFICANT SURFACE CONVERGENCE AND MINIMAL UPPER LEVEL
SUPPORT...OVERALL CHANCES FOR THESE SHOWERS AND STORMS ARE LOW.
ALSO...SHEAR IS VERY WEAK ACROSS THE REGION SO EVEN IF A STORM OR
TWO DEVELOPS SEVERE WEATHER IS NOT EXPECTED. THE SURFACE BOUNDARY
THEN STAYS NEARLY STATIONARY THIS EVENING AND THEN STARTS TO
RETREAT BACK TO THE NORTHWEST OVERNIGHT INTO FRIDAY. MESOSCALE
MODELS ARE SUGGESTING THERE COULD BE AN ISOLATED SHOWERS OR TWO
OVERNIGHT AS THE BOUNDARY EDGES BACK TO THE NORTHEAST. THINKING
THE MAIN IMPACT TONIGHT WILL BE SOME SCT-BKN CLOUDS NEAR THE
BOUNDARY WITH CLOUD BASES IN GENERALLY IN THE 2500 TO 3500 FT
RANGE. ALSO...WITH THE MOIST AIRMASS IN PLACE ACROSS THE REGION
AND PLENTY OF BREAKS IN THE CLOUD COVER...AND EVEN SOME CLEAR
SKIES AT TIMES...WE SHOULD SEE SOME PATCHY TO AREAS OF FOG
OVERNIGHT. THE FOG COULD BE LOCALLY DENSE ACROSS PORTIONS OF
SOUTHWEST INTO CENTRAL WISCONSIN. THE FRONT IS EXPECTED TO
CONTINUE PUSHING OFF TO THE NORTHEAST ON FRIDAY WITH MOSTLY TO
PARTLY SUNNY SKIES EXPECTED ACROSS THE AREA. PLAN ON HIGHS RANGING
FROM AROUND 80 ACROSS NORTHERN WISCONSIN TO THE UPPER 80S TO
AROUND 90 ACROSS PORTIONS OF NORTHEAST IOWA INTO FAR SOUTHWEST
WISCONSIN.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 336 PM CDT THU SEP 3 2015

WARM AND HUMID CONDITIONS WILL CONTINUE THROUGH EARLY SATURDAY THEN
UPPER RIDGING STARTS TO BREAK DOWN AS WE TRANSITION TO
SOUTHWESTERLY FLOW LATE SATURDAY NIGHT INTO SUNDAY. A WEAK
SHORTWAVE MOVES ACROSS THE REGION ON SATURDAY BUT APPEARS TO STAY
JUST NORTHWEST OF THE FORECAST AREA. ANOTHER WAVE MOVES THROUGH
SUNDAY MORNING BUT A STRONGER WAVE TAKES AIM ON THE REGION LATE
SUNDAY AFTERNOON INTO SUNDAY NIGHT...PUSHING A COLD FRONT THROUGH
THE AREA. SHOWERS AND STORMS LOOK TO DEVELOP ALONG THE FRONT
SUNDAY AFTERNOON ACROSS PORTION OF NORTH CENTRAL IOWA....SOUTHEAST
MINNESOTA...AND WESTERN WISCONSIN. THEY THEN LOOK TO RACE EAST
ACROSS THE FORECAST AREA. THE STORMS LOOK TO INITIATE A LITTLE
FURTHER EAST WITH TODAYS MODEL RUNS. WHILE MOST OF THE STRONGER
SHEAR LAGS BEHIND THE FRONT THE 0-3KM SHEAR STARTS TO CATCH UP.
OVERALL CAPE AND DEEP LAYER SHEAR LOOKS TO BE THE LIMITING FACTOR
FOR SEVERE WEATHER POTENTIAL. STORMS ARE LOOKING LIKELY LATE
SUNDAY AFTERNOON INTO SUNDAY NIGHT....BUT IT APPEARS THE THREAT
FOR SEVERE WEATHER WILL BE LOW...ESPECIALLY EAST OF THE
MISSISSIPPI RIVER. LOCATIONS WEST OF THE MISSISSIPPI COULD SEE A
STRONG TO SEVERE STORM LATE SUNDAY AFTERNOON INTO EARLY SUNDAY
EVENING. COOLER AIR FILTERS INTO THE REGION IN THE WAKE OF THE
FRONT FROM MONDAY INTO TUESDAY WITH HIGHS FALLING BACK INTO THE
70S AND 80S. A FEW WEAK DISTURBANCES COULD IMPACT THE REGION FROM
MONDAY NIGHT THROUGH THURSDAY. FORECAST CONFIDENCE IS RATHER LOW
DURING THIS TIMEFRAME SO WILL LEAN TOWARD A MODEL CONSENSUS BLEND
FOR PRECIPITATION CHANCES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1148 PM CDT THU SEP 3 2015

DESPITE SOME MIXING AT THE SURFACE FROM THE SOUTHEAST WINDS...MVFR
VISIBILITIES HAVE ALREADY DEVELOPED AT KRST. THE 04.00Z NAM
FORECAST SOUNDINGS SUGGESTS THE SURFACE WILL STAY NEARLY SATURATED
THROUGH THE NIGHT...SO WILL CONTINUE THE MVFR VISIBILITY
REDUCTION...BUT STILL THINK THE WINDS AT THE SURFACE AND ALOFT
WILL BE TOO STRONG TO ALLOW IFR CONDITIONS TO DEVELOP. THERE WAS
STILL A 7 DEGREE TEMP/DEW POINT SPREAD AT 04.04Z AT KLSE AND THE
NAM FORECAST SOUNDINGS NOW DO NOT SHOW SATURATION OCCURRING
OVERNIGHT SO HAVE GONE BACK TO A PREVAILING MVFR VISIBILITY LATE
TONIGHT IN SOME FOG WITH JUST A SHORT PERIOD WITH SOME IFR
POSSIBLE. ONCE THE FOG BURNS OFF FRIDAY MORNING SHOULD BE VFR
CONDITIONS FOR THE REST OF THE PERIOD. A PASSING SHORT WAVE TROUGH
FRIDAY EVENING COULD BRING IN SOME MID LEVEL CLOUDS TO KRST FOR A
HIGH VFR CEILING.

&&

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

$$

SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...04


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