523
FXUS63 KARX 202234
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
534 PM CDT WED AUG 20 2025
KEY MESSAGES
- ISOLATED SHOWERS ARE POSSIBLE (10-20%) ACROSS PORTIONS OF
WESTERN WISCONSIN AND NORTHEAST IOWA THIS AFTERNOON. FOG IS
ANTICIPATED AGAIN TONIGHT INTO THURSDAY MORNING.
- SHOWERS AND STORMS ARE POSSIBLE FRIDAY AFTERNOON AND EVENING
(20-40%). SOME STORMS COULD BE STRONG TO SEVERE.
- BELOW NORMAL TEMPERATURES ARE EXPECTED THIS WEEKEND INTO EARLY
NEXT WEEK. HIGHS IN THE MID 60S AND LOWS IN THE MID 40S ARE
EXPECTED.
DISCUSSION
ISSUED AT 141 PM CDT WED AUG 20 2025
THIS AFTERNOON AND THURSDAY
HIGH PRESSURE AND UPPER RIDGING CONTINUE TO INFLUENCE THE
REGION'S WEATHER TODAY INTO THURSDAY, ALLOWING FOR
PREDOMINANTLY DRY CONDITIONS. DESPITE THESE FEATURES THOUGH,
ISOLATED SHOWERS MAY DEVELOP ACROSS PORTIONS OF WESTERN
WISCONSIN AND NORTHEAST IOWA THIS AFTERNOON (10-20%) ASSOCIATED
WITH AVAILABLE MOISTURE IN THE 900-800HPA LAYER FROM
NORTHEASTERLY FLOW OFF THE GREAT LAKES, A FEW HUNDRED J/KG OF
SBCAPE, AND WEAK INVERTED SURFACE TROUGHING. SHOWERS THAT DO
DEVELOP WILL DIMINISH AS DIURNAL HEATING COMES TO AN END THIS
EVENING.
PATCHY FOG APPEARS PROBABLE AGAIN TONIGHT INTO THURSDAY MORNING
WITH A SIMILAR SET-UP TO THE PAST FEW DAYS WITH HIGH PRESSURE
OVERHEAD, LIGHT WINDS, AND DEWPOINT DEPRESSIONS OF 2 DEGREES OR
LESS.
SHOWERS AND STORMS POSSIBLE FRIDAY
AS THE RIDGE AND SURFACE HIGH PRESSURE BEGIN TO SHIFT EASTWARD
THURSDAY, A LONGWAVE TROUGH CURRENTLY EVIDENT OVER THE WEST
COAST OF CANADA ON WATER VAPOR IMAGERY SHIFTS EASTWARD,
DEEPENING ACROSS SOUTHERN CANADA. SURFACE CYCLOGENESIS
ASSOCIATED WITH THIS TROUGH WILL ALLOW A COLD FRONT TO DIVE
SOUTHEASTWARD ACROSS THE UPPER MIDWEST ON FRIDAY, ENTERING OUR
AREA BY FRIDAY EVENING. INSTABILITY BUILDS AHEAD OF THE FRONT
WITH MUCAPE VALUES OF 1000-2000 J/KG WHICH COMBINED WITH 0-6KM
BULK SHEAR VALUES OF 25-35KTS COULD SUPPORT SOME STRONGER STORMS
WITH HAIL AND STRONG WINDS THE PRIMARY THREATS.
THE THREAT OF STRONG TO SEVERE STORMS ACROSS OUR AREA REMAINS
CONDITIONAL THOUGH, LARGELY IN PART TO UNCERTAINTY IN THE AMOUNT
OF CAPPING IN PLACE ACROSS THE REGION. THE 20.06Z GFS/GEFS
FAVOR SLIGHTLY WARMER 850-700HPA TEMPERATURES (I.E., MORE
CAPPED) AS COMPARED TO THE 20.00Z ECMWF/ENS. GIVEN THESE
TEMPERATURE VARIATIONS, THE GFS/GEFS TEND TOWARDS A SOLUTION
LESS FAVORABLE FOR STRONG/SEVERE CONVECTION ACROSS OUR AREA
WHEREAS THE ECMWF/ENS TEND TOWARDS A SOLUTION MORE FAVORABLE FOR
STRONG/SEVERE CONVECTION ACROSS OUR AREA.
OVERALL, UNCERTAIN IN THE EVOLUTION OF FRIDAY'S WEATHER, BUT
THE THERMODYNAMICS AND KINEMATICS COULD SUPPORT SOME STRONGER
STORMS DEPENDENT ON THE INFLUENCE OF THE CAPPING. AS SUCH, THE
SPC HAS PLACED A MARGINAL RISK (LEVEL 1 OUT OF 5) FOR SEVERE
WEATHER ACROSS PORTIONS OF OUR AREA.
BELOW NORMAL TEMPERATURES
IN THE WAKE OF THE COLD FRONT, A COOLER AND DRIER AIRMASS WILL
BE USHERED INTO THE UPPER MIDWEST UNDER NORTHWEST FLOW, ALTHOUGH
SCATTERED SHOWERS WILL BE POSSIBLE, PRIMARILY ON SUNDAY, OWING
TO THE CYCLONIC FLOW AND STEEPER LOW LEVEL LAPSE RATES
ASSOCIATED WITH THE LOW.
BELOW NORMAL TEMPERATURES CONTINUE TO BE FAVORED AMONGST THE
ENSEMBLE GUIDANCE WITH ONLY A FEW DEGREES OF SPREAD NOTED IN THE
20.13Z NBM 25-75TH PERCENTILES. THE 20.00Z EFI ALSO DEPICTS
70-90% OF THE MEMBERS ARE BELOW THE MODEL CLIMATOLOGY FOR BOTH
HIGH AND LOW TEMPERATURES INDICATING ANOMALOUSLY LOW
TEMPERATURES ARE FAVORED. CURRENTLY EXPECTING HIGHS GENERALLY IN
THE MID 60S AND LOWS IN THE MID 40S FOR MUCH OF THE AREA. WILL
NEED TO MONITOR TRENDS OVER THE COMING DAYS REGARDING LOW
TEMPERATURES THOUGH AS THE LOWER PERCENTILES OF THE NBM SUGGEST
LOWS COULD DIP INTO THE UPPER 30S ACROSS NORTHERN WISCONSIN,
LIKELY DEPENDENT ON OVERNIGHT CLOUD COVERAGE.
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 535 PM CDT WED AUG 20 2025
THERE HAVE BEEN NO SIGNIFICANT CHANGES TO THE FORECAST OVER THE
PAST 6 HOURS. THE 20.18Z MODELS CONTINUE TO SHOW THAT THE LIGHT
WINDS EXTEND UP TO 500 MB. THEY ALSO SHOW A BIT MORE CLOUDS
OVERNIGHT. DUE TO THIS, KEPT THE FOG IN THE FORECAST OVERNIGHT.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...FALKINHAM
AVIATION...BOYNE
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