662
FXUS63 KARX 140530
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1230 AM CDT THU AUG 14 2025
KEY MESSAGES
- HEAVY RAIN LOOKS TO BE A THREAT FROM FRIDAY NIGHT INTO SUNDAY
NIGHT. THIS COULD RESULT IN SOME FLASH FLOODING. HOWEVER,
UNCERTAINTY REMAINS HIGH ON LOCATION AND AMOUNTS.
- HEAT INDICES ON SATURDAY WILL RANGE FROM THE MID-90S TO AROUND
100F SOUTH OF INTERSTATE 94.
DISCUSSION
ISSUED AT 142 AM CDT WED AUG 13 2025
THURSDAY NIGHT
AS WARM AIR ADVECTION INCREASES ON THURSDAY NIGHT, SHOWERS AND
STORMS WILL DEVELOP ACROSS THE REGION. WITH WEAK, DEEP SHEAR
ACROSS THE REGION, ORGANIZED CONVECTION IS NOT EXPECTED.
FRIDAY IN THE WEEKEND
THE MODELS ARE IN GENERAL AGREEMENT THAT SEVERAL MESOSCALE
CONVECTIVE COMPLEXES WILL INITIALLY DEVELOP OVER THE NORTHERN
PLAINS AND AND WESTERN MINNESOTA FROM FRIDAY NIGHT INTO THE
WEEKEND AND THEN TRACK ALONG THE PERIPHERY OF 700 MB CAP. THERE
IS STILL PLENTY ON UNCERTAINTY ON WHERE THE EDGE OF THE CAP
WILL BE LOCATED ACROSS THE UPPER MISSISSIPPI RIVER VALLEY AND
GREAT LAKES. THE 700 MB 10TH TO 90TH PERCENTILES CURRENTLY RANGE
FROM 12 TO 14C IN NORTHEAST IOWA, SO THERE IS HIGHER CONFIDENCE
THESE COMPLEXES WILL LIKELY MOVE NORTH AND NORTHEAST OF THIS
AREA. MEANWHILE, FOR THE REMAINDER OF THE AREA, THE 700 MB 10TH
TO 90TH PERCENTILES CURRENTLY RANGE FROM 11 TO 13C. THIS
RESULTS IN PLENTY UNCERTAINTY ON HOW THE MESOSCALE COMPLEXES
WILL MOVE ACROSS MINNESOTA AND WISCONSIN. THE DETERMINISTIC RUNS
OF THE GFS, NAM, AND ECMWF SUGGEST THAT THE FRIDAY NIGHT AND
SATURDAY MORNING MESOSCALE CONVECTIVE SYSTEM WOULD LIKELY TRACK
ACROSS THE NORTHERN TWO-THIRDS OF THE FORECAST AREA, THE
SATURDAY NIGHT INTO SUNDAY MESOSCALE COMPLEX WOULD TRACK ACROSS
EITHER THE NORTHERN THIRD OR NORTHERN HALF OF THE AREA ON
SATURDAY NIGHT AND SUNDAY MORNING, AND THE ONE ON SUNDAY NIGHT
LOOKS TO MOVE ACROSS MUCH OF THE FORECAST AREA.
WITH PRECIPITABLE WATER VALUES RANGING FROM 2 TO 2.5 INCHES,
WARM CLOUD LAYER DEPTHS AROUND 4 KM, AND 0-1 KM MIXED-LAYER
CAPES RANGING FROM 1500 TO 3000 J/KG UNDERNEATH THE CAP, HEAVY
RAIN WILL BE A CONCERN. WPC CURRENTLY HAS A MARGINAL RISK OF
FLASH FLOODING THROUGH THIS TIME PERIOD.
WHILE THE DEEP SHEAR REMAINS WEAK THROUGH THIS TIME PERIOD, THE
850 MB AND 700 MB WINDS DO CLIMB INTO THE 30 TO 40 KNOT RANGE AT
TIMES, SO THERE IS CONCERN THAT A DAMAGING WIND GUST THREAT MAY
DEVELOP, BUT AT THIS TIME THE CONFIDENCE REMAINS LOW THAT THIS
WILL OCCUR.
HEAT INDICES ON SATURDAY WILL BE IN THE 80S NORTH OF INTERSTATE
94 AND RANGE FROM THE MID-90S TO AROUND 100F.
MONDAY INTO FRIDAY
THE 500 MB RIDGE EXTENDING FROM THE NORTHERN PLAINS INTO THE
CANADIAN PRAIRIES PROVINCES FLATTENS EARLY IN THIS PERIOD. AS
THIS OCCURS, A COLD FRONT WILL MOVES SOUTH THROUGH THE AREA ON
MONDAY AND MONDAY NIGHT. AS THIS OCCURS, THE HEAVY RAIN THREAT
WILL GRADUALLY SHIFT SOUTH OF THE AREA.
IN THE WAKE OF THIS FRONT, A CANADIAN HIGH PRESSURE SYSTEM WILL
BUILD SOUTH INTO THE AREA FOR TUESDAY INTO FRIDAY. THIS WILL
RESULT IN NEAR-NORMAL TEMPERATURES AND SLIGHTLY HIGHER (33-40
PERCENT) PROBABILITIES FOR BELOW-NORMAL PRECIPITATION. NORMAL
HIGH TEMPERATURES ARE NEAR 80 AND LOW TEMPERATURES ARE NEAR 60.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1230 AM CDT THU AUG 14 2025
MAIN AVIATION CONCERN THROUGH THE TAF PERIOD WILL BE VALLEY FOG
EARLY THIS MORNING WITH FOG ALREADY DEVELOPING IN THE WISCONSIN
RIVER AND VARIOUS TRIBUTARIES AS KOVS HAS OBSERVED 5SM VSBY JUST
BEFORE MIDNIGHT. CONSEQUENTLY, CONFIDENCE IS INCREASING (40-60%
CHANCE) FOR VALLEY FOG TO SPREAD INTO THE MAIN CHANNEL OF THE
MISSISSIPPI AS LOW DEWPOINT DEPRESSIONS (3-5F OVER THE LAST 30
MINUTES), CALM TO LIGHT SOUTHEAST WINDS AND A 5000FT LIGHT WIND
LAYER IN THE RECENT RAP/HRRR HAVE ALL BEEN OBSERVED AT KLSE. THE
ONLY THING THAT LOWERS CONFIDENCE FOR VALLEY FOG IS SOME MID TO
UPPER-LEVEL CLOUDS THAT ARE ATTEMPTING TO WORK THEIR WAY IN FROM THE
WEST. GUIDANCE CONFLICTS ON HOW THESE WILL EVOLVE OVER THE NEXT
6 HOURS BUT WOULD SEEM FAIRLY LIKELY FOR FOG DEVELOPMENT ON THE
MISSISSIPPI RIVER IF THEY CLOUDS HOLD OFF GIVEN THE AFOREMENTIONED
CONDITIONS. OTHERWISE, VFR CONDITIONS ARE EXPECTED THROUGHOUT THE
PERIOD WITH WINDS INCREASING TO AROUND 8-12 KTS FROM THE SOUTHEAST
FOR THE AFTERNOON.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...BOYNE
AVIATION...NAYLOR
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