903
FXUS63 KARX 240355
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1055 PM CDT WED APR 23 2025
KEY MESSAGES
- PERIODIC CHANCES OF SHOWERS AND STORMS ARE ON TAP THROUGH
FRIDAY. SOME STORMS COULD BECOME STRONG TO SEVERE THIS
EVENING, WITH LARGE HAIL BEING THE MAIN THREAT, AND LOCALLY
DAMAGING WINDS AS A LESSER, SECONDARY THREAT.
- THERE IS A LOW RISK OF LOCALIZED FLOODING DUE TO HEAVY
RAINFALL POSSIBLE THURSDAY NIGHT. TOTAL RAINFALL AMOUNTS
THROUGH FRIDAY ARE EXPECTED TO RANGE BETWEEN 0.5" TO 1.5",
HEAVIEST OVER SOUTHEAST MN AND NORTHEAST IA.
- A STRONG TROUGH COULD BRING ANOTHER RISK OF SEVERE WEATHER AND
HEAVY RAINFALL TO THE REGION NEXT MONDAY AND TUESDAY, ALONG
WITH SEASONABLY WARM TEMPERATURES IN THE 70S.
DISCUSSION
ISSUED AT 303 PM CDT WED APR 23 2025
WE WILL CONTINUE TO SEE PERIODIC CHANCES OF SHOWERS AND
THUNDERSTORMS THROUGH THE DAY FRIDAY, WITH THE MOST LIKELY CHANCES
COMING THURSDAY NIGHT (70 TO 90%). BEFORE THURSDAY NIGHT, ZONAL FLOW
ALOFT SHOULD PROVIDE ONLY WEAK FORCING FOR ASCENT OVERALL. HOWEVER,
WE ARE KEEPING AN EYE ON A COLD FRONT THAT WILL SWEEP THROUGH THE
AREA LATE THIS AFTERNOON INTO THE EVENING HOURS. THERE COULD BE
ENOUGH INSTABILITY TO SPARK OFF SOME STORMS DURING THIS TIME. THE
THREAT FOR STRONG TO SEVERE STORMS REMAINS PRETTY MARGINAL, GIVEN
MUCAPE VALUES TO AROUND 500 TO 1000 J/KG PER THE 23.12Z HREF
ENSEMBLE, WITH MID-LEVEL LAPSE RATES PROGGED AROUND 6 TO 7 C/KM.
THIS WOULD SUPPORT THE THREAT FOR LARGE HAIL. LOCALLY STRONG WIND
GUSTS APPEAR TO BE MORE OF A SECONDARY THREAT WITH ANY STRONG STORMS
AS THERE IS A BRIEF WINDOW OF TIME BEFORE THE BOUNDARY LAYER
DECOUPLES AND STABILIZES THE LOWER LEVELS. SPC HAS MAINTAINED A
MARGINAL RISK (LEVEL 1 OF 5) FOR SEVERE WEATHER THIS EVENING FOR
AREAS ALONG AND SOUTH OF A LINE FROM OSAGE, IA TO MONROE CENTER, WI.
AS WE GO INTO THE DAY THURSDAY, THE ZONAL FLOW ALOFT WILL GRADUALLY
BREAKDOWN, MAKING WAY FOR A MID-LEVEL IMPULSE TO SWEEP THROUGH THE
UPPER MS VALLEY REGION THURSDAY NIGHT INTO FRIDAY MORNING.
INCREASING CHANCES (70-90+%) OF MAINLY SHOWERS ARE EXPECTED WITH
THIS WAVE, GIVEN MEAGER INSTABILITY AND MID-LEVEL LAPSE RATES.
HOWEVER, THE MAIN FOCUS FOR THURSDAY NIGHT WILL BE HEAVIER DOWNPOURS
DUE TO COPIOUS MOISTURE. PWAT VALUES BETWEEN 1 TO 1.4" ARE PROGGED
WITH THIS ACTIVITY, WHICH IS ABOVE THE 90TH PERCENTILE ON THE EC
ENSEMBLE PERCENTILES FOR PRECIPITABLE WATER. THE BULK OF THE
PRECIPITATION FOR TONIGHT THROUGH FRIDAY SHOULD COME DURING THIS
TIME. TOTAL RAINFALL SHOULD RANGE BETWEEN 0.5" TO 1.5", BUT SOME
LOCALLY HIGHER AMOUNTS TO AROUND 2" ARE POSSIBLE, PER THE HREF LPMM
QPF FIELDS.
EVENTUALLY, CONDITIONS WILL DRY OUT FRIDAY, THANKS TO AN AREA OF
HIGH PRESSURE THAT WILL BUILD OUT OF THE CANADIAN PRAIRIES. THIS
SHOULD RESULT IN A SEASONAL SATURDAY, WITH HIGH TEMPERATURES WARMING
TO THE LOWER 60S ACROSS THE AREA AND DRY CONDITIONS UNDER MOSTLY
SUNNY SKIES. SUNDAY APPEARS TO BE MOSTLY DRY TO START, ALTHOUGH
SHORTWAVE RIDGING COULD SPARK OFF SOME MORE SHOWERS AND PERHAPS AN
ISOLATED THUNDERSTORMS LATER IN THE DAY.
AS WE LOOK AHEAD TOWARDS THE START OF THE WORK WEEK, WE CONTINUE TO
KEEP AN EYE ON AN INCREASED THREAT FOR STRONG TO SEVERE STORMS OVER
THE UPPER MS VALLEY AS A LONGWAVE UPPER-LEVEL TROUGH APPROACHES THE
REGION. AN ATTENDANT COLD FRONT WILL EVENTUALLY MOVE THROUGH THE
AREA BY LATE MONDAY, WHICH SHOULD SUPPORT SOME LIKELY CHANCES (50-
70%) OF SHOWERS AND STORMS. THE CONVECTIVE PARAMETER SPACE APPEARS
SUPPORTIVE OF THE POTENTIAL FOR STRONG TO SEVERE CONVECTION, GIVEN
MLCAPE VALUES ON THE ORDER OF 1000-2000 J/KG, AND DEEP-LAYER SHEAR
VALUES OF 40 TO 50 KNOTS. ECMWF EFI VALUES FOR CAPE-SHEAR ARE
LEANING TOWARDS VALUES OF 0.6 TO 0.7 - ON THE LOWER-END OF THE
SCALE. HOWEVER, THE CSU-ML SEVERE PROBABILITIES SUGGEST A NOTABLE
SIGNAL FOR SEVERE WEATHER, WITH AN ALL-HAZARDS SCENARIO POSSIBLE.
FOR NOW, SPC HAS OUTLOOKED THE ENTIRE FORECAST AREA IN A SLIGHT RISK
(LEVEL 2 OF 5) FOR SEVERE WEATHER LATE MONDAY, SO STAY TUNED TO THE
LATEST FORECAST! IT WILL ALSO FEEL WARMER BY MONDAY, WITH HIGH
TEMPERATURES BUILDING INTO THE MIDDLE TO UPPER 70S FOR MOST
LOCATIONS.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1052 PM CDT WED APR 23 2025
VFR CONDITIONS CURRENTLY PRESENT AT THE TERMINALS. SHOWERS AND
STORMS HAVE REMAINED ACROSS NORTHEASTERN IOWA AND FAR
SOUTHWESTERN WISCONSIN SO FAR THIS EVENING BUT ACTIVITY IS
EXPECTED TO SPREAD NORTH AND EAST INTO THE OVERNIGHT HOURS. HAVE
ADDED TEMPO GROUPINGS AT BOTH TERMINALS WITH INCREASED CONFIDENCE
IN COVERAGE FOR SHOWERS/STORMS AFTER 08Z. AFTERWARDS, WE'LL SEE
A LULL IN ACTIVITY UNTIL LATER IN THE AFTERNOON WITH ACTIVITY
FILLING IN FROM THE WEST. HAVE ADJUSTED PREVAILING AND PROB30
GROUPS TO ALIGN WITH THE LATEST HI-RESOLUTION GUIDANCE. ACTIVITY
WILL REALLY PICK UP AFTER 21Z THURSDAY WITH MVFR AND IFR
CEILINGS AND VISIBILITIES BUILDING INTO THE AREA - IMPACTING RST
FIRST AROUND 22Z AND LSE LATER AROUND 04Z FRIDAY. CEILINGS MAY
DROP TO LIFR FOR RST AROUND 06Z BUT DID NOT HAVE ENOUGH
CONFIDENCE TO INCLUDE WITH THIS PACKAGE. WILL HAVE TO MONITOR
THIS POSSIBILITY FOR FUTURE PACKAGE UPDATES.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...ZAPOTOCNY
AVIATION...BARENDSE
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