332
FXUS63 KARX 170934
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
434 AM CDT FRI APR 17 2026
KEY MESSAGES
- A COMPLEX SEVERE WEATHER FORECAST FOR THIS AFTERNOON AS
POSSIBLY TWO WAVES OF STORMS ARE IN THE OFFING, WITH THE
STRENGTH AND TIMING OF THE FIRST WAVE OF STORMS PLAYING INTO
HOW THE SECOND WAVE OF STORMS EVOLVES.
- LARGE HAIL UP TO 2-3" IN DIAMETER, DAMAGING WINDS OF 60 TO 70
MPH, A FEW TORNADOES (SOME STRONG), AND LOCALLY HEAVY
RAINFALL ARE ALL ON THE TABLE WITH THESE STORMS.
- MUCH COLDER FOR THE WEEKEND WITH LOW TEMPERATURES FALLING
BELOW FREEZING STARTING TONIGHT THROUGH SUNDAY NIGHT. DAYTIME
HIGHS OVER THE WEEKEND WILL BE STUCK IN THE 40S. CAN'T RULE
OUT SOME FLURRIES ON SATURDAY.
- DRY CONDITIONS AND WARMING TEMPERATURES EXPECTED FOR THE START
OF NEXT WEEK.
DISCUSSION
ISSUED AT 430 AM CDT FRI APR 17 2026
SEVERE WEATHER THREAT FOR THIS AFTERNOON
EVEN AT THE 11TH HOUR, SOME CRITICAL DETAILS ON THE EVOLUTION
OF OUR AFTERNOON SEVERE WEATHER THREAT REMAIN TO BE NAILED DOWN.
THIS IS A SITUATION WHERE ATTENTION NEEDS TO BE PAID TO THE
WEATHER THROUGHOUT THE AFTERNOON AS THE THREATS UNFOLD.
THE EARLY MORNING SURFACE ANALYSIS ACROSS THE UPPER MIDWEST
SHOWS OUR CULPRIT COLD FRONT STRETCHING FROM SIOUX FALLS, SD TO
INTERNATIONAL FALLS, MN AND MARCHING STEADILY TO THE ESE, AIDED
BY AN APPROACHING SEASONABLY STRONG UPPER TROPOSPHERIC NORTHERN
STREAM TROUGH AND STRONG CAA PURSUING OVER THE DAKOTAS. A
994-MB SURFACE LOW PRESSURE CELL OVER EASTERN NEBRASKA WILL
PROPAGATE QUICKLY NORTHEAST ALONG THE FRONT, LIFTING A WARM
FRONT WITH IT THROUGH THE REGION THIS MORNING. STRONG SURFACE
THETA-E ADVECTION IS BEING OBSERVED ACROSS WESTERN IOWA AHEAD OF
THIS LOW WITH DEWPOINTS REACHING THE LOW TO MID 60S JUST AHEAD
OF THE FRONT. THIS IS A CLASSIC "NICK OF TIME" SEVERE WEATHER
SCENARIO WHERE THE FAVORABLE THERMODYNAMIC SEVERE WEATHER
ENVIRONMENT WILL ARRIVE JUST AHEAD OF STORM INITIATION.
THERE ARE TWO WINDOWS OF OPPORTUNITY FOR STORMS TO FORM LATER
THIS MORNING INTO THE AFTERNOON, ONE WAVE ALONG THE LEADING
WARM FRONTAL BOUNDARY AND THE SECOND WITH THE COLD FRONT COMING
THROUGH A FEW HOURS LATER. RAPID DESTABILIZATION IS PROGGED TO
OCCUR IN THE WARM SECTOR AS THE WARM FRONT LIFTS THROUGH THE
REGION BETWEEN 16-19Z WITH WARM SECTOR MLCAPE VALUES OF
2000-2500 J/KG AND DEEP SHEAR PROFILES OF 30-50+ KTS. LOW LEVEL
HODOGRAPHS ALONG THE WARM FRONT WILL FEATURE VERY FAVORABLE
PROFILES IN THE 0-1 TO 0-6-KM LAYER SUPPORTIVE OF STRONGLY
ROTATING UPDRAFTS AND TORNADOES. THIS PARAMETER SPACE EXISTS FOR
SEVERAL HOURS IN THE WARM SECTOR IN THE WAKE OF THE WARM FRONT
UNTIL THE COLD FRONT BLASTS THROUGH BETWEEN 18-00Z TODAY FROM
WEST TO EAST.
THE TIMING OF THE STORMS WILL BE ABSOLUTELY CRITICAL TODAY TO
DETERMINE HOW THE EXACT SEVERE HAZARDS WILL UNFOLD WITH SEVERAL
DIFFERENT SCENARIOS IN PLAY. THE LATEST RUNS OF THE HRRR ARE
FAVORING ELEVATED CONVECTION DEVELOPING NORTH OF THE TRIPLE
POINT AND KICKSTARTING CONVECTION DOWN THE WARM FRONT AS IT
LIFTS INTO THE FORECAST AREA. HOWEVER, THE UPDRAFT STRENGTH IN
THESE MODEL RUNS HAS NOT BEEN OVERLY STRONG WITH THIS ROUND OF
CONVECTION AT FIRST, LIKELY OWING TO THE MEAN STORM MOTIONS (FOR
STORMS DEVELOPING ALONG THE FRONT) OUTPACING THE BOUNDARY AND
RESULTING IN THE STORMS TRACKING INTO A MUCH HIGHER INHIBITION
AIRMASS AHEAD OF THE FRONT BEFORE DEVIANT RIGHT MOVING STORM
MOTIONS CAN BE ACHIEVED. A FEW CAM SOLUTIONS SHOW MORE ROBUST
UPDRAFTS ABLE TO SLOW DOWN AND STAY WITHIN THE MORE FAVORABLE
THERMODYNAMIC ENVIRONMENT, SO HOW THE THREAT ALONG THIS BOUNDARY
EVOLVES MAY HAVE TO BE ASSESSED ON A STORM BY STORM BASIS IN
REAL TIME.
CAN'T FULLY RULE OUT MORE OPEN WARM SECTOR CONVECTION LAGGING
THE WARM FRONT GIVEN THE DYNAMIC ENVIRONMENT IN PLACE, WHICH
WOULD RESULT IN STORMS POSING AN ALL HAZARDS RISK RATHER
QUICKLY. THIS LOOKS TO BE MORE OF A LOWER CONFIDENCE, BUT
POTENTIALLY HIGHER IMPACT SCENARIO.
ATTENTION THEN TURNS TO THE COLD FRONT AS IT CRUISES TO THE ESE
THROUGH THE FORECAST AREA THIS AFTERNOON. RECENT CAM RUNS ARE
HINTING AT A BETTER RISK FOR LARGER AND MORE ROBUST STORMS
FURTHER SOUTH ALONG WHAT WOULD NOW BE MORE OF A PREFRONTAL
TROUGH VERSUS A TRUE WARM FRONT IN IOWA. SHOULD ROBUST
CONVECTION DEVELOP WITHIN THIS CORRIDOR--THE INFLOW FOR OUR COLD
FRONTAL STORMS--THIS MAY CHOKE OFF DEVELOPMENT FURTHER NORTH
ALONG THE COLD FRONT. HOW FAR NORTH REMAINS TO BE SEEN. A
LINEAR UPSCALE GROWTH PROGRESSION IS EXPECTED ALONG THE FRONT AS
THE AFTERNOON GOES ON, WITH THE LINE ADVANCING OUT OF THE
REGION BY 00Z. BOTH SUPERCELLULAR AND QLCS TORNADOES WOULD BE
POSSIBLE ALONG THE LINE GIVEN THE FAVORABLE RESPECTIVE SHEAR
PROFILES FOR BOTH SETUPS.
ALOT TO HAPPEN IN A SHORT 6-7 HOUR WINDOW THIS AFTERNOON AND
ONLY SMALL CHANGES TO THE TIMING OF ANY ONE OF THESE VARIABLES
COULD HAVE A DOMINO EFFECT ON THE REST OF THE EVENT.
THIS WEEKEND & EARLY NEXT WEEK: DRIER & COOLER
AS WE HEAD PAST TODAY, COOLER AIR WORKS ITS WAY IN WITHIN THE
BROADER TROUGHING REGIME ON SATURDAY WITH HIGHS LIKELY
PLUMMETING INTO THE 40S TO LOWER 50S FOR THE WEEKEND. CANNOT
RULE OUT SOME FLURRIES OR LIGHT SNOW SHOWERS NORTH OF I-94
DURING THE MORNING HOURS ON SATURDAY. OVERNIGHT LOWS ON
SATURDAY NIGHT WILL LIKELY FALL BELOW FREEZING FOR MANY SPOTS SO
BE SURE TO COVER ANY PLANTS YOU HAVE SET OUT! HOWEVER, NO
ACCUMULATIONS WOULD BE EXPECTED. OTHERWISE, SURFACE HIGH
PRESSURE MOVES INTO THE REGION FOR SUNDAY KEEPING US RELATIVELY
PRECIPITATION FREE INTO EARLY NEXT WEEK.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1250 AM CDT FRI APR 17 2026
VFR CONDITIONS CONTINUE FOR THE REST OF THE NIGHT WITH AN MVFR
CU FIELD DEVELOPING TOWARDS LATE MORNING AND CONTINUING INTO THE
AFTERNOON. THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG AND AHEAD
OF A COLD FRONT THAT MOVES THROUGH DURING THE AFTERNOON, SOME OF
WHICH COULD BE SEVERE AND PRODUCE LARGE HAIL AND DAMAGING WINDS.
SOUTH TO SOUTHEAST WINDS OF 10-20G25-30KTS INCREASE THROUGH THE
MORNING WITH WINDS BACKING TO THE NORTHWEST AT 10-20G20-25KTS
BEHIND THE FRONT FOR THE EVENING AND OVERNIGHT.
HYDROLOGY
ISSUED AT 430 AM CDT FRI APR 17 2026
A FLOOD WATCH HAS BEEN ISSUED FOR SOUTHWEST WISCONSIN AND
PORTIONS OF WEST CENTRAL WISCONSIN GIVEN THE CHANCE FOR
ADDITIONAL SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING.
THESE AREAS HAVE ALREADY SEEN COPIOUS AMOUNTS OF RAINFALL OVER
THE LAST WEEK WITH MANY RIVERS EXPERIENCING SIGNFICIANT FLOODING
(ENOUGH TO CLOSE SOME ROADS IN MULTIPLE COUNTIES). A
WIDESPREAD 1/2 INCH OF RAIN IS LIKELY WITH LOCALIZED POCKETS OF
1-2 INCHES--ANY ADDITIONAL RAIN WILL BE PROBLEMATIC AND ONLY
EXACERBATE EXISTING PROBLEMS. MUDSLIDES ALSO LOOK TO BE A
PROBLEM AS WE HAVEN'T SEEN A FULL GREEN UP YET SO ROOTS HAVE NOT
TAKEN A STRONG HOLD YET. RIVERS ACROSS WISCONSIN ARE LIKELY TO
SEE ADDITIONAL RISES, ESPECIALLY THE KICKAPOO, YELLOW, BLACK,
AND WISCONSIN.
ARX WATCHES/WARNINGS/ADVISORIES
WI...FLOOD WATCH FROM 1 PM CDT THIS AFTERNOON THROUGH SATURDAY
MORNING FOR WIZ042>044-053>055-061.
MN...NONE.
IA...NONE.
DISCUSSION...SKOW/NAYLOR
AVIATION...SKOW
HYDROLOGY...SKOW/BARENDSE
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