870
FXUS63 KARX 021727
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1227 PM CDT WED SEP 2 2026
KEY MESSAGES
- ISOLATED TO SCATTERED SHOWERS AND STORMS ARE POSSIBLE THIS
AFTERNOON, MAINLY ALONG AND SOUTH OF HIGHWAY 18 (10-20%).
- SHOWERS AND STORMS DEVELOP THURSDAY MORNING (40-70%) BEFORE A
POTENTIAL MCS MOVES THROUGH THE AREA THURSDAY NIGHT.
- PERIODIC SHOWERS AND STORMS CONTINUE THROUGH THE HOLIDAY
WEEKEND.
DISCUSSION
ISSUED AT 1158 AM CDT WED SEP 2 2026
THIS AFTERNOON - TONIGHT: ISOLATED TO SCATTERED SHOWERS/STORMS
THE QUASI-STATIONARY BOUNDARY THAT HAS PLAGUED THE UPPER
MISSISSIPPI RIVER VALLEY THE LAST SEVERAL DAYS REMAINS SITUATED
ALONG AND SOUTH OF I-90 THROUGH THE REST OF TODAY. WITH THE
BOUNDARY IN PLACE AND WEAK 850HPA WARM AIR ADVECTION AND
MOISTURE TRANSPORT INTO IT, THERE IS SOME LOW POTENTIAL FOR THE
SHOWERS AND STORMS ONGOING ACROSS NORTH-CENTRAL IOWA TO CONTINUE
EASTWARD INTO NORTHEAST IOWA AND SOUTHWEST WISCONSIN (10-20%).
GIVEN LITTLE IN THE WAY OF AIRMASS CHANGE, FAIRLY IMPRESSIVE
INSTABILITY IS EXPECTED TO BUILD ACROSS THE REGION AGAIN THROUGH
THE AFTERNOON HOURS WITH RAP/HRRR SOUNDINGS SUGGESTING MUCAPE
SHOULD BE UPWARDS OF 1500-2500 J/KG. HOWEVER, MORE FAVORABLE
INSTABILITY IS EXPECTED SOUTH AND EAST OF OUR AREA AND THE LOW
LEVEL CAPPING ALSO REMAINS SO CONFIDENCE IN HOW THE ONGOING
STORMS EVOLVE IS FAIRLY LOW AS THE LOW LEVEL JET WEAKENS AND
PIVOTS INTO EASTERN IOWA.
IF STORMS ARE ABLE TO CONTINUE EASTWARD THIS AFTERNOON, THERE
IS A LOW POSSIBILITY THEY WILL BE ABLE TO PRODUCE SOME HIGHER
RAINFALL TOTALS GIVEN FAVORABLE STORM MOTION VECTORS PARALLEL TO
THE BOUNDARY WHICH WOULD LEAD TO TRAINING STORMS. TRAINING HAS
ALREADY BEEN OBSERVED WITH THEM ACROSS NORTH-CENTRAL IOWA, SO
THIS WILL BE SOMETHING TO MONITOR THROUGH THE AFTERNOON IF STORM
COVERAGE BEGINS TO INCREASE. ALSO CAN'T RULE OUT A STRONGER
STORM GIVEN THE ENERGY AVAILABLE, BUT DIMINISHING 500HPA WINDS
WILL RESULT IN LESS THAN FAVORABLE EFFECTIVE SHEAR VALUES AND
SHOULD LARGELY INHIBIT ANY STRONG/SEVERE THREAT.
THURSDAY - FRIDAY: STRONG TO SEVERE STORM POTENTIAL
EARLY THURSDAY MORNING, WARM ADVECTION AND MOISTURE TRANSPORT
INCREASE ACROSS THE REGION AS THE NOCTURNAL LOW LEVEL JET
INCREASES. WHEN COMBINED WITH A WEAK SHORTWAVE AT 700-500HPA
MOVING THROUGH THE REGION, CONVECTIVE DEVELOPMENT SHOULD BE ABLE
TO OCCUR ACROSS MUCH OF THE UPPER MISSISSIPPI RIVER VALLEY,
CONTINUING THROUGH THE REMAINDER OF THE MORNING HOURS. THERE IS
QUITE A BIT OF MODEL INCONSISTENCY REGARDING THE TIMING AND
EVOLUTION OF THIS CONVECTION AND OVERALL CONFIDENCE IN PRECISELY
WHAT WILL HAPPEN IS LOW, BUT CONFIDENCE IS MEDIUM TO HIGH THAT
CONVECTION WILL DEVELOP (40-70%). SIMILAR TO THE LAST FEW DAYS,
SUFFICIENT INSTABILITY FOR STRONGER STORMS REMAINS ACROSS THE
REGION, THOUGH WIND SHEAR WILL BE THE BE THE PRIMARY LIMITING
FACTOR FOR SEVERE WEATHER. SOUTH OF I-94, EFFECTIVE SHEAR IS
FAIRLY WEAK, ON THE ORDER OF 20-30KTS WHEREAS NORTH OF I-94 THIS
INCREASES TOWARDS 35-45KTS WITH STRAIGHT HODOGRAPHS. IF STORMS
DEVELOP NORTH OF I-94, SUCH AS THE 02.12Z HRRR SUGGESTS, SOME
MORE DISCRETE TO SUPERCELLULAR STRUCTURES ARE POSSIBLE. THE
02.09Z RAP SUGGESTS MID-LEVEL LAPSE RATES STEEPEN TO 7- 7.5 C/KM
IN THIS ALREADY FAVORABLE ENVIRONMENT WHICH WOULD SUPPORT HAIL
DEVELOPMENT ALONG WITH DAMAGING WINDS GIVEN DCAPE AROUND 1000
J/KG. SOUTH OF I-94, IT CURRENTLY LOOKS AS THOUGH CONVECTIVE
DEVELOPMENT WOULD BE ON THE WEAKER SIDE GIVEN THE LESS FAVORABLE
SHEAR PROFILES.
THURSDAY EVENING AND OVERNIGHT, THERE'S THE POTENTIAL FOR AN
MCS TO ROLL THROUGH THE AREA AS STORMS THAT DEVELOP NEAR THE
MINNESOTA/NORTH DAKOTA/SOUTH DAKOTA BORDER. CONFIDENCE IN WHEN,
WHERE, OR EVEN IF THIS SYSTEM DEVELOPS IS PRETTY LOW AS ITS
EVOLUTION WILL LARGELY HINGE ON HOW THE CONVECTION EARLIER IN
THE DAY PLAYS OUT. AS OF RIGHT NOW, WOULD EXPECT DAMAGING WINDS
TO BE THE PRIMARY THREAT THOUGH A TORNADO OR TWO CAN'T BE RULED
OUT WITHIN FAVORABLY ORIENTED BOWING SEGMENTS GIVEN 0-3KM SHEAR
OF 30-35KTS, ASSUMING THE SYSTEM BECOME SURFACE BASED.
ANOTHER BOUT OF SHOWERS AND STORMS ARE EXPECTED FRIDAY
AFTERNOON ALONG THE BOUNDARY THAT REMAINS SITUATED ACROSS THE
REGION. A RINSE AND REPEAT ATMOSPHERIC SET-UP REGARDING LOW
LEVEL MOISTURE AND WARMTH WILL LEAD TO INSTABILITY FAVORABLE FOR
SOME STRONGER UPDRAFTS, BUT WEAK 500HPA WINDS AND RISING
HEIGHTS MAY LARGELY LIMIT ANY SORT OF STRONG/SEVERE POTENTIAL.
THE SPC CURRENTLY HAS PART OF OUR AREA OUTLINED IN A MARGINAL
RISK (LEVEL 1 OUT OF 5) AND WILL BE ANOTHER PERIOD TO MONITOR.
HOLIDAY WEEKEND: PERSISTING SHOWERS AND STORMS
THE UPPER MIDWEST REMAINS ON THE NORTHERN EDGE OF A MID TO
UPPER LEVEL RIDGE THROUGH THE WEEKEND. SEVERAL SHORTWAVE TROUGHS
MOVE ALONG THE NORTHERN EXTENT OF THIS RIDGE, DIRECTLY OVER THE
UPPER MISSISSIPPI RIVER VALLEY, WHICH WILL SUPPORT PERIODIC
SHOWER AND STORM DEVELOPMENT THROUGH THE WEEKEND. DAILY
PROBABILITIES FOR RAINFALL SIT AROUND 20-40% IN THE 02.13Z NBM.
WHILE INSTABILITY WILL BE PRESENT FOR SOME RUMBLES OF THUNDER,
EFFECTIVE SHEAR IS EXPECTED TO BE FAIRLY WEAK, LIMITING THE
POTENTIAL FOR SEVERE WEATHER THROUGH THE WEEKEND. THIS IS
SUPPORTED BY AI/ML GUIDANCE WHICH HAVE LITTLE TO NO FOOTPRINT
FOR STRONG/SEVERE STORMS ACROSS THE UPPER MISSISSIPPI RIVER
VALLEY.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1225 PM CDT WED SEP 2 2026
LARGELY VFR CONDITIONS PRESENT ACROSS THE AREA OUTSIDE OF PORTIONS
OF NE IOWA SEEING SOME MVFR VISIBILITIES FROM A SMALL LINE OF
SHOWERS AND THUNDERSTORMS EARLY THIS AFTERNOON. THIS LINE OF SHOWERS
AND STORMS IS EXPECTED TO SLOWLY SAG SOUTH INTO CENTRAL AND EASTERN
IOWA BY LATER IN THE AFTERNOON WITH VFR CONDITIONS EXPECTED TO
REMAIN EVERYWHERE ELSE. LIGHT WINDS GENERALLY OUT OF THE SOUTH
AND/OR EAST WILL CONTINUE THROUGH THE PERIOD AT OR BELOW 12 KTS. AN
AREA OF SHOWERS AND STORMS IS EXPECTED TO DEVELOP LATE OVERNIGHT AND
INTO TOMORROW MORNING WITH CONFIDENCE IN POPS INCREASING AFTER 12Z
FOR BOTH TERMINALS. HAVE ADDED PREVAILING SHOWERS WITH PROB30
THUNDER AT THIS TIME. HOW THIS ACTIVITY WILL EVOLVE TOMORROW
MORNING IS STILL PRETTY UNCERTAIN SO HAVE CONTINUED THE PROB30
THROUGH THE END OF THE PERIOD.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...FALKINHAM
AVIATION...BARENDSE
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page