291
FXUS63 KFSD 110338
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1038 PM CDT THU SEP 10 2026
KEY MESSAGES
- STORMS MAY DEVELOP FRIDAY LATE AFTERNOON AND EVENING. IF
STORMS DEVELOP, THEY MAY QUICKLY BECOME STRONG TO SEVERE.
CONFIDENCE IN DEVELOPMENT AND COVERAGE REMAINS LOW DUE TO
STRONG CAPPING POTENTIAL.
- ADDITIONAL CHANCES FOR SHOWERS AND THUNDERSTORMS RETURN SUNDAY
MORNING AND CONTINUE INTO THE MIDDLE OF NEXT WEEK. SOME STORMS
MAY BECOME STRONG TO SEVERE.
- COOLER CONDITIONS ARRIVE THIS WEEKEND INTO MUCH OF NEXT WEEK.
OCCASIONAL SHOWER AND STORM CHANCES LINGER MID NEXT WEEK.
UPDATE
ISSUED AT 913 PM CDT THU SEP 10 2026
MODELS CONTINUE TO BE VERY AGREEABLE THAT SURFACE BASED
CONVECTION WILL BE HARD TO COME BY ON FRIDAY AFTERNOON WITH
FAIRLY STRONG CAPPING AND ONLY WEAK CONVERGENCE ALONG THE
SURFACE FRONT. SO FOR NOW, THUNDERSTORM CHANCES BEFORE ABOUT 7
PM LOOK SLIM. THERE IS SOME AGREEMENT ON INCREASING THE LLJ FROM
ABOUT 925MB TO 850MB EARLY TOMORROW EVENING WITH CONVERGENCE
FOCUSING MAINLY EAST OF I-29. IF THE ELEVATED CAP LIFTING FROM
THIS LEVEL CAN WEAKEN ENOUGH WE WOULD LIKELY SEE 1500-2000 J/KG
CAPE WITH ABOUT 30 KNOTS OF DEEP LAYER SHEAR. THIS WOULD BE
ENOUGH TO PRODUCE HAIL TO PING PING BALL AND WIND GUSTS TO 65
MPH. ONE OTHER AREA TO WATCH WILL BE OVER PARTS OF SOUTHWEST MN.
CAPPING MAY WEAKEN ENOUGH EARLY IN THE EVENING TO ALLOW STORMS
TO EITHER DEVELOP OR BUILD SOUTHWARD INTO THE AREA. SHEAR IS A
LITTLE STRONGER IN THIS AREA WITH SIMILAR INSTABILITY SO A
COUPLE OF STRONGER UPDRAFTS WILL BE POSSIBLE. OVERALL CONTINUES
TO LOOK LIKE AN ISOLATED TO SCATTERED AT BEST SCENARIO.
DISCUSSION
ISSUED AT 145 PM CDT THU SEP 10 2026
THIS AFTERNOON WILL BE DRY AND BREEZY WITH GUSTS 25-35 MPH, MOSTLY
CLEAR SKIES, AND HIGHS IN THE UPPER 70S TO 80S. DEW POINTS WILL BE
LOWER THIS AFTERNOON AT AROUND 60 OR LESS. OVERALL A PLEASANT DAY IS
IN STORE. OVERNIGHT LOWS WILL BE IN THE MID TO UPPER 60S WITH THE
BREEZY WINDS CONTINUING INTO FRIDAY.
FRIDAY WILL BE ANOTHER WARM DAY WITH HIGHS IN THE 80S FOR MOST OF
THE CWA, AND THE LOW 90S WEST OF THE JAMES RIVER VALLEY. THROUGHOUT
THE DAY A NARROW PLUME OF THETA-E AIR WILL ADVECT IN FROM THE SOUTH,
ALONG AND EAST OF HIGHWAY 81. INSTABILITY WILL INCREASE ALONG AND
EAST OF THE PLUME WITH MUCAPE VALUES CLIMBING TO 1500-2000 J/KG.
MODEST MID-LEVEL LAPSE RATES AROUND 7+ DEG C/KM WILL ALIGN WELL WITH
THE PLUME OF INSTABILITY. BULK SHEAR WILL BE 35-40 KTS. WITH
CLOCKWISE CURVED HODOGRAPHS THIS SET UP IS MARGINAL TO SLIGHTLY
FAVORABLE FOR ALL MODES OF SEVERE WEATHER. THIS IS ALSO OUTLINED IN
THE SPC DAY 2 OUTLOOK WITH A SLIGHT RISK (LEVEL 2 OF 5) FOR SEVERE
WEATHER. HOWEVER, A FEW ITEMS OF UNCERTAINTY KEEP CONFIDENCE IN
CONVECTION INITIATION AND COVERAGE LOW. PROBABLY THE MOST IMPORTANT
FACTOR IS DESPITE THE MOISTURE ADVECTION MODEL SOUNDINGS REMAIN
DRY THROUGH MOST OF THE COLUMN FOR AREAS WEST OF I-29. FORCING
IS ON THE STRONG SIDE IN THE FORM OF THE UPPER TROUGH AND
SURFACE LOW/COLD FRONT, BUT WITHOUT MOISTURE NOT MUCH IS GOING
TO HAPPEN BESIDES SOME CUMULUS CLOUDS. EAST OF I-29 MOISTURE
RETURN FLOW IS BETTER, HOWEVER THE ENVIRONMENT WILL BE STRONGLY
CAPPED. AS THE WHOLE SYSTEM PROGRESSES EAST THROUGH THE EVENING
AND INTO THE OVERNIGHT THE AIRMASS SLOWLY SATURATES. BUT BY
THIS POINT THE FORCING SHOULD BE ALONG OUR EASTERN CWA BORDER
IF NOT INTO CENTRAL IOWA. IN THIS SCENARIO WE WILL GET VERY
LITTLE IF ANY CONVECTION. THIS IS THE MOST LIKELY SCENARIO AT
THIS TIME.
THE OTHER SCENARIO IS THE BETTER MOISTURE RETURN DRIFTS FARTHER
WEST. THEN AS THE SYSTEM PASSES THROUGH WE COULD SEE SATURATION
OCCUR SOONER, AND THUS CONVECTION BEGIN EARLIER EAST OF HIGHWAY 81
BETWEEN 4 AND 7 PM, AND ALONG AND EAST OF THE I-29 CORRIDOR
ROUGHLY BETWEEN 7 PM AND 10 PM. STORMS WOULD TRACK EAST AND BE
OUT OF THE CWA ROUGHLY BETWEEN MIDNIGHT AND 3 AM SATURDAY. THE
FINAL SCENARIO IS WE ARE ABLE TO LIFT OFF THE 850-700 MB LAYER
AND SCATTERED STRONG TO SEVERE STORMS COULD DEVELOP. ALL THIS TO
SAY A VERY CONDITIONAL ENVIRONMENT WILL BE IN PLACE WITH RISKS
FOR LARGE HAIL AND DAMAGING WIND GUSTS. THOUGH THE RISK IS LOW, A
TORNADO CANNOT BE RULED OUT.
BEHIND THE COLD FRONT OVERNIGHT LOWS WILL COOL INTO THE 50S AND LOW
60S OVER NORTHWEST IOWA. THROUGH THE MORNING HOURS A FEW
ISOLATED ELEVATED SHOWERS ARE POSSIBLE. WINDS WILL BECOME
NORTHERLY AND LIGHT DURING THE DAY. MID-LEVEL TEMPERATURES WILL
FALL INTO THE TEENS C AND AT THE SURFACE HIGHS WILL BE SLIGHTLY
BELOW AVERAGE FOR THIS TIME OF YEAR, IN THE LOW 70S NORTH OF
I-90 AND THE MID TO UPPER 70S TO THE SOUTH. MUCH DRIER AIR WILL
ADVECT IN FROM THE NORTH BRINGING DEW POINTS DOWN TO THE 40S TO
MID 50S. SATURDAY WILL BE A PLEASANT TASTE OF FALL.
EARLY SUNDAY MORNING THE FLOW ALOFT BECOMES MOSTLY ZONAL AND HIGH
PRESSURE BUILDS IN AT THE SURFACE. MODEST MOISTURE RETURN ON
SOUTHEAST WINDS AND WAA AHEAD OF AN APPROACHING LOW AMPLITUDE WAVE
MAY BE ENOUGH TO TRIGGER LIGHT SCATTERED SHOWERS AND THUNDERSTORMS
BY THE LATE MORNING TO EARLY AFTERNOON. THESE ARE NOT EXPECTED TO BE
SEVERE BUT COULD BRING RAIN TO A LARGER PORTION OF THE REGION.
SUNDAY EVENING INTO THE OVERNIGHT A STRONG UPPER TROUGH SWINGS
THROUGH NORTHWEST OF THE REGION. AN ASSOCIATED SURFACE LOW EJECTS
OUT OF COLORADO ONTO THE CENTRAL PLAINS AND ACCELERATES NORTHEAST
INTO OUR CWA. THOUGH MANY DETAILS ARE UNCLEAR AT THIS TIME, SOME
STORMS COULD BE STRONG TO SEVERE SUNDAY NIGHT INTO MONDAY MORNING.
STORMS MAY LINGER INTO THE AFTERNOON.
NORTHWEST FLOW ALOFT IS EXPECTED FOR THE FIRST HALF OF NEXT WEEK. AT
THE SURFACE HIGHS WILL BE CLOSER TO SEASONAL AVERAGES, IN THE 70S.
ANOTHER ROUND OF STORMS IS POSSIBLE MID-WEEK.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1037 PM CDT THU SEP 10 2026
VFR THROUGH THE PERIOD. BREEZY SOUTHERLY WINDS THROUGH THE
PERIOD WITH SOME GUSTS OF 35 TO 40 MPH LIKELY DURING THE DAY
FRIDAY. A FEW EARLY MORNING ACCAS SHOWERS WILL BE POSSIBLE
FRIDAY MORNING, BUT CONFIDENCE IS LOW. A STRONG TO SEVERE STORM
WILL BE POSSIBLE AFTER ABOUT 22Z FRIDAY, BUT CONFIDENCE IS LOW
AND ANY STORMS THAT MAY DEVELOP SHOULD REMAIN VERY ISOLATED. THE
BETTER CHANCES WILL BE NEAR AND EAST OF I-29.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...08
DISCUSSION...AJP
AVIATION...08
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