828
FXUS63 KFSD 210406
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1106 PM CDT THU AUG 20 2026
KEY MESSAGES
- WARMER TEMPERATURES CONTINUE ON FRIDAY, WITH ANOTHER LOW
CHANCE (20%) FOR THUNDERSTORMS IN THE AFTERNOON AND EVENING
ALONG AND SOUTH OF THE MISSOURI RIVER.
- SLIGHTLY COOLER WEATHER FOR THE WEEKEND. SATURDAY SHOULD
REMAIN DRY. RAIN CHANCES (40-70%) RETURN TO WESTERN PORTIONS
OF THE AREA BY SUNDAY MORNING, EXPANDING EAST THROUGH SUNDAY
NIGHT.
- ADDITIONAL CHANCES FOR RAIN, AND POTENTIALLY THUNDERSTORMS
(5-10%), ARE POSSIBLE THROUGH THE FIRST HALF OF NEXT WEEK.
DETAILS ARE UNCERTAIN, SO CONTINUE TO CHECK THE LATEST
FORECAST FOR THE MOST UP TO DATE INFORMATION.
UPDATE
ISSUED AT 1106 PM CDT THU AUG 20 2026
A FEW SEVERE THUNDERSTORMS WHICH DEVELOPED AHEAD OF A WEAK COOL
FRONT EARLY THIS EVENING HAVE LARGELY ENDED, WITH JUST A STRAY
STORM LINGERING NORTHEAST OF WINDOM. THE REST OF TONIGHT SHOULD
BE QUIET, THOUGH WE COULD SEE SOME PATCHY FOG MAINLY EAST OF
I-29 TOWARD DAYBREAK. WIDESPREAD DENSE FOG IS NOT EXPECTED AT
THIS TIME.
STORM CHANCES FOR FRIDAY HAVE SHIFTED A BIT FARTHER SOUTH THAN
PREVIOUS FORECASTS, THOUGH PORTIONS OF THE MISSOURI RIVER VALLEY
MAY BE CLIPPED BY AN ISOLATED STORM OR TWO. SEVERE WEATHER RISKS
ARE LOW.
DISCUSSION
ISSUED AT 210 PM CDT THU AUG 20 2026
A LIGHT SHOWER OR TWO PERSISTS ACROSS SOUTHWEST MINNESOTA THIS
AFTERNOON. THESE SHOWERS REMAIN AHEAD OF A COLD FRONT THAT IS JUST
PUSHING INTO THE FORECAST AREA. THIS FRONT WILL SERVE AS THE FOCAL
POINT FOR POTENTIAL SEVERE STORM DEVELOPMENT LATER THIS AFTERNOON.
THE MAIN SHORTWAVE IS JUST NORTH AND EAST OF THE FORECAST AREA.
HOWEVER, THE UPPER LEVEL JET WILL BE NOSING ITS EXIT REGION INTO THE
SOUTHWESTERN HALF OF THE FORECAST AREA. THIS PRESENTS A BIT OF A
DISPLACEMENT IN WHERE THE BETTER SHEAR AND FORCING WILL LIE. SOME
CAPPING REMAINS ACROSS THE AREA BUT THE WEAKEST AMOUNT OF CAPPING
LOOKS TO BE JUST ALONG THE FRONT ITSELF. THINK THAT 1 TO 4 STORMS IS
POSSIBLE THIS AFTERNOON AND EVENING IF STORMS ARE ABLE TO DEVELOP.
IF STORMS DEVELOP, MORE THAN SUFFICIENT INSTABILITY WILL BE IN PLACE
WITH CAPE VALUES UP TO 2,000 J/KG TO 2,500 J/KG AS MOISTURE POOLS
AHEAD OF THE FRONT. WITH PART OF THE UPPER LEVEL JET OVERHEAD,
VERTICAL SHEAR WILL ALSO BE SUFFICIENT WITH DEEP LAYER SHEAR VALUES
BETWEEN 40 TO 50 KNOTS. DCAPE VALUES WILL BE HIGHEST ALONG AND JUST
BEHIND THE FRONT WITH MAGNITUDES UP TO 1,200 J/KG. THUS, LARGE HAIL
TO 2+ INCHES AND DAMAGING WINDS TO 50-70 MPH WILL BE THE MAIN
HAZARDS. A LOW 2% CHANCE EXISTS FOR A TORNADO AS THE LOW LEVEL JET
BEGINS TO STRENGTHEN THIS EVENING, SLIGHTLY EXPANDING LOW LEVEL
HODOGRAPHS AND INCREASING 0-3KM STORM RELATIVE HELICITY (SRH) VALUES
UP TO 100+ M2/S2. ANY CHANCE FOR SEVERE STORMS FOR BE WANING THROUGH
THE EVENING HOURS AS NOCTURNAL STABILIZATION INCREASES CAPPING. THE
PREVIOUSLY MENTIONED COLD FRONT WILL STALL OUT OVER THE FORECAST
AREA TONIGHT, LEAVING MUGGY CONDITIONS IN PLACE. WITH LIGHT WINDS
EXPECTED, PATCHY FOG IS ONCE AGAIN POSSIBLE.
HIGHS WILL REMAIN IN THE 80S ACROSS THE AREA ON FRIDAY. THE
PREVIOUSLY MENTIONED COLD FRONT WILL PUSH THROUGH THE FORECAST AREA
AND END UP RIGHT ALONG THE MISSOURI RIVER. THIS COULD RESULT IN A
FEW STORMS DEVELOPING ON THIS BOUNDARY BEFORE QUICKLY PUSHING OFF TO
THE SOUTH AND EAST. HOWEVER, LATEST LREF PROBABILITIES REMAIN LOW
(20-30%) FOR A TENTH OF AN INCH OF RAIN OR MORE. THE HREF SHOWS
LITTLE TO NO PROBABILITIES FOR ANY PRECIPITATION. THIS IS IN LINE
WITH THE LATEST HI-RES GUIDANCE AS THE BULK OF THIS GUIDANCE SHOWS
STORMS DEVELOPING SOUTH OF THE SURFACE FRONT IN NEBRASKA. WILL KEEP
AN EYE ON THIS POTENTIAL IN CASE STORMS TREND BACK NORTH, BUT FOR
NOW, IT LOOKS MOST LIKELY THAT THE FORECAST AREA WILL REMAIN DRY
TOMORROW. LOW TEMPERATURES WILL FALL TO THE UPPER 50S AND LOW 60S
OVERNIGHT.
SATURDAY WILL BE A DRY DAY AS HIGH PRESSURE PASSES THROUGH THE
FORECAST AREA. HIGH TEMPERATURES WILL BE A LITTLE COOLER, ONLY
WARMING TO THE UPPER 70S TO LOW TO MID 80S. THE DRY CONDITIONS WILL
BE BRIEF AS THE NEXT ROUND OF RAIN WILL RETURN ON SUNDAY AS ANOTHER
SHORTWAVE TROUGH WILL PUSH INTO THE NORTHERN PLAINS. LATEST
ENSEMBLES SHOW A 40-70% CHANCE FOR RAINFALL TOTALS TO EXCEED A TENTH
OF AN INCH THROUGH THE DAY. LATEST MACHINE LEARNING (ML) GUIDANCE
KEEPS THE HIGHEST CHANCES FOR SEVERE STORMS TO THE WEST OF THE
FORECAST AREA. THIS MAY CHANGE OVER THE NEXT FEW DAYS SO WILL
CONTINUE TO MONITOR THE POTENTIAL FOR SEVERE STORMS ON SUNDAY.
HIGH TEMPERATURES WILL REMAIN NEAR SEASONABLE IN THE UPPER 70S AND
80S FOR THE FIRST HALF OF NEXT WEEK. ACTIVE ZONAL TO NORTHWEST FLOW
WILL PERSIST ALOFT AS WELL, CONTRIBUTING TO ADDITIONAL RISKS FOR
SHOWERS AND STORMS. ML GUIDANCE DOES SHOWS A SMALL INCREASE IN
POTENTIAL SEVERE STORM RISK, THOUGH THE PROBABILITIES ONLY 5 TO 10%.
SOMETHING TO KEEP AN EYE ON GOING FORWARDS AS WEAK SHORTWAVES WITHIN
THE ACTIVE FLOW CAN DELIVER ADDITIONAL CHANCES FOR POTENTIAL SEVERE
STORMS.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1106 PM CDT THU AUG 20 2026
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT THE TAF SITES THROUGH
THIS PERIOD, THOUGH CANNOT RULE OUT SOME PATCHY MVFR LOW-LYING
FOG AROUND DAYBREAK FRIDAY.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...JH
DISCUSSION...MEYERS
AVIATION...JH
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