670
FXUS63 KFSD 211725
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1225 PM CDT FRI AUG 21 2026
KEY MESSAGES
- PATCHY FOG, POSSIBLY LOCALLY DENSE, CONTINUES THROUGH MID
MORNING. VISIBILITY MAY DROP BELOW A MILE AT TIMES.
- LOW CHANCES (LESS THAN 20%) FOR SHOWERS NEAR AND NORTH OF US
HIGHWAY 14 THIS AFTERNOON AND EVENING. LOW CHANCES FOR
THUNDERSTORMS IN THE LATE AFTERNOON AND INTO TONIGHT ALONG AND
SOUTH OF THE MISSOURI RIVER. SEVERE WEATHER RISK IS LOW.
- 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
(10-20%), 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 321 AM CDT FRI AUG 21 2026
LIGHT WINDS, CLEAR SKIES, AND TEMPERATURES/DEW POINTS IN THE 60S ARE
LEADING TO PATCHY FOG DEVELOPMENT ONCE AGAIN EARLY THIS MORNING. A
FEW CAMS AND ENSEMBLES ARE SHOWING THE POTENTIAL FOR DENSE FOG, SO
WILL KEEP AN EYE ON POTENTIAL FOR HEADLINES IF THIS DEVELOPS AND
BECOMES WIDESPREAD.
MOST OF TODAY SHOULD BE DRY WITH TEMPERATURES WARMING INTO THE 80S.
SHOWERS/SPRINKLES ARE POSSIBLE LATER TODAY NORTH OF US HWY 14 WITH A
WEAK WAVE, ALTHOUGH CHANCES ARE LOW (LESS THAN 15%) DUE TO DRY AIR.
FURTHER SOUTH TO THE MO RIVER VALLEY INTO NE, A STRONGER WAVE IS
PROGGED TO MOVE THROUGH THIS AFTERNOON AND THIS EVENING, WHICH COULD
LEAD TO SOME ISOLATED STORMS. WILL ALSO HAVE TO WATCH FOR WHERE
CONVECTION THIS AFTERNOON/EVENING IN WESTERN SD TRACKS TONIGHT AS
THIS MAY ALSO GRAZE THE MO RIVER VALLEY. ALTHOUGH WE DO HAVE SOME
INSTABILITY, SHEAR, AND MODEST MID LEVEL LAPSE RATES, SOUNDINGS SHOW
A FAIRLY ROBUST CAP WHICH SHOULD LIMIT CONVECTION. ADDITIONALLY,
BETTER DYNAMICS AND BOUNDARY LIE ACROSS NE, FURTHER REDUCING
CONVECTIVE POTENTIAL AND MINIMIZING POTENTIAL SEVERE RISK. AS HAS
BEEN THE TREND WITH THIS CONTINUED NORTHWESTERLY FLOW REGIME, CAMS
ARE SHOWING LITTLE AGREEMENT IN CONVECTION TODAY/TONIGHT.
PLEASANT DAY EXPECTED SATURDAY, WITH RAIN CHANCES RETURNING TO THE
AREA SUNDAY INTO MONDAY.
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 /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1225 PM CDT FRI AUG 21 2026
VFR CONDITIONS ARE EXPECTED FOR THE TAF PERIOD. HIGH PRESSURE IS
RESULTING IN CLEAR SKIES AND LIGHT WINDS ACROSS THE AREA. WINDS WILL
REMAIN LIGHT AND NORTHERLY THROUGH THE REST OF THE DAYLIGHT HOURS
BEFORE GOING LIGHT AND VARIABLE THIS EVENING. PATCHY VALLEY FOG IS
AGAIN POSSIBLE TONIGHT THOUGH CONFIDENCE IS TOO LOW TO INCLUDE IN A
TAF. LIGHT NORTHERLY WINDS WILL PICK UP TOMORROW MORNING TO END THE
TAF PERIOD.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...SG
DISCUSSION...MEYERS
AVIATION...MEYERS
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