860
FXUS63 KFSD 201952
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
252 PM CDT WED AUG 20 2025
KEY MESSAGES
- PATCHY FOG IS POSSIBLE TOMORROW MORNING TO THE EAST OF I-29.
- CHANCES FOR STRONG TO SEVERE STORMS RETURN TO THE AREA LATE
THURSDAY AND FRIDAY. SOME UNCERTAINTY REMAINS, MAINLY
REGARDING THE TIMING OF STORMS, SO KEEP UP WITH THE LATEST
FORECAST FOR THE MOST UP TO DATE INFORMATION.
- THE FIRST TASTE OF FALL RETURNS TO THE AREA FOR THE WEEKEND
AND PERSISTS THROUGH THE FIRST HALF OF NEXT WEEK. HIGHS IN
THE 60S, 70S, AND 80S ARE LIKELY ALONG WITH LOWS FALLING TO
THE 40S AND 50S.
DISCUSSION
ISSUED AT 251 PM CDT WED AUG 20 2025
CLEAR SKIES AND LIGHT WINDS PERSIST THIS AFTERNOON AS SURFACE
RIDGING CONTINUES TO OFF TO THE EAST. HIGHS HAVE WARMED TO THE UPPER
70S AND 80S WHILE DEW POINTS REMAIN IN THE 60S AND 70S WILL KEEP
HUMID CONDITIONS AROUND. WITH DEW POINTS REMAINING IN THE 60S, LOW
TEMPERATURES WILL ONLY FALL TO THE 60S AS WELL TONIGHT. THIS WILL
AGAIN KEEP CHANCES FOR FOG IN THE FORECAST, MAINLY ALONG AND EAST OF
I-29 WHERE THE BEST HUMIDITY AND LIGHTEST WINDS WILL LIE.
THURSDAY LOOKS TO BE MOSTLY QUIET DURING THE DAYLIGHT HOURS. HIGHS
WILL AGAIN WARM TO THE 80S AND 90S, WARMEST WEST OF THE JAMES RIVER.
WITH DEW POINTS REMAINING IN THE 60S AND 70S, HEAT INDICES WILL
AGAIN REACH UP TO THE 80S AND 90S. THE NEXT CHANCE FOR SHOWERS AND
STORMS, SOME OF WHICH COULD BE STRONG TO SEVERE, RETURNS ON
THURSDAY. SOME UNCERTAINTY REMAINS REGARDING THE TIMING OF STORMS.
LOOKING AT THE DYNAMICS, AN UPPER LEVEL SHORTWAVE TROUGH WILL ROUND
THE TOP OF AN UPPER LEVEL RIDGE SITTING OVER THE FOUR CORNERS AREA.
A COLD FRONT WILL BE TIED TO THIS WAVE BUT THE BEST FORCING FOR
ASCENT WILL BE NORTH OF THE FORECAST AREA. WHILE THE FRONT ITSELF
WILL BE IN PLAY, THINK THAT LITTLE IF ANY CONVECTION WILL DEVELOP
ALONG THE FRONT GIVEN HOW AN UPPER LEVEL JETS RIGHT ENTRANCE REGION
WILL BE PARKED OVER THE NORTHERN PLAINS. THE INDIRECT THERMAL
CIRCULATION (ITC) FROM THE EXIT REGION OF THE JET WILL RESULT IN
PREDOMINANTLY LARGE SCALE SUBSIDENCE ACROSS THE AREA. AT THE SAME
TIME, CAPPING WILL BE IN PLACE AND THE FRONT WILL BE SITUATED WEST
OF THE AREA DURING THE AFTERNOON HOURS ON THURSDAY. AS THE FRONT
SLIDES INTO THE AREA THURSDAY EVENING AND NIGHT, CONVECTIVE CHANCES
LOOK TO INCREASE. COULD SEE CONVECTION DEVELOP ON THE ELEVATED
BOUNDARY BETWEEN 850 TO 750 MB. HOWEVER, THIS LAYER IN THE
ATMOSPHERE LOOKS GENERALLY DRY. WHILE FURTHER ELEVATED SHOWERS AND
STORMS ARE POSSIBLE, THINK THAT HIGHLY ELEVATED CONVECTION WOULD BE
SUB SEVERE. IF CONVECTION IS ABLE TO DEVELOP ON THIS BOUNDARY,
ELEVATED INSTABILITY VALUES UP TO 1,500 TO 2,000 J/KG IS POSSIBLE.
EFFECTIVE SHEAR WILL REMAIN MODEST AT AROUND 30 TO 35 KNOTS VIA A
STRAIGHT HODOGRAPH. CONVECTION LOOK TO DEVELOP WEST OF THE JAMES
RIVER VALLEY AND PUSH EASTWARDS THROUGH THE NIGHT INTO FRIDAY
MORNING.
CHANCES FOR CONVECTION WILL PERSIST THROUGH THE DAYLIGHT HOURS ON
FRIDAY AS THE FRONT CONTINUES TO PUSH THROUGH THE FORECAST AREA. AS
OF NOW, CHANCES FOR STORMS (30-60%) ARE HIGHEST DURING THE MORNING
HOURS. MOST OF THE LATEST 12Z GUIDANCE DOES NOT GO PAST 7 AM FRIDAY
MORNING. HOWEVER, A FEW MODELS DO. THE RRFS AND THE NAM3KM SHOW THE
POTENTIAL FOR CONVECTION TO DEVELOP ALONG THE SOMEWHAT WASHED OUT
FRONT FRIDAY AFTERNOON ACROSS PARTS OF SOUTHEAST SOUTH DAKOTA,
SOUTHWEST MINNESOTA, AND NORTHWEST IOWA. THIS POTENTIAL IS MORE
UNCERTAIN THOUGH AS LITTLE FORCING WILL BE IN PLACE AND THE
ATMOSPHERE LOOKS TO BE SOMEWHAT CAPPED. THAT SAID, THE ENSEMBLES DO
SHOW A 20-30% CHANCE FOR A TENTH OF AN INCH OF RAIN FRIDAY
AFTERNOON. THE HIGHEST PROBABILITIES RESIDE ACROSS NORTHWEST IOWA.
ASIDE FROM SHOWER AND STORM CHANCES, FRIDAY WILL BE THE LAST HUMID
DAY ACROSS THE AREA AS HIGHS WILL COOL A BIT TO THE UPPER 70S AND
80S WHILE DEW POINTS WILL REMAIN IN THE 60S AND 70S. LOW
TEMPERATURES WILL FALL TO THE 50S TO 60S OVERNIGHT.
SATURDAY DELIVERS THE FIRST TASTE OF FALL TO THE AREA AS HIGHS WILL
WARM TO ONLY THE UPPER 60S AND 70S WHILE DEW POINTS FALL TO THE 50S.
NORTHWEST FLOW WILL MAKE FOR A MARGINALLY BREEZY DAY WITH GUSTS UP
TO 20-25 MPH EXPECTED. SUNDAY WILL BE THE COOLEST DAY OF THE WEEKEND
WITH HIGHS REMAINING IN THE 60S AND 70S BUT DEW POINTS WILL FALL
FURTHER DOWN TO THE UPPER 40S AND 50S. WITH A WEAKER SURFACE
PRESSURE GRADIENT IN PLACE THANKS TO A SURFACE HIGH SLOWLY SPILLING
INTO THE NORTHERN PLAINS, WINDS WILL BE A BIT WEAKER. WITH DRY
CONDITIONS EXPECTED, THE WEEKEND WILL BE WONDERFUL FOR OUTDOOR
ACTIVITIES! LOW TEMPERATURES WILL FALL TO THE 40S AND 50S SATURDAY
AND SUNDAY NIGHTS, COLDEST ON SUNDAY NIGHT.
THE FIRST HALF OF NEXT WEEK LOOKS TO CONTINUE TO BE DRY AS A BROAD
UPPER LEVEL WAVE MEANDERS ACROSS THE NORTHEASTERN CONUS. THIS WILL
KEEP BROAD NORTHWEST FLOW ALOFT IN PLACE ALONG WITH HIGH PRESSURE AT
THE SURFACE. THUS, HIGHS IN THE 60S, 70S, AND 80S LOOK TO PERSIST
DURING THIS PERIOD OF TIME ALONG WITH LOWS FALLING TO THE 40S AND
50S. WITH HIGH PRESSURE IN PLACE, WIND WILL BE LIGHT, MAKING FOR A
SOLID START TO THE WORK WEEK.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1222 PM CDT WED AUG 20 2025
MAINLY VFR CONDITIONS BEGIN THE TAF PERIOD EARLY THIS AFTERNOON.
LOCATIONS ACROSS PARTS OF THE MISSOURI RIVER VALLEY INTO ADJACENT
AREAS IN NORTHWEST IOWA ALONG WITH A A FEW LOCATIONS ALONG THE
BUFFALO RIDGE IN SOUTHWEST MINNESOTA ARE REPORTING CEILINGS DOWN TO
MVFR/IFR LEVELS. THIS IS MAINLY IN THE FORM OF A CU FIELD THAT HAS
DEVELOPED. THE CU FIELD COULD EXPAND IN COVERAGE THROUGH THE REST OF
THE AFTERNOON HOURS. HOWEVER, THINK THAT DRIER AIR MIXING DOWN MAY
DISSIPATE THE CU FIELD IN TIME. WINDS WILL BE LIGHT AT 5-15 KNOTS
AND OUT OF THE EAST/SOUTHEAST THIS AFTERNOON.
FOG IS ONCE AGAIN ON THE TABLE FOR TONIGHT. AS OF NOW, FOG IS MOST
LIKELY EAST OF I-29. HAVE LEFT ANY MENTION OF BR OR FG OUT OF KFSD
AND KHONS TAFS AT THIS TIME. TRENDS WILL BE MONITORED. WINDS WILL
TURN SOUTHERLY TO END THE TAF PERIOD TOMORROW.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...MEYERS
AVIATION...MEYERS
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