415
FXUS63 KFSD 101131
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
631 AM CDT THU SEP 10 2026
KEY MESSAGES
- PATCHY VALLEY FOG MAY LEAD TO VISIBILITY BELOW ONE MILE AT
TIMES THROUGH 9 AM OR SO. OTHERWISE, DRY AND WARMER TODAY;
BREEZY WEST OF I-29.
- 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 MODERATE TO HIGH CHANCES (50-80 PERCENT) FOR
SHOWERS AND THUNDERSTORMS RETURN LATE SATURDAY NIGHT INTO
EARLY NEXT WEEK. HEAVY RAIN IS POSSIBLE SUNDAY, WITH ISOLATED
STRONG STORMS POSSIBLE MONDAY.
- COOLER CONDITIONS ARRIVE THIS WEEKEND INTO MUCH OF NEXT WEEK.
OCCASIONAL SHOWER AND STORM CHANCES LINGER MID NEXT WEEK.
UPDATE
ISSUED AT 313 AM CDT THU SEP 10 2026
NO SIGNIFICANT CHANGES TO THE FORECAST THIS MORNING. KEEPING AN EYE
ON POTENTIAL FOR VALLEY FOG, BUT THUS FAR HAVE NOT SEEN MUCH
DEVELOPMENT. ANY FOG THAT DOES DEVELOP THIS MORNING SHOULD BE
LARGELY CONFINED TO RIVER VALLEYS AND QUICKLY MIX OUT AN HOUR OR TWO
AFTER DAYBREAK, BUT VISIBILITY MAY FALL BELOW ONE MILE AT TIMES.
TEMPERATURES ARE NEAR SEASONAL AVERAGES, IN THE 50S THIS MORNING.
STILL ANTICIPATE A WARMER DAY AS SURFACE HIGH PRESSURE SLIDES EAST
AND SOUTHERLY LL FLOW RETURNS. HIGHS IN THE 80S FOR MOST, WITH
BREEZY CONDITIONS (GUSTS 30-35 MPH) WEST OF I-29. WINDS INCREASE
TONIGHT AS THE SURFACE PRESSURE GRADIENT COMPRESSES AHEAD OF A COLD
FRONT FRIDAY. LOWS A BIT WARMER WITH WAA AND SOUTHERLY FLOW - IN THE
60S. HAVE KEPT THE FORECAST DRY FOR TONIGHT INTO FRIDAY MORNING AS
ANY MOIST LAYER ALOFT IS VERY NARROW AND ANY SHOWER/SPRINKLE THAT
DEVELOPS IN THE WAA/WEAK WAVE WILL STRUGGLE.
NO MAJOR CHANGES TO THE SEVERE THREAT FRIDAY AFTERNOON/EVENING, AS
GUIDANCE CONTINUES TO SHOW THE BETTER FORCING AND DYNAMICS TO OUR
NORTH AND EAST, WITH A STRONG CAP OVERHEAD. CAMS LARGELY KEEP
CONVECTION OUT OF OUR AREA, BUT IF WE'RE ABLE TO BREAK THE CAP,
STORMS MAY QUICKLY BECOME STRONG TO SEVERE. MORE DETAILS BELOW IN
THE DISCUSSION SECTION.
SCATTERED SHOWERS AND STORMS CONTINUE INTO EARLY NEXT WEEK. LOCALLY
HEAVY RAIN LOOKS TO THE MAIN THREAT SUNDAY, WITH ISOLATED STRONGER
STORMS POSSIBLY RETURNING TO THE AREA MONDAY.
DISCUSSION
ISSUED AT 1251 PM CDT WED SEP 9 2026
HIGH PRESSURE SETTLE SOUTH TONIGHT AND SHOULD LEAD TO SOME CRISP
MORNING TEMPERATURES ON THURSDAY. LOOK FOR MORNING LOWS FROM THE MID
40S IN THE LOWER SPOTS TO THE LOWER 50S.
RETURN FLOW SETS UP THROUGH THE DAY THURSDAY WITH SOUTHERLY WINDS
LIKELY GUSTING TO 25 MPH WEST OF I-29. HIGHS WILL GENERALLY CLIMB
INTO THE 80S, WITH SOME 70S ACROSS PARTS OF NORTHWEST IA AND
SOUTHWEST MN.
THE LEADING EDGE OF A MID LEVEL WAVE WILL SNEAK INTO CENTRAL SD
LATE THURSDAY NIGHT INTO FRIDAY MORNING, RESULTING IN INCREASED LOW
TO MID LEVEL WARM ADVECTION. WHILE MOST OF THE AREA IS CAPPED DUE TO
DRY AIR, A SMALL WEDGE OF INCREASED MOISTURE AROUND 8000 FEET MAY
BRING WEAK, 200-400 J/KG, ELEVATED INSTABILITY BASED AROUND 8000
FEET. THIS COULD RESULT IN SOME ACCAS ON FRIDAY MORNING, WITH
IMPACTS ON THE MINOR SIDE.
THIS WAVE WILL DEEPEN A BIT AND TRACK JUST NORTH OF THE AREA ON
FRIDAY AFTERNOON AND EVENING, LEADING TO A WEDGE OF INCREASED
TEMPERATURES IN THE LOW LEVELS. THIS WILL LEAD TO WIDESPREAD HIGHS
IN THE MID 80S TO LOWER 90S. THE QUESTION THEN COMES TO WHAT ARE THE
CONVECTIVE CHANCES AS THIS WEDGE OF WARM AIR SETTLE SOUTH AND COOLER
AIR FILTERS IN BEHIND ON FRIDAY NIGHT. THE ENVIRONMENT AHEAD OF THIS
FRONT WILL BE FAIRLY UNSTABLE, 2000-3000 J/KG, WITH ABOUT 40 KNOTS
OF DEEP LAYER SHEAR. THE LOWER LEVELS SHOW A NICE SOUTH TO SOUTHWEST
INFLOW, SUGGESTING THAT NEW UPDRAFTS MAY BE ON THE SOUTHWEST FLANK
OF ANY DEVELOPMENT. GIVEN THE INSTABILITY AND SHEAR AS WELL AS THE
POTENTIAL FOR DISCRETE CELLULAR DEVELOPMENT, ALL MODES OF SEVERE
WEATHER WILL BE POSSIBLE, INCLUDING GOLF BALL SIZED HAIL, WIND GUSTS
TO 70 MPH AND ISOLATED TORNADOES. THE MAIN NEGATIVE WILL BE THE
POTENTIAL FOR A FAIRLY STRONG CAPPING INVERSION. THIS SUGGESTS THAT
THERE MAY BE A VERY SMALL WINDOW SHORTLY BEFORE SUNSET TO GET ANY
STRONG UPDRAFTS GOING THAT COULD PRODUCE HIGHER END SEVERE WEATHER.
AS THIS SYSTEM LIFTS EAST NORTHEAST FRIDAY NIGHT, COOLER AND DRIER
AIR WILL SETTLE SOUTHWARD AND BRING A PLEASANT SATURDAY WITH HIGHS
IN THE 70S AND DEW POINTS IN THE 45 TO 55 DEGREE RANGE.
A STRONGER SYSTEM WORKS ONTO THE NORTHERN PLAINS SUNDAY INTO EARLY
MONDAY AND SHOULD BRING A MORE WIDESPREAD AREA OF SHOWERS AND
THUNDERSTORMS TO THE REGION. THE LATEST ENSEMBLE OUTPUT FROM THE
GEFS, EC AND CANADIAN ALL SUGGEST ABOUT A 30-60 PERCENT CHANCE FOR
A HALF AN INCH OR MORE OF RAINFALL FOR MUCH OF THE AREA WITH A
SLIGHT LEAN TOWARDS THE BETTER CHANCES NEAR AND NORTH OF I-90.
WEST TO SOUTHWEST FLOW ALOFT CONTINUES THROUGH MID WEEK KEEPING THE
CHANCES FOR SHOWERS AND THUNDERSTORMS IN THE AREA DURING THIS TIME.
WITH SLIGHTLY COOLER AIR IN PLACE BEHIND THE SUNDAY SYSTEM AND THE
POTENTIAL FOR CLOUDS AND PRECIPITATION, TEMPERATURES WILL BE A BIT
COOLER WITH HIGHS IN THE 70S AND LOWS IN THE UPPER 40S TO MID 50S.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 625 AM CDT THU SEP 10 2026
VERY PATCHY VALLEY FOG IS LEADING TO SOME REDUCED VISIBILITY
THIS MORNING, WITH SOME LOCATIONS BRIEFLY TO LIFR CONDITIONS.
FOG SHOULD QUICKLY MIX OUT BY 14Z. OTHERWISE, VFR CONDITIONS
PREVAIL THROUGH THE PERIOD WITH A FEW HIGH CLOUDS AROUND THE
REGION.
WINDS INCREASE DURING THE DAY, BECOMING SOUTHERLY WITH GUSTS 20
TO 25 KNOTS (HIGHER LATE TODAY IN SOUTH CENTRAL SD). GUSTS
CONTINUE THROUGH THE OVERNIGHT. ALTHOUGH THE LLJ INCREASES, LLWS
APPEARS MORE MARGINAL FOR BOTH DIRECTIONAL AND SPEED SHEAR,
ESPECIALLY WITH GUSTS CONTINUING OVERNIGHT.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...SG
DISCUSSION...08
AVIATION...SG
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