300
FXUS63 KFSD 281755
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1255 PM CDT FRI AUG 28 2026
KEY MESSAGES
- WARM AND HUMID CONDITIONS RETURN TODAY AND INCREASE FURTHER
THROUGH THE WEEKEND. AFTERNOON HEAT INDICES MAY APPROACH 100F
IN PORTIONS OF THE MISSOURI RIVER VALLEY SATURDAY/SUNDAY AS
TEMPERATURES CLIMB INTO THE 90S.
- A MARGINAL RISK (LEVEL 1 OF 5) FOR SEVERE THUNDERSTORMS
REMAINS IN PLACE FOR THIS AFTERNOON AND OVERNIGHT. OVERALL
CONFIDENCE IN AFTERNOON STORM DEVELOPMENT IS LOW, WITH BETTER
CHANCES TONIGHT. STRONGER STORMS MAY PRODUCE UP TO TWO INCH
HAIL AND 60 MPH WIND GUSTS.
- PERIODIC SHOWER AND STORM CHANCES CONTINUE THIS WEEKEND INTO
EARLY NEXT WEEK. CONFIDENCE ON ANY DETAILS IS LOW.
UPDATE
ISSUED AT 439 AM CDT FRI AUG 28 2026
FORECAST REMAINS ON TRACK EARLY THIS MORNING, WITH JUST MINOR
ADJUSTMENTS TO COVERAGE OF EARLY MORNING LOW POPS FOR VERY WEAK
ACCAS SHOWERS DRIFTING SOUTHEAST. EAST OF THIS MORE EXPANSIVE
CLOUD COVER, TEMPERATURES HAVE DIPPED INTO THE LOWER 50S, BUT
ANTICIPATE READINGS WILL LEVEL OFF OR PERHAPS RISE SLIGHTLY AS
THE CLOUDS SLIDE EAST BEFORE DAYBREAK.
ISSUED AT 844 PM CDT THU AUG 27 2026
MAIN CHANGE TO THE FORECAST THIS EVENING WAS TO ADD SOME ISOLATED
POPS TO THE AREA WEST OF I-29 LATE TONIGHT INTO EARLY FRIDAY
MORNING, WITH A VERY ISOLATED CELL ALREADY DEVELOPING WEST OF THE
JAMES THIS EVENING. ENOUGH DYNAMIC FORCING SHOULD EXIST WITH A
SUBTLE WAVE, WAA, AND ELEVATED INSTABILITY NEAR THE NOSE OF THE LLJ
FOR SOME SHOWERS AND ISOLATED THUNDERSTORMS TO DEVELOP. SEVERE
WEATHER IS NOT EXPECTED. STORMS SHOULD MOVE TO AND EAST OF I-29
BETWEEN DAYBREAK AND THE MORNING RUSH, TAPERING OFF BY MID MORNING.
STILL A WARM, HUMID, AND BREEZY DAY FRIDAY.
BIGGEST QUESTIONS FOR FRIDAY REMAIN CONVECTIVE CHANCES DURING THE
AFTERNOON AND EARLY EVENING, WHICH WOULD BE HIGHLY INFLUENCED BY
COVERAGE OF MORNING CLOUDS AND CONVECTIVE DEBRIS, WHICH MAY KEEP US
MORE STABLE. WITH GUIDANCE SPLIT ON ANY WAVES MOVING THROUGH (AND
THE STRENGTH OF THESE) DURING THE DAY, CONFIDENCE IN ANY
SHOWERS/STORMS DURING THE EVENING REMAINS LOW. GUIDANCE IS ALSO
SPLIT ON THE TIMING OF THE WAVES TOMORROW NIGHT. GFS IS THE QUICKER
OF THE MODELS WITH THE MAIN WAVE ENTERING OUR WESTERN FORECAST AREA
AROUND MID/LATE EVENING, WHILE CANADIAN AND NAM ARE SLOWER, CLOSER
TO MIDNIGHT. NO CHANGES TO THE SEVERE RISK/POTENTIAL, WITH SEVERE
STORMS POSSIBLE INTO THE OVERNIGHT WITH THE SLOWER SOLUTIONS - MAX
HAIL SIZE GOLF BALL TO 2 INCHES AND WIND GUSTS TO 60 MPH IN THE
STRONGEST STORMS.
DISCUSSION
ISSUED AT 304 PM CDT THU AUG 27 2026
ONE MORE VERY PLEASANT DAY TODAY WITH HIGHS IN THE UPPER 70S TO MID
80S, WITH LOW RELATIVE HUMIDITY, AND LIGHT WINDS. OUTSIDE OF SOME
THIN SMOKE FROM WILDFIRES, SKIES ARE EXPECTED TO BE MOSTLY CLEAR
TODAY AND TONIGHT. GOOD NEWS FOR THOSE OF YOU WHO WISH TO CATCH A
GLIMPSE OF THE PARTIAL LUNAR ECLIPSE TONIGHT. WITH ONE CAVEAT....
THOSE IN SOUTH CENTRAL SOUTH DAKOTA HAVE A LOW CHANCE (<30%) OF
SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND INTO THE EVENING. A
SUBTLE SHORT WAVE AND WEAK TO MID-LEVEL CONVERGENCE MAY WORK
TOGETHER TO TRIGGER CONVECTION. MUCAPE VALUES RANGE WIDELY BETWEEN
SHORT TERM GUIDANCE, FROM 500 TO NEARLY 2000 J/KG AND A MODERATELY
STRONG CAP WILL BE IN PLACE. HOWEVER, STEEP LOW-LEVEL LAPSE RATES
AND 35 KTS OF 0-6 BULK SHEAR COULD SUPPORT A STRONGER UPDRAFT OR
TWO. RISKS WITH STRONGER STORMS IS DAMAGING WIND GUSTS TO 60 MPH AND
MARGINALLY SEVERE HAIL TO 1 INCH IN DIAMETER. LOWS FOR TONIGHT WILL
FALL TO THE 50S AND LOW 60S.
FRIDAY A FEW SCATTERED STORMS MAY LINGER ALONG AN AREA OF WEAK MID-
LEVEL CONVERGENCE. THESE SHOULD CEASE BY LATE MORNING. THEN WE WILL
SEE THE RETURN OF HIGHER RELATIVE HUMIDITY AS SOUTHERLY WINDS USHER
IN A RICH THETA-E RIDGE. HIGHS ARE EXPECTED TO CLIMB TO THE 80S WITH
A FEW 90S SPRINKLED IN. TO THE WEST WE SEE A STRONGER MID-LEVEL WAVE
AND ASSOCIATED SURFACE LOW PRESSURE PUSHING EAST OUT OF THE ROCKIES.
THIS WILL WORK TO TIGHTEN THE SPG AND INDUCE A STRONG LLJ THROUGH
THE AFTERNOON. WITH GOOD MIXING WE'LL SEE GUSTS ALONG AND WEST OF I-
29 IN THE 25-35 MPH RANGE. SOUTH CENTRAL SOUTH DAKOTA WILL SEE THE
HIGHEST GUSTS. TO THE EAST OF I-29 GUSTS WILL BE 25 MPH OR LESS. AS
THE LOW PUSHES CLOSER A WARM FRONT WILL DRIFT NORTH THROUGH THE CWA,
POSSIBLY TRIGGERING SHOWERS AND THUNDERSTORMS IN THE MID TO LATE
AFTERNOON. THROUGH THE REMAINDER OF THE AFTERNOON AND EVENING THE
SYSTEM WILL BECOME MORE COMPACT. THE LLJ RAMPS UP RAPIDLY THROUGH
THE EVENING AND WAA INTENSIFIES WHICH COULD POTENTIALLY EXPAND STORM
COVERAGE AND SEVERITY AROUND MIDNIGHT. A MARGINALLY UNSTABLE
ENVIRONMENT WILL BE IN PLACE WITH MUCAPE VALUES OF 1000-2000 J/KG,
MID-LEVEL LAPSE RATES OF 7 C/KM OR HIGHER, AND 35-45 KTS OF 0-6 BULK
SHEAR. THERE REMAINS A COUPLE OF FACTORS THAT KEEP CONFIDENCE IN
STORMS LOW. WHILE MARGINALLY UNSTABLE, SOUNDINGS INDICATE A STRONG
CAP WILL BE IN PLACE ACROSS MOST OF THE REGION. WITHOUT STRONGER
FORCING IT IS UNCERTAIN IF CONVECTION WILL BE ABLE TO INITIATE.
HOWEVER, SHOULD STORMS FORM THEY HAVE THE POTENTIAL TO RAPIDLY
BECOME STRONG TO SEVERE. RISKS INCLUDE LARGE HAIL TO 2 INCHES IN
DIAMETER AND WIND GUSTS TO 60 MPH.
STORMS WILL CONTINUE INTO SATURDAY MORNING BEFORE PUSHING EAST OF
THE REGION. THE REST OF SATURDAY LOOKS TO BE DRY, WARM, AND HUMID
WITH HIGHS CLIMBING INTO THE MID 80S TO MID 90S, WARMEST OVER SOUTH
CENTRAL SOUTH DAKOTA. HEAT INDEX VALUES WILL BE VERY NEAR TO
CRITICAL (100 F) THROUGH THE JAMES RIVER VALLEY. SUNDAY WILL BE VERY
SIMILAR, WITH THE 90S EXPANDED EAST INTO NORTHWEST IOWA. HEAT INDEX
VALUES WILL ONCE AGAIN BE VERY NEAR TO CRITICAL. WE WILL CONTINUE TO
MONITOR THESE TRENDS. SUNDAY AFTERNOON A COLD FRONT WILL MOVE
THROUGH THE REGION, POSSIBLY BRINGING ANOTHER ROUND OF SHOWERS AND
THUNDERSTORMS.
FOR THE FIRST HALF OF NEXT WEEK THE UPPER RIDGE WE'VE BEEN UNDER
WILL BE SQUASHED SOMEWHAT BY A STRONG UPPER LOW OVER CENTRAL CANADA.
FLOW REMAINS SOUTHWEST WITH MULTIPLE SHORT WAVES TRAVERSING THROUGH.
THIS WILL KEEP SHOWER AND THUNDERSTORM CHANCES IN THE FORECAST
THROUGH AT LEAST WEDNESDAY.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1255 PM CDT FRI AUG 28 2026
VFR CONDITIONS FOR THE FIRST HALF OF THE PERIOD. THUNDERSTORMS MOVE
IN FROM CENTRAL SOUTH DAKOTA THIS EVENING AND PROCEED EAST THROUGH
THE OVERNIGHT. AN ISOLATED STORM OR TWO COULD BECOME STRONG TO
SEVERE SHORTLY AFTER CONVECTION INITIALIZATION, PRODUCING HEAVY
RAIN, 1.5 TO 2 INCH HAIL, AND DAMAGING WIND GUSTS TO 65 MPH. AS
STORMS PROGRESS EAST THEY WILL LIKELY BECOME ELEVATED AND THE
PRIMARY THREAT WILL TRANSITION TO DAMAGING WIND GUSTS. UNDER STORMS
IFR TO POSSIBLY LIFR CEILINGS AND VISIBILITIES ARE POSSIBLE. AREAS
ALONG AND NORTH OF I-90 ARE MOST LIKELY TO SEE SEVERE WEATHER.
STORMS MOVE TO THE EAST THROUGH MID-SATURDAY MORNING.
LLWS IS POSSIBLE BEGINNING LATE THIS EVENING AND CONTINUING THROUGH
MID-MORNING. AREAS ALONG AND SOUTH OF HIGHWAY 18, INCLUDING KSUX,
ARE THE MOST LIKELY TO SEE LONGER DURATION DIRECTIONAL SHEAR.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...SG/JH
DISCUSSION...AJP
AVIATION...AJP
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