736
FXUS63 KFSD 111837
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
137 PM CDT TUE AUG 11 2026
KEY MESSAGES
- WIDESPREAD THUNDERSTORM RISKS REMAIN LOW TONIGHT, BUT IT'S
POSSIBLE ONE OR TWO STRONGER STORMS OR CLUSTERS OF STORMS
COULD PASS THROUGH THE MO RIVER VALLEY LATE TONIGHT. THESE
STORMS COULD POSE A WIND AND MARGINAL SEVERE HAIL THREAT IF
THEY SURVIVE.
- DENSE FOG AND WIDESPREAD LOW STRATUS MAY FORM AGAIN INTO
WEDNESDAY MORNING.
- FOLLOWING A WARM AND DRY WEDNESDAY, AN INFLUX OF MOISTURE WILL
BRING A CHANCE OF THUNDERSTORMS INTO THURSDAY. VERY UNCERTAIN,
BUT A HIGHLY LOCALIZED HEAVY RAIN RISK COULD DEVELOP.
- CLOUD COVER AND COOLER TEMPERATURES MOVE IN FOR THURSDAY AND
FRIDAY, ALONG WITH ANOTHER RISK OF RAIN THURSDAY NIGHT.
DISCUSSION
ISSUED AT 115 PM CDT TUE AUG 11 2026
THIS AFTERNOON: VERY HUMID CONDITIONS CONTINUE EARLY THIS AFTERNOON,
BUT A WIDE ARRAY OF TEMPERATURES IN THE REGION. EARLY MORNING
STRATUS AND FOG HAS KEPT A LID ON TEMPERATURES NORTH OF I-90, BUT
SOUTH OF THE INTERSTATE WE'VE SEEN HIGHS CLIMB TOWARDS THE 90S. HEAT
INDEX IN A FEW AREAS MAY REACH THE 100 DEGREE MARK. A COUPLE
PATCHES OF ACCAS BASED AOA 600 MB CONTINUE TO MOVE ALONG I-90
THIS AFTERNOON, BUT DEVELOPMENT POTENTIAL REMAINS LOW AS THIS
MOVES INTO NW IOWA. WILL CONTINUE TO MONITOR.
THIS EVENING/TONIGHT: CAMS CONTINUE TO STRUGGLE RESOLVING THE MYRIAD
OF WEAK FORCING WAVES MOVING THROUGH THE PLAINS, AND THESE TRENDS
CONTINUE TODAY. THE RESULT IS SPORADIC CONVECTION DEVELOPING OVER
THE WESTERN HIGH PLAINS IN THE LATE AFTERNOON AND EVENING AND THEN
GRADUAL TRACKS SOUTHEAST OVERNIGHT. DESPITE THE HIGH LEVEL OF
INSTABILITY ACROSS THE DAKOTAS, VERY FEW STRONG FOCUSING
MECHANISMS FOR CONVECTION REMAIN APPARENT THIS AFTERNOON. WHAT
MAY HAPPEN IS GRADUAL UPSLOPE FLOW OVER THE WESTERN DAKOTAS
COMBINED WITH INCREASING SE 850MB FLOW COULD INDUCE A CLUSTER OR
TWO OF STORMS. THIS ACTIVITY WILL TEND TO FOLLOW THE MEAN FLOW
AND PUSH EAST SOUTHEAST INTO THE OVERNIGHT HOURS. HOWEVER, A
CLOSER LOOK AT SOUNDINGS CONTINUES TO SHOW FAIRLY STRONG
INHIBITION BOTH TO SURFACE BASED PARCELS BUT ALSO TO ELEVATED
PARCELS. SO WITH THAT IN MIND, PLANNING ON KEEPING POPS LOW,
WITH SOME FOCUS ALONG I-90 AND AREAS MORESO OVER THE MISSOURI
RIVER VALLEY. CONTINUE TO MONITOR TRENDS THIS EVENING, AS STRONG
STORMS COULD BRING SOME HIGHER WIND GUSTS IF THEY SURVIVE.
HIGHER CONFIDENCE AGAIN IN THE DEVELOPMENT OF STRATUS AND FOG GIVEN
THE CONTINUED LIGHT NORTHEAST WIND AND TRAPPED BOUNDARY LAYER
MOISTURE. MUCH LIKE THIS MORNING, AREAS OF LOCALLY DENSE FOG MAY
FORM WITH WIDESPREAD STRATUS POTENTIAL POSSIBLE.
WEDNESDAY-WENDESDAY NIGHT: ASSUMING STRATUS/FOG DOES NOT HINDER THE
WARMUP TOMORROW SIGNIFICANTLY, WE'LL CONTINUE TO SEE ANOTHER WARM
AFTERNOON ON WEDNESDAY WITH DRY CONDITIONS. DEW POINTS WILL REMAIN
IN THE 70S, WHICH SHOULD CAP HIGH TEMPERATURES IN TO THE MIDDLE
80S. A SLIGHT SHIFT IN THE MID-LVL FLOW BEGINS WEDNESDAY, WITH
PERSISTENT RIDGING OVER THE FOUR CORNERS TRANSLATING EASTWARD
INTO THE SOUTHERN PLAINS THROUGH THE DAY. THIS WILL RESULT IN
PULLING A SUB-TROPICAL MOISTURE PLUME WITH EMBEDDED VORTICITY
NORTHWARD THROUGH THE ROCKIES AND INTO THE PLAINS LATE IN THE
DAY AND OVERNIGHT. SLIGHTLY BETTER SIGNALS FOR CONVECTION TIED
TO THIS WAVE WILL BEGIN TO FOCUS OVER WESTERN SD/NE LATE IN THE
AFTERNOON, WITH RAIN GRADUALLY SHIFTING EASTWARD INTO THURSDAY
MORNING. THE SEVERE WEATHER RISKS REMAIN ON THE LOWER SIDE BUT
NOT NON-ZERO AS SOME LINGERING WIND THREAT COULD PRESENT ITSELF
ALONG THE MO RIVER VALLEY. MID-LVL LAPSE RATES QUICKLY WORSEN AS
YOU MOVE INTO THE OVERNIGHT HOURS HOWEVER. ONE NOTICEABLE THING
TO WATCH IS THE INCREASING PWAT VALUES WHICH APPROACH 1.75" BY
THURSDAY MORNING. THIS COULD SIGNAL AT LEAST THE POTENTIAL FOR
HIGHLY LOCALIZED HEAVIER RAIN AMOUNTS, WHICH THE HREF PMM
SIGNALS IN THE 2-4" RANGE. THE KEY TO WATCH WILL BE WHERE THE
RESIDUAL SURFACE BOUNDARY FALLS BY LATE WEDNESDAY, AS THIS COULD
PULL BETTER CONVECTION RISKS SOUTH OF THE CWA.
THURSDAY-FRIDAY: QUITE A BIT OF CLOUD COVER MAY BE IN THE AREA FOR
THURSDAY AS COOLER NORTHEASTERLY FLOW RETURNS AND WE'LL BE ON THE
EDGE OF THE BAROCLINIC ZONE TO OUR SOUTH. AT THIS POINT, HIGHS IN
THE 70S ARE LIKELY, WITH A GRADUALLY INCREASING RAIN CHANCE INTO
FRIDAY AS MID-LVL FLOW SHIFTS BACK TO THE SOUTHWEST, MID-LVL
VORTICITY SLIDES THROUGH THE CENTRAL PLAINS, AND THE BAROCLINIC ZONE
LIFTS NORTHWARD. THE HIGHEST POPS WILL BE FOCUSED THURSDAY NIGHT
INTO FRIDAY.
SATURDAY-MONDAY: A FLATTENED MID-LVL RIDGE REMAINS OVER THE CENTRAL
CONUS INTO THE UPCOMING WEEKEND, BRINGING ANOTHER RISK FOR RAIN BY
SATURDAY AS ENERGY TRACKS BACK NORTHWARD INTO THE UPPER MIDWEST.
CONFIDENCE IS RISING THAT WE'LL SEE A DRY SUNDAY AND MONDAY AS HIGH
PRESSURE ARRIVES, MID-LVL RIDGING SHIFTS BACK WESTWARD, AND QUASI-
NORTHWEST FLOW MOVES BACK IN. TEMPERATURES MAY BEGIN TO RISE BACK
INTO THE 80S BY SUNDAY AND MONDAY.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1214 PM CDT TUE AUG 11 2026
MVFR STRATUS MOSTLY NORTH OF I-90 WILL CONTINUE TO MIX UPWARDS
THIS AFTERNOON. LEAVING A LIGHT AND VARIABLE TO NORTHEAST FLOW
IN PLACE INTO THE EVENING.
CONVECTION RISKS CONTINUE TO REMAIN LOW INTO THE OVERNIGHT
HOURS, WITH A FEW STORMS FAR WEST RIVER ATTEMPTING TO MOVE
THROUGH THE MO RIVER VALLEY OVERNIGHT. PROBABILITIES REMAIN TOO
LOW TO INDICATE IN CURRENT TAF.
MORE CONCERNING WILL AGAIN BE THE POTENTIAL FOR LOW STRATUS AND
FOG INTO THE MID MORNING HOURS. AS LONG AS LIGHT WINDS AND EVEN
A COOLER NORTHEAST WIND PREVAIL, GIVEN THE SOUPY BOUNDARY LAYER
FOG SHOULD AGAIN DEVELOP. POTENTIALLY DENSE FOG IS POSSIBLE, AND
FUTURE TAFS COULD TREND CONDITIONS LOWER.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...DUX
AVIATION...DUX
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