141
FXUS63 KFSD 120152
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
852 PM CDT TUE AUG 11 2026
KEY MESSAGES
- WHILE SOME UNCERTAINTY LINGERS, CONCERNS ARE GROWING THAT A
CLUSTER OF STRONGER STORMS COULD PASS THROUGH AREAS NEAR TO
SOUTH OF I-90 AFTER MIDNIGHT INTO EARLY WEDNESDAY. PRIMARY
THREAT WOULD BE DAMAGING WINDS TO 75 MPH, WITH A MARGINAL
SEVERE HAIL THREAT.
- AREAS OF DENSE FOG AND LOW STRATUS MAY FORM AGAIN LATE TONIGHT
INTO WEDNESDAY MORNING, THOUGH CONFIDENCE IN COVERAGE IS LOW.
- 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.
UPDATE
ISSUED AT 850 PM CDT TUE AUG 11 2026
SIMILAR TO LAST EVENING, MULTIPLE CAMS ARE SHOWING AN EVOLUTION
OF ISOLATED SEVERE STORMS IN WESTERN SOUTH DAKOTA TURNING MORE
EASTERLY AND EVOLVING INTO A BOWING LINE THAT TRACKS THROUGH OUR
AREA OVERNIGHT. WHILE THIS SCENARIO DID NOT MATERIALIZE LAST
NIGHT, LATEST RADAR TRENDS IN WESTERN SOUTH DAKOTA ARE CAUSING
A SLIGHT UPTICK IN CONFIDENCE THAT WE COULD SEE THIS PLAY OUT
LATER TONIGHT.
THE STORM APPEARS TO HAVE MADE A SLIGHT EASTWARD TURN OVER THE
PAST 15-30 MINUTES AND CONTINUES TO PRODUCE SEVERE WIND GUSTS.
STILL AWAITING MOST OF THE 12/00Z MODEL DATA, BUT LATEST HRRR
RUNS MAINTAIN THE IDEA OF A BOWING CLUSTER, WITH THE MAIN
QUESTION BEING WHEN THE STORM BEGINS ITS TURN TO THE EAST AND
THE EVENTUAL TRACK OF THE RESULTING STORM CLUSTER. WILL CONTINUE
TO WATCH TRENDS CLOSELY OVER THE NEXT HOUR OR TWO, BUT GIVEN THE
RELATIVE CONSISTENCY IN MOST RECENT HRRR RUNS, BUMPED POPS UP A
BIT FOR THE LATTER HALF OF TONIGHT ACROSS THE SOUTHERN HALF OF
THE FORECAST AREA.
NOTABLY, THE 01Z UPDATE FROM SPC EXPANDED A LEVEL 2 OF 5 (SLIGHT)
RISK EASTWARD THROUGH THE SOUTHERN HALF OF OUR FORECAST AREA
FOR THE BALANCE OF TONIGHT TO ACCOUNT FOR THIS SCENARIO, WHICH
WOULD BRING A GROWING RISK OF DAMAGING WIND AFTER MIDNIGHT INTO
THE EARLY MORNING HOURS WEDNESDAY.
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 /00Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 655 PM CDT TUE AUG 11 2026
VFR CONDITIONS AS WE BEGIN THIS PERIOD WITH SPOTTY HIGH-BASED
LIGHT SHOWERS FROM AROUND KFSD EAST ALONG THE I-90 CORRIDOR.
THIS ACTIVITY IS EXPECTED TO WANE BY SUNSET, WITH ATTENTION
TURNING TO ONGOING SEVERE STORMS IN FAR WESTERN SD. SIMILAR TO
LAST NIGHT, SOME HIGH-RES MODEL SOLUTIONS SHOW A TRANSFORMATION
FROM ISOLATED SUPERCELLS INTO A BOWING LINE AS THE STORMS MOVE
SOUTHEAST TOWARD SOUTH-CENTRAL SD AND THE MISSOURI RIVER VALLEY.
WHILE CONFIDENCE IS LOW, DID INTRODUCE A MENTION OF THUNDER FOR
KSUX IN A FAVORED WINDOW AROUND DAYBREAK WEDNESDAY.
ALSO WATCHING FOR POTENTIAL REDEVELOPMENT OF FOG/STRATUS LATER
TONIGHT INTO WEDNESDAY MORNING, THOUGH 18Z HREF PROBABILITIES
FOR BOTH HAVE DECREASED FROM EARLIER GUIDANCE. GIVEN THE ROBUST
BOUNDARY LAYER MOISTURE, WILL CERTAINLY HAVE TO MONITOR TRENDS,
THOUGH, AS A REPEAT OF THIS MORNING'S MORE EXPANSIVE FOG AND LOW
STRATUS COULD DEVELOP IF STORM COVERAGE IS LACKING.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...JH
DISCUSSION...DUX
AVIATION...JH
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