345
FXUS63 KFSD 311946
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
246 PM CDT MON AUG 31 2026
KEY MESSAGES
- STRONG TO SEVERE STORMS LOOK TO RETURN TO THE AREA TOMORROW
(TUESDAY) BETWEEN 6 PM TO 2 AM. LARGE HAIL UP TO THE SIZE OF
GOLF BALLS, DAMAGING WINDS TO 70 MPH, AND AN ISOLATED TORNADO
ARE THE MAIN HAZARDS. SOME UNCERTAINTY REGARDING STORM MODE
REMAINS.
- NEAR TO ABOVE NORMAL TEMPERATURES LOOK TO CONTINUE THROUGH
THIS WEEK. CONFIDENCE CONTINUES TO INCREASE IN FURTHER
INCREASING TEMPERATURES AND HUMIDITY FOR THE END OF THIS WEEK
AND WEEKEND.
- LOW CHANCES (15-30%) FOR RAIN WILL ACCOMPANY THE END OF WEEK
INCREASING HEAT AND HUMIDITY.
DISCUSSION
ISSUED AT 245 PM CDT MON AUG 31 2026
SUNNY AND WARM CONDITIONS PERSIST THIS AFTERNOON AS TEMPERATURES
HAVE WARMED TO 80S. WITH A COLD FRONT NOW SOUTHEAST OF THE AREA, DEW
POINTS HAVE LOWERED TO 50S AND 60S. STILL SEEING HEAT INDICES UP TO
80S TO LOW 90S, SO SOME HUMID CONDITIONS REMAIN THOUGH NOT AS HUMID
AS WHAT WE SAW THIS WEEKEND. A WEAK LOW LEVEL JET (LLJ) IS EXPECTED
TO DEVELOP TONIGHT WHICH WILL DEVELOP SHOWERS AND POTENTIALLY AN
ISOLATED THUNDERSTORM ACROSS NEBRASKA. THESE SHOWERS WILL PUSH
EAST/NORTHEASTWARDS INTO A WORSENING ENVIRONMENT. THEY COULD STILL
BE CAPABLE OF LIGHTNING THOUGH NOT EXPECTED TO BE STRONG NOR SEVERE.
LOW TEMPERATURES WILL REMAIN QUITE MILD OVERNIGHT, WITH LOWS ONLY
FALLING TO THE 60S.
THE SHOWERS WILL PUSH THROUGH THE AREA DURING THE MORNING TO EARLY
AFTERNOON HOURS. THIS WILL LEAVE THE REST OF THE AFTERNOON ON THE
DRY SIDE OF THINGS. WITH SOME CLOUD COVER REMAINING ALOFT, HIGHS
LOOK TO REMAIN WARM BUT BE SLIGHTLY COOLER THAN MONDAY'S HIGHS WITH
TEMPERATURES IN THE 80S UP TO ABOUT 90F. CHANCES FOR SEVERE STORMS
BEGIN TO INCREASE AFTER 6 PM AS A SHORTWAVE TROUGH EJECTS OUT OF THE
ROCKIES AND INTO THE NORTHERN PLAINS. THE PREVIOUSLY MENTIONED FRONT
WILL BEGIN TO RETURN NORTHWARDS AS A WARM FRONT DUE TO THE MASS
RESPONSE FROM THE WAVE. A SUFFICIENT WARM SECTOR WILL BE IN PLACE
AHEAD OF THE BOUNDARY WITH DEW POINTS IN THE 60S TO 70S. SOME
CAPPING WILL BE IN PLACE WHICH MAY LIMIT THE EXTENT OF CONVECTION
EARLY ON. LATEST HI-RES GUIDANCE CONTINUES TO SHOW MODERATE VARIANCE
BUT IS BEGINNING TO SHOW A CONSENSUS OF STORMS DEVELOPING ACROSS
CENTRAL AND NORTH CENTRAL NEBRASKA AND POSSIBLY SOUTH CENTRAL SOUTH
DAKOTA. THESE SHOWERS AND STORMS WILL PUSH INTO THE AREA DURING THE
EVENING TIMEFRAME BUT THE REMAINING UNCERTAINTY REVOLVES AROUND
STORM MODE. THINK A CUSTER OF STORMS IS POSSIBLE WITH EMBEDDED MULTI-
CELLS TO EVEN SUPERCELLS. AS THE STORMS PUSH FURTHER INTO THE
FORECAST AREA, THEY WILL BECOME MORE ELEVATED DUE TO INCREASED
CAPPING OVER THE AREA. STORM MODE BECOMES MORE QUESTIONABLE HERE AS
STORMS MAY REMAIN A BIT MORE DISCRETE TO PERHAPS REMAINING IN A
CLUSTER. OR IF THEY CAN CONGEAL COLD POOLS PROPERLY, UPSCALE GROWTH
INTO A LINE IS POSSIBLE. TOUGH TO SAY WHICH STORM MODE IS CORRECT AT
THIS TIME. ASIDE FROM CAPPING, SUFFICIENT ELEVATED INSTABILITY WILL
BE IN PLACE WITH CAPE VALUES UP TO 1,000 J/KG TO 2,000 J/KG WITH
EFFECTIVE SHEAR VALUES BETWEEN 40-50 KNOTS. THUS, DAMAGING WINDS TO
70 MPH AND GOLF BALL SIZE HAIL WILL BE THE MAIN HAZARDS. IF A STORM
IS ABLE TO TAP INTO THE BOUNDARY LAYER, THEN AN ISOLATED TORNADO
WILL BE POSSIBLE. ESPECIALLY IF THE SURFACE WARM FRONT CAN PUSH INTO
THE FORECAST AREA. THE STORMS WILL PUSH THROUGH THE AREA THROUGH THE
EVENING AND AT LEAST THE FIRST HALF OF THE OVERNIGHT HOURS BEFORE
PUSHING EASTWARDS WITH THE VEERING LOW LEVEL JET.
THE DAYLIGHT HOURS ON WEDNESDAY LOOK TO BE A QUIET AS SUBSIDENCE
PREVAILS ON THE BACKSIDE OF THE DEPARTING WAVE. HIGHS WILL REMAIN
CONSISTENT IN THE 80S TO EVEN LOW 90S IN A FEW LOCATIONS. THE BREAK
FROM RAIN WILL BE SHORT LIVED THOUGH AS ANOTHER SHORTWAVE TROUGH
WILL BE PUSHING INTO THE PLAINS WEDNESDAY NIGHT. THE ENSEMBLES
SUPPORT THIS AS THEY SHOW INCREASING PROBABILITIES UP TO A 20-50%
CHANCE FOR RAINFALL TOTALS TO EXCEED A TENTH OF AN INCH. THE
ENSEMBLES HAVE THE HIGHEST CHANCES FOR RAIN EAST OF I-29. SOME
ELEVATED INSTABILITY LOOKS TO BE AVAILABLE, SUGGESTING THAT
THUNDERSTORMS WILL AGAIN BE POSSIBLE. WHETHER THEY WILL BE STRONG TO
SEVERE IS UNCERTAIN AT THIS TIME.
UPPER LEVEL RIDGING WILL BE STRENGTHENING ALOFT FOR THE END OF THIS
WEEK AND WEEKEND. HIGH TEMPERATURES LOOK TO NOT ONLY REMAIN ABOVE
AVERAGE BUT FURTHER WARM AS THE RIDGE BECOMES MORE PRONOUNCED ALOFT.
THE ENSEMBLES NOT ONLY SUPPORT THIS RIDGE DEVELOPING, BUT ALSO 850
MB TEMPERATURES BEING PUSHED TO THE THE 99TH PERCENTILE OF
CLIMATOLOGY. THE EURO EXTREME FORECAST INDEX (EFI) FURTHER SUPPORTS
THIS AS IT SHOWS 60-80% OF ITS MEMBERS SUGGESTING ABOVE AVERAGE
TEMPERATURES ARE POSSIBLE. HUMID CONDITIONS LOOK TO ACCOMPANY THE
ABOVE AVERAGE TEMPERATURES AS THE ENSEMBLES SHOW A BROAD 50-90%
CHANCE FOR HEAT INDICES TO EXCEED 90F. CHANCES FOR RAIN ARE POSSIBLE
(15-30% CHANCE) DURING THIS PERIOD OF TIME BUT DETAILS ARE HIGHLY
UNCERTAIN. THERE ARE SOME SIGNALS THAT THIS PATTERN COULD BEGIN TO
BREAK DOWN NEXT WEEK. HOWEVER, MEDIUM RANGE GUIDANCE CONTINUES TO
SHOW INCREASING VARIANCE IN THIS POTENTIAL. SOMETHING TO WATCH TO
SEE IF THESE CONDITIONS WILL PERSIST INTO NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1225 PM CDT MON AUG 31 2026
MAINLY CLEAR SKIES AND LIGHT AND VARIABLE WINDS BEGIN THE TAF
PERIOD. CLOUD COVER WILL INCREASE ALOFT LATE THIS EVENING AND NIGHT.
SOME LIGHT RAIN SHOWERS ARE POSSIBLE NEAR HIGHWAY-20 DURING THE
MORNING HOURS TOMORROW. VISIBILITIES AND CEILINGS ARE EXPECTED TO
REMAIN VFR IN THE SHOWERS. THE LIGHT RAIN SHOWERS AND LIGHT AND
VARIABLE WINDS WILL FINISH OUT THE TAF PERIOD.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...MEYERS
AVIATION...MEYERS
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