942
FXUS63 KFSD 281736
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1236 PM CDT MON JUL 28 2025
KEY MESSAGES
- INCREASING CONCERN AND PROBABILITY FOR STRONG TO SEVERE STORMS
ACROSS THE PLAINS THIS AFTERNOON THROUGH TONIGHT, WITH THE
POTENTIAL FOR A SIGNIFICANT WIND EVENT. MONITOR THE FORECAST,
AND HAVE A PLAN WITH MULTIPLE WAYS TO RECEIVE WARNINGS.
- MAIN HAZARD FOR TODAY IS WIND GUSTS OF 80 MPH OR HIGHER. A FEW
TORNADOES, LARGE HAIL TO TENNIS BALL SIZED, AND LOCALLY HEAVY
RAINFALL ARE ADDITIONAL HAZARDS. GREATEST TIMING WILL BE 4 PM
THROUGH MIDNIGHT.
- AN EXTREME HEAT WARNING AND A HEAT ADVISORY IN EFFECT TODAY
FROM NOON TO 8 PM WITH HEAT INDEX VALUES UP TO 110 DEGREES.
USE CAUTION TO PREVENT HEAT ILLNESS TODAY.
- ADDITIONAL ISOLATED STRONG TO SEVERE STORMS POSSIBLE TUESDAY
EVENING INTO WEDNESDAY.
- TEMPERATURES COOL SIGNIFICANTLY BY THE MIDDLE OF THE WEEK,
PEAKING IN THE 70S TO NEAR 80 DEGREES WEDNESDAY ONWARD.
DISCUSSION
ISSUED AT 347 AM CDT MON JUL 28 2025
NOW THROUGH TONIGHT: CONVECTION HAS MOVED OFF TO THE EAST THIS
MORNING. SOME UNCERTAINTY WITH HOW MUCH WE'LL RECOVER FOR
TEMPERATURES AND DEW POINTS GIVEN HOW WIDESPREAD CONVECTION WAS LAST
NIGHT AND EARLY THIS MORNING. THAT SAID, NO PLANNED CHANGES TO THE
HEAT HEADLINES FOR THE DAY.
FOCUS OF THE FORECAST IS ON THE GROWING CONCERN AND POSSIBILITY OF A
POTENTIALLY SIGNIFICANT WIND EVENT AND POSSIBLE DERECHO TODAY INTO
TONIGHT ACROSS THE PLAINS.
MID AND UPPER LEVEL RIDGE REMAINS IN PLACE OVER THE PLAINS STATES,
WITH A COUPLE OF SHORT WAVES MOVING THROUGH THE PATTERN - INCLUDING
A STRONGER WAVE LATER THIS AFTERNOON THROUGH TONIGHT WITH UPPER
LEVEL SUPPORT FROM THE ENTRANCE REGION OF THE JET. THUNDERSTORMS
SHOULD DEVELOP BY THIS AFTERNOON TO OUR NORTH, DIVING SOUTH WITH THE
WAVE AND INTENSIFYING INTO AN MCS AS IT MOVES INTO A FAVORABLE
ENVIRONMENT. EVEN IF WE DON'T RECOVER QUITE AS MUCH DUE TO THIS
MORNING'S CONVECTION, ENVIRONMENT IS PROGGED TO RECOVER ENOUGH FOR
UPWARDS OF 3000 J/KG OF CAPE (AND AS HIGH AS 5000 J/KG OF MUCAPE OR
MORE). STEEP MID LEVEL LAPSE RATES OVER 7.5 DEG C/KM (WITH VALUES
FOR SOME NEAR AND ABOVE 9 DEG C/KM) AND 0-6 KM SHEAR VALUES OVER 45
KNOTS (HIGHEST IN OUR NORTH). THIS SHEAR NEARLY PARALLEL TO THE
BOUNDARY SUPPORTS QUICK UPSCALE GROWTH, AND THESE PARAMETERS ARE
SUPPORTIVE OF AN MCS AND POTENTIAL DERECHO. MAIN THREAT WILL BE WIND
GUSTS OVER 70 MPH WITH HREF MAX HOURLY GUSTS SHOWING THE POTENTIAL
FOR WIND GUSTS OVER 80 MPH. 0-1 SRH OVER 100 M^2/S^2, STP VALUES
OVER 1, AND LOWERING LCLS SUPPORT THE POTENTIAL FOR A FEW TORNADOES
ALONG THE LINE. IF MORE ISOLATED CELLS DEVELOP, HAIL UP TO PING PONG
BALL SIZE IS POSSIBLE. FINALLY, FAVORABLE MOISTURE TRANSPORT AND
DEEP WARM CLOUD LAYER SUPPORT LOCALLY HEAVY RAINFALL OF AN INCH OR
MORE PER HOUR RATES.
A COUPLE OF POINTS OF UNCERTAINTY EXIST WITHIN THE FORECAST THIS
AFTERNOON AND EVENING. ONE IS HOW FAR SOUTH AND WEST STORMS DEVELOP
OVER OUR AREA (DO WE SEE MUCH SOUTH OF I-90 IN SD?) AND IF SO, DOES
OUR AREA SEE TWO ROUNDS OF SEVERE STORMS/WINDS. CAMS ARE SPLIT ON
THIS SOLUTION, AND THE 28.00Z HREF SUPPORTS STRONG WIND POTENTIAL
OVER NEARLY OUR ENTIRE FORECAST AREA. THE NEXT QUESTION IS WHERE THE
MCS DEVELOPS LATER THIS MORNING/EARLY THIS AFTERNOON AND HOW QUICKLY
DOES IT DIVE SOUTHEAST. FINALLY, DOES THE MCS CARRY A MORE
SOUTHEASTERLY OR EASTERLY MOTION WITH BOUNDARIES AROUND THE REGION
FROM THIS MORNING'S CONVECTION - WHICH WILL DETERMINE ITS TRACK OVER
THE PLAINS.
STAY UP TO DATE WITH THE LATEST FORECAST INFORMATION AND HAVE
MULTIPLE WAYS TO RECEIVE WARNINGS. HAVE A PLAN SHOULD A WARNING BE
ISSUED AND TAKE ACTION QUICKLY.
TUESDAY-TUESDAY NIGHT: NOT AS HOT ON TUESDAY WITH HIGHS IN THE 80S
AND LOWER 90S. - HOTTEST TOWARD THE US HWY 20 CORRIDOR. MORE DEFINED
COLD FRONT, MID LEVEL WAVE, AND ENTRANCE REGION OF THE UPPER LEVEL
JET MOVE THROUGH TUESDAY EVENING INTO TUESDAY NIGHT. BETTER SHEAR
AND INSTABILITY ARE OFFSET (SHEAR TO THE NORTH AND INSTABILITY
SOUTH) BUT DO HAVE ENOUGH OF BOTH ACROSS THE AREA WITH BOUNDARIES
AND STEEP MID LEVEL LAPSE RATES FOR AT LEAST AN ISOLATED SEVERE
WEATHER RISK. LOCALLY HEAVY RAINFALL IS ALSO POSSIBLE, WITH MORE
CONCERN FOR AREAS THAT HAVE SEEN HEAVY RAINFALL OVER THE LAST COUPLE
OF DAYS. EVERYTHING PUSHES TO THE EAST THROUGH THE OVERNIGHT HOURS,
AND RAIN SHOULD EXIT BY MID WEDNESDAY MORNING.
WEDNESDAY-SUNDAY: PATTERN CHANGES MID WEEK AS TROUGHING ALOFT
DEEPENS OVER BOTH US COASTS, RETURNING US TO A NORTHWESTERLY FLOW
REGIME. COOLER SURFACE HIGH PRESSURE SNEAKS DOWN FROM CANADA INTO
CENTRAL MN, AND WITH THE NORTHWESTERLY FLOW, BRINGS MUCH COOLER
TEMPERATURES TO THE REGION WITH HIGHS IN THE 70S TO NEAR 80 AND LOWS
IN THE 50S. SINCE WE'LL BE ON THE PERIPHERY OF THE HIGH, A COUPLE
SHORT WAVES COULD BRING SHOWER CHANCES TO THE REGION, BUT DETAILS
ARE UNCERTAIN AND WE SHOULD STAY MOSTLY DRY. EXPECT PERIODICALLY
BREEZY CONDITIONS WITH A COMPRESSED SURFACE PRESSURE GRADIENT. BY
NEXT WEEKEND, SURFACE HIGH PRESSURE SLIDES EAST AND THE PATTERN
ALOFT FLATTENS AS A STRONGER WAVE TREKS THROUGH THE PLAINS. WARMER
TOWARD THE WEEKEND WITH INCREASING SOUTHERLY FLOW.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1233 PM CDT MON JUL 28 2025
THE MAIN CONCERN WILL BE THUNDERSTORM DEVELOPMENT IN THE FIRST
HALF OF THE TAF PERIOD. SCATTERED SUPERCELLS WILL LIKELY DEVELOP
IN CENTRAL SD LATE THIS AFTERNOON, THEN TRANSITION TO A LINE
PRODUCING VERY STRONG STRAIGHT LINED WINDS NEAR AND EAST OF
HIGHWAY 81 FROM ABOUT 2Z TO 7Z. LATE TONIGHT INTO TUESDAY
MORNING SOME IFR OR MVFR CEILINGS WILL BE POSSIBLE. CONFIDENCE A
BIT LOW ON THIS ACTIVITY.
FSD WATCHES/WARNINGS/ADVISORIES
SD...EXTREME HEAT WARNING UNTIL 8 PM CDT THIS EVENING FOR SDZ050-
052>055-057>071.
HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR SDZ038>040-056.
MN...EXTREME HEAT WARNING UNTIL 8 PM CDT THIS EVENING FOR MNZ098.
HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR MNZ071-072-080-
081-089-090-097.
IA...EXTREME HEAT WARNING UNTIL 8 PM CDT THIS EVENING FOR
IAZ001>003-012>014-020>022-031-032.
NE...EXTREME HEAT WARNING UNTIL 8 PM CDT THIS EVENING FOR NEZ013-
014.
DISCUSSION...SG
AVIATION...08
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