264
FXUS63 KFSD 162305
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
605 PM CDT SAT AUG 16 2025
KEY MESSAGES
- BUILDING HEAT AND HUMIDITY MAINLY SOUTH OF I-90 WILL LEAD
HEAT INDEX VALUES BETWEEN 95 TO 105 DEGREES. WITH THIS IN
MIND, A HEAT ADVISORY REMAINS IN EFFECT THROUGH THIS EVENING.
- A FEW STRONGER STORMS COULD RETURN OVERNIGHT MAINLY ACROSS THE
HIGHWAY-14 CORRIDOR AND PORTIONS OF SOUTHWESTERN MN. THE MAIN
THREATS WOULD BE PING-PONG BALL SIZED HAIL AND DAMAGING WINDS
UP TO 65 MPH.
- NEXT CHANCES FOR ORGANIZED CONVECTION LIKELY COME ON SUNDAY
AND MONDAY WITH A HEAVY RAINFALL THREAT. HOWEVER, SOME DETAILS
STILL REMAIN UNCERTAIN AT THIS TIME.
- MUCH QUIETER CONDITIONS LIKELY RETURN FOR MUCH OF THE WEEK
BRINGING IN LOWER DEW POINTS, NEAR-NORMAL TEMPERATURES, AND
LIMITED PRECIPITATION CHANCES.
DISCUSSION
ISSUED AT 228 PM CDT SAT AUG 16 2025
CURRENTS & TONIGHT: ANOTHER WARM AND HUMID DAY CONTINUES! TAKING A
LOOK ACROSS THE AREA, AREAS OF STRATUS WITH POCKETS OF SPRINKLES TO
LIGHT SHOWER CONTINUE TO DEVELOP MAINLY ALONG A BONESTEEL TO SIOUX
FALLS TO SLAYTON, MN LINE THIS AFTERNOON. WITH THIS BEING FUELED BY
LINGERING CONVERGENCE ALONG A WARM FRONT DRAPED ALONG I-90 CORRIDOR
AND A WEAKENING LLJ, NOT EXPECTING THIS ACTIVITY TO LAST PAST THE
EARLY AFTERNOON BEFORE DISSIPATING. OTHERWISE, THE FOCUS CONTINUES
TO BE ON THE MUGGY CONDITIONS. AS OF 18Z, DEW POINTS HAVE REACHED
THE MID TO UPPER 70S ACROSS MOST OF THE AREA WITH TEMPERATURES
VARYING BETWEEN THE LOW TO MID 80S. GIVEN THE SET UP, WE'RE STILL ON
TRACK FOR MANY AREAS SOUTH OF I-90 TO SEE HEAT INDEX VALUES IN THE
95 TO 105 DEGREE RANGE THROUGH THIS EVENING. HOWEVER, THE COMBINATION
OF THIS MORNING'S RAINFALL AND LINGERING STRATUS WILL LIKELY KEEP
THINGS MORE ISOLATED VS WIDESPREAD THAN ORIGINALLY EXPECTED. NONETHELESS,
OUR HEAT ADVISORY REMAINS IN EFFECT THROUGH 8 PM.
LOOKING ALOFT, A TRUE "REX BLOCKING" PATTERN CONTINUES WITH OUR AREA
LOCKED INTO SOUTHWESTERLY TO WESTERLY FLOW. AS THE PREVIOUSLY
MENTIONED WARM FRONT CONTINUES TO LIFT NORTHWARDS TOWARDS THE
HIGHWAY-14 CORRIDOR THROUGHOUT THE EVENING AND INTERSECTS AN
APPROACHING SHORTWAVE OVERNIGHT, SHOULD SEE SCATTERED SHOWERS AND
THUNDERSTORMS DEVELOP JUST TO THE NORTH OF THE NEAR-SURFACE FEATURE.
WHILE MOST OF OUR AREA SHOULD STAY CLEAR OF THIS DEVELOPING
ACTIVITY, CAN'T COMPLETE RULE OUT SOME OF THESE SHOWERS AND
THUNDERSTORMS MOVING ACROSS PORTIONS OF THE HIGHWAY-14 CORRIDOR AND
SOUTHWESTERN MN BETWEEN 09Z-13Z (4AM TO 8AM). WITH THIS IN MIND, AN
ISOLATED LARGE HAIL RISK WILL BE POSSIBLE THROUGH DAYBREAK ON SUNDAY
WITH STRONGER STORMS BEING CAPABLE OF PRODUCING UP TO PING-PONG BALL
SIZED (1.5") GIVEN THE LAPSE RATES AROUND 6.5-7 DEG C/KM AND
LINGERING INSTABILITY (1000-1500 J/KG). CAN'T ALSO RULE OUT A
FEW ISOLATED GUSTS UP TO 65 MPH GIVEN DCAPE VALUES BETWEEN
1000-1200 J/KG. LASTLY, SHOULD SEE OVERNIGHT TEMPERATURES
GRADUALLY DECREASE INTO THE UPPER 60S TO LOW 70S.
SUNDAY & MONDAY: LOOKING INTO SUNDAY, AN ACTIVE PATTERN CONTINUES
ALOFT AS A MID-LEVEL WAVE LIFTS ACROSS THE NORTHERN PLAINS. WHILE
THE BULK OF THE ACTIVITY WILL LIKELY CONTINUE NEAR THE WARM FRONT
CLOSER TO CENTRAL MN AND THE ND/SD BORDER, INCREASING LIFT AND DPVA
IN ASSOCIATION WITH AN APPROACHING COLD FRONT SHOULD TRIGGERING
SCATTERED SHOWERS AND THUNDERSTORMS FROM THE EARLY AFTERNOON TO
EVENING HOURS. GIVEN A DECENTLY UNSTABLE ENVIRONMENT CHARACTERIZED
BY 1500-2500 J/KG OF INSTABILITY AND 20-30 KTS OF SHEAR, AN ISOLATED
TO SCATTERED SEVERE RISK WILL BE POSSIBLE ALONG AND AHEAD OF THE
FRONT WITH HALF DOLLAR SIZED HAIL (1.25") AND DAMAGING WINDS UP TO
65 MPH BEING THE PRIMARY RISKS.
WHILE THE BETTER SEVERE RISK WILL LIKELY OCCUR BETWEEN 1 PM TO 8 PM,
COULD SEE ADDITIONAL SHOWER AND THUNDERSTORM CHANCES DEVELOP INTO
THE OVERNIGHT HOURS AS A NOCTURNAL LLJ (30-40 KT) STRENGTHENS ACROSS
AREAS EAST OF I-29. BY MONDAY, QUASI-ZONAL FLOW RETURNS ALOFT ALONG
WITH QUIETER CONDITIONS FOR MOST OF THE DAY. TEMPERATURES WILL BEGIN
TO TREND COOLER AS NORTHERLY TO NORTHWESTERLY SURFACE WINDS AND
LINGERING COLD AIR ADVECTION (CAA) LEADS TO HIGHS IN THE LOW 80S TO
LOW 90S WITH THE COOLEST CONDITIONS NORTH OF I-90. SHOWER AND
THUNDERSTORM CHANCES (20%-30%) WILL ONCE AGAIN INCREASE OVERNIGHT AS
ANOTHER WEAK WAVE MOVES THROUGH AREAS WEST OF THE JAMES RIVER
VALLEY. WHILE THERE COULD BE ANOTHER ISOLATED SEVERE RISK WITH THIS
SYSTEM, THERE IS STILL SOME LINGERING UNCERTAINTY AS FAR AS
EVOLUTION AND TIMING OF THIS DEVELOPING ACTIVITY.
TUESDAY ONWARDS: HEADING INTO THE EXTENDED PERIOD, MUCH QUIETER
CONDITIONS SHOULD RETURN BY TUESDAY AS SURFACE RIDGING BEGINS TO
STRETCH DOWN FROM THE GREAT LAKES REGION. WITH AN INFLUX OF CAA
ALOFT AND LIGHT EASTERLY TO SOUTHEASTERLY SURFACE WINDS, EXPECT
TEMPERATURES TO TREND TOWARDS OUR SEASONAL NORMALS WITH HIGHS MAINLY
IN THE LOW TO UPPER 80S. BY THURSDAY, COULD SEE A SLIGHT BOOST IN
TEMPERATURES AS INCREASING WAA AHEAD OF A COLD FRONT LEADS TO HIGHS
IN THE 80S AND 90S WITH THE WARMEST CONDITIONS WEST OF THE JAMES
RIVER VALLEY. OUR NEXT RAIN CHANCES LIKELY COME BETWEEN THURSDAY
NIGHT AND FRIDAY MORNING WITH THE COLD FRONT. HOWEVER, THE FINER
DETAILS REMAIN UNCERTAIN AT THIS TIME. LASTLY, LONG-RANGE GUIDANCE
CONTINUES TO KEEP TEMPERATURES AROUND OUR SEASON RANGES HEADED INTO
THE WEEKEND SO EXPECT HIGHS IN THE 80S.
AVIATION /00Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 601 PM CDT SAT AUG 16 2025
PATCHY MVFR CEILINGS WILL BE POSSIBLE NEAR AND NORTH OF I-90
INTO THE EVENING. THEN LATE TONIGHT INTO SUNDAY MORNING MVFR
CEILINGS MAY RETURN IN MANY LOCATIONS. OUTSIDE OF THIS MVFR
THREAT, SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE, MAINLY NEAR
HIGHWAY 14 LATER TONIGHT INTO SUNDAY MORNING. A FEW STRONGER
STORMS WILL BE POSSIBLE. BY EARLY AFTERNOON STRONG TO SEVERE
THUNDERSTORMS WILL BE POSSIBLE IN SOUTHEAST SD, SOUTHWEST MN AND
NORTHWEST IA WITH THIS THREAT LIKELY CONTINUING INTO THE
EVENING.
FSD WATCHES/WARNINGS/ADVISORIES
SD...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR SDZ050-063>071.
MN...NONE.
IA...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR IAZ001>003-
012>014-020>022-031-032.
NE...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR NEZ013-014.
DISCUSSION...05
AVIATION...08
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