418
FXUS63 KFSD 151149
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
649 AM CDT MON SEP 15 2025
KEY MESSAGES
- TEMPERATURES REMAIN ABOVE NORMAL THROUGH TOMORROW BEFORE A COOLDOWN
BACK TO NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES IS
EXPECTED FOR THE SECOND HALF OF THE WEEK.
- ISOLATED STRONG TO SEVERE STORMS ARE POSSIBLE TOMORROW
AFTERNOON AND EVENING, ALONG WITH A HEAVY RAIN POTENTIAL
TOMORROW NIGHT. PLENTY OF UNCERTAINTY REMAINS, SO KEEP UP TO
DATE WITH THE LATEST FORECAST.
- A MULTI-DAY RAIN RISK DEVELOPS INTO THE UPCOMING WEEKEND, WITH
HEAVY RAIN POSSIBLE AGAIN WEDNESDAY AND THURSDAY. THERE'S
AROUND A 40-70% CHANCE OF AT LEAST A HALF OF RAIN ON
WEDNESDAY, AND A 20-50% CHANCE OF THAT ON THURSDAY.
DISCUSSION
ISSUED AT 353 AM CDT MON SEP 15 2025
SCATTERED SHOWERS AND STORMS FROM EARLIER HAVE DISSIPATED AS
THE UPPER-LOW CONTINUES LIFTING NORTH AND THE LLJ CONTINUES ON
THE DOWNWARD TREND. LINGERING STRATUS AROUND DAYBREAK MAINLY
ALONG HIGHWAY-14 COULD SPIT OUT A FEW SPRINKLES WITH RAP
SOUNDINGS SHOWING A LITTLE BIT OF ELEVATED INSTABILITY AROUND 10
KFT. HOWEVER, ANY RAIN THAT FALLS WILL ENCOUNTER SOME DRY AIR
ON ITS WAY DOWN AND THUS MOST, IF NOT ALL OF US SHOULD BE DRY
DURING THE MORNING COMMUTE. CLOUDS WILL CLEAR OUT THROUGH THE
MORNING HOURS, LEADING TO MOSTLY SUNNY SKIES ACROSS THE AREA. IT
WILL BE BREEZY WITH SOUTHERLY WINDS AROUND 10-15 MPH WITH GUSTS
UP TO 25-30 MPH, STRONGEST WEST OF I-29. HIGHS TODAY WITH THE
SOUTHERLY FLOW AND SUNSHINE WILL CLIMB ABOVE NORMAL ONCE AGAIN
WITH TEMPERATURES IN THE LOW-TO-MID-80S THIS AFTERNOON. SOME PVA
AROUND 700 MB LATE THIS AFTERNOON INTO THE EARLY EVENING COULD
TRIGGER A ROGUE STORM IN NORTHWEST IOWA WHERE THE CAP IS
WEAKEST, BUT THE BETTER CHANCES WILL BE EAST OF THE CWA. IF A
STORM DOES HAPPEN TO DEVELOP, THERE WILL BE AROUND 1500-2500
J/KG OF MLCAPE TO WORK WITH, BUT LESS THAN 15 KTS OF BULK SHEAR
AND THE CHANCE FOR SEVERE WEATHER IS LOW, THOUGH AN ISOLATED 60
MPH WIND GUST CANNOT BE ENTIRELY RULED OUT. BUT AGAIN, CHANCES
FOR EVEN STORM DEVELOPMENT ARE QUITE LOW (<15%) TO BEGIN WITH,
SO NO MAJOR CONCERNS ARE EXPECTED AT THIS TIME. WINDS DIE DOWN
TONIGHT, AND WITH MAINLY CLEAR SKIES AND SATURATED GROUNDS FROM
YESTERDAY'S RAIN, CAN'T RULE OUT SOME PATCHY FOG TOMORROW
MORNING MAINLY ALONG THE I-29 CORRIDOR AND INTO NORTHWEST IOWA
WHERE WINDS WILL BE LIGHTEST OVERNIGHT. LOWS TONIGHT WILL DROP
MAINLY TO THE LOWER-60S.
HEADING INTO THE DAY TUESDAY, AN UPPER-LOW AND ITS ATTENDANT
TROUGH WILL MOVE ACROSS THE NORTHERN ROCKIES AND INTO THE HIGH
PLAINS. AT THE SURFACE, A FRONTAL BOUNDARY WILL DRIFT INTO OUR
AREA AND ALL THIS WILL BE THE NEXT FOCUS FOR SHOWERS AND STORMS
ACROSS THE AREA MAINLY LATE TUESDAY INTO WEDNESDAY. IN TERMS OF
STORM TIMING, THE CAMS DIVERGE WITH THE HRRR AND FV3 SHOWING
EARLIER DEVELOPMENT THAN THE OTHERS AS THE CAP IS BROKEN FASTER
IN THOSE RUNS. THE NAM AND ARW HOLD OFF CONVECTION UNTIL THE
EVENING AS THE MAIN UPPER WAVE GETS CLOSER TO THE AREA, SO
LEANING TOWARDS THAT LATER SOLUTION AS OF NOW. THIS IS CURRENTLY
REFLECTED IN THE NBM POPS AS WELL, SO WILL MAINTAIN THOSE FOR
NOW BUT TRENDS WILL BE MONITORED. THE ATMOSPHERE WILL BE QUITE
UNSTABLE FOR THIS TIME OF YEAR TUESDAY AFTERNOON AND EVENING,
WITH MLCAPE VALUES POSSIBLY AS HIGH AS 2000-3000 J/KG. THERE IS
SOME UNCERTAINTY AS TO HOW MUCH BULK SHEAR WILL BE IN PLACE,
WITH SOME GUIDANCE SHOWING LESS THAN 15 KTS, WHILE OTHERS SHOW
AS MUCH AS 30 KTS. SO AT THIS POINT, ISOLATED SEVERE STORMS DO
LOOK POSSIBLE, BUT IT WILL ALSO DEPEND ON TIMING SO MAKE SURE TO
KEEP UP TO DATE WITH THE LATEST FORECAST. THE MAIN THREAT AT
THIS POINT APPEARS TO DAMAGING WIND GUSTS AS SOUNDINGS INDICATE
THE POTENTIAL FOR DECENT DRY AIR ENTRAINMENT TO OCCUR. SLOWER
STORM MOTION IS LIKELY AS OVERALL FLOW WILL BE WEAK AND THUS
THERE WILL BE A THREAT FOR HEAVY RAIN AS WELL MAINLY TUESDAY
NIGHT. SINCE WE WILL STILL BE AHEAD OF THE FRONTAL BOUNDARY ON
TUESDAY, EXPECT ANOTHER VERY WARM DAY WITH HIGHS IN THE
UPPER-80S TO EVEN THE LOW-90S.
THIS RATHER DIFFUSE FRONTAL BOUNDARY WILL MOVE ACROSS THE AREA
TUESDAY NIGHT, BUT RAIN CHANCES LOOK TO CONTINUE INTO WEDNESDAY AS
THE UPPER-LOW WILL STALL AND MEANDER OVER THE AREA THROUGH THE
REMAINDER OF THE WEEK AND INTO THE WEEKEND. RAIN CHANCES WILL BE
AROUND 60-80% WEDNESDAY AND THURSDAY, AND THIS RAIN COULD BE LOCALLY
HEAVY AT TIMES. ENSEMBLES SHOW AROUND A 40-70% CHANCE OF RAINFALL
GREATER THAN A HALF AN INCH ON WEDNESDAY, AND A 20-50% CHANCE OF AT
LEAST A HALF AN INCH ON THURSDAY. MODEST MUCAPE VALUES WILL STICK
AROUND THE AREA AS WELL, LEADING TO THE POTENTIAL FOR SOME
THUNDERSTORMS, THOUGH SEVERE WEATHER WOULD BE UNLIKELY DURING THE
LATE WEEK PERIOD. RAIN CHANCES LOOK TO CONTINUE INTO THE START OF
THE WEEKEND BEFORE THE UPPER-LOW FINALLY DEPARTS THE AREA LATE IN
THE WEEKEND. TEMPERATURE WISE, WE'LL START TO GRADUALLY COOL OFF
BEHIND THE AFOREMENTIONED FRONTAL BOUNDARY WITH HIGHS IN THE 70S
WEST OF I-29 ON WEDNESDAY. EAST OF I-29, THE COOLER AIR MAY TAKE A
LITTLE LONGER TO MOVE IN AND SO HIGHS MAY STILL CLIMB TO THE 80S
THERE. BY THURSDAY THROUGH SATURDAY, WE SHOULD ALL BE SEEING HIGHS
IN THE 70S, THOUGH THESE COOLER TEMPERATURES WILL BE MORE DUE TO THE
CONTINUED CLOUDINESS EXPECTED AS OPPOSED TO ANY MAJOR PUSHES OF COLD
AIR ADVECTION. IN FACT, ONCE THIS UPPER-LOW EXITS, THE POTENTIAL
RETURN OF RIDGING ALOFT MAY MEAN ANOTHER WARM UP HEADING INTO NEXT
WEEK.
AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 647 AM CDT MON SEP 15 2025
A FEW LINGERING SHOWERS ARE MOVING THROUGH AREAS FROM ROUGHLY NORTH
OF KMHE TO KHON TO START THE PERIOD, THOUGH THIS ACTIVITY
SHOULD EXIT THE AREA OVER THE NEXT HOUR OR TWO. SHALLOW FOG HAS
DEVELOPED FROM TIME TO TIME AT KSUX THIS PAST NIGHT, AND THAT
WILL LIKELY CONTINUE THROUGH 13Z BEFORE THE COMBINATION OF THE
SUN AND WINDS PICKING UP GETS RID OF ANY FOGGY SPOTS. VFR
CONDITIONS ARE EXPECTED OTHERWISE THROUGH THE PERIOD, ALTHOUGH
SOME MORE FOG MAY DEVELOP ALONG THE I-29 CORRIDOR INTO NORTHWEST
IOWA LATE TONIGHT WITH THE WET GROUNDS AND AS WINDS LIGHTEN UP.
SPEAKING OF WINDS, IT WILL BE BREEZY TODAY WITH SUSTAINED WINDS
OUT OF THE SOUTH AROUND 10- 15 KTS. PEAK GUSTS WILL BE AROUND
20-25 KTS THIS AFTERNOON, STRONGEST WEST OF I-29. WINDS TURN
LIGHT AND VARIABLE OVERNIGHT.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...SAMET
AVIATION...05/SAMET
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