263
FXUS63 KFSD 170535
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1235 AM CDT THU SEP 17 2026
KEY MESSAGES
- SCATTERED RAIN AND DRIZZLE WILL PUSH EAST OF THE AREA AROUND
MIDNIGHT.
- FOG LOOKS TO DEVELOP TONIGHT ACROSS MUCH OF THE REGION.
VISIBILITY MAY DROP TO 2 MILES OR LESS AT TIMES ALONG AREAS OF
ELEVATION SUCH AS BUFFALO RIDGE, ALONG RIVERS AND WATER WAYS,
AND VALLEYS. BE PREPARED FOR RAPIDLY CHANGING VISIBILITY
CONDITIONS.
- CONFIDENCE CONTINUES TO INCREASE IN WIDESPREAD RAINFALL MOVING
INTO THE AREA THURSDAY LATE EVENING THROUGH FRIDAY. RAIN COULD
BE HEAVY AT TIMES, AND MINOR IMPACTS TO RIVERS AND STREAMS ARE
POSSIBLE.
- NEAR NORMAL TEMPERATURES PERSIST THIS WEEKEND AND INTO NEXT
WEEK. ANY PRECIPITATION CHANCES ARE MOST LIKELY (30-70%) TO
REMAIN LIGHT AND NON-SEVERE THROUGH THE WEEKEND AND INTO NEXT
WEEK.
UPDATE
ISSUED AT 823 PM CDT WED SEP 16 2026
LIGHT RAIN AND DRIZZLE CURRENTLY LOCATED ALONG AND EAST OF I-29 WILL
CONTINUE TO PUSH EAST INTO THE LATE EVENING HOURS BEFORE ENDING
AROUND TO SHORTLY AFTER MIDNIGHT. WINDS WILL BECOME LIGHT AND
VARIABLE OVERNIGHT. PATCHY DENSE FOG HAS ALREADY BEGUN TO FORM
IN AREAS OF NORTHWEST IOWA. PATCHY FOG IS EXPECTED TO EXPAND
NORTH THROUGH MUCH OF THE REGION. VISIBILITY SHOULD REMAIN ABOVE
4 MILES FOR THE MOST PART, BUT AREAS ALONG THE BUFFALO RIDGE,
RIVERS, STREAMS, AND IN VALLEYS MAY SEE VISIBILITY FALL TO 2
MILES OR LESS AT TIMES. NO FOG HEADLINES AT THIS TIME, HOWEVER
THE TRENDS AND VISIBILITIES WILL BE MONITORED THROUGHOUT THE
NIGHT. OVERNIGHT LOWS WILL FALL TO THE MID 50S TO LOW 60S.
FOG SHOULD BURN OFF BY MID-MORNING THURSDAY. CLOUDS GRADUALLY BREAK
UP AND BECOME SCATTERED BY THE AFTERNOON. SHOULD CLOUDS CLEAR ENOUGH
WE HAVE THE POTENTIAL TO WARM NICELY AT THE SURFACE INTO THE MID-TO-
UPPER 70S. THROUGH THE DAY A SHORT AMPLITUDE RIDGE WILL BUILD OVER
THE CENTRAL US, WHILE AT THE SAME TIME AN UPPER TROUGH AND CLOSED
LOW WILL DEEPEN AND DIG SOUTH OVER THE PACIFIC NORTHWEST. A BAND OF
THETA-E PUSHES NORTH AHEAD OF A WARM FRONT DRAPED THROUGH KANSAS IN
THE AFTERNOON. THIS WILL WORK TO WEAKLY DESTABILIZE THE ENVIRONMENT
FOR MUCH OF THE CWA. IN THE EVENING AND OVERNIGHT A SHORTWAVE WILL
WORK THROUGH THE PATTERN. THIS WILL WORK TO INDUCE A
STRENGTHENING LLJ. THIS JET WILL WORK TO RAMP UP WAA IN THE
MID-LEVELS. ALL OF THIS WILL WORK TO FORM A BAND OF
FRONTOGENESIS IN THE 850-700 MB LAYER. THIS WILL TAP INTO THE
ELEVATED INSTABILITY PRESENT AND SHOWERS AND THUNDERSTORMS WILL
RESULT. CURRENT GUIDANCE HAS THE STRONGEST FORCING ROTATE AROUND
THE CWA FROM THE WESTERN BORDER TO THE NORTHERN BORDER, KEEPING
THE HEAVIEST RAINFALL OVER CENTRAL SOUTH DAKOTA AND ALONG AND
NORTH OF I-90. HOWEVER, THE BAND OF FGEN WILL EXPAND SOUTH AND
BENEFICIAL RAIN WILL FALL OVER MOST OF THE REGION THURSDAY
NIGHT INTO FRIDAY MORNING.
EARLY FRIDAY MORNING THE SHORTWAVE STRENGTHENS AND A CLOSED SURFACE
LOW EJECTS OUT ONTO WESTERN NEBRASKA. WARM AIR AND MOISTURE
ADVECTION INCREASE AS WELL AS INSTABILITY, ESPECIALLY ALONG AND
EAST OF THE I-29 CORRIDOR. THE SURFACE LOW ACCELERATES NORTHEAST
AND DRAGS AN ASSOCIATED COLD FRONT THROUGH THE REGION BY LATE
FRIDAY AFTERNOON INTO THE EVENING. SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO FORM ALONG THE FRONT. SOME OF THESE COULD BE STRONG
TO SEVERE PRODUCING MARGINALLY SEVERE HAIL AND DAMAGING WIND
GUSTS. AREA MOST AT RISK IS ALONG AND EAST OF HIGHWAY 60 IN
NORTHWEST IOWA. THIS FORECAST ALIGNS WELL WITH THE CURRENT SPC
DAY 3 MARGINAL RISK FOR SEVERE WEATHER (LEVEL 1 OF 5). STORMS
WILL CLEAR OUT THROUGH THE EARLY PART OF SATURDAY MORNING. HIGHS
FOR FRIDAY WILL DEPEND ON HOW FAR NORTH THE WARM FRONT PUSHES
BEFORE IT IS OVERTAKEN BY THE COLD FRONT. FOR NOW AREAS NORTH OF
I-90 SHOULD SEE HIGHS IN THE MID 70S, ALONG AND SOUTH OF I-90
WILL SEE HIGHS CLIMB INTO THE MID 80S, WARMEST ALONG THE
SOUTHERN MISSOURI RIVER.
DISCUSSION
ISSUED AT 243 PM CDT WED SEP 16 2026
WE ARE STARTING TO SEE SPRINKLES TO VERY LIGHT SHOWERS BREAK OUT
ACROSS PARTS OF THE AREA THIS AFTERNOON AS WARM AIR ADVECTION (WAA)
STRENGTHENS ALOFT. WITH SATURATION IN THE LOW LEVELS BUT A DRY
DENDRITIC GROWTH ZONE (DGZ), SPRINKLES/DRIZZLE IS EXPECTED. AT THE
SAME TIME, LOW LEVEL STRATUS NOT ONLY CONTINUES TO BLANKET MOST OF
THE FORECAST AREA BUT IS LOWERING IN HEIGHT. THESE CONDITIONS WILL
PERSIST THROUGH THE REST OF THE AFTERNOON AND EVENING HOURS BEFORE
RAIN CHANCES ENDING AFTER MIDNIGHT. THOUGH WITH LOWERING CEILINGS,
SPRINKLES/DRIZZLE LOOKS TO PERSIST THROUGH THE NIGHT. AT THE SAME
TIME, WITH SUFFICIENT LOW LEVEL MOISTURE IN PLACE, CEILINGS LOOK TO
LOWER TO POTENTIALLY DOWN TO FOG ACROSS THE AREA. AS OF NOW, THINK
THAT IT IS MAINLY ACROSS THE HIGHER ELEVATION AREAS ALONG THE
BUFFALO RIDGE IN SOUTHWEST MINNESOTA, DOWNS THROUGH NORTHWEST IOWA,
AND ALONG THE MISSOURI RIVER VALLEY. WITH THE STRATUS/FOG IN PLACE,
TEMPERATURES WILL NOT MOVE MUCH, ONLY LOWERING TO THE 50S TO LOW
60S.
FOG ALONG WITH SPRINKLES/DRIZZLE WILL CONTINUE INTO THE MORNING
HOURS BEFORE LIFTING THROUGH THE MORNING HOURS. THIS SHOULD ALLOW
FOR TEMPERATURES TO WARM TO THE 70S FOR THE AFTERNOON HOURS. WHILE
THE AFTERNOON HOURS WILL BE QUIET, THINGS WILL CHANGE THURSDAY
EVENING AND ESPECIALLY FOR THURSDAY NIGHT AS A SHORTWAVE TROUGH
ROUNDS THE WESTERN FLANK OF AN UPPER LEVEL RIDGE, PARKED OVER THE
SOUTHERN CONUS. THIS WAVE WILL STRENGTHEN LOW LEVEL WAA AND BEGIN TO
DEVELOP SHOWERS ACROSS CENTRAL SOUTH DAKOTA THURSDAY EVENING. THE
WAA WILL BE DRIVEN BY THE LOW LEVEL JET (LLJ), TIGHTENING THE
TEMPERATURE GRADIENT, RESULTING IN FRONTOGENESIS (FGEN). THIS BAND
OF FGEN LOOKS TO BE THE MAIN DRIVER FOR RAIN AS THE RAIN BECOMES
MORE WIDESPREAD AS THE FORCING FOR ASCENT INCREASES. THERE ALSO
LOOKS TO BE INSTABILITY ABOVE THE FRONT WHICH LOOKS TO RESULT IN A
TIGHTER BAND OF RAIN. THIS TIGHTER BAND OF RAIN CONTINUES TO LOOK
MOST LIKELY NEAR AND NORTH OF HIGHWAY-14. THE BEST FORCING FOR
ASCENT WILL PUSH OFF TO THE NORTHEAST OF THE AREA FRIDAY MORNING,
RESULTING IN SLOWLY WANING RAIN ACROSS THE AREA. COULD STILL SEE
LIGHTER RAIN PERSIST THROUGH THE REST OF THE MORNING HOURS. THERE
REMAINS SOME UNCERTAINTY IN WHERE THIS HEAVIEST BAND SETS UP. LATEST
12Z DETERMINISTIC GUIDANCE SHOWS A SLIGHT WOBBLE BACK SOUTHWARDS
FROM THE PREVIOUS 00Z GUIDANCE. HOWEVER, THE ENSEMBLES SHOW SIMILAR
PLACEMENT WITH THIS BAND NEAR AND NORTH OF HIGHWAY-14. THE ENSEMBLES
MEAN QPF REMAINS A BROAD 0.5 INCHES TO UP TO ABOUT 2.0 INCHES BUT
THEIR 90TH PERCENTILE QPF ALSO REMAINS UP TO 2.0 TO 3.0+ INCHES.
THINK THIS 90TH PERCENTILE IS REPRESENTATIVE OF THE HIGHEST AMOUNTS
THAT FALL WITHIN THE BAND ITSELF. THE ENSEMBLES PROBABILITIES DO
SUPPORT THESE TOTALS AS THEY ALL HAVE A NEAR 100% CHANCE FOR 0.50
INCHES OR MORE OF RAIN. THE PROBABILITY FOR AN INCH OR MORE IS
BETWEEN 40-90% AND LOWERS TO A 20-40% CHANCE FOR 2 INCHES OR MORE.
HAVE SLIGHTLY TRENDED TOTAL QPF UPWARDS AND THINK THE OVERALL
RAINFALL AMOUNTS WILL BE A BROAD 0.5 INCH TO 2.0 INCHES OF RAIN
ACROSS THE AREA. LOCALLY HIGHER AMOUNTS UP TO AND EXCEEDING 3.0
INCHES IS POSSIBLE, MAINLY UNDER THE BAND ITSELF. THIS MAY LEAD TO
MINOR RISES IN RIVERS AND STREAMS AS WELL ALL PONDING ON ROADWAYS
AND POOR DRAINAGE AREAS.
A SMALL BREAK IN THE ACTION IS POSSIBLE FOR PART OF THE AFTERNOON
HOURS ON FRIDAY AS SOME BREAKS IN THE CLOUDS OCCUR. THIS WILL ALLOW
FOR HIGH TEMPERATURES TO WARM TO THE LOW 70S TO MID 80S, WARMEST
SOUTH OF I-90. THE POCKETS OF SUNSHINE AND DIURNAL HEATING MAY ALLOW
FOR SUFFICIENT CAPE VALUES TO RETURN NORTHWARDS, POTENTIALLY
RESULTING IN STRONG TO SEVERE STORMS. THIS POTENTIAL IS HIGHLY
CONDITIONAL AND DEPENDENT ON HOW QUICKLY MORNING SHOWERS AND CLOUD
COVER CAN EXIT THE AREA. IF A SEVERE WEATHER THREAT WERE TO
MATERIALIZE, IT WOULD BE FRIDAY AFTERNOON AND EVENING FOR LOCATIONS
SOUTH OF I-90.
SATURDAY LOOKS TO BE A DRY DAY ACROSS THE AREA WITH HIGH
TEMPERATURES NEAR SEASONABLE IN THE UPPER 60S TO LOW 70S. THE BREAK
FROM THE RAIN WILL BE SHORT LIVED AS ANOTHER UPPER LEVEL WAVE LOOKS
TO EJECT INTO THE PLAINS ON SUNDAY. THIS CHANCE FOR RAIN IS
SUPPORTED BY THE ENSEMBLES AS THEY SHOW A BROAD 30-70% CHANCE FOR
RAINFALL AMOUNTS TO EXCEED A TENTH OF AN INCH. GOOD NEWS IS THAT
INSTABILITY IS NOT EXPECTED, SO THIS LOOKS TO BE MORE STRATIFORM
RAIN RATHER THAN CONVECTIVE RAIN.
MEDIUM RANGE GUIDANCE DIVERGES IN HOW THE UPPER LEVEL PATTERN WILL
EVOLVE FOR NEXT WEEK. THERE COULD BE ADDITIONAL CHANCES FOR RAIN BUT
DETAILS ARE UNCERTAIN THIS FAR OUT. TEMPERATURES ON THE OTHER HAND
LOOK TO REMAIN SEASONABLE IN THE 60S AND 70S.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1233 AM CDT THU SEP 17 2026
PATCHY DENSE FOG IS EXPECTED TO EXPAND THROUGHOUT MOST OF THE REGION
OVER THE NEXT FEW HOURS. CURRENT CEILINGS AND VISIBILITY RUN FROM
MVFR DOWN TO LIFR. THIS IS EXPECTED TO REMAIN THE CASE THROUGH MID
TO LATE THURSDAY MORNING BEFORE FOG FINALLY LIFTS. LIGHT AND
VARIABLE WINDS BECOME EASTERLY AND SLIGHTLY BREEZY BY AFTERNOON.
GUSTS OF 15-20 KTS ARE EXPECTED FOR AREAS ALONG AND WEST OF THE
JAMES RIVER VALLEY.
AFTER 18.00Z GUSTY WINDS WILL EXPAND EAST AS A SURFACE LOW AND WARM
FRONT APPROACH FROM THE SOUTHWEST. PRECIPITATION WILL BEGIN
OVER WESTERN SOUTH DAKOTA AND NEBRASKA AND FLOW NORTHEAST INTO
THE CWA. SEVERE WEATHER IS NOT ANTICIPATED AT THIS TIME, HOWEVER
VERY HEAVY RAINFALL IS POSSIBLE AT TIMES FOR AREAS ALONG AND
NORTH OF I-90. MODERATE TO HEAVY RAIN CONTINUES THROUGH THE END
OF THE PERIOD.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...AJP
DISCUSSION...MEYERS
AVIATION...AJP
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