798
FXUS63 KFSD 200930
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
430 AM CDT SUN SEP 20 2026
KEY MESSAGES
- FOG RISK IS DECREASING FOR THE REST OF TONIGHT, BUT AREAS OF
DRIZZLE MAY RESULT IN OCCASIONAL MINOR DROPS IN VISIBILITY
INTO THE MORNING.
- THE NEXT BETTER CHANCE FOR RAIN WILL COME TONIGHT INTO MONDAY.
THUNDERSTORMS WILL BE VERY ISOLATED AND SEVERE WEATHER IS NOT
EXPECTED, BUT LOCALIZED RAINFALL TOTALS IN EXCESS OF AN INCH
ARE POSSIBLE.
- BELOW NORMAL TEMPERATURES WILL PERSIST THROUGH NEXT WEEK.
UPDATE
ISSUED AT 430 AM CDT SUN SEP 20 2026
NORTHEAST FLOW HAS BECOME A BIT MORE MIXY BENEATH THE STRATUS
LAYER EARLY THIS MORNING, WHICH HAS ALLOWED FOR IMPROVEMENT IN
VISIBILITY AND SLOW INCREASE IN CLOUD BASE HEIGHTS. WHILE THIS
WILL LIMIT EXTENT OF FOG THROUGH THE REMAINDER OF THE NIGHT,
WEAK LIFT ATOP A DEEP STRATUS DECK IS STILL PRODUCING AREAS OF
DRIZZLE BASED ON WEB CAM IMAGERY AND SPOTTY TRACE-0.01" PRECIP
AMOUNTS ON AREA METARS. EXPECT THE POTENTIAL FOR LIGHT DRIZZLE
TO CONTINUE INTO THE MID-LATE MORNING WHEN THIS LIFT DIMINISHES.
HOWEVER, BROADER LIFT AND EVEN A SHALLOW CONVECTIVE LAYER BELOW
850MB WILL BRING INCREASING CHANCES FOR LIGHT RAIN TO PORTIONS
OF SOUTHEAST SD INTO NORTHWEST IA BY MID-LATE AFTERNOON.
RAIN COVERAGE IS THEN EXPECTED TO INCREASE THROUGH TONIGHT AS A
BROAD MID-UPPER LEVEL WAVE SLOWLY SPINS EASTWARD ACROSS THE
REGION. HREF LPMM (LOCALIZED PROBABILITY-MATCHED MEAN) INDICATES
A POTENTIAL FOR A BAND OF HEAVIER RAINFALL, UPWARDS OF AN INCH
TO LOCALLY OVER 2 INCHES. WHILE THE LOCATION IS STILL SOMEWHAT
UNCERTAIN, TRENDS FAVOR THIS BAND EXTENDING FROM PORTIONS OF THE
I-90 CORRIDOR IN SOUTHEAST SD, INTO THE HIGHWAY 18 CORRIDOR IN
NORTHWEST IA. LATEST NBM HAS CAUGHT ON TO THIS AND HAS BEGUN
TRENDING QPF AMOUNTS UPWARD FROM PREVIOUS RUNS, THOUGH STILL
FALLING SHY OF AN INCH MOST LOCATIONS. THIS MAY NEED TO BE
REFINED FURTHER BY LATER SHIFTS.
OTHERWISE, A COOL AND BREEZY DAY IS ON TAP WITH HIGHS MOSTLY IN
THE LOWER 60S AND NORTHEAST WINDS GUSTING NEAR 25 MPH AT TIMES
TODAY.
DISCUSSION
ISSUED AT 1247 PM CDT SAT SEP 19 2026
THE LOW LEVELS REMAIN SATURATED TO NEAR SATURATED TONIGHT INTO
SUNDAY MORNING WHICH WILL KEEP THE POTENTIAL FOR FOG IN PLACE, AS
WELL AS PATCHY DRIZZLE. DENSE FOG WILL AGAIN BE FAIRLY SPARSE, BUT
SOME LOCATIONS WILL SEE THE VISIBILITY FALL TO A HALF MILE OR LESS
AT TIMES.
OVERALL, SUNDAY LOOKS TO BE A PRETTY DREARY DAY WITH LOW LEVEL
SATURATION DEEPENING THROUGH THE DAY. WHILE THE VISIBILITIES WILL
LIKELY IMPROVE A BIT THROUGH THE MORNING, STRATUS WILL REMAIN FAIRLY
LOW AND WILL NOT DISSIPATE. AS THIS LOW LEVEL MOISTURE DEEPENS, A
WEAK WAVE WILL APPROACH FROM THE SOUTH AND BRING SLIGHTLY COOLER
TEMPERATURES ALOFT AND A BIT MORE ELEVATED MOISTURE. THIS SHOULD
ALLOW FOR SCATTERED SHOWERS TO DEVELOP, BUT WITH ONLY VERY WEAK
INSTABILITY THUNDER LOOKS UNLIKELY. AS THIS WAVE ROTATES NORTHWARD,
A SLIGHTLY STRONGER WAVE WILL MOVE EASTWARD THROUGH NORTHERN NE INTO
NORTHWEST IA WHICH SHOULD KEEP AN EXPANDING AREA OF RAIN IN PLACE
ACROSS THE AREA. GIVEN THE PLACEMENT OF THE UPPER LEVEL WAVE AND THE
ASSOCIATED INSTABILITY, PARTS OF SOUTH CENTRAL AND SOUTHEAST SD DOWN
THE MISSOURI RIVER WILL LIKELY SEE THE BETTER CHANCES FOR AN INCH OR
SO OF RAIN. THE 12Z NAM, RRFS AND HRRR ALL PAINT THESE HIGHER
RAINFALL AMOUNTS NEAR AND SOUTH OF I-90.
THIS WAVE SLOWLY MOVES THROUGH ON MONDAY, SO EXPECT TO SEE SHOWERS
SLOWLY DISSIPATE FROM WEST TO EAST THROUGH LATE AFTERNOON. STRATUS
WILL ONCE AGAIN BE DIFFICULT TO SHAKE AS THE PUSH BEHIND THIS WAVE
IS PRETTY WEAK AND LIGHTER NORTHEAST TO EAST FLOW WILL BE IN PLACE IN
THE LOWER LEVELS. SOME HINTS IN THE SOUNDINGS THAT CLEARING WILL BE
POSSIBLE ON MONDAY NIGHT, BUT WITH LIGHT WINDS AND A MOIST BOUNDARY
LAYER, FOG WILL THEN BECOME MOIRE LIKELY FOR LATE MONDAY NIGHT INTO
TUESDAY MORNING.
TUESDAY AND WEDNESDAY WILL SEE SOME WEAK UPPER LEVEL RIDGING WITH
AFTERNOON TEMPERATURES LIKELY ONLY RISING INTO THE 60S.
WEDNESDAY NIGHT INTO THURSDAY A TROUGH OF LOW PRESSURE WILL APPROACH
FROM THE WEST AND BRING A CHANCE FOR SHOWERS AND ISOLATED
THUNDERSTORMS. SEVERE WEATHER LOOKS UNLIKELY. FOR NOW THE BETTER
CHANCES WILL LIKELY BE WEST OF I-29.
TEMPERATURES SHOULD REMAIN A TOUCH BELOW NORMAL THURSDAY INTO FRIDAY
WITH SOME POTENTIAL FOR SPOTTY SHOWERS. HIGHS GENERALLY IN THE UPPER
60S TO LOWER 70S.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1242 AM CDT SUN SEP 20 2026
THE AREA CONTINUES TO REMAIN SOCKED IN IFR TO MVFR STRATUS
EARLY THIS MORNING, WITH GRADUAL IMPROVEMENTS EXPECTED THROUGHOUT
THE DAY TODAY BEFORE DROPPING AGAIN LATER THIS EVENING. PATCHY FOG
AND DRIZZLE REMAINS LIKELY THIS MORNING IN SPOTS, THOUGH THE CIGS
WILL CONTINUE TO BE THE MOST IMPACTFUL. RAIN CHANCES WILL INCREASE
FROM SOUTHWEST TO NORTHEAST THROUGH THE DAY TODAY, WITH LOCALLY
HEAVY RAINFALL THE MAIN CONCERN BY THE EVENING. THUNDER IS
UNLIKELY.
WINDS WILL BE MAINLY OUT OF THE NORTHEAST THROUGH THE PERIOD.
HIGHEST GUSTS WILL BE AROUND 20-22 KTS DURING THE DAYTIME HOURS
BEFORE LESSENING BY THE LATE AFTERNOON AND EVENING.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...JH
DISCUSSION...08
AVIATION...SAMET
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