400
FXUS63 KFSD 212346
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
646 PM CDT MON SEP 21 2026
KEY MESSAGES
- COOL AND DAMP INTO TUESDAY: LINGERING CLOUDS, DRIZZLE, AND
LIGHT SHOWERS WILL KEEP HIGH TEMPERATURES 10 TO 15 DEGREES
BELOW NORMAL (NEAR 60 DEGREES).
- MID-WEEK RAIN: WIDESPREAD SOAKING RAIN (0.50 TO 1.0+) AND
ISOLATED, NON-SEVERE THUNDERSTORMS RETURN LATE WEDNESDAY INTO
THURSDAY MORNING.
- MORE RAIN BY THE WEEKEND: AN ACTIVE WEATHER PATTERN CONTINUES
BRINGING A HIGH CHANCE (>60%) OF ADDITIONAL RAIN FRIDAY NIGHT
INTO SATURDAY.
- GRADUAL WARMING TREND: TEMPERATURES WILL REBOUND TO NEAR-
NORMAL HIGHS IN THE UPPER 60S TO LOWER 70S STARTING THURSDAY
AND LASTING THROUGH THE WEEKEND.
DISCUSSION
ISSUED AT 121 PM CDT MON SEP 21 2026
THIS AFTERNOON: WIDESPREAD STRATUS, DRIZZLE, AND SHOWERS PERSIST,
WITH NEW DEVELOPMENT OVER NW IOWA EXPECTED TO CONTINUE INTO THE
EVENING HOURS. TEMPERATURES WITH THE CLOUDS ARE QUITE COOL TODAY,
ONLY REACHING THE MID-50S, SOME 10-15 DEGREES BELOW NORMAL.
TONIGHT: THE LARGE UPPER LOW WILL SLOWLY WOBBLE SOUTHEAST TONIGHT,
MOST LIKELY BRINGING AN END TO THE WIDESPREAD SHOWER ACTIVITY
THROUGH THE NIGHT. HOWEVER, SOUNDINGS SHOW AN EXTENSIVE LOW
STRATUS LAYER PERSISTING, WITH THE DEPTH OF THIS LOW-LVL AIRMASS
COMBINED WITH WEAK FORCING ALLOWING DRIZZLE AND AREAS OF LOWER
VISIBILITY TO CONTINUE INTO DAYBREAK TUESDAY.
TUESDAY: THE UPPER LOW MOVES AWAY FROM THE AREA WITH A VERY SLOW
ARRIVAL OF SHORTWAVE RIDGING BY MID-DAY. DRIZZLE MAY LINGER INTO
MID-LATE MORNING IN A FEW AREAS AS ANOTHER WEAK 700MB VORTICITY AREA
SLIDES TOWARDS THE TRI-STATE AREA MID-MORNING. WIDESPREAD CLOUD
COVER IS NOW ANTICIPATED INTO EARLY/MID AFTERNOON. EVENTUALLY
WE MAY SEE STRATUS THIN AND SOME BREAKS APPEAR BY THE LATE
AFTERNOON, BUT TEMPERATURES WILL AGAIN REMAIN NEARLY 10 DEGREES
BELOW NORMAL EITHER SIDE OF 60 DEGREES.
WEDNESDAY-THURSDAY: MID-LVL HEIGHTS RISE AS WE HEAD INTO WEDNESDAY,
PARTIALLY IN RESPONSE TO A DEEPER TROUGH LIFTING TOWARDS THE CENTRAL
AND NORTHERN ROCKIES. THE ARRIVAL OF THIS TROUGH WILL ACCOMPLISH A
FEW THINGS. FIRSTLY, INDUCING LEE SIDE TROUGHING IN THE WESTERN
HIGH PLAINS AND TURNING SURFACE WINDS NEARBY TOWARDS THE SOUTH.
SECONDLY, INDUCING A 40 KNOT SOUTHERLY LOW LEVEL JET BY WEDNESDAY
AFTERNOON ALLOWING LOW-LVL MOISTURE TO STREAM BACK NORTHWARD INTO
THE CENTRAL DAKOTAS. FINALLY, BRINGING A BIT MORE WARM AIR NORTHWARD
WHICH SHOULD ALLOW US TO WARM INTO THE 60S IN MOST AREAS WITH THE
LOWER 70S IN SOUTH CENTRAL SOUTH DAKOTA.
SHOWER AND ISOLATED THUNDERSTORM DEVELOPMENT MAY DEVELOP BY LATE
WEDNESDAY AFTERNOON AND SLIDE EAST IN THE EVENING AND OVERNIGHT
HOURS, DRIVEN BY BROAD WARM ADVECTION, WEAK DPVA FROM THE WAVE TO
OUR NORTHWEST, BUT ALSO THE ARRIVAL OF A SECONDARY AREA OF VORTICITY
LIFTING OUT OF THE SOUTHWEST US. RAINFALL AMOUNTS ARE NOT EXPECTED
TO BE EXCESSIVE, BUT THE 25/75TH 24 HR QPF FROM THE NBM WOULD
SUGGEST AMOUNTS BETWEEN 0.25 AND 1.5. THE GEFS/EC/GEPS MEAN QPF
SITS AROUND 1.1 IN MOST LOCATIONS. AT THIS JUNCTION I'M NOT
ANTICIPATING ANY SEVERE WEATHER RISKS, WITH MUCAPE AROUND 500 J/KG
ON AVERAGE WITH THE PASSAGE OF THIS PRECIPITATION.
WE'LL GRADUALLY CLEAR OUT DURING THE SECOND HALF OF THURSDAY, BUT
THERE WILL BE SOME POTENTIAL FOR ADDITIONAL CLOUDS TO MOVE IN BY
FRIDAY MORNING. TEMPERATURES BEHIND THE PRECIPITATION THURSDAY WILL
REBOUND BACK TO THE UPPER 60S TO LOWER 70 DEPENDING ON CLEARING.
FRIDAY-SUNDAY: A WET SEPTEMBER WILL CONTINUE AS WE APPROACH NEXT
WEEKEND WITH YET ANOTHER PROGRESSIVE UPPER TROUGH LIFTING THROUGH
THE ROCKIES AND INTO THE PLAINS BY LATE FRIDAY INTO SATURDAY. THIS
WAVE WILL BRING HIGH RAIN CHANCES (>60% AS OF THIS PRODUCT) FRIDAY
NIGHT INTO SATURDAY MORNING. TEMPERATURES WILL TREND SLIGHTLY WARMER
FOR THE UPCOMING WEEKEND WITH MOST GUIDANCE SETTLING ON HIGHS NEAR
NORMAL (UPPER 60S TO LOWER 70S).
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 646 PM CDT MON SEP 21 2026
LOW LEVEL STRATUS CONTINUES TO BLANKET THE VAST MAJORITY OF THE AREA
EARLY THIS EVENING. THE STRATUS IS SITTING AT MAINLY MVFR/IFR LEVELS
WITH VISIBILITIES MAINLY BETWEEN VFR/MVFR. SOME DRIZZLE IS ALSO
FALLING BENEATH THE STRATUS. THIS STRATUS WILL PERSIST FOR THE REST
OF THE TAF PERIOD AND WILL LOWER TO MVFR/IFR/LIFR LEVELS THROUGH THE
REST OF THE EVENING HOURS. THIS MAY RESULT IN SOME PATCHY FOG,
MAINLY ACROSS THE BUFFALO RIDGE IN SOUTHWEST MINNESOTA. DRIZZLE ALSO
REMAINS POSSIBLE BENEATH THE STRATUS THROUGH THE REST OF THE EVENING
AND NIGHT. THE STRATUS WILL BEGIN TO LIFT THROUGH THE MORNING AND
EARLY AFTERNOON HOURS TOMORROW. THIS LOOKS TO BRING A RETURN OF
VFR/MVFR CEILINGS TO THE AREA TO FINISH OUT THE PERIOD.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...DUX
AVIATION...MEYERS
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