232
FXUS63 KFSD 151738
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1238 PM CDT TUE SEP 15 2026
KEY MESSAGES
- VERY LIGHT RAIN, SPRINKLES, OR DRIZZLE WILL BE POSSIBLE
WEDNESDAY AFTERNOON INTO THE EVENING.
- RAIN, POTENTIALLY HEAVY, WILL BE POSSIBLE LATE THURSDAY NIGHT
INTO FRIDAY. WHILE UNCERTAINTY REMAINS ON THE AXIS OF HEAVY
RAIN PLACEMENT, SOME MINOR IMPACTS TO RIVERS AND STREAMS
COULD BE POSSIBLE.
- NEAR NORMAL TEMPERATURES PERSIST THIS WEEKEND AND INTO NEXT
WEEK. ANY PRECIPITATION CHANCES ARE LIKELY TO REMAIN LIGHT
AND NON-SEVERE THROUGH THE WEEKEND.
DISCUSSION
ISSUED AT 1232 PM CDT TUE SEP 15 2026
THIS AFTERNOON: SUNNY SKIES CONTINUE TUESDAY AFTERNOON AS DRY AIR
FILTERS INTO THE REGION. TEMPERATURES WILL CONTINUE TO RISE INTO
THE UPPER 60S TO LOWER 70S.
TONIGHT: MOST NOTABLE CHANGE TONIGHT WAS TO CONTINUALLY LOWER DEW
POINTS FROM THE NBM GUIDANCE. SHORT TERM MODELS HAVE DONE A BETTER
JOB CAPTURING LOWER DEW POINTS THOUGH THE REGION AND KEEP SURFACE
WINDS EASTERLY THROUGH THE OVERNIGHT HOURS. THESE WINDS WILL KEEP
REINFORCING THE MIDDLE TO UPPER 40 DEW POINTS CURRENTLY IN THE AREA.
MID-LVL CLOUDS WILL GRADUALLY FILTER BACK INTO THE REGION AFTER
MIDNIGHT, AND MAY LEAD TO SOME STABILIZATION OF THE DIURNAL
TEMPERATURE FALL OVERNIGHT.
WEDNESDAY: A GENERALLY QUIET DAY IS ON TAP FOR THE REGION
WEDNESDAY. BY MID-MORNING THE 850MB RIDGE AXIS WILL SLIDE EAST
OF THE TRI- STATE AREA ALLOWING GRADUAL MOISTURE ADVECTION
NORTHWARD BY MID-DAY. SOUNDINGS INDICATE A THICKENING LOW-LVL
MOISTURE PROFILE THROUGH THE AFTERNOON AS WEAK WARM ADVECTION
PASSES ACROSS THE TRI-STATE AREA. THIS MAY RESULT IN WIDELY
SCATTERED VERY LIGHT SHOWERS THROUGH THE AFTERNOON AND EVENING.
AT TIMES BY THE EVENING, A BIT OF PATCHY DRIZZLE COULD ALSO BE
POSSIBLE AS CEILINGS REMAIN QUITE LOW AND THERE REMAINS WEAK
WARM ADVECTION AT THE TOP OF THE SATURATED LAYER.
THURSDAY-FRIDAY: THE MOST IMPACTFUL WEATHER IN THE NEXT 7 DAYS WILL
TAKE PLACE THURSDAY NIGHT INTO FRIDAY. LOW-LVL MOISTURE AND WEAK
BOUNDARY LAYER FLOW MAY KEEP CLOUDS AROUND THE AREA EARLY THURSDAY
MORNING. HIGH PRESSURE OVER NORTHERN MINNESOTA MAY LIMIT THE RISE
IN DEW POINTS EARLY IN THE MORNING, AGAIN WHICH MAY BE A DEVIATION
FROM THE NBM OR AT LEAST POINTED TOWARDS THE 25TH PERCENTILE. IF WE
HAVE QUITE A BIT OF CLOUD COVER, THEN THE PERSISTENT EASTERLY WINDS
MAY PREVENT TEMPERATURES FROM REACHING THE MIDDLE 70S.
MODELS ARE IN STRONG AGREEMENT THAT A PROGRESSIVE OPEN WAVE EXITS
THE CENTRAL ROCKIES AND CROSSES THE DAKOTAS THURSDAY NIGHT AND
FRIDAY. THIS SYSTEM WILL BE VERY MUCH LIKE A LATE FALL TO EARLY
WINTER SYSTEM, BRINGING STRONG LAYERED FRONTOGENESIS AND ELEVATED
INSTABILITY INTO THE TRI-STATE AREA AFTER MIDNIGHT. DETERMINISTIC
MODELS REMAIN A BIT VARIABLE WITH THE NORTHWARD EXTENT OF THE 700MB
FORCING, WITH THE GFS NOTABLY FURTHER NORTH THAN OTHER SOLUTIONS.
ENSEMBLE BASED SOLUTIONS ARE CLUSTERED FAIRLY WELL WITH A CORRIDOR
OF HEAVY RAIN NEAR HIGHWAY 14, BUT AI BASED ENSEMBLES OF THE GEFS/EC
WHICH SEEMED TO PICK UP EARLY LOCATION SHIFTS LAST WINTER, ARE
SUPPORTING OF A TRACK SOMEWHERE BETWEEN HIGHWAY 14 AND ALONG
I-90. RAINFALL WILL BE SLOW TO LEAVE THE AREA ON FRIDAY, WITH
SOME GUSTY NORTHERLY WINDS BY THE AFTERNOON. AREAS NEAR THE
MISSOURI RIVER AND HIGHWAY 20 AREAS HAVE THE HIGHEST CHANCE OF
SEEING SOME SUN IN THE AFTERNOON THOUGH THE CURRENT TEMPERATURE
FORECAST REMAINS HIGHLY VARIABLE GIVEN TRACK OF RAIN.
GIVEN THE INFLUX OF MOISTURE NORTHWARD, RAINFALL FORECAST AMOUNTS
COULD RISE SHARPLY OVER THE 24 HR PERIOD ENDING MID-DAY FRIDAY.
ENSEMBLES SUPPORT A GREATER THAN 40% CHANCE OF MORE THAN 2" OF QPF,
WITH 95 PERCENTILE DATA ALREADY AS HIGH AS 2.50-3" WHEREVER
THIS BAND OF PRECIPITATION FALLS. AS WE BEGIN TO INGEST MORE
HIGHER RESOLUTION DATA SETS, WE'LL LIKELY SEE THESE BROAD AREAS
OF HIGH PROBABILITIES FOCUS BETTER, BUT ALSO SEE THOSE HIGHER
END VALUES RISE. WITH THAT SAID, THE WPC "SLIGHT" RISK OF
EXCESSIVE RAINFALL SEEMS WARRANTED, WITH AI BASED OUTLOOKS
SUGGESTING HIGHER RISKS MAY BE POSSIBLE IF THE FORCING ZONE CAN
BE DETERMINED. THIS RAINFALL, ESPECIALLY AS YOU BEGIN TO PASS
THE 2-3" MARK, COULD LEAD TO SOME INCREASES IN LOCAL RIVER
LEVELS, AS RAINFALL THIS MONTH HAS BEEN ABOVE NORMAL AND WE'RE
BEGINNING TO SEE BETTER RESPONSES IN LEVELS AFTER RAIN ENDS.
SATURDAY-MONDAY: THE WEEKEND WILL REMAIN SLIGHTLY UNSETTLED AS UPPER
TROUGHING LINGERS OVER THE NORTHERN ROCKIES. BRIEF SHORTWAVE
RIDGING SHOULD ALLOW MOST AREAS TO DRY OUT ON SATURDAY, BUT
FEATURE COOLER THAN NORMAL TEMPERATURES. AN UPPER LOW THEN
DRIFTS SLOWLY SOUTHEAST ACROSS THE DAKOTAS INTO SUNDAY AND
MONDAY. INITIAL INDICATIONS SUGGEST THE GREATEST LIFT STAYS OVER
THE WESTERN DAKOTAS ON SUNDAY WITH RAIN CHANCES RETURNING AGAIN
BY MONDAY.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1201 PM CDT TUE SEP 15 2026
VFR CONDITIONS AND LIGHT WINDS WILL PERSIST INTO WEDNESDAY
MORNING. DEPENDING ON CLOUD COVER AND TEMPERATURES, PATCHY FOG
MAY DEVELOP IN VALLEY AREAS.
MID-UPPER CLOUD COVER WILL INCREASE THROUGH THE MORNING OF
WEDNESDAY AS A BREEZY SOUTHEAST WIND DEVELOPS.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...DUX
AVIATION...DUX
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