862
FXUS63 KFSD 160840
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
340 AM CDT WED SEP 16 2026
KEY MESSAGES
- SCATTERED SHOWERS WILL DEVELOP FROM EARLY AFTERNOON INTO THE
EVENING MAINLY ALONG AND EAST OF I-29.
- 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.
UPDATE
ISSUED AT 335 AM CDT WED SEP 16 2026
TAKING A LOOK ACROSS THE AREA, MOSTLY CLEAR CONDITIONS CONTINUE
ACROSS MOST OF THE AREA AS A SURFACE HIGH CONTINUES TO PUSH EAST
THIS MORNING. WITH LIGHT AND VARIABLE SURFACE WINDS, CAN'T RULE OUT
SOME PATCHY VALLEY FOG ALONG OUR WATER WAYS AND LOW LYING AREAS.
HOWEVER, NOT EXPECTING ANY WIDESPREAD DEVELOPMENT MAINLY DUE TO
SLIGHTLY LARGE DEW POINT DEPRESSION. EITHER WAY, SHOULD ANY
LINGERING FOG DISSIPATE JUST AFTER DAYBREAK. OTHERWISE, MOSTLY CLEAR
CONDITIONS WILL GIVE WAY TO OVERCAST SKIES BY EARLY AFTERNOON AS
ANOTHER WEAK MID-LEVEL WAVE DRIFTS ACROSS THE AREA. SCATTERED
SHOWERS WILL BE POSSIBLE MAINLY EAST OF I-29 WITH PERHAPS A RUMBLE
OF THUNDER OR TWO. FROM HERE, THE FOCUS TURNS TOWARDS THE LATER
PARTS OF THE WEEK AS A STRONGER WAVE LIFTS OUT OF THE COLORADO
ROCKIES INTO WESTERN SD AND NE. INITIAL DEVELOPMENT WILL LIKELY TAKE
PLACE ALONG THE MISSOURI RIVER VALLEY AS A RIBBON OF VORTICITY
LIFTS NORTHEASTWARDS DURING THE SECOND HALF OF THURSDAY.
HOWEVER, THE MAIN COURSE WILL START THURSDAY NIGHT AS THE WARM
AIR ADVECTION REGIME STRENGTHENS AHEAD OF A DEVELOPING SURFACE/850MB
LOW. WITH THIS AND STRENGTHENING LLJ IN PLACE, SHOWERS AND
THUNDERSTORMS LIKELY DEVELOP ACROSS THE BLACK HILLS AND LIFT
NORTHEASTWARDS DURING THE NIGHT INTO CENTRAL AND SOUTHEASTERN
SD. WHILE THE SEVERE WEATHER RISK IS LOW, LOCALLY HEAVY RAINFALL
WILL BE THE MAIN THREAT AS PWATS APPROACH THE TOP 1% TO MAX OF
ENSEMBLE GUIDANCE. EVEN THROUGH THERE ARE STILL SOME LINGERING
QUESTIONS ABOUT WHERE THE AXIS OF HEAVIEST PRECIPITATION SETS
UP, WE'VE CONTINUED TO SEE A NORTHEAST SHIFT IN THE HEAVIEST
AMOUNTS WITH THE LATEST RUNS OF GUIDANCE. THIS SHIFT IS ALSO
ECHOED IN THE ENSEMBLE GUIDANCE WITH BOTH THE GEFS/GEPS SHOWING
MODERATE TO HIGH CONFIDENCE (40%-70%) IN 0.50" OR GREATER OF QPF
ALONG AND NORTH OF I-90 WITH THE HIGHEST CONFIDENCE ALONG U.S.
HIGHWAY-14 CORRIDOR. EITHER WAY, THE WETTEST CONDITIONS ARE
EXPECTED FROM THURSDAY NIGHT INTO THE DAY ON FRIDAY WITH MOST OF
THIS ACTIVITY TAPERING EAST BY LATE FRIDAY NIGHT INTO SATURDAY
MORNING.
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 THROUGH 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 /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1249 AM CDT WED SEP 16 2026
A FEW SPOTS OF LIGHT FOG HAVE DEVELOPED NORTH OF I-90 TO START
THE PERIOD, BUT DRIER AIR THAN YESTERDAY SHOULD PREVENT THIS FROM
BECOMING WIDESPREAD. MVFR STRATUS WILL MOVE INTO THE MISSOURI RIVER
VALLEY BY THE MIDDLE PART OF THE MORNING AND MOVE NORTHEASTWARD
THROUGH THE AFTERNOON, COVERING ALMOST THE ENTIRE AREA EAST OF THE
JAMES RIVER BY THE EVENING. IFR CEILINGS WILL ALSO BECOME MORE
PREVALENT LATE THIS AFTERNOON INTO THE EVENING HOURS MAINLY EAST OF
I-29. PATCHY DRIZZLE WILL ALSO BE POSSIBLE WITH ANY IFR CIGS. THE
STRATUS MAY BEGIN TO ERODE FROM WEST TO EAST TOWARDS THE END OF THE
PERIOD AS WINDS JUST ABOVE THE SURFACE TURN MORE NORTHWESTERLY,
THOUGH CONFIDENCE ON THE TIMING OF THIS IS LOW AND THUS KEPT
THE STRATUS THROUGH 17.06Z AT KFSD AND KSUX.
WINDS WILL INCREASE OUT OF THE SOUTHEAST THROUGH THE MORNING HOURS
NEAR AND AFTER SUNRISE. HIGHEST WIND GUSTS WILL BE NEAR AND WEST OF
THE JAMES, WHERE OCCASIONAL GUSTS TO 20-25 KTS WILL BE POSSIBLE.
WINDS WILL THEN SLOWLY DECREASE THROUGH THE AFTERNOON HOURS,
BECOMING LIGHT AND VARIABLE THIS EVENING.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...05
DISCUSSION...DUX
AVIATION...SAMET
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