543
FXUS63 KFSD 061722
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1222 PM CDT SUN SEP 6 2026
KEY MESSAGES
- THUNDERSTORMS INCREASE IN COVERAGE THROUGH THE MORNING AND
CONTINUING THROUGH THE LATE AFTERNOON. AN ISOLATED STRONGER
STORM COULD PRODUCE PING PONG BALL SIZE HAIL AND 60-65 MPH
WIND GUSTS.
- HIGHER RISKS FOR LOCALLY HEAVY RAIN DEVELOP BY EARLY
AFTERNOON SUNDAY, WITH POTENTIAL FOR POCKETS OF 2-4" OF RAIN
AND LOCALIZED AMOUNTS TO 6". LOCALIZED FLASH FLOODING IS
POSSIBLE INTO EARLY EVENING.
- A SHIFTING PATTERN MAY BRING HIGHER RAIN CHANCES, SLIGHTLY
COOLER TEMPERATURES, AND A SEVERE WEATHER RISK BY MONDAY
EVENING AND EARLY OVERNIGHT. THIS RISK COULD CONTINUE TUESDAY
AFTERNOON SOUTH OF I-90.
- DRY AND CONTINUED ABOVE NORMAL TEMPERATURES ARE FAVORED FOR
MOST OF THE UPCOMING WEEK.
UPDATE
ISSUED AT 1026 AM CDT SUN SEP 6 2026
ONGOING STORM DEVELOPMENT IN A CORRIDOR OF MODERATE INSTABILITY
BUT POOR SHEAR WILL CONTINUE TO PRODUCE VERY ISOLATED HAIL AND
BRIEF GUSTY WINDS. A BIGGER THREAT DEVELOPING WILL BE LOCALLY
HEAVY RAINFALL WITH ESTIMATED HOURLY RATES AS HIGH AS 4 TO 5"
PER HOUR IN A FEW LOCATIONS.
LATEST CAMS ALL INDICATE A CORRIDOR OF INCREASED POTENTIAL IN SW
MINNESOTA, NW IOWA, AND ADJACENT AREAS OF SD WHERE RAPID
DEVELOPING AND SLOW MOVING STORMS COULD LEAD TO FLASH FLOODING.
FOR THIS REASON, WILL ISSUE A FLOOD WATCH FOR FLASH FLOODING
INTO THE EVENING.
DEPENDING ON COLD POOL DEVELOPMENT, THIS THREAT COULD END
EARLIER THAN THE 03Z EXPIRATION TIME, HOWEVER SEVERAL CAMS ALL
HINT AT LINGERING ELEVATED CONVECTION ON THE LLJ INTO THE
EVENING IN NW IOWA.
DISCUSSION
ISSUED AT 218 PM CDT SAT SEP 5 2026
THIS AFTERNOON: WE'RE SLOWLY RECOVERING THE AIRMASS POST CONVECTION
THIS AFTERNOON, THOUGH CONTINUED OVERRUNNING OF THE CONVECTIVE
OUTFLOW TO OUR SOUTH HAS PERSISTED IN DEVELOPING ADDITIONAL
CLOUD COVER IN NORTHEAST NEBRASKA AND NORTHWEST IOWA.
TEMPERATURES WILL CONTINUE TO RISE AND IT APPEARS WE'LL REACH
INTO THE UPPER 80S TO LOWER 90S ONCE AGAIN. ACROSS NW IOWA
TEMPERATURES HAVE BEEN COOLER, BUT A LATE DAY TEMPERATURE SURGE
IS STILL POSSIBLE IF CLOUDS CLEAR. DEW POINTS WILL ALSO RECOVER
SLOWLY AND SHOULD END UP INTO THE UPPER 60S TO 70S BY THIS
EVENING. THE RESULTANT HEAT INDEX VALUES CLIMB BACK TO THE 95 TO
102 RANGE IN QUITE A FEW LOCATIONS.
TONIGHT: WE'LL BE WATCHING MODEST THETA-E ADVECTION KICKING OFF
ADDITIONAL SHOWERS AND THUNDERSTORMS OVER THE WESTERN HIGH PLAINS
LATER THIS AFTERNOON AND EARLY EVENING. THIS ACTIVITY WILL
LIKELY STRUGGLE AS IT TRIES TO REACH CENTRAL SOUTH DAKOTA LATER
THIS EVENING. GREATER CONCERNS BEGIN TO DEVELOP AFTER MIDNIGHT
AS THE LLJ INTENSIFIES. THE MAJORITY OF GUIDANCE IS NOW SHOWING
TWO AREAS OF CONCERN...ONE ALONG THE MINNESOTA RIVER VALLEY AND
BUFFALO RIDGE WHERE SOME INCREASED CONVERGENCE AND INFLUENCE OF
MID-LVL VORTICITY COULD SPARK ELEVATED STORMS. A SECOND AREA
OVER WESTERN/CENTRAL NEBRASKA AND CENTRAL SOUTH DAKOTA WHERE A
POTENTIALLY STRONGER MID- LVL AREA OF VORTICITY ENTERS THE STATE
AND BEGINS TO SLOWLY DRIFT EAST NORTHEAST. ELEVATED CONVECTION
IN BOTH OF THESE AREAS WOULD FAVOR BRIEF MARGINALLY SEVERE HAIL
AND A FEW 40-60 MPH WIND GUSTS. THE BIGGEST UNCERTAINTY IS THE
TIME OF DEVELOPMENT WHICH MAY RANGE FROM 4AM TO 7AM.
SUNDAY: WHILE THERE ISN'T A LOT OF CERTAINTY IN METEOROLOGY, MY
CONFIDENCE IS GROWING THAT WE'LL BE DEALING WITH SOME TYPE OF
IMPACTFUL WEATHER DURING THE DAY. ALREADY ONGOING CONVECTION AT
DAYBREAK MAY CONTINUE TO SPREAD BOTH EAST (FROM WESTERN COMPLEX),
AND SOUTHEAST (FROM ELEVATED RIDGE CONVECTION)...AN INTERESTING
ARTIFACT OF BEING STUCK UNDER THE MID-LVL RIDGE AXIS. OCCASIONALLY
STRONG UPDRAFTS MAY STILL PRODUCE ISOLATED SEVERE WEATHER THROUGH
THE MORNING AS THIS ACTIVITY MEANDERS. SOUNDINGS BY MID-DAY EITHER
SIDE OF THE I-29 CORRIDOR SHOW A NEARLY UNCAPPED ENVIRONMENT WHICH
COULD SIGNAL SOME POTENTIAL FOR ONGOING ELEVATED STORMS TO TAP INTO
THE SURFACE LAYER AND INTENSIFY. SHEAR REMAINS QUITE MARGINAL, BUT
2000-2500 J/KG MLCAPE AND DECENT MID-LVL LAPSE RATE COULD SUGGEST
SOME LARGE HAIL AND DOWNDRAFT POTENTIAL. WHILE EXTREMELY LOW
PROBABILITIES...THE LOW LCL AND CHAOTIC SFC WIND PATTERN COULD LEAD
TO A FEW FUNNELS. GRADUAL COLD POOL DEVELOPMENT AND CONTINUED
SOUTHEAST SHIFT IN THE UPPER VORT MAX SHOULD PUSH THIS CONVECTIVE
CLUSTER SOUTHEAST AND OUT OF THE CWA BY EARLY EVENING.
ANOTHER CONCERN, WHICH MAY END UP BEING THE BIGGEST CONCERN WILL BE
HEAVY RAIN. AS EVIDENT THIS MORNING, THE ENVIRONMENT OVERHEAD
REMAINS RICH FOR LOCALLY HEAVY RAINFALL WITH SEVERAL AREAS OF 4-6"
OF RAIN. A SIMILAR SITUATION WILL BE IN PLACE TOMORROW WITH
ANOTHER DEEP WARM CLOUD LAYER, HIGH PWAT, AND SLOW STORM MOTION (AOA
10-15 KNOTS) EVENT. REFS/HREF 6 HR PMM THROUGH 00Z ALL INDICATE
LOCALIZED TOTALS OF 2-4"...HOWEVER AS SHOWN BY LAST NIGHT'S
DATA...THE MANY OF THE TOTALS WERE CLOSER TO THE ENSEMBLE MAX. IN
THIS CASE THE POTENTIAL SHIFTS TO HIGHER LOCALIZED VALUES OF 3 TO
5"+. ALL THIS TO SAY THAT THESE HIGH END AMOUNTS MAY BE QUITE
SPATIALLY VARIABLE WHICH MAKES PINNING DOWN A POTENTIAL FLOOD
WATCH MORE DIFFICULT. AREAS FROM MITCHELL TO TYNDALL ARE BY FAR
THE MOST SUSCEPTIBLE TO FLOODING, WITH 3 HR FFG IN MOST OTHER
AREAS BETWEEN 2.5-3.25". WILL ALLOW NEXT SHIFT TO TAKE A CLOSER
LOOK AND TRY TO PIN POINT ANY AREAS OF CONCERN AS DATA FOCUSES
IN ON THE POTENTIAL.
SUNDAY NIGHT: ANY MCS THAT DEVELOPS SUNDAY AFTERNOON SHOULD EXIT THE
AREA EARLY IN THE EVENING LEAVING SUBSIDENCE IN IT'S WAKE. THERE
STILL REMAINS A 30-40 KNOT LLJ THAT WILL DEVELOP AND MAY PRODUCE
SCATTERED CONVECTION INTO THE JAMES RIVER VALLEY INTO MONDAY
MORNING.
MONDAY-TUESDAY: THE MID-LVL RIDGE AXIS SLIDES EAST BY MONDAY, WITH
DEEPER TROUGHING MOVING INTO THE PACNW AND NORTHERN ROCKIES. LEE-
SIDE TROUGHING DEVELOPS A SURFACE BOUNDARY OVER THE WESTERN DAKOTAS
EARLY ON MONDAY WITH AN INCREASING SPG BRINGING GUSTY WINDS TO THE
CWA MONDAY AFTERNOON. TEMPERATURES MAY ALSO WARM BACK TOWARDS THE
90S AHEAD OF THE FRONT. WHILE WE'LL HAVE TO WATCH RETURN FLOW AND
BOUNDARY LAYER MOISTURE ALONG THE BOUNDARY, THERE MAY BE SUFFICIENT
POOLING OF MOISTURE TO OVERCOME LINGERING CAPPING BY LATE IN THE
AFTERNOON IN CENTRAL SOUTH DAKOTA. SHOULD STORMS DEVELOP, THEN A
NARROW FOCUS FOR SEVERE CONVECTION MAY EXTEND INTO THE WESTERN HALF
OF THE CWA INTO THE EARLY OVERNIGHT HOURS. DEPENDING ON THE EXTENT
OF COVERAGE OF STORMS, THE AFOREMENTIONED FRONT MAY DIP INTO
NORTHERN NEBRASKA AND IOWA BY TUESDAY. CONVECTION MAY AGAIN
DEVELOP ALONG THIS BOUNDARY WITH SOME INCREASED SEVERE WEATHER
POTENTIAL FOCUSED MOSTLY IN THE SOUTHERN THIRD OF THE CWA.
WEDNEDAY-FRIDAY: THE REST OF THE WORK WEEK FAVORS SLIGHTLY COOLER
TEMPERATURES AND DRIER CONDITIONS AS HIGH PRESSURE MOVES INTO THE
PLAINS. TEMPERATURES WILL REMAIN SLIGHTLY ABOVE SEASONAL NORMALS IN
THE LOWER TO MIDDLE 80S.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1219 PM CDT SUN SEP 6 2026
SCATTERED CONVECTION WILL CONTINUE TO DEVELOP EARLY THIS
AFTERNOON, AND CONTINUE INTO EARLY EVENING. IN THUNDERSTORMS,
BRIEF 40 TO 60 MPH WIND WILL BE POSSIBLE, ALONG WITH SMALL HAIL,
AND TORRENTIAL RAINFALL. THE COVERAGE NEAR THE TAF SITES
REMAINS FAIRLY UNCERTAIN, AND IMPACTS MAY BE BRIEF IF THEY TAKE
PLACE.
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS CONTINUE SOUTH OF
I-90 INTO THE EVENING AND EARLY OVERNIGHT HOURS. AGAIN, BRIEF
REDUCTION TO MVFR OR IFR CONDITIONS ARE POSSIBLE, BUT WILL BE
DRIVING BY ANY SPORADIC UPDRAFT THAT PASSES THROUGH. COVERAGE IN
SUX HIGH ENOUGH TO INCLUDE PREVAILING WORDING ATTM.
VFR CONDITIONS MAY FALL TO MVFR LEVELS INTO MONDAY MORNING,
THOUGH SIGNIFICANT UNCERTAINTY REMAINS AS FAR AS ANY STRATUS
DEVELOPMENT.
FSD WATCHES/WARNINGS/ADVISORIES
SD...FLOOD WATCH UNTIL 10 PM CDT THIS EVENING FOR SDZ062-067-071.
MN...FLOOD WATCH UNTIL 10 PM CDT THIS EVENING FOR MNZ080-081-089-
090-097-098.
IA...FLOOD WATCH UNTIL 10 PM CDT THIS EVENING FOR IAZ001>003-
012>014-020>022-031-032.
NE...NONE.
UPDATE...DUX
DISCUSSION...DUX
AVIATION...DUX
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