420
FXUS63 KFSD 060230
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
930 PM CDT WED AUG 5 2026
KEY MESSAGES
- PATCHY TO AREAS OF FOG LOOK TO DEVELOP TONIGHT/EARLY TOMORROW
MORNING MAINLY OVER NORTHWEST IOWA AND NEARBY PORTIONS OF
NORTHEAST NEBRASKA AND SOUTHEAST SOUTH DAKOTA. BE PREPARED FOR
CHANGING VISIBILITY ON YOUR MORNING COMMUTE IN THESE AREAS,
WITH ANY FOG LIFTING BY THE MID-MORNING HOURS.
- TEMPERATURE WILL CONTINUE TO TREND NEAR TO ABOVE NORMAL INTO
THE WEEKEND WITH HIGHS MAINLY IN THE 80S TO LOW 90S.
- BESIDES SOME SMALLER PERIODIC RAIN CHANCES (20% OR LESS),
MOSTLY DRY CONDITIONS ARE EXPECTED THROUGH SUNDAY.
UPDATE
ISSUED AT 929 PM CDT WED AUG 5 2026
NO MAJOR CHANGES TO THE FORECAST FOR TONIGHT AND
TOMORROW. THE MAIN CONCERN INTO TOMORROW MORNING WILL BE PATCHY TO
AREAS OF FOG THAT LOOK TO DEVELOP MAINLY OVER NORTHWEST IOWA, FAR
NORTHEAST NEBRASKA, AND ADJACENT AREAS OF FAR SOUTHEASTERN SOUTH
DAKOTA. SOME DENSE FOG IS LIKELY, WITH 05.18Z REFS AND 05.12Z HREF
PROBABILITIES OF LESS THAN A QUARTER MILE VISIBILITY AROUND 40-60%,
HIGHEST NEAR AND SOUTHEAST OF A SIOUX CITY TO STORM LAKE LINE.
UNCERTAINTY REMAINS ON HOW WIDESPREAD ANY DENSE FOG WOULD BE, SO
CURRENT PLAN IS TO HOLD OFF ON ISSUING ANY HEADLINES AT THIS TIME.
STILL BE PREPARED TO TAKE EXTRA PRECAUTIONS WHILE HEADING OUT ON THE
ROADS DURING THE THURSDAY MORNING COMMUTE. FOG LOOKS TO FORM BY 1-3
AM TONIGHT AND THEN ERODE BY THE MID-MORNING HOURS TOMORROW.
COOLER THAN NORMAL TEMPERATURES CONTINUE TONIGHT, THOUGH IT
WON'T BE NEARLY AS COOL AS LAST NIGHT WITH LOWS BY THURSDAY
MORNING MAINLY IN THE 50S, WARMEST NORTHWEST AND GRADUALLY
COOLER WITH SOUTHEASTWARD EXTENT.
HIGH TEMPERATURES WILL CONTINUE TO WARM INTO THE DAY ON THURSDAY AS
SOUTHERLY FLOW INCREASES AND ALSO BRINGS IN HIGHER DEW POINTS TO THE
AREA. STILL WON'T BE THAT HUMID, BUT DEW POINTS IN THE 60S WEST OF I-
29 COULD PUSH THE HEAT INDEX SLIGHTLY ABOVE THE AIR TEMPERATURE
TOMORROW AFTERNOON. SPEAKING OF AIR TEMPERATURES, LOOK FOR HIGHS TO
RANGE FROM THE MIDDLE 80S TO AROUND 90 NEAR AND WEST OF THE JAMES
RIVER, WITH MAINLY LOWER 80S ELSEWHERE. INSTABILITY LOOKS TO SURGE
INTO AREAS NEAR AND WEST OF THE JAMES RIVER TOMORROW AFTERNOON AHEAD
OF A BOUNDARY THAT WILL PUSH TOWARDS CENTRAL SOUTH DAKOTA. SOUNDINGS
SHOW A STOUT CAP IN PLACE, SO THUNDERSTORMS ARE UNLIKELY (LESS THAN
15% CHANCE). IF A STORM CAN BREAK THE CAP IN THE LATE AFTERNOON AS
SHOWN IN THE TYPICALLY AGGRESSIVE HIRESW-FV3 MODEL, THEN SEVERE
WEATHER WILL BE A POSSIBILITY IN SOUTH-CENTRAL SOUTH DAKOTA
WHERE THE STORM PREDICTION CENTER CURRENTLY DEPICTS A MARGINAL
(LEVEL 1 OF 5) RISK. MAIN SEVERE WEATHER HAZARDS IN THE VERY LOW
CHANCE A STORM DEVELOPS WILL BE WIND GUSTS TO 65 MPH AND HAIL
TO THE SIZE OF PING PONG BALLS.
DISCUSSION
ISSUED AT 137 PM CDT WED AUG 5 2026
TODAY WILL BE MOSTLY SUNNY AND QUIET UNDER HIGH PRESSURE WITH LIGHT
WINDS AND HIGHS IN THE UPPER 70S TO LOW 80S. NORTHWEST FLOW ALOFT
WILL BRING SMOKE INTO THE REGION FROM WILDFIRES OUT WEST. THE SMOKE
IS EXPECTED TO REMAIN MOSTLY ALOFT AND CURRENTLY THROUGHOUT OUR CWA
THE AIR QUALITY IS GOOD. FOR MORE ON AIR QUALITY AND TO GET AN AIR
QUALITY FORECAST FOR YOUR LOCATION PLEASE SEE AIRNOW.GOV
PATCHY VALLEY FOG IS POSSIBLE EARLY THURSDAY MORNING AS WINDS
BECOME LIGHT TO CALM. FOG IS MOST LIKELY EAST OF I-29 OVER
NORTHWEST IOWA. ANY FOG THAT FORMS SHOULD BURN OFF BY MID-
MORNING. AS THE HIGH PRESSURE MOVES OFF TO THE EAST THIS
AFTERNOON AND EVENING WINDS WILL BECOME SOUTHERLY. AT THE SAME
TIME FROM THE WEST AN UPPER SHORTWAVE WILL APPROACH THE REGION,
STRENGTHENING THE LLJ. OVERNIGHT WINDS WILL BEGIN TO INCREASE
FROM THE WEST TO THE EAST. DURING THE DAY THURSDAY GOOD MIXING
UP THROUGH THE 850 MB LEVEL WILL BRING DOWN STRONGER GUSTS OF 20
TO 30 MPH FOR MUCH OF THE REGION. PORTIONS OF NORTHWEST IOWA
WILL REMAIN LIGHTER AT 15 TO 20 MPH GUSTS. CONDITIONS ARE
EXPECTED TO BE DRY AND WARMER THANKS TO MODEST WAA. HIGHS WILL
RANGE FROM THE LOW TO UPPER 80S WITH WARMEST CONDITIONS OVER
CENTRAL SOUTH DAKOTA.
THURSDAY NIGHT ANOTHER SUBTLE UPPER WAVE WILL PIVOT OVER THE REGION
BRINGING CHANCES FOR SHOWERS AND THUNDERSTORMS. THERE ARE A FEW
TRENDS WE WILL NEED TO MONITOR OVER THE NEXT 24 TO 36 HOURS. A
NARROW BAND OF MODEST MOISTURE RETURN LOOKS TO SET UP OVER
CENTRAL SOUTH DAKOTA, BUT AREAS TO THE EAST LOOK TO REMAIN
FAIRLY DRY. MODERATE SURFACE BASED INSTABILITY OF AROUND 1000
J/KG OF CAPE WILL BUILD THROUGH THURSDAY AFTERNOON OVER CENTRAL
SOUTH DAKOTA. HOWEVER, AS YOU MOVE EAST THERE IS AN INCREASINGLY
STRONG CAP IN PLACE. INSTABILITY ABOVE THE CAP IS LACKING, SO
ELEVATED CONVECTION WOULD STRUGGLE TO INITIATE. SO WHILE AN
ISOLATED STRONG TO SEVERE STORM IS POSSIBLE OVER CENTRAL SOUTH
DAKOTA, CONFIDENCE IN ANY STRONG STORMS MAKING IT FARTHER EAST
THAN US HIGHWAY 281 IS LOW. IF STORMS SHOULD FORM IT WOULD
BETWEEN ROUGHLY 6 PM AND MIDNIGHT.
FRIDAY SEES THE RETURN OF HIGHER DEW POINTS IN THE UPPER 60S TO LOW
70S. WITH HIGHS IN THE 70S TO 80S IT WILL BE A BIT OF A MUGGY DAY. A
SERIES OF SUBTLE WAVES WILL KEEP LOW POPS IN THE FORECAST FOR MUCH
OF THE DAY. A MORE DEFINED WAVE PIVOTS THROUGH FRIDAY EVENING INTO
SATURDAY MORNING BRINGING CHANCES FOR MORE ORGANIZED CONVECTION,
MAINLY EAST OF I-29. PERIODIC STORM CHANCES CONTINUE THROUGH THE
REST OF THE WEEKEND AND INTO THE BEGINNING OF NEXT WEEK. HOWEVER,
CONFIDENCE IN TIMING, COVERAGE, AND SEVERITY OF STORMS IS LOW AS
THIS IS THE POINT WHERE MID-RANGE GUIDANCE BEGINS TO DIVERGE.
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 621 PM CDT WED AUG 5 2026
VFR CONDITIONS BEGIN THE TAF PERIOD. LIGHT EASTERLY WINDS BEGIN THE
PERIOD BUT THE WIND WILL GO LIGHT AND VARIABLE LATER THIS EVENING.
THE MAIN UNCERTAINTY FOR THE PERIOD REVOLVES AROUND FOG DEVELOPMENT
TONIGHT. PROBABILITIES FOR FOG ARE MODESTLY HIGH AROUND 60-70%.
HOWEVER, LATEST GUIDANCE VARIES ON HOW EXPANSIVE THE FOG WILL BE.
NORTHWEST IOWA HAS THE HIGHEST CHANCES FOR SEEING FOG BUT LEFT OUT
OF KSUX'S TAF DUE TO THIS UNCERTAINTY. WILL MONITOR TRENDS IN THE
FOG POTENTIAL THROUGH THE EVENING AND NIGHT. ANY FOG THAT DOES
DEVELOP WILL BURN OFF TOMORROW MORNING, LEAVING GUSTY SOUTHERLY
WINDS FOR THE REST OF THE PERIOD, WITH GUSTS UP TO 15 TO 25
KNOTS.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
UPDATE...SAMET
DISCUSSION...AJP
AVIATION...MEYERS
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