Severe Thunderstorm Warning 255, NWS Sioux Falls, SD

Area Forecast Discussion
National Weather Service Sioux Falls SD
114 PM CDT Tue Sep 1 2026

.KEY MESSAGES...

- Severe weather risks increase quickly after 5pm in South
  Central South Dakota and North Central Nebraska, and will
  spread east northeast into the early overnight hours.

- A few discrete storms could initially produce 2"+ hail, 70
  mph wind gusts, and even a tornado. Eventually, storms may
  merge into a wind driven line as they move towards MN/IA.
  Storms exit around 2am.

- Temperatures remain well above normal through the rest of
  this week and into the upcoming weekend, with highs in the 90s
  possible by mid-late week.

- The heat and humidity may bring occasional risks for
  overnight thunderstorms, with some focus around late Wednesday
  night and again Friday morning. Exact locations of storms
  remain uncertain.

&&

.DISCUSSION...
Issued at 111 PM CDT Tue Sep 1 2026

THIS AFTERNOON: A complex convective setup this afternoon as a pair
of mid-lvl vorticity centers continue to pivot northeast. One
such area continues to push north of Sioux Falls, with a second
stronger area of energy now lifting northward through the
Nebraska panhandle. The result thus far has been a significantly
contaminated warm sector with plenty of mid-upr clouds over the
Tri-State region. At the surface, a stationary boundary/warm
front currently stretches from the Platte River to north of
Omaha and north of Ames. The airmass north of this boundary
continues to warm, suggesting some potential for a northward
push in this front by evening as deeper synoptic lift arrives,
but for the most part this area will remain capped to surface
based convection into late afternoon.

LATE AFTERNOON/EVENING/TONIGHT:  We'll continue to see MLCAPE values
climb upwards through the afternoon, potentially between
2000-3000 J/KG, but how far north with this instability reach is
still uncertain. Ongoing elevated convection in NC Nebraska may
keep some areas north of I-90 from any significant level of
destabilization, with the largest reservoir of CAPE along and
especially south of I- 90. Most guidance would favor new
convective development along an surface convergence zone in NE
Nebraska or SC South Dakota after 5pm in a narrow corridor of
deeper instability. Given favorable shear profiles (effective
shear 40+ knots), any initial development should have
supercellular characteristics capable of 2" hail and 70 mph
winds. Additional convection may try to develop over central
Nebraska and lift northward to the MO River in the evening. As
we move through the mid-late evening hours, 0-1km shear will be
on the rise as the LLJ develops, introducing at least the low
end potential for a brief tornado south of I-90 if storms can
stay discrete. Though boundary layer stabilization will be on
the increase and LCLs remain quite high. Otherwise, watch for
gradual clustering of storms as they track east northeast into
MN/IA which would increase the potential of 70+ mph winds, with
a continued very low probability of a QLCS- like tornado into NW
Iowa. 17Z SSCRAM-HRRR data would support the rising potential
for high winds extending north of Highway 20, with brief hail
potential in new updrafts driven by the LLJ further north into
western MN. Latest projections continue to push convection east
of the CWA by 2am, with light winds and wet ground perhaps
allowing patch fog to develop.

WEDNESDAY: Brief shortwave ridging tries to move in early Wednesday
as the surface front settles back into eastern Nebraska and
north central Iowa. A few lingering elevated
showers/thunderstorms may persist into NW Iowa through mid-
morning. With a slightly drier easterly wind, temperatures again
rise into the middle to upper 80s, with the latest guidance
supporting a strong enough EML to prevent convection along the
boundary. The return of the nocturnal LLJ Wednesday night could
again lead to isolated to scattered elevated convection into
Thursday morning.

THURSDAY-FRIDAY: Confidence remains rather high that temperatures
continue to rise towards the lower 90s in most locations for the end
of the week. Increasing mid-lvl heights through the Plains will help
push low-lvl temperatures well above normal, with H850 temps +26C
Thursday and Friday.  The greatest challenge in the medium range
will be timing and tracking one or more weak ridge riders that will
cross the Plains into the weekend.  Once such wave may drop down
from the NW into MInnesota early Friday morning, perhaps leaving an
outflow boundary near the Minnesota River/Ridge areas for the
afternoon.

SATURDAY-MONDAY:  Temperatures remain above normal through the
weekend and into early next week as the 500 mb ridge peaks through
the central CONUS.  One or more weak waves top the ridge during the
weekend, creating a very low confidence PoP forecast during the
overnight hours.  Should one of these waves track close enough to
the CWA they could lead to some temperature reductions.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1146 AM CDT Tue Sep 1 2026

VFR conditions continue early this afternoon as a broken mid-lvl
cloud deck continues to move northeast. A few showers and
isolated thunderstorms are possible along and west of the James
River valley into mid-afternoon.

Convection risks later this evening begin to develop in NC
Nebraska and SC South Dakota after 5pm. Several individual
storms may begin to cluster and move east into the early
overnight hours. Initially large hail and even a tornadic threat
will develop, but as storms move east, risks may shift to
straight line winds and brief QLCS tornadoes as they move into
NW Iowa or Southern Minnesota. IN any thunderstorm brief periods
of IFR to MVFR visibility/ceilings may be possible. Storm
threats should move east of I-29 by midnight, with some
potential for fog by daybreak Wednesday if skies clear.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

DISCUSSION...Dux
AVIATION...Dux

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
157 PM CDT Tue Sep 1 2026

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-021900-
Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson-
Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-Brookings-Gregory-
Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook-
Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton-
Union-
157 PM CDT Tue Sep 1 2026

This Hazardous Weather Outlook is for northwest Iowa, west central
Iowa, southwest Minnesota, northeast Nebraska, central South
Dakota, east central South Dakota, south central South Dakota and
southeast South Dakota.

.DAY ONE...This afternoon and tonight.

Scattered thunderstorms will increase in coverage late this afternoon
and evening. A few of these storms may become severe capable of 2
inch hail and 70 mph winds. While very low, a brief tornado could be
possible in areas south of I-90 towards the Missouri River this
evening.

One or more clusters of storms may form and move east northeast into
the early overnight hours, with areas along and south of a line from
Gregory to Sioux Falls to Tracy with the greatest risks. These storm
clusters could bring 70 mph or locally greater winds.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Periodic thunderstorm chances continue through Thursday with spotty
rain chances potentially into the weekend. Severe weather is not
expected or should remain very isolated.

Heat will build into the area with heat indices from 90 to 100
Thursday through Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed in areas especially along and south
of I-90 after 6pm and continue through 2am.

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
442 PM CDT Tue Sep 1 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0440 PM     Hail             Fairfax                 43.02N 98.89W
09/01/2026  E1.00 Inch       Gregory            SD   Trained Spotter

            Heavy rainfall accompanied mostly dime sized
            hail, but a few stones were as big as a
            quarter.

&&

TRM

Preliminary Local Storm Report
National Weather Service Sioux Falls SD
445 PM CDT Tue Sep 1 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0439 PM     Hail             1 SSW Fairfax           43.01N 98.90W
09/01/2026  E0.88 Inch       Gregory            SD   Trained Spotter

&&

TRM

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