Severe Thunderstorm Warning 157, NWS Sioux Falls, SD

Area Forecast Discussion
National Weather Service Sioux Falls SD
633 PM CDT Wed Jul 1 2026

.KEY MESSAGES...

- Scattered strong to severe thunderstorms are possible this
  evening mainly near and east of the I-29 corridor. The
  strongest storms will be capable of damaging winds to 70+ mph
  and/or 2 inch diameter hail. A tornado or two cannot be ruled
  out.

- Beyond this evening's threat, concerns are growing for more
  widespread severe storms Thursday evening into Friday and
  again Friday into Saturday with one or more overnight storm
  complexes possible.

- Multiple rounds of rain and storms over the next few days,
  combined with recent rainfall, may lead to growing concerns
  of localized flash flooding and minor river flooding through
  the end of the week.

- Above normal temperatures continue through the rest of this
  week and into the weekend, with humidity increasing daily.
  However, we'll remain below heat advisory levels.

&&

.DISCUSSION...
Issued at 240 PM CDT Wed Jul 1 2026

Skies have mostly cleared out from last night's storms except over
portions of northwest Iowa where clouds linger from remnant showers
that moved through during the mid morning hours. This is also where
a boundary is roughly located that will be the focus for stronger
convection to develop late this afternoon into the early evening.
The latest HRRR runs have been trending convective initiation
farther west into northeast Nebraska, and this is likely because
those areas have cleared quicker and have thus been able to
destabilize more efficiently whereas clouds have lingered over
portions of northwest Iowa. Latest mesoanalysis shows around
1500-2000 J/kg of MLCAPE that will increase into the afternoon
in an uncapped environment. A weak wave will also move across
the area and help develop showers and storms by about 4-5 pm.
Due to the lack of CIN across a fairly large area, there is a
chance that numerous thunderstorms quickly develop around the
over the Highway 20 corridor of northwest Iowa and far northeast
Nebraska. If we get numerous storms developing at once, storms
may be competing for the strongest updraft and thus lowering the
overall severe threat. But if convection remains more isolated,
storms initially will be capable of 2 inch diameter hail and
damaging wind gusts to 70 mph. A tornado cannot be ruled out if
a storm can get rooted to the boundary. Storms will push
eastward and grow northward through the evening and possibly
merge into organized clusters which will enhance the damaging
wind threat to greater than 70 mph as storms push into northern
Iowa and southern Minnesota. These stronger storms will exit the
area around midnight, but additional weaker showers and
thunderstorms will continue to develop overnight over northwest
Iowa along the boundary as the low level jet feeds more moisture
into the area. The main threat with this would be if these
showers/storms train over the same area, it could result in
minor flash flooding.

Troughing over the western US will continue to send upper waves
through the region heading into the day on Thursday and Friday. A
very weak wave on Thursday morning may set off a few showers and
storms along a boundary over eastern Nebraska and western Iowa, but
guidance is in fairly good agreement that the more intense
parts of this convection will remain south of the area. Heading
into Thursday afternoon, daytime heating should result in the
cap eroding especially over portions of south-central South
Dakota, which may allow for isolated supercells to develop given
the 40-45 kts of bulk shear that will be in place. With lapse
rates around 7.5-8 C/km, large hail to 2 inches in diameter will
be the main threat with these storms, along with 70 mph
straight-line wind gusts. The tornado threat looks low, though
there may be brief window in the early evening as these storms
move east where the low level jet can help increase 0-1 km SRH
before storms turn more elevated heading into the later evening
hours. This afternoon supercell threat is a conditional one as
overall forcing will be weak.

The main threat for severe storms will arrive overnight Thursday
into Friday as a stronger wave ejects across the northern
Plains towards Thursday evening and fires up isolated to
scattered thunderstorms over western South Dakota. These
thunderstorms look to develop into either an organized line or
into a few linear clusters and then progress through our area
from west to east during the overnight time frame. Due to the
linear nature of these storms, damaging straight-line winds to
70+ mph will be the main severe weather threat with this round.
If storms form into a few different clusters and trail one
another (thus move over the same area multiple times), will
also have to watch out of a threat for flash flooding Thursday
night/Friday morning. Yet another wave moves through the area on
Friday, which will likely form more strong to severe
thunderstorms especially in the afternoon and early evening
hours. Uncertainty in how storms evolve Thursday night and
differences amongst guidance precludes details on the exact
threats for Friday, but certainly keep up to date with the
latest forecast especially if you have outdoor plans for the
July Fourth weekend. Speaking of July Fourth, the day itself
will feature another wave passing through the region; however,
uncertainty remains high on where any storms develop. The
01.12Z GEFS keeps the best chances of rain near and south of the
Missouri River Valley while the EC Ensemble keeps it east of
the area. Bottom line, there will be at least a broad area of 20-40%
PoPs in place especially heading into Saturday night until the
spread in guidance can be better resolved. From Sunday onwards,
the active upper pattern may relax a bit as upper ridging tries
to build in over the intermountain West.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 630 PM CDT Wed Jul 1 2026

Showers and thunderstorms will develop in northeast NE and
northwest IA this evening. Hail and strong winds are likely with
the stronger storms. A few storms could reach parts of southeast
SD to near the MN/IA border in northwest IA. Outside of the
thunderstorms, mainly VFR conditions are expected. Some patchy
MVFR fog will be possible but somewhat low confidence on just
where.

&&

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

&&

DISCUSSION...Samet
AVIATION...08

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
425 PM CDT Wed Jul 1 2026

MNZ071-072-097-SDZ038>040-050-052>066-068-069-022130-
Lincoln-Lyon-Pipestone-Beadle-Kingsbury-Brookings-Gregory-Jerauld-
Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook-
Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton-
425 PM CDT Wed Jul 1 2026

This Hazardous Weather Outlook is for southwest Minnesota, central
South Dakota, east central South Dakota, south central South Dakota
and southeast South Dakota.

.DAY ONE...Tonight.

Isolated thunderstorms may be possible late this evening and through
the overnight hours. At this time, any strong storm could produce
localized 60 mph winds and ping pong ball size hail. However the
greatest storm risk this evening and overnight will be across
southern Minnesota and northwest Iowa.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Risks for strong to severe thunderstorms continue Thursday and
Thursday night with the potential all severe weather hazards at
times. Isolated to scattered strong storms Thursday afternoon and
evening, may be replaced by a larger complex of storms Thursday
night into Friday. Any storm during the upcoming 24 hours will be
capable of 70+ mph winds and 2 inch hail.

Multiple severe weather risks will be possible Friday and Saturday.
While a great deal of uncertainty remains in storm timing and
placement, it's important to monitor the forecast over the coming
days heading into the holiday weekend.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

IAZ001>003-012>014-020>022-031-032-MNZ080-081-089-090-098-NEZ013-014-
SDZ067-070-071-022130-
Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Murray-Cottonwood-Nobles-Jackson-Rock-Dixon-
Dakota-Lincoln-Union-
425 PM CDT Wed Jul 1 2026

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

.DAY ONE...Tonight.

Scattered strong to severe storms are expected to develop Wednesday
evening and continue into the early overnight hours. The primary
risks will be 70 mph winds and 2 inch hail.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Risks for strong to severe thunderstorms continue Thursday and
Thursday night with the potential all severe weather hazards at
times. Isolated to scattered strong storms Thursday afternoon and
evening, may be replaced by a larger complex of storms Thursday
night into Friday. Any storm during the upcoming 24 hours will be
capable of 70+ mph winds and 2 inch hail.

Multiple severe weather risks will be possible Friday and Saturday.
While a great deal of uncertainty remains in storm timing and
placement, it's important to monitor the forecast over the coming
days heading into the holiday weekend.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed from 7pm to 1am.