Severe Thunderstorm Warning 38, NWS Sioux Falls, SD

Area Forecast Discussion
National Weather Service Sioux Falls SD
Issued by National Weather Service Lincoln IL
120 PM CDT Sun May 17 2026

.KEY MESSAGES...

- There is high confidence that severe thunderstorms will
  develop this afternoon and evening, producing large hail,
  destructive straight-line winds, and a few tornadoes. An
  Enhanced Risk (level 3 of 5) of severe storms is in place.

- A transitioning storm mode will shift hazards from large hail
  and tornadoes initially, to widespread wind damage as an
  intense line of storms tracks east of Interstate 29 this
  evening.

- A lower risk of severe weather exists late Monday afternoon
  and evening, mainly over northwest IA, before quieter weather
  moves in for the mid-week period.

&&

.DISCUSSION...
Issued at 120 PM CDT Sun May 17 2026

The short-term convective outlook presents a highly volatile
spring severe weather setup. Latest surface analysis shows a
complex pattern, anchored by a strong 994 mb low over northwest
KS. An inverted trough extended north of the low through
central SD, while a well-defined warm front stretched northeast
of the low into east central NE. A weaker low was also noted in
north central NE. Visible satellite imagery revealed stable
wave clouds advancing northeast over far northeast NE and
extreme SE SD, ahead of the advancing warm front. Regional
radar imagery showed a complex of strong to severe storms over
north central NE. This storm complex is forecast by short range
guidance to continue tracking east this afternoon, intensifying
as interacts with the richer low- level moisture pool near and
south of the warm front.

Moderate to strong instability will be in place over the
southern to eastern CWA by late afternoon with MLCAPE nearing
3000 J/kg. In addition, deep layer shear will increase to around
50 kt, coincident with a mid level speed max ejecting from the
deep upper trough to our west. As the system evolves over the
next several hours, it appears the ingredients for a significant
severe weather event will be most favored over the southern to
eastern CWA. Ahead of the main convective line, some CAMs show
supercell development along the northward advancing warm front.
These storms would present a risk of very large hail (2"+) and
tornadoes. Given the amount of low level SRH/curved hodographs
present, a couple strong tornadoes are possible. The convective
cluster currently entering our far southwest CWA should
strengthen as it shifts east, with an initial hail and tornado
threat transitioning to a damaging straight line wind threat
(70+ MPH) as it grows upscale into a squall line/QLCS. Some
line-embedded QLCS tornadoes are possible, especially for any
line segments that become oriented north/south or
northwest/southeast, given southwesterly 0-3 km shear vectors.
Timing from latest high-res guidance suggests this activity
exits to the east of our CWA late this evening.

Precipitation amounts will vary significantly based on convective
tracks, though NBM guidance and HREF probability match mean
fields project a widespread 0.50 to 1.50 inches of rainfall,
particularly across northwest Iowa and southwest Minnesota. On
Monday, the cold front finally pushes into the area. Instability
and shear are forecast to be much lower than today, however,
there will be a conditional risk of severe storms over the
eastern CWA during the late afternoon to evening, if the airmass
can destabilize sufficiently ahead of the front. SPC's Day 2
outlook indicates as Marginal Risk (level 1 of 5), for our MN
and IA counties.

Behind the departing upper wave, quasi-zonal flow sets up for
Tuesday and Wednesday, yielding quiet conditions and seasonally
cool high temperatures moderating from the upper 50s Tuesday to
mid-upper 60s Wednesday.

The next upper wave moves in for the Thursday to Friday period,
however Gulf moisture remains cutoff ahead of this system.
Evaluating the ECMWF Extreme Forecast Index (EFI) reveals no
significant climatological anomalies for precipitation or wind
across the upper Midwest during this period, reinforcing the
the idea of a low-impact system for our area. The current
forecast sticks closely to the NBM consensus, maintaining broad
20-30 percent probabilities for light rain for late Thursday
into Saturday.

By late this week and especially this weekend, temperatures
will embark on a steady upward trajectory, as the mid level flow
backs west, then southwest. The Climate Prediction Center (CPC)
6-10 day outlook favors above-normal temperatures across the
Northern Plains and Upper Midwest, which supports blended
guidance high temperatures reaching well into the 80s on
Sunday.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1248 PM CDT Sun May 17 2026

Showers and storms move through the region this afternoon into
tonight. Intermittent MVFR/IFR conditions will be possible throughout
this timeframe, especially in heavier rain. TSRA was included at
least in PROB30 groups, but is expected to be the dominant weather
type at times. Widespread MVFR/IFR cigs setting in overnight for much
of Monday.

&&

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

&&

DISCUSSION...ILX/25
AVIATION...DYE

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
Issued by National Weather Service Lincoln IL
129 PM CDT Sun May 17 2026

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-181830-
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-
129 PM CDT Sun May 17 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.

A significant severe weather event is possible this afternoon and
evening. Very large hail, damaging wind gusts, and tornadoes are all
possible. If you have outdoor plans know where your nearest shelter
is located. Please ensure you have multiple ways to receive warnings.
Have a plan to take shelter and act immediately if your area comes
under a severe weather warning.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

Strong to severe storms are possible again Monday afternoon and
evening, particularly over northwest Iowa and southwest Minnesota.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will likely be needed this afternoon and evening.

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