WW 664 SEVERE TSTM SD 080005Z - 080700Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 664
NWS Storm Prediction Center Norman OK
705 PM CDT Mon Sep 7 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Southeast South Dakota
* Effective this Monday night and Tuesday morning from 705 PM
until 200 AM CDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2.5
inches in diameter possible
Isolated damaging wind gusts to 70 mph possible
A tornado or two possible
SUMMARY...Supercells should pose a threat for mainly large to very
large hail this evening into early Tuesday morning as they track
generally northeastward across parts of southeast South Dakota. Some
severe wind risk may develop if a cluster can form, but this remains
uncertain. A tornado or two also appears possible with any supercell
that can remain surface-based this evening, but the tendency should
be for convection to become mostly elevated with time.
The severe thunderstorm watch area is approximately along and 45
statute miles north and south of a line from 50 miles west southwest
of Mitchell SD to 25 miles north northeast of Sioux Falls SD. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU4).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 663...
AVIATION...A few severe thunderstorms with hail surface and aloft to
2.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 550. Mean storm motion vector
25025.
...Gleason
WW 0664 Status Updates
STATUS REPORT ON WW 664
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 SE 9V9 TO
20 ESE FSD.
..KERR..09/08/26
ATTN...WFO...FSD...
STATUS REPORT FOR WS 664
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
SDC009-023-027-043-053-067-083-125-135-080540-
SD
. SOUTH DAKOTA COUNTIES INCLUDED ARE
BON HOMME CHARLES MIX CLAY
DOUGLAS GREGORY HUTCHINSON
LINCOLN TURNER YANKTON
THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE
REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL
INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES
CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES.
WW 0663 Status Updates
STATUS REPORT ON WW 663
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 40 SSW DVL
TO 30 NW DVL TO 70 NNW DVL.
REMAINING VALID PORTION OF WW MAY BE CANCELLED PRIOR TO SCHEDULED
04Z EXPIRATION.
..KERR..09/08/26
ATTN...WFO...FGF...BIS...
STATUS REPORT FOR WS 663
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
NDC071-095-080340-
ND
. NORTH DAKOTA COUNTIES INCLUDED ARE
RAMSEY TOWNER
THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE
REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL
INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES
CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES.
MD 2269 CONCERNING SEVERE THUNDERSTORM WATCH 664... FOR PARTS OF SOUTHEASTERN SOUTH DAKOTA...NORTHEASTERN NEBRASKA AND ADJACENT PORTIONS OF THE MIDDLE MISSOURI VALLEY
Mesoscale Discussion 2269
NWS Storm Prediction Center Norman OK
1128 PM CDT Mon Sep 07 2026
Areas affected...parts of southeastern South Dakota...northeastern
Nebraska and adjacent portions of the middle Missouri Valley
Concerning...Severe Thunderstorm Watch 664...
Valid 080428Z - 080630Z
The severe weather threat for Severe Thunderstorm Watch 664
continues.
SUMMARY...Localized strong wind gusts remain possible in lingering
thunderstorm development, but the risk for severe weather, in
general, appears to be waning. A new severe weather watch is not
anticipated, but trends will continue to be monitored.
DISCUSSION...Warm advection along a convective outflow reinforced,
quasi-stationary low-level baroclinic zone, aided by a 40-45+ kt
southerly 850 mb jet, has been providing support for a persistent
band of convection. This has been focused southeast of Chamberlain
through the Yankton vicinity, with perhaps some northward/eastward
drift to the north of the Missouri River the past hour or two.
Forecast soundings near this activity indicate the lingering
presence of some combination of remnant elevated mixed-layer air and
subsidence induced warming/drying in the the 850-700 mb layer.
Entrainment of this air, and subsequent evaporative cooling and
downward mixing of momentum, may have provided support for an
eastward surging segment/small evolving cluster overspreading the
Yankton vicinity. However, lapse rates near and just above the
surface appear to have become stable enough to limit much more than
rather localized strong surface gust potential. And this potential
seems likely to wane further with continuing convective development
into the 06-07Z time frame.
..Kerr.. 09/08/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...FSD...OAX...LBF...
LAT...LON 43359871 43459690 43209637 42739653 42659729 42859897
43359871
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0758 PM CDT Mon Sep 07 2026
Valid 080100Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER CENTRAL NORTH
DAKOTA AND SOUTHEAST SOUTH DAKOTA...
...SUMMARY...
The threat for widely scattered severe storms capable of large hail
and perhaps a tornado or two will continue over central North Dakota
and southeast South Dakota into tonight. More isolated occurrences
of large hail and severe wind gusts remain possible this evening
over the central High Plains.
...Northern Plains...
Two separate severe thunderstorm regimes have evolved late this
afternoon into evening. The first is over northwest into central ND,
where widely scattered storms --including a supercell-- are ongoing
ahead of a cold front pushing through western ND. The 00Z BIS
sounding showed modestly steep low-level lapse rates and a moist
boundary layer with MLCAPE CAPE of around 3000 J/kg. The
corresponding wind profile was quite supportive of updraft rotation
with effective SRH of around 300 m2/s2 and 60 kt of effective bulk
shear, suggesting the supercell north of BIS will remain capable of
large hail and a tornado or two for the next hour or two.
Thereafter, increasing convective inhibition may result in the
gradual weakening of the storms with a decreasing severe weather
threat.
For additional near-term guidance on that regime, see recently
issued MCD #2268.
The second thunderstorm regime is evolving across portions of
northeast NE into southeast SD, near the intersection of a
differential heating zone/outflow boundary and a pre-frontal trough.
The boundary layer to the north of the baroclinic zone over
southeast SD is slightly cooler with some convective inhibition
noted in latest objective analysis fields. However, the presence of
MLCAPE up to 2000-3000 J/kg, which coincides with 35-40 kt of
deep-layer shear is supportive of supercells with the primary hazard
being large hail, potentially in excess of two inches. The nocturnal
strengthening of the low-level jet is resulting in enlarging
low-level hodographs with effective SRH of 300-400+ m2/s2, per
objective analysis. A tornado recently occurred with the ongoing
storms near the NE-SD border with an additional tornado or two
remaining possible this evening before convective inhibition
increases further.
..Mead.. 09/08/2026
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1238 AM CDT Tue Sep 08 2026
Valid 081200Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
IOWA AND EASTERN NEBRASKA...
...SUMMARY...
Widely scattered severe storms capable of mainly severe wind gusts
appear possible across portions of Iowa and eastern Nebraska Tuesday
afternoon and evening. More sporadic occurrences of severe winds and
large hail may occur from portions of the upper Midwest into the
central Plains.
...Synopsis...
An intense upper low moving into southern SK late this evening will
continue northeast through central MB into northern ON ahead of a
secondary short-wave trough tracking from the northern Rockies into
the northern Plains. A belt of enhanced mid/upper-level winds will
be maintained between those features from the northern High Plains
into the upper Great Lakes. At the surface, a cold front will
advance through the eastern Dakotas and upper MS Valley with the
trailing extension of the boundary moving more slowly southeast
through the mid-MO Valley and central High Plains.
...Central Plains into the upper Midwest...
Clusters of thunderstorms are likely to be ongoing at 12Z Tuesday
from portions of the mid-MO Valley into the upper Midwest within a
zone of warm advection and moisture transport along a nocturnal
low-level jet (LLJ). Showers and storms may linger through the
morning across parts of WI and the U.P. of MI, limiting the degree
of air mass destabilization and associated severe weather risk
during the afternoon. Farther to the southwest from IA through
eastern and southern NE into northern KS, stronger daytime heating
on the southern fringe of lingering mid/high-level cloudiness will
contribute to a well-mixed boundary layer, featuring steep low-level
lapse rates. When combined with boundary-layer dewpoints in the 60s
to low/mid 70s F, the air mass is expected to become moderately to
strongly unstable by late afternoon with MLCAPE of 2000-3000 J/kg.
In the absence of appreciable height falls/large-scale forcing for
ascent, convergence along the front and any preceding confluence
zones/outflow boundaries is expected to foster a gradual increase in
storm coverage and intensity by mid to late afternoon amidst the
destabilizing air mass. The strongest deep-layer shear is expected
to be displaced to the north of the effective warm sector with
around 30-35 kt forecast along the frontal zone. A largely parallel
shear-vector orientation with the front suggests that initial storms
should grow upscale into line segments or a broken band with an
associated risk for severe wind gusts from mid afternoon through
evening. Isolated occurrences of marginally severe hail are
possible; however, poor mid-level lapse are expected to limit the
overall threat. The 00Z models do indicate some LLJ enhancement over
central IA by late afternoon into evening, resulting in a corridor
of stronger low-level shear. While a brief tornado or two are
possible, a more robust threat is expected to be limited by largely
outflow-dominant storms.
..Mead/Chalmers.. 09/08/2026
SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1213 AM CDT Tue Sep 08 2026
Valid 091200Z - 101200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
PLAINS TO THE EASTERN GREAT LAKES...
...SUMMARY...
Isolated strong to severe thunderstorms are possible across portions
of the central Plains to the eastern Great Lakes on Wednesday.
...Upper Ohio Valley and eastern Great Lakes...
An upper trough will move from the Upper Midwest to the Great Lakes
and Northeast on Wednesday. Stronger deep-layer flow will be focused
across the Great Lakes and Northeast, to the north of a corridor of
modest instability. As a surface cold front develops southeast
toward the Ohio Valley and western NY during the evening, isolated
to scattered thunderstorm development is expected. While modest
instability will limit a more substantial severe risk, stronger
deep-layer flow will support sporadic strong gusts.
...Central Plains to Lower Ohio Valley...
Stronger instability is forecast within a moist and hot airmass from
KS to the Lower MO and Lower OH Valleys Wednesday afternoon and
evening. This area will remain well south of strong westerly flow
aloft associated with the Great Lake upper trough, resulting in
modest vertical shear, especial across KS. Despite modest shear,
MLCAPE around 1500-2500 amid steeper low and midlevel lapse rates
will support some risk of strong to severe convection. Storms
developing along a surface boundary will mainly pose a risk for
damaging gusts. Where marginally stronger shear will be located
across the Lower MO Valley vicinity, small hail could also occur
with the strongest updrafts.
..Leitman.. 09/08/2026
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