WW 640 SEVERE TSTM IA MN NE SD 020245Z - 021000Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 640
NWS Storm Prediction Center Norman OK
945 PM CDT Tue Sep 1 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northwest into North-Central Iowa
Southwest into South-Central Minnesota
Far Northeast Nebraska
Extreme Southeast South Dakota
* Effective this Tuesday night and Wednesday morning from 945 PM
until 500 AM CDT.
* Primary threats include...
Scattered damaging winds likely with isolated significant gusts
to 75 mph possible
Scattered large hail and isolated very large hail events to 2
inches in diameter possible
A tornado or two possible
SUMMARY...Severe thunderstorm currently moving through extreme
southeast South Dakota is expected to continue northeastward
tonight, tracking through southwest Minnesota and northwest Iowa.
Strong wind gusts from 65 to 75 mph are possible with this storm.
Additional thunderstorms are development across south-central
Minnesota. Some large hail is possible with these storms over the
next hour or two. A lone supercell is also progressing northeastward
across far northeast Nebraska, with an attendant threat for damaging
gust and large hail it is gradually moves northeastward.
The severe thunderstorm watch area is approximately along and 45
statute miles north and south of a line from 40 miles north
northwest of Sioux City IA to 35 miles north northeast of Mason City
IA. For a complete depiction of the watch see the associated watch
outline update (WOUS64 KWNS WOU0).
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 638...WW 639...
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 65 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
24035.
...Mosier
WW 639 SEVERE TSTM IA MN NE SD 012050Z - 020400Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 639
NWS Storm Prediction Center Norman OK
350 PM CDT Tue Sep 1 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Far Northwest Iowa
Far Southwest Minnesota
North-Central and Northeast Nebraska
Southeast South Dakota
* Effective this Tuesday afternoon and evening from 350 PM until
1100 PM CDT.
* Primary threats include...
Scattered damaging winds likely with isolated significant gusts
to 80 mph possible
Scattered large hail likely with isolated very large hail events
to 2 inches in diameter possible
A tornado or two possible
SUMMARY...Initial supercells will likely pose a threat for large
hail up to 2 inches in diameter. A tornado or two may also occur
with any sustained supercell, especially if thunderstorms can remain
at least semi-discrete through early evening as low-level shear
increases. Otherwise, a bowing cluster is expected to eventually
develop and pose a greater threat for severe/damaging winds up to
70-80 mph as it tracks generally eastward across southeast South
Dakota/northeast Nebraska and vicinity.
The severe thunderstorm watch area is approximately along and 60
statute miles north and south of a line from 60 miles northwest of
Burwell NE to 35 miles east southeast of Sioux Falls SD. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU9).
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 638...
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 70 knots. A
few cumulonimbi with maximum tops to 550. Mean storm motion vector
25030.
...Gleason
WW 0640 Status Updates
STATUS FOR WATCH 0640 HAS NOT BEEN ISSUED YET
WW 0639 Status Updates
STATUS REPORT ON WW 639
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 5 SSW BUB TO
25 ESE 9V9.
..LEITMAN..09/02/26
ATTN...WFO...FSD...OAX...LBF...
STATUS REPORT FOR WS 639
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
MNC117-133-020440-
MN
. MINNESOTA COUNTIES INCLUDED ARE
PIPESTONE ROCK
NEC003-015-027-071-089-107-139-179-183-020440-
NE
. NEBRASKA COUNTIES INCLUDED ARE
ANTELOPE BOYD CEDAR
GARFIELD HOLT KNOX
PIERCE WAYNE WHEELER
SDC003-009-023-027-035-043-053-061-067-079-083-087-097-099-101-
111-125-135-020440-
SD
. SOUTH DAKOTA COUNTIES INCLUDED ARE
AURORA BON HOMME CHARLES MIX
WW 0638 Status Updates
STATUS REPORT ON WW 638
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 20 S UNV TO
35 WNW IPT TO 15 SSE IPT TO 40 W ABE TO 30 SW ABE TO 15 WNW PHL
TO 10 ENE ILG TO 20 SSE PHL TO 20 WSW NEL TO 10 ESE NEL TO 55 ESE
NEL.
..WENDT..09/02/26
ATTN...WFO...PHI...LWX...OKX...BGM...CTP...
STATUS REPORT FOR WS 638
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
DEC001-003-005-020240-
DE
. DELAWARE COUNTIES INCLUDED ARE
KENT NEW CASTLE SUSSEX
MDC011-015-025-029-035-041-020240-
MD
. MARYLAND COUNTIES INCLUDED ARE
CAROLINE CECIL HARFORD
KENT QUEEN ANNE'S TALBOT
NJC001-009-011-029-033-020240-
NJ
. NEW JERSEY COUNTIES INCLUDED ARE
ATLANTIC CAPE MAY CUMBERLAND
MD 2193 CONCERNING SEVERE THUNDERSTORM WATCH 640... FOR PORTIONS OF SOUTHERN MN INTO WESTERN WI
Mesoscale Discussion 2193
NWS Storm Prediction Center Norman OK
1156 PM CDT Tue Sep 01 2026
Areas affected...portions of southern MN into western WI
Concerning...Severe Thunderstorm Watch 640...
Valid 020456Z - 020700Z
The severe weather threat for Severe Thunderstorm Watch 640
continues.
SUMMARY...Thunderstorm clusters could continue to produce strong to
severe wind gusts and hail into the overnight hours. A downstream
watch into parts of southeast Minnesota and western Wisconsin is
uncertain, but a small downstream watch may be needed depending on
storm trends.
DISCUSSION...A cluster of storms over southern MN has weakened some
over the past 30-60 minutes as it has continued to lift northeast.
With this storm motion, convection has shifted further away from the
modest low-level jet oriented across IA, and northward into more
modest instability and midlevel lapse rates. Most recent observed
wind gusts have generally been in the 40-55 mph range, with 1.75
inch hail reported nearly an hour ago. Overall convective
organization has become more messy with time. Given overall
environment, sporadic severe wind gusts or hail could persist into
the overnight hours across southeast MN and perhaps west-central WI.
Damaging wind potential could increase if the cluster can track more
easterly near a surface boundary across southern MN. Depending on
short term trends, a small downstream watch could become necessary,
but remains uncertain.
..Leitman.. 09/02/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MKX...ARX...MPX...DMX...FSD...
LAT...LON 43919524 44239508 44469362 44479226 44349118 44139021
43858990 43638982 43449035 43379137 43379330 43319483
43489522 43919524
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
0759 PM CDT Tue Sep 01 2026
Valid 020100Z - 021200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE CENTRAL PLAINS AND MIDWEST AS WELL AS THE MID ATLANTIC...
...SUMMARY...
Scattered strong to severe thunderstorms remain likely into tonight
across parts of the northern/central Plains and Upper Midwest, and
parts of southern New York into the Mid-Atlantic. Large hail and
damaging winds should be the main threats.
...Southern NY/The Mid Atlantic...
A mid-level shortwave trough and enhanced west-northwesterly flow
were observed from the Northeast/Mid Atlantic States to the lower
Great Lakes this evening. A front was draped from northwest to
southeast across southern NY/New England, with numerous showers and
storms ongoing along and south of it this evening. The air mass here
is unstable and moderately sheared which is supporting organized
supercells and short linear segments. Damaging gusts remain likely
through this evening, along with some hail and perhaps a brief
tornado, especially near the from across southeastern PA and NJ
where low-level sear is maximized. Convection should eventually
begin to weaken with the loss of diurnal heating and as it
approaches the coast later this evening.
...Central Plains and Midwest...
Several supercells have developed ahead of a weak surface low along
a stalled front from NE into SD. A very unstable air mass (MLCAPE of
3000+ J/kg) is in place and extended downstream of the cluster
across eastern SD, northern IA and southern MN. A belt of strong
mid-level westerly flow along the front will continue to support
organized storms. Upscale growth is possible this evening with one
or more clusters or an MCS expected to eventually develop and track
across portions of northern IA and far southern MN. This will pose a
threat for severe wind gusts and perhaps a tornado along the front
through tonight.
Farther southwest along the surface lee trough, scattered high-based
storms were ongoing in eastern CO and western KS. Buoyancy and shear
are much weaker, but steep lapse rates and T/TD spread of 30-40
degrees could support a sporadic severe gusts with these storms
before they weaken near sunset.
...Great Lakes...
A secondary mid-level vort max and upper low, currently over the
western Great lakes, may serve as a focus for additional storm
development tonight across eastern WI and lower MI. The eastern
portions of the quasi stationary front remain very warm and
unstable. As ascent from the upper low/shortwave approach after
midnight, they may support a modest enhancement of the southwestern
low-level jet. Warm advection at the nose of this feature could
allow for a cluster of thunderstorms to develop and intensify. The
large elevated buoyancy and 40-50 kt westerly flow would favor a
risk for hail and damaging gusts before moving into southern ON by
12z Wed. However, confidence in how this scenario evolves remains
low and only 5% wind/hail probabilities will be maintained given the
uncertainty in storm development.
...Coastal Southeast Texas/Southwest Louisiana...
Tropical Storm Edouard will continue tracking northwestward across
southeast TX and southwest LA per latest NHC forecasts. Some
enhancement to the low-level wind field and hodographs has been
noted in outer bands along the northern portions of the circulation.
This may support transient updraft rotation with any cells. A brief
tornado or two may occur across parts of coastal southeast
TX/southwest LA through tonight as the system weakens.
..Lyons.. 09/02/2026
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