WW 128 SEVERE TSTM MN WI 171420Z - 172200Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 128
NWS Storm Prediction Center Norman OK
920 AM CDT Fri Apr 17 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
East-Central and Far Southeast Minnesota
Northwest and North-Central Wisconsin
* Effective this Friday morning and afternoon from 920 AM until
500 PM CDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2
inches in diameter possible
Isolated damaging wind gusts to 70 mph possible
SUMMARY...Ongoing line of thunderstorms over southeast MN is
forecast to continue northeastward. The overall environment ahead of
this line is expected to become more supportive of strong to severe
storms with time. Additional thunderstorm development is anticipated
as well. Large hail is the primary severe risk, although isolated
strong gusts are possible as well.
The severe thunderstorm watch area is approximately along and 75
statute miles east and west of a line from 105 miles north of Eau
Claire WI to 10 miles east of La Crosse WI. For a complete depiction
of the watch see the associated watch outline update (WOUS64 KWNS
WOU8).
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.
&&
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
24030.
...Mosier
WW 0128 Status Updates
STATUS REPORT ON WW 128
THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA.
FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 0473
..THORNTON..04/17/26
ATTN...WFO...MPX...ARX...DLH...GRB...
STATUS REPORT FOR WS 128
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
MNC025-039-045-049-055-099-109-115-157-163-169-171740-
MN
. MINNESOTA COUNTIES INCLUDED ARE
CHISAGO DODGE FILLMORE
GOODHUE HOUSTON MOWER
OLMSTED PINE WABASHA
WASHINGTON WINONA
WIC001-003-005-007-011-013-017-019-031-033-035-051-053-057-063-
069-073-081-085-091-093-095-097-099-107-109-113-119-121-125-129-
141-171740-
WI
. WISCONSIN COUNTIES INCLUDED ARE
ADAMS ASHLAND BARRON
BAYFIELD BUFFALO BURNETT
CHIPPEWA CLARK DOUGLAS
DUNN EAU CLAIRE IRON
JACKSON JUNEAU LA CROSSE
LINCOLN MARATHON MONROE
MD 0473 CONCERNING SEVERE POTENTIAL...TORNADO WATCH LIKELY FOR NORTHEASTERN IOWA...SOUTHEASTERN MINNESOTA...SOUTHERN/WESTERN WISCONSIN
Mesoscale Discussion 0473
NWS Storm Prediction Center Norman OK
1148 AM CDT Fri Apr 17 2026
Areas affected...northeastern Iowa...southeastern
Minnesota...southern/western Wisconsin
Concerning...Severe potential...Tornado Watch likely
Valid 171648Z - 171915Z
Probability of Watch Issuance...80 percent
SUMMARY...Increasing potential for supercells capable of all
hazards.
DISCUSSION...Visible satellite trends show two areas of cumulus
increasing near the cold front/dry line in north-central
Iowa/southern Minnesota and further east in a confluence band in
northeastern Iowa. A few attempts are note on radar near the front
over the last 30 minutes. Across the open warm sector in
central/eastern Iowa into southern WI/northern Illinois, strong warm
air advection within the 40-45 kt southerly LLJ is ongoing with
moderate to strong MLCAPE and strong deep layer shear profiles
supportive of supercells. Uncertainty remains in what the exact
evolution of storms will be. Two scenarios are possible: initial
supercell development in eastern Iowa ahead of the front and
supercell development along the cold front.
Confidence is highest that there will be development further west
along the cold front, which will initially be supercelluar given,
the favorable profiles. The time period for more discrete supercells
may be cut short across this region as the cold front undercuts
convection. Nonetheless, initially large to very large hail will be
possible with an increasing tornado threat as convection matures. As
more clustering/upscale growth occurs, threat to damaging winds will
increase with a line embedded tornado threat continuing through the
afternoon/evening.
Further east, isolated supercells may develop within the open warm
sector across northeastern Iowa nearer to the warm front. These
would also be capable of large to very large hail. Should they
persist, there would also be enhanced potential for strong tornadoes
given the SRH rich environment.
A Tornado watch will likely be needed in the next 1-2 hours.
..Thornton/Mosier.. 04/17/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GRB...LOT...MKX...DVN...ARX...MPX...DMX...
LAT...LON 44529149 44128969 44028899 43828843 43318829 42138908
42058925 41818999 42049121 42329258 42619354 43299446
43999375 44629338 45079327 45179313 44919236 44529149
MOST PROBABLE PEAK TORNADO INTENSITY...140-170 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...2.75-4.25 IN
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0739 AM CDT Fri Apr 17 2026
Valid 171300Z - 181200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
THE UPPER AND MID MISSISSIPPI VALLEY SOUTHWESTWARD INTO KANSAS AND
OKLAHOMA...
...SUMMARY...
Numerous severe thunderstorms are likely this afternoon into tonight
across parts of the Upper Midwest southward across the lower
Missouri Valley into central Great Plains. Initially this may be
accompanied by a risk for large to giant hail and a few strong
tornadoes, before severe wind gusts 60 to 90 mph become the
most prominent hazard by this evening.
...Synopsis...
Surface analysis this morning depicts a front bisecting MN north to
south to a low near the NE-IA-SD border, with the front extending
southwestward into the central High Plains. Water-vapor imagery
shows a prominent upper trough near the MT-ND border
south-southwestward into eastern UT. A belt of increasingly strong
southwesterly 500-mb flow will overspread a destabilizing warm
sector today as the upper trough eventually reaches the Upper
Midwest and central Great Plains late tonight. Concurrently, the
aforementioned cyclone will develop northeast to Lake Superior as a
warm front over IA advances northward into the western Great Lakes.
Meanwhile, the cold front will sweep southeast reaching the central
Great Lakes southwestward into the southern Great Plains by early
Saturday.
...Upper and Mid Mississippi Valley...
A northward expanding warm/moist sector on the nose of a 50+ kt
southerly LLJ will continue to destabilize as large-scale ascent
approaches from the west. A large-hail threat may develop this
morning with developing convection across southern MN (see
forthcoming MCD #472 for short-term details). Heating and advection
of 60s deg F surface dewpoints beneath steep mid-level lapse rates
will support the development of a moderately to very unstable
airmass from IA-IL northward into the upper MS Valley to the east of
the front and southeast of the low. Upwards of 1500-3000 J/kg
MLCAPE is forecast immediately ahead of the front with strengthening
flow aloft, strongly favoring organized storms, including
supercells. Recent model guidance continues to show the development
of discrete supercells later this afternoon ahead of the front over
parts of central/northern WI near the low, and farther south in the
vicinity of eastern IA into adjacent portions of WI/northwest IL.
All hazards will be possible with this potential activity, including
the possibility for an intense tornado. Large to giant hail will be
possible with supercells. Other storms likely to evolve quickly
into a band of severe thunderstorms will develop farther west and
push east coincident with the front. Damaging wind gusts will tend
to become more prevalent during the evening with linear storm modes.
Some tornado risk may continue into the evening as maturing bands of
storms yield a threat for bowing segments and embedded mesovortices,
before this activity gradually diminishes late as it moves east into
IN/Lower MI late.
...KS-OK eastward into the lower MO Valley...
Continued moistening and heating of an airmass to the east of a
dryline/cold front and associated triple point will lead to a very
unstable airmass from OK into KS by early to mid afternoon. A
capping inversion will likely inhibit storm development until mid
afternoon near the front. Initial storm development will likely be
supercellular near the triple point before a more extensive band of
cellular storms develops along the boundary. Both a supercell and
QLCS tornado risk is apparent given the appreciably large
CAPE/shear. A coalescing of cold pools and intensification of a
squall line with embedded surges and bowing segments may result in
focused swaths of more intense severe gusts (i.e., locally 75-90
mph) from south-central and eastern KS into west-central MO.
Farther south, a more conditional setup south of the triple point
along the dryline is expected. Large to giant hail could accompany
any mature/sustained supercell along with a tornado risk.
Eventually the front will sweep southeastward with a convective line
yielding a risk for wind/hail.
..Smith/Dean.. 04/17/2026
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
1203 PM CDT Fri Apr 17 2026
Valid 171630Z - 181200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM FAR
NORTHWEST OKLAHOMA THROUGH CENTRAL AND EASTERN KANSAS INTO
WEST-CENTRAL MISSOURI...
CORRECTED FOR ORIENTATION OF THE 45% HAIL PROBABILITIES
...SUMMARY...
Numerous severe thunderstorms are likely this afternoon into tonight
across parts of the Upper Midwest southward across the lower
Missouri Valley and central/southern Great Plains. Initially this
may be accompanied by a risk for large to giant hail and a few
strong tornadoes, before severe wind gusts of 60 to 90 mph become
the most prominent hazard by this evening.
...Synopsis...
Recent surface analysis places a low over south-central MN, with a
cold front extending southwestward to another low over central KS. A
warm front also extends southwestward from the MN low through far
southwest MN and far northern IL into central IN. This warm front is
demarcated well by the 56 deg F isodrosotherm. Farther south, a
dryline extends from the triple point KS low back southwestward
through the TX Panhandle and into far southeast NM. A broad, moist
warm sector exists to the east of the cold front and dryline,
characterized largely by dewpoints in the low to mid 60s.
A well-defined shortwave trough is apparent on satellite imagery,
extending from southern Saskatchewan back southwestward into the
eastern Great Basin. This wave is forecast to continue eastward,
with a attendant increase in the mid-level flow across much of the
Plains and Upper/Mid MS Valley. The cold front will surge
eastward/southeastward in response to this wave as well, interacting
with the warm sector to support numerous strong to severe
thunderstorms from parts of the Upper Midwest southward across the
lower Missouri Valley into southern Plains.
...Upper/Mid MS Valley...
Moderate to strong low-level moisture advection is expected across
the Upper MS Valley today as the surface low mentioned in the
synopsis progresses northeastward, with an attendant northward shift
of the warm front as well. The risk across this region may evolve in
several phases, beginning with the elevated thunderstorms currently
ongoing across northwest WI. This storms will likely continue
northeastward, posing a risk for severe hail and isolated damaging
gusts. Additional development is possible northwest of this activity
along the occluded front, with some hail possible here as well.
Farther south, the northeastward advecting low-level moisture
coupled with strong heating and steep lapse rates will result in a
strongly unstable airmass along and just south of the warm front by
the early afternoon. Storm initiation is anticipated within this
open warm sector by early afternoon, forced by a mix of warm-air
advection, low-level confluence, and subtly increasing large-scale
ascent. This activity should be ahead of the front and initially
discrete. The overall parameter space will be characterized by
strong to very strong buoyancy, moderate deep-layer vertical shear,
and strong low-level helicity. Supercells capable of all hazards are
expected, including large to very large (i.e. 3"+ hail), strong to
intense tornadoes, and severe wind gusts. Storm interactions are
expected to strongly influence the tornado risk, with the initially
discrete mode likely becoming messy quickly.
Farther west, other storms are likely to evolve quickly along the
front, developing into a band of severe thunderstorms that will push
east coincident with the front. Damaging wind gusts will tend to
become more prevalent during the evening with linear storm modes.
Some tornado risk may continue into the evening as maturing bands of
storms yield a threat for bowing segments and embedded mesovortices,
before this activity gradually diminishes late as it moves east into
IN/Lower MI late.
...KS/OK/MO...
A very unstable airmass is expected to develop along and ahead of
the triple point over south-central KS an associated cold front and
dryline. Strong low-level convergence will likely lead to initial
storm development near the triple point. This initial activity will
be supercellular and capable of very large to giant hail (over
3-3.5" in diameter). Highest coverage of very large hail is expected
over from far northwest OK into south-central KS. Strong downdrafts
(60 to 80 mph) are possible as well. With a largely
boundary-parallel orientation to the deep-layer shear, the tornado
risk appears relatively lower. However, given the supercell mode and
potential interactions with outflow, a low-probability tornado risk
remains. A more north-south configuration to the dryline supports a
conditional tornado risk into far northwest TX.
With time, upscale growth and the development of a
forward-propagating MCS is anticipated across central and eastern
KS. Very strong gusts (80+ mph) are possible with this MCS.
Additionally, some QLCS tornado risk will exist within this line as
long as it stays ahead of the surging cold front. The front will
continue sweeping southeastward, with storms along this boundary
yielding a risk for wind/hail.
..Mosier/Chalmers.. 04/17/2026
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1014 AM CDT Fri Apr 17 2026
Valid 171700Z - 181200Z
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF THE SOUTHERN HIGH
PLAINS INTO CENTRAL/SOUTHERN NEW MEXICO...
Minor expansions were made to the Elevated/Critical areas in New
Mexico and the southern High Plains based on the latest observations
and high-resolution forecast guidance. Elevated to locally critical
conditions are already occurring in portions of west Texas and
central/eastern New Mexico, with several hours of elevated/critical
conditions expected in the outlook areas. Otherwise, the forecast
remains on track, and please see the previous discussion for more
details.
..Nauslar.. 04/17/2026
.PREV DISCUSSION... /ISSUED 0107 AM CDT Fri Apr 17 2026/
...Synopsis...
An upper trough will move into the central U.S. and deepen Friday as
an associated mid-level speed max intensifies over the central
Plains. During the afternoon, surface pressure gradients will
tighten across much of the High Plains with a cold front progressing
southwestward into southern Kansas and the Oklahoma Panhandle. This
will promote Critical fire weather conditions throughout eastern New
Mexico, Texas Panhandle, and West Texas. A second shortwave impulse
will exit the eastern U.S. supporting above normal temperatures and
some lingering dry/breezy conditions over the central Appalachians
and Mid-Atlantic.
...Southern Plains...
As the upper trough moves east of the Rockies, increasing mid level
flow will overspread much of the southern High Plains. At the
surface, a strengthening low will quickly traverse the upper
Midwest, dragging a cold front southward. Poor expected overnight
humidity recoveries will encourage RH in the single digits by peak
afternoon heating combined with strong southwest winds of 20-25 mph
(gusts up 40 mph). These conditions amid receptive fuels will
support Critical fire weather conditions for much of the region on
Friday. As the cold front passes through Friday evening, an abrupt
northerly wind shift with strong gusts of up to 40 mph continuing
for a few hours could impact any ongoing wildfires. However, higher
relative humidity and cooler temperatures behind the front are
expected to improve the fire weather environment into the overnight
hours.
Farther north, gusty post-frontal northerly winds are expected over
parts of the central Plains. RH values will climb quickly throughout
the day as temperatures cool. Brief locally elevated fire weather
conditions are possible where fuels have remained dry.
...Central Appalachians and Mid-Atlantic...
In the wake of the departing shortwave trough, westerly flow aloft
will linger over the Appalachians with weak lee surface troughing.
Westerly winds of 10 mph (gusts up to 20 mph) and decreasing RH to
less than 30 percent are expected by peak heating. These conditions
atop a drought ridden landscape and exceptionally dry fuels will
support an Elevated fire weather threat this afternoon.
...Please see www.spc.noaa.gov/fire for graphic product...
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