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

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