ACUS11 KWNS 171738
SWOMCD
SPC MCD 171737=20
WIZ000-IAZ000-MNZ000-171900-

Mesoscale Discussion 1164
NWS Storm Prediction Center Norman OK
1237 PM CDT Wed Jun 17 2026

Areas affected...portions of the upper Mississippi River Valley

Concerning...Severe potential...Watch possible=20

Valid 171737Z - 171900Z

Probability of Watch Issuance...60 percent

SUMMARY...A few severe thunderstorms will develop from portions of
southeastern Minnesota into northeastern Iowa and southwestern
Wisconsin this afternoon, with a threat for primarily large hail and strong/damaging wind gusts.

DISCUSSION...Regional radar imagery depicts increasing thunderstorm
activity in close proximity to a surface low analyzed west of
Minneapolis, MN, and immediately downstream of a potent mid-level
shortwave trough. Cold mid-level temperatures and ascent preceding
this feature are coupling with modest surface heating to support
weak destabilization (500 J/kg MLCAPE), with 500-1000 J/kg expected
by peak heating this afternoon. Very strong westerly mid-level flow
(70+ kts sampled at 4 km AGL by the DMX/ARX VAD profiles) is
contributing 40-50+ kts of effective shear, supportive of supercell development. While mid-level lapse rates are forecast to remain
modest (6-6.5 C/km), this strong shear and elongated, relatively
straight hodographs will promote large hail as the primary severe
risk, with a localized instance or two of hail to 2" in diameter
possible pending the development of a sustained supercell.
Strong/damaging wind gusts are also possible owing to downward
momentum transport of strengthening low-level flow within
downdrafts. A brief tornado also cannot be ruled out owing to the
overlap between increasing low-level buoyancy and enhanced surface
vertical vorticity in close proximity to the aforementioned surface
low. A Severe Thunderstorm Watch may be needed in the next 1-2 hours
to cover these threats.

..Chalmers/Hart.. 06/17/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!8I4dNy0a5-qceVQ_0miH-18R5z5Udzp3Lmmu9UKMZ4h4CGlgJOVbTJmHiPLjXo9QWtmPeXVb4= VaYqKDMtSMSlaMbX9c$ for graphic product...

ATTN...WFO...ARX...MPX...DMX...

LAT...LON 45089430 45199356 45019268 44809211 44389138 43979096
43639084 43319093 43009142 42889205 42929285 43209342
43669420 43849448 44139483 44449497 44849470 45089430=20

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN


=3D =3D =3D
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