485
ACUS11 KWNS 122137
SWOMCD
SPC MCD 122136
MIZ000-WIZ000-122330-

Mesoscale Discussion 0709
NWS Storm Prediction Center Norman OK
0436 PM CDT Tue May 12 2026

Areas affected...Eastern Wisconsin...southwest upper Michigan...and
northwest lower Michigan

Concerning...Severe potential...Watch unlikely

Valid 122136Z - 122330Z

Probability of Watch Issuance...5 percent

SUMMARY...Isolated occurrences of locally strong wind gusts and/or
sub-severe hail are possible with the strongest storms late this
afternoon into early evening. A Severe Thunderstorm Watch is not
anticipated.

DISCUSSION...Recent trends in radar and lightning data indicate a
gradual deepening of convection into thunderstorms across parts of
northeast WI, southwest through north of Green Bay, as of 21:30z.
The developing thunderstorms are occurring in close proximity to an
eastward-moving surface low that is being driven by a potent
short-wave trough moving into the upper Great Lakes. The air mass
ahead of the low and trailing cold front has warmed in to the low to
mid 70s at some locations, which coupled with dewpoints in the 40s
and steep low/mid-level lapse rates is resulting in a pocket of
MUCAPE of up to 500 J/kg.

The current KGRB VWP is sampling 40-50 kt westerly winds in the
2-4-km layer, which could potentially be transferred to the ground
by any stronger downdrafts, resulting in similar surface wind gusts.
Some hail is also possible, given the steep lapse rates and cold
mid-level temperatures. The meager instability is expected to limit
overall hail size, with the majority of hailstones remaining below
1".

Latest short-term guidance suggest that the evolving storms will
spread east across far southwest upper MI and Lake Michigan into
northwest lower MI by 00z. At that time, forecast soundings suggest
that storms will likely be elevated atop a stable near-surface
layer, with the potential for sub-severe hail to continue.

Given the expected marginally of severe-weather potential, a watch
is not expected.

..Mead/Gleason.. 05/12/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...APX...GRR...MQT...GRB...MKX...

LAT...LON   44308913 44998893 45588852 45858738 45678538 45208484
            44458504 43888533 43708588 43698700 43708781 43728835
            43858889 44308913

MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN