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

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0254 PM CDT Tue May 12 2026

Valid 122000Z - 131200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE GREAT LAKES...CENTRAL PLAINS AND FLORIDA...

...SUMMARY...
Severe storms remain possible across parts of the Florida Peninsula
today, and potentially from southeast Kansas into parts of the Great
Lakes late this afternoon and early evening.

...20z Update Great Lakes...
Afternoon visible imagery shows the cold core of an upper-level
trough beginning to impinging on modest low-level moisture south of
a stalled front near the MI/WI border. While moisture and resulting
buoyancy remain very limited (200-300 J/kg MUCAPE), steep mid-level
lapse rates and continued heating should support enough
destabilization for a few storms this afternoon and evening. Hail is
possible, especially with any storms elevated above the surface
given fairly strong mid-level flow. Have adjusted 5% hail
probabilities northward toward the warm front across the MI/WI
border.

...FL...
Numerous storms are ongoing this afternoon south of an east-west
oriented baroclinic zone across the FL Peninsula. To the south, the
environment remains moderately unstable and sheared, which has
supported a few organized clusters and supercells so far. Hail,
damaging winds, and a brief tornado remain possible with the
strongest storms as the boundary is forecast to sag southward
through tonight. Have removed severe probabilities and trimmed
thunder behind the boundary where the air mass has stabilized.

Otherwise, the prior outlooks remains valid with only minor
adjustments. See the previous discussion for more information.

..Lyons.. 05/12/2026

.PREV DISCUSSION... /ISSUED 1127 AM CDT Tue May 12 2026/

...Florida...
A very moist airmass is in place across the FL Peninsula today, with
surface observations showing dewpoints in the low to mid 70s.
Mesoanalysis estimates MLCAPE is at or above 1500 J/kg for much of
the peninsula already. A shortwave trough is currently moving into
the central Gulf Coast vicinity, with continued
eastward/southeastward progress expected throughout the day. The
prevailing buoyancy coupled with ascent attendant to this wave will
result in scattered to numerous thunderstorms. Low-level flow is
generally weak, but the shift from low-level easterly winds to
moderate southwesterly aloft is supporting moderate deep-layer
vertical shear. Some increased shear is possible in the vicinity of
the east-coast sea-breeze, with the strongest storms anticipated
near this boundary as a result. The overall expectation is for some
organized multicells and a few supercells, posing a risk of damaging
wind gusts and hail, particularly across the east-central portions
of the peninsula.

...Upper Midwest through the Mid MO Valley into southeast
KS/northeast OK...
Recent satellite imagery shows a well-defined shortwave trough
moving through the Upper Midwest towards the Upper Great Lakes.
Surface analysis places the low associated with this shortwave over
the northern MN/WI border vicinity, with an attendant cold front
extending back southwestward through northwest IA,
southeast/south-central NE, and far northwest KS. A modest
pre-frontal trough is in place just ahead of this cold front. The
shortwave trough is forecast to continue eastward, while the cold
front progresses eastward/southeastward. Northern portion of this
front (closer to the surface low and parent shortwave) will make
notably more eastward/southeastward progress than the
southern/western portion, which will move more gradually
southeastward.

Low-level moisture advection is anticipated ahead of the front, but
with mid 50s dewpoints currently in central OK, the extent and
quality of this moisture will likely be somewhat limited. Filtered
heating and mixing could also reduce dewpoints. Even so, dewpoints
will likely still reach at least the mid 40s across southern WI,
gradually increasing into the mid 50s across southeast KS/southwest
MO/northeast OK. This is expected to be enough moisture to support a
narrow corridor of modest buoyancy. Strongest ascent will be near
the surface low and shortwave trough across the Upper/Mid MS Valley,
supporting higher storm coverage than areas farther southwest. A few
high-based storms capable of wind damage and isolated hail are
possible. 

Farther southwest, lower storm coverage is expected, particularly
from west-central IL into southeast KS. Thunderstorm chances across
much of this area appear low enough to remove severe probabilities.
The only exception is over the southeast KS/southwest MO vicinity.
Here, greater low to mid-level moisture could still support a storm
or two. Shear is strong enough to support hail with any storms that
mature.

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1233 PM CDT Tue May 12 2026

Valid 131200Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR NORTH-CENTRAL
MONTANA...

...SUMMARY...
Scattered severe thunderstorms are possible across portions of the
northern High Plains Wednesday afternoon and evening.  Severe wind
gusts are the primary hazard.

...Northern Rockies and High Plains into northern Utah...
A potent mid-level shortwave trough over western OR/WA will move
east across the northern Rockies into the northern High Plains as a
downstream ridge shifts east into the Upper Midwest by early
Thursday morning.  An attendant 80-90 kt 500 mb speed max will
overspread ID/MT by peak heating as a cold front sweeps east across
portions of the northern Rockies into the northern parts of the
Great Basin.  Forcing for ascent and diurnal destabilization will
lead to scattered thunderstorms developing by mid afternoon. 
Forecast soundings show large surface temperature-dewpoint
depressions and inverted-V thermodynamic profiles.  Increasing flow
through the cloud-bearing layer will result in relatively swift
storm motions within pre-conditioned, dry-adiabatic 0-3 km lapse
rates.  Isolated to scattered storms developing over the higher
terrain will move into the lower elevations and increase in coverage
as a couple of linear clusters evolve towards early evening across
central MT, and to a lesser degree, across eastern ID.  The primary
risk will be severe gusts (60-80 mph) accompanying the stronger
cores and outflow.  Farther south, very deeply mixed boundary layers
evident in forecast soundings across northern UT into southern ID
will favor severe gusts with the stronger cores.  

...Ohio Valley/Central Appalachians...
An upper-level trough initially over the central Great Lakes will
move east-southeastward to the Lower Great Lakes and Mid-Atlantic
states vicinity during the period.  Strong cyclonically curved,
500-mb flow (50+ kt) will move through the base of the trough.  A
surface low will move eastward across southwestern Ontario as a cold
front advances east-southeastward into the central Appalachians. 
Ahead of the front, surface dewpoints in the lower to mid 50s F will
contribute to weak instability as surface temperatures warm during
the day.  Increasing low-level convergence near the front will lead
to scattered thunderstorm development, with additional storms
forming due to topographic forcing in the central Appalachians.
Ahead of the front, low to mid-level lapse rates are forecast to
steepen by midday/early afternoon, lending the potential for several
stronger thunderstorms capable of an isolated risk for wind damage
and localized severe gusts.

...TX Panhandle...
Despite a 500-mb ridge overhead, very strong boundary layer heating
may sufficiently erode convective inhibition and yield a couple of
thunderstorms developing near the Caprock (22-00 UTC).  Very steep
lapse rates will support an isolated risk for hail/wind if sustained
storms develop.  This activity will likely dissipate by mid evening.

..Smith.. 05/12/2026

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0229 PM CDT Tue May 12 2026

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
CENTRAL AND EASTERN KANSAS...

...SUMMARY...
Widely scattered severe thunderstorms are possible on Thursday over
the central Great Plains.  Large to very large hail and severe gusts
will likely be the primary severe hazards.

...Central Great Plains into the lower MO Valley...
Weak elevated showers/storms will likely be ongoing over eastern KS
Thursday morning owing to warm advection as low-level southerly flow
strengthens.  A mid-level disturbance is forecast to move from the
CO Front Range to the mid MS Valley during the period invoking
poleward moisture transport via southerly flow.  Model guidance
suggests surface dewpoints to rise into the 60s deg F in an narrow
tongue along and east of I-35 in OK and I-135 in central  KS.  An
elevated mixed layer featuring steep 700-500 mb lapse rates (in
excess of 8 deg C/km) will contribute towards maintaining a cap
through mid afternoon as a moderately to locally very unstable
airmass develops east of a dryline.  Strong heating and large-scale
ascent associated with the eastward-migrating impulse will act to
erode convective inhibition.  Isolated to widely scattered storms
are possible during the 21-00 UTC period.  Forecast soundings favor
supercells with mainly a risk for large to very large hail.  Severe
gusts are also possible and would likely focus if small clustering
can occur during the early evening as this activity moves east
towards the lower MO Valley.  A south-southwesterly LLJ is forecast
to slightly veer and favor strengthening warm-air advection Thursday
night into the lower MO Valley, perhaps facilitating a lingering
risk for wind/hail and/or additional elevated thunderstorms posing
an overnight hail threat.

..Smith.. 05/12/2026