Mesoscale Discussion 2231
NWS Storm Prediction Center Norman OK
0340 AM CDT Fri Sep 04 2026

Areas affected...Portions of southern lower Michigan

Concerning...Severe potential...Watch possible 

Valid 040840Z - 041045Z

Probability of Watch Issuance...40 percent

SUMMARY...An organizing convective cluster/MCS may produce severe
wind gusts or some hail overnight and continuing into the morning. A
Watch is possible but uncertain.

DISCUSSION...Recent radar trends with a convective cluster over
eastern WI point toward organization into an MCS potentially capable
of severe gusts and hail in the coming hours. Continued low-level
warm air advection at the nose of a 30-40 kt low-level jet has
supported an increase in convective coverage across eastern WI where
cloud top cooling has been noted. This has likely strengthened a
preexisting cold pool with the lead elements of this convective
complex. These storms will cross the lake and move into lower MI in
the next 1-2 hours. The air mass downstream remains moderately
unstable and sheared aloft south of a warm front. Despite the
buoyancy likely being elevated above the immediate surface stable
layer, the environment is more than sufficient to maintain
intensity/organization of the ongoing storms. This suggests severe
wind gusts and some hail are possible as convection moves across the
lake, into lower MI and eventually OH/IN later this morning.

It remains unclear if the stronger gusts from this cluster will make
it to the surface. The strengthening cold pool, more organized
linear mode and recent CAM guidance suggest it's possible. Given the
potential increase in severe threat, conditions are being closely
monitored for a Severe Thunderstorm Watch.

..Lyons/Mosier.. 09/04/2026

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

ATTN...WFO...CLE...DTX...IWX...GRR...

LAT...LON   42038339 41908336 41758348 41708376 41678439 41688524
            41848593 42058645 42178672 42528707 42898733 43118731
            43338722 43608706 43688651 42258366 42038339 

MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1237 AM CDT Fri Sep 04 2026

Valid 041200Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY THROUGH
TONIGHT IN A CORRIDOR ACROSS THE SOUTHERN GREAT LAKES AND
MIDDLE/UPPER OHIO VALLEY INTO MID ATLANTIC...

...SUMMARY...
A couple of organized clusters of thunderstorms may develop across
the southern Great Lakes and mid/upper Ohio Valley today through
tonight, accompanied by the risk for damaging wind gusts.  More
widely scattered strong thunderstorms east of the Blue Ridge may
also pose potential for damaging wind gusts this afternoon and
evening.

...Discussion...
Mid/upper flow is forecast to undergo further amplification today
though tonight across southern Canada and the U.S., downstream of
positively tilted large-scale troughing which continues to evolve
offshore of the Pacific coast through Intermountain West.  It
appears that this will include building ridging across and north of
the international border, from the Rockies through upper Great
Lakes, to the north of a high centered over the central Great
Plains.  Downstream, large-scale troughing is forecast to continue
slowly digging across the northern and middle Atlantic Seaboard.  As
it does, it likely will suppress a prominent high initially centered
near the southern Appalachians.

Accompanying the eastern trough, reinforcing surges of cooler
low-level air will continue to overspread portions of the Great
Lakes and Northeast today through tonight.  It appears that this
will contribute to a slow south and southwestward progression of the
primary surface front across the Mid Atlantic and through the upper
into middle Ohio Valley.

...Southern Great Lakes into Mid Atlantic...
A moist boundary layer, and remnant plume of relatively steep
lower/mid-tropospheric lapse rates, particularly across the Upper
Midwest and southern Great Lakes vicinity into the western slopes of
the Appalachians, may continue to support moderate to strong
potential instability along the quasi-stationary to slow moving
frontal zone.  Latest convection allowing guidance suggests that
this front may already be providing a focus for organizing
thunderstorm development across southern Lower Michigan by the
beginning of the period, beneath the favorably sheared southwestern
periphery of the stronger westerlies.  As the boundary-layer
destabilizes ahead of it with insolation, it appears that this
activity may intensify further, accompanied by increasing potential
to produce strong to severe wind gusts while propagating
southeastward across parts of northern/eastern Ohio into the
Allegheny Plateau by this afternoon.

It remains unclear whether forcing for ascent and destabilization to
the immediate lee of the Allegheny Mountains and Blue Ridge will
maintain this cluster.  However, convection allowing guidance
suggests that the initiation of at least scattered vigorous diurnal
thunderstorm activity is probable downstream, closer to and across
the coastal plain, where the environment is likely to be supportive
of a few downbursts with strong to severe surface gusts late this
afternoon into evening.

Late this evening into the overnight hours, downstream of another
short wave perturbation digging to the east of the amplifying
mid-level ridging, there is a notable signal within
convection-allowing and related guidance that forcing for ascent may
support another evolving cluster of storms.  This may track close
to, but probably at least a bit to the southwest of, the early day
cluster, from the southern Lower Michigan through Ohio and West
Virginia vicinity.

..Kerr/Chalmers.. 09/04/2026

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1204 AM CDT Fri Sep 04 2026

Valid 051200Z - 061200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
APPALACHIANS TO COASTAL NORTH CAROLINA...

...SUMMARY...
Severe thunderstorms capable of damaging gusts are possible across
portions of the central Appalachians and Carolinas on Saturday
afternoon and evening. Isolated occurrences of large hail and severe
wind gusts also appear possible over parts of the northern Plains
and vicinity Saturday afternoon into night.

...Ohio Valley to southern Mid-Atlantic/Carolinas...

An upper shortwave disturbance will migrate through northwesterly
flow aloft, leading to modest height falls across the region on
Saturday. As this occurs, midlevel northwesterly flow will
strengthen, supporting effective shear magnitudes in the 25-35 kt
range. At the surface, a cold front will develop south across the
Midwest and Mid-Atlantic after 00z. Ahead of the front, a very warm
and moist airmass will foster a corridor of moderate to strong
instability. 

Forecast guidance varies with regards to possible morning
convection, resulting in some uncertainty in the forecast for
Saturday. Early convection could be ongoing anywhere from the Lower
Ohio Valley toward the WV/VA mountains as remnants from Day 1
thunderstorm activity. Whether this early day activity will
dissipate or re-intensify as it moves into the moist and
destabilizing downstream airmass is uncertain. Regardless, the
overall environment will support afternoon and evening thunderstorm
activity ahead of the southward-advancing front and along a surface
trough through the parts of the VA/NC/SD Piedmont. Organized
clusters will mainly pose a damaging wind risk as convection spreads
east/southeast during the afternoon and evening.

...Northern/Central Plains vicinity...

Substantial upper ridging will be centered over the Plains on
Saturday. However, most guidance depicts one of more shortwave
disturbances migrating northeast from the central Rockies into the
NE/SD vicinity. Additionally, convection could be ongoing at the
start of the period across the Mid-MO Valley. Southeasterly
low-level flow will result in modest boundary layer moisture along a
surface trough across the northern/central High Plains, with
increasing dewpoints further east toward the MO River along a
surface boundary. Steep midlevel lapse rates will support modest
instability across the High Plains, with moderate to strong
instability further east. 

If storms are occurring at the beginning of the period across the MO
Valley, hail and strong wind gusts will be possible, with some
intensification possible toward midday/early afternoon within the
very moist/unstable and favorably sheared environment. Additional
widely scattered thunderstorms are expected to develop along the
surface trough over the High Plains during the late
afternoon/evening. This activity could produce strong outflow wind
gusts given a deeply mixed boundary layer and modest shear, along
with isolated large hail.

..Leitman.. 09/04/2026

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0136 AM CDT Fri Sep 04 2026

Valid 061200Z - 071200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHEAST...AND THE NORTHERN PLAINS...

...SUMMARY...
Strong wind gusts are possible across the Southeast Sunday afternoon
and early evening. A more uncertain and conditional risk for severe
wind and hail is expected across parts of the northern Plains.

...Northern Plains...

An amplified upper ridge will remain in place from the central
Plains to the Upper Midwest on Sunday. Some modest weakening of the
ridge may occur as an upper shortwave trough digs across the
Northwest and weak shortwave disturbances crest the ridge through
the period. At the surface, low pressure will persist across the
western Dakotas. Boundary layer moisture will spread across eastern
MT on the back side of the surface low, while deep low-level
moisture extends across ND into eastern SD and the Mid-MO Valley
along another surface boundary. Capping will be a main limiting
factor for storm development. However, if the cap can be overcome,
or if elevated convection develops during the day into evening,
strong wind gusts and large hail will be possible given supercell
wind profiles and corridor of moderate to strong instability. 

Deep-layer southwesterly flow is forecast to increase with the
approach of the Northwest upper shortwave trough late in the period
across parts of the northern Rockies toward the northern High
Plains. This could also support possible severe convection overnight
into parts of MT, but timing and overlap of stronger shear and
better instability remains uncertain. 

Overall, severe potential appears conditional on Sunday across
portions of the northern Plains. But, if storms can develop, some
risk for severe wind/hail will be possible. 

...Southeast...

Weak northwesterly flow aloft will persist on Sunday as a surface
front develops south/southwest into the Southeast. Ahead of the
surface boundary, a very moist airmass will support a corridor of
moderate to strong instability focused across southern GA.
Thunderstorms are expected to develop during the afternoon. Vertical
shear will remain weak, but high PW values could support sporadic
wet microbursts and locally strong wind gusts. Some guidance
suggests sufficient clustering and outflow consolidation could occur
such that a forward propagating cluster could spread south/southwest
across the area. If this occurs, damaging wind potential could
increase.

..Leitman.. 09/04/2026