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
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