Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0255 PM CDT Thu Sep 03 2026
Valid 032000Z - 041200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
OHIO AND WESTERN PENNSYLVANIA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MIDWEST AND GREAT LAKES TO MID-ATLANTIC...
...SUMMARY...
Scattered strong/severe thunderstorms are expected through tonight,
including a few organizing clusters, posing a risk for severe wind
and hail across parts of the southern Great Lakes into Mid Atlantic
and portions of the northern Great Plains to the Upper Midwest.
...20Z Update...
Minor adjustments have been made to the outlook to account for
recent convective trends and the latest high-resolution forecast
guidance. Portions of the Slight Risk in North Dakota have been
trimmed behind the ongoing convective complex that has since moved
into northern Minnesota, given the trailing airmass has stabilized
and is less likely to see additional convective development.
Additionally, the Marginal Risk was expanded northward from
Wisconsin into portions of Upper Michigan to account for recent
guidance trending northward with the overnight convective complex
and its associated damaging-wind threat. Otherwise, the previous
forecast remains unchanged and on-track for this evening.
..Halbert/Weinman.. 09/03/2026
.PREV DISCUSSION... /ISSUED 1140 AM CDT Thu Sep 03 2026/
...Lake Michigan/upper Ohio River Valley/Northeast...
Several clusters of storms are ongoing at midday across the Lake
Michigan vicinity and lower Michigan, including a smaller lead
cluster entering Ontario, while other convection farther
east-southeast has weakened/diminished across southern
Pennsylvania/Maryland. Regarding the easternmost activity, steady
air mass recovery/diminishing cloud cover appears likely, with ample
insolation across the Northeast along/south of the primary synoptic
front including much of Pennsylvania.
Available regional 12z observed soundings/RAOBs sampled a belt of
moderately strong northwesterly flow aloft that overlies the primary
frontal zone, with moderate to locally strong destabilization
expected outside of the ongoing convection. Some initial supercells
are possible, but more prevalent will be the possibility of
upscale-growing linear bands/clusters, potentially with multiple
rounds of strong/severe convection this afternoon into tonight with
wind damage. This currently appears most probable across northern
Ohio into Pennsylvania.
...Upper Midwest - eastern North Dakota/northern Minnesota...
A slow-moving linear cluster of occasionally severe storms may
persist and gradually accelerate east and maybe eventually
east-southeastward today, potentially becoming more surface based by
later in the afternoon as it parallels the immediate north side of a
surface frontal zone. This development is being influenced by a
northeastward-transitioning shortwave trough along the international
border, with a belt of strong mid/high-level winds extending
eastward across the northern half of Minnesota toward the Lake
Superior vicinity.
A mixed convective mode seems probable, with a prominent
quasi-linear mode but also the possibility of south-end
semi-discrete development including supercells. Large hail and
damaging winds are the primary hazards, but some tornado risk may
exist as well. One or more clusters may persist east-southeastward
across the region this evening.
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