SPC Sep 3, 2026 2000 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 2000Z Day 1 Outlook


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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SPC Sep 3, 2026 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0712 AM CDT Thu Sep 03 2026

Valid 031300Z - 041200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY THROUGH
TONIGHT ACROSS PARTS OF THE SOUTHERN GREAT LAKES INTO MID ATLANTIC
AND PARTS OF THE NORTHERN GREAT PLAINS...

...SUMMARY...
Scattered strong thunderstorm development is likely today through
tonight, perhaps 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 into
Upper Midwest.

...PA to Delmarva...
A broad upper ridge remains over the TN Valley, with fast zonal flow
stretching across the Great Lakes into the Mid-Atlantic region.
Multiple clusters of thunderstorms are ongoing this morning over
western PA and northern MD. These storms will progress
southeastward today across an air mass affected by storms last
evening, where there is uncertainty how much destabilization can
occur. Damaging winds will be possible in those areas where
sufficient heating can occur, especially by early afternoon.

...WI to PA...
A common scenario in recent CAM solutions is that a mid-level speed
max associated with convection over MN/IA will track across WI and
into Lower MI by mid/late afternoon. Morning convection will result
in an outflow boundary from southeast WI into southern Lower MI,
likely providing the focus for rapid afternoon thunderstorm
development. Ample low-level moisture/CAPE and favorable westerly
flow aloft suggest an initial risk of supercells, but increasing
linear organization with time. Storms will track into northern
IN/OH by late afternoon, and eventually into western NY/PA this
evening. Damaging wind gusts are the primary concern with this
activity.

...ND/MN...
Morning water vapor imagery suggests a strong shortwave trough
lifting northeastward across WY. This feature will move into the
Dakotas today, aiding the development of intense thunderstorms over
eastern ND by mid-afternoon. Initial supercells will be capable of
large hail and a tornado or two. Activity will likely persist
through much of the evening, tracking eastward across parts of
northern/central MN and perhaps into northern WI. Damaging winds
and hail would be the main concerns during that period.

..Hart/Dean.. 09/03/2026


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SPC Sep 3, 2026 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1253 AM CDT Thu Sep 03 2026

Valid 031200Z - 041200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY THROUGH
TONIGHT ACROSS PARTS OF THE SOUTHERN GREAT LAKES INTO MID ATLANTIC
AND PARTS OF THE NORTHERN GREAT PLAINS...

...SUMMARY...
Scattered strong thunderstorm development is likely today through
tonight, perhaps 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 into
Upper Midwest.

...Discussion...
Large-scale mid-level troughing has overspread much of the Pacific
coast through the Rockies. However, models indicate that further
eastward progress will slow, as at least one significant embedded
short wave trough digs offshore and contributes to amplification of
the larger-scale trough near and offshore of the Pacific coast. As
this occurs, downstream ridging is forecast to build across the
northern Great Plains/middle Missouri Valley vicinity by late
tonight, in the wake of a short wave trough now emerging from the
Great Basin and forecast to progress north-northeast of the northern
Rockies through the eastern Canadian Prairies and northwestern
Ontario. Farther east, it appears that mid-level troughing and an
embedded remnant low will slowly dig southeast of western
Quebec/southern Ontario through the northern Atlantic Seaboard.

A surface cold front accompanying the eastern Canadian perturbation
is preceded by considerable ongoing thunderstorm activity
overspreading the northern Mid Atlantic through Lake Erie vicinity.
It appears that an outflow boundary associated with this convection
may become quasi-stationary across parts of southeastern
Pennsylvania/New Jersey, before the initially stalled upstream
front, across southern portions of the Great Lakes vicinity into
Upper Midwest, advances southeast of the lower Great Lakes through
much of the northern Mid Atlantic and upper Ohio Valley by late
tonight.

...Southern Great Lakes into northern Mid Atlantic...
The initially stalled composite outflow boundary and surface front
appear likely to provide the focus for renewed thunderstorm
development later today through tonight. Across the southeastern
Wisconsin through southern Lower Michigan/northern Indiana and Ohio
vicinity, it appears that the corridor of stronger destabilization
along this boundary will remain in relatively close proximity to the
southern fringe of the westerlies. East-southeastward into the
northern Mid Atlantic this remains more unclear.

Regardless, where the seasonably moist boundary layer becomes
strongly heated, thermodynamic profiles a bit further aloft into
mid-levels, aided by elevated mixed-layer air, will remain
characterized by steep lapse rates of temperature and potential
wet-bulb temperature. This will promote the risk for strong
downbursts and evolving cold pools capable of producing strong to
severe wind gusts in developing thunderstorm activity.

There appears potential for one or two organizing clusters across
and east-southeast of the southern Great Lakes region this afternoon
into tonight. It is possible that severe wind probabilities could
still be increased further, once forcing for convection and the
potential negative impacts of early day convection become clearer.

...Northern Great Plains into Upper Midwest...
Forcing for ascent, near and downstream of the short wave emerging
from the Great Basin, appears likely to overspread northern/eastern
North Dakota into northwestern Minnesota during peak boundary-layer
instability this afternoon and evening. Latest convection-allowing
guidance suggests that this will provide support for intensifying
thunderstorm development, which may include a few supercells in the
leading warm advection regime, ahead of a possible upscale growing
cluster near the crest of the building larger-scale mid-level
ridging. Aided by pronounced veering of lower through mid-level
wind fields, deep-layer shear appears conducive to the risk for
large hail, in the presence of thermodynamic profiles with steep
mid-level lapse rates and large CAPE in mid/upper levels. A few
strong downbursts also appear possible.

..Kerr/Wendt.. 09/03/2026


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SPC Sep 3, 2026 0100 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 0100Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0759 PM CDT Wed Sep 02 2026

Valid 030100Z - 031200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS PARTS OF THE SOUTHERN TIER OF NEW YORK INTO NORTHERN AND
CENTRAL PENNSYLVANIA...

...SUMMARY...
Thunderstorms posing a risk for potentially damaging wind gusts may
continue into late evening across parts of the Southern Tier of New
York into northern and central Pennsylvania.

...01Z Update...

...Great Lakes into Mid Atlantic...
To the south of a modest lower/mid-tropospheric cyclone, now
migrating to the east of James Bay, the leading edge of broad
mid-level troughing is in the process of gradually shifting
east-southeast of the lower Great Lakes region. Forcing for ascent
associated with this feature has contributed to the evolution of an
organizing cluster of storms now spreading across western New York
state, ahead of a southward advancing segment of the surface frontal
zone trailing the cyclone. However, in the wake of an early day
convective cluster, appreciable warm sector boundary-layer
instability is becoming confined to a narrowing corridor across the
Allegheny Plateau. As the ongoing convective system continues
east-southeastward, and the onset of boundary-layer cooling
progresses, more stable southeasterly near-surface updraft inflow
seems likely to weaken convection and reduce the associated risk for
severe weather as it spreads toward northern Mid Atlantic coastal
areas tonight.

Upstream, convection-allowing guidance suggests that forcing for
ascent associated with lower/mid-tropospheric warm advection may
support renewed widely scattered thunderstorm development overnight.
This is mostly likely to focus near/to the cool side of the
stalling trailing frontal zone on the southern fringe of the
westerlies, across southern portions of the Great Lakes into Upper
Midwest. Aided by modest strengthening of westerly flow in excess
of 30 kt around 850 mb, and steep lapse rates of
lower/mid-tropospheric temperature and potential wet-bulb
temperature, there appears potential for one or two upscale growing
clusters which may pose a risk for severe hail and wind.

...Northern Rockies and adjacent Great Plains...
The risk for severe weather has diminished considerably in the wake
of weakening convection now overspreading the Montana international
border. As the supporting vigorous short wave impulse continues to
pivot north of the border into the Canadian Prairies this evening,
this appears unlikely to change. An isolated strong storm to the
east-southeast of Miles City MT does appear supported by updraft
inflow of relatively moist boundary-layer air characterized by
sizable CAPE in excess of 2000 J/kg. However, it is not clear how
long this will be maintained, as inhibition increases with
boundary-layer cooling and perhaps some further warming aloft.

..Kerr.. 09/03/2026


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