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


Read more CHECK UPDATE ZOOM GRAPHIC


http://dlvr.it/TVJmCX

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


Read more CHECK UPDATE ZOOM GRAPHIC


http://dlvr.it/TVJRQV

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


Read more CHECK UPDATE ZOOM GRAPHIC


http://dlvr.it/TVJBjp

SPC Sep 2, 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
0300 PM CDT Wed Sep 02 2026

Valid 022000Z - 031200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WESTERN NEW YORK...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
MONTANA...

...SUMMARY...
Scattered to numerous severe thunderstorms are likely across parts
of the Great Lakes to the Mid-Atlantic this afternoon through
tonight. Damaging winds are the main threat, though some large hail
and a few tornadoes may also occur. Scattered severe gusts and
isolated large hail appear possible over the northern Rockies/High
Plains this afternoon and evening.

...20Z Update...
The Enhanced Risk in NY was expanded slightly eastward, driven by
45-percent wind probabilities. Here, temperatures are gradually
warming into the upper 70s to lower 80s (higher than earlier
guidance suggested). This will yield a corridor of moderate
surface-based buoyancy ahead of developing storms this afternoon.
Strong deep-layer shear oriented favorably to an expected cluster of
storms and the destabilizing air mass should support a swath of wind
damage (supported by the latest time-lagged HRRR/RRFS ensemble
guidance). For additional details, see MCD 2201.

Farther west, severe probabilities were trimmed behind a strongly
forced, northeastward-moving band of convection in the northern
Rockies. For details on the near-term severe threat, see MCD 2200
and Severe Thunderstorm Watch 644.

..Weinman.. 09/02/2026

.PREV DISCUSSION... /ISSUED 1128 AM CDT Wed Sep 02 2026/

...Lower Michigan into the Mid-Atlantic...
An ongoing cluster across south-central PA has a well established
cold pool and a history of producing damaging winds across
western/central PA. This convection is expected to continue moving
quickly southeastward through the afternoon across parts of
MD/DC/northern VA and vicinity. There is still some uncertainty on
whether this cluster will be able to maintain intensity with
southward extent into the Mid-Atlantic, as it becomes increasingly
removed from the stronger forcing aloft/mid-level flow over the
Great Lakes into NY. Still, a differential heating zone remains
apparent along/near the Chesapeake Bay per recent visible satellite
imagery and surface observations. The cluster should tend to remain
on the warm side of this boundary, with steepening low-level lapse
rates developing as daytime heating continues to destabilize the
downstream airmass. Scattered damaging winds will likely remain a
threat with these thunderstorms as they track across the southern
Mid-Atlantic before eventually weakening.

In the wake of this late morning/early afternoon activity, it
appears likely that robust destabilization will occur across parts
of lower MI into western NY. 12Z observed soundings from APX/DTX/BUF
showed moderate to very strong MUCAPE and modestly steepened
mid-level lapse rates with an EML. This favorable airmass will
spread eastward through the day in tandem with a mid-level shortwave
trough and 50-60 kt mid-level jet also advancing eastward over the
Great Lakes and ON. Even with some cloud cover present, moderate to
strong instability will likely be in place across western NY by late
afternoon, to the west of a differential heating zone/front.
Thunderstorms are expected to develop along/ahead of a cold front
from parts of southeast Lower MI to the lower Great Lakes, with 50+
kt of deep-layer shear supporting organized updrafts. A mix of
supercells and multicells will likely pose a threat for both severe
hail and scattered to numerous damaging winds. Sufficient low-level
shear should also be present to support a few tornadoes, with some
chance for a strong tornado this evening if a supercell mode can be
maintained across western NY and vicinity. Confidence has increased
in a corridor of greater severe/damaging wind potential late this
afternoon/evening across parts of western NY, where an Enhanced Risk
has been introduced.

...Northern Rockies/High Plains...
High-based thunderstorms have already developed over the higher
terrain of central ID this morning. Enhanced winds aloft associated
with a northeastward-ejecting mid-level shortwave trough and steep
low-level lapse rates will support a risk for scattered
severe/damaging winds as this activity spreads northeastward across
MT this afternoon and evening. Occasional 75+ mph gusts may occur,
even though instability should remain weak. Isolated thunderstorms
may also develop later this evening/tonight in a low-level warm
advection regime across eastern MT into western ND, with some hail
threat.

...Eastern Utah into the Central Rockies/High Plains...
Thunderstorms are expected to increase in coverage this afternoon
over eastern UT into the higher terrain of northern/western CO and
southern WY. This activity will spread northeastward into eastern
WY/western NE where a very deep/well-mixed boundary layer should
support locally severe gusts.


Read more CHECK UPDATE ZOOM GRAPHIC


http://dlvr.it/TVJ3T0