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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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.


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SPC Sep 2, 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
0723 AM CDT Wed Sep 02 2026

Valid 021300Z - 031200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHEAST STATES...AND ACROSS PARTS OF MONTANA...

...SUMMARY...
Severe thunderstorms are possible across portions of the eastern
Great Lakes to the Mid-Atlantic today and tonight. Damaging wind
gusts are the main threat, though some large hail and a few
tornadoes may also occur. Scattered severe gusts and more sporadic
occurrences of large hail appear possible from the northern Rockies
into northern High Plains today into night.

...Northeast States...
A complex but potentially active convective day is in store for
parts of the northeast US today. A fast-moving MCS and associated
mid-level shortwave trough is over Lake Michigan. This system is
forecast to track rapidly eastward across Lower MI and southwest ON
this morning before emerging into western NY/PA this afternoon. A
consensus of overnight CAM solutions indicate this will be the focus
for strong-severe thunderstorms that track east-southeastward during
the afternoon and evening toward the Mid-Atlantic coast. Ample
low-level moisture is present in this corridor. This along with
daytime heating well into the 80s and steep low-level lapse rates
will favor damaging wind gust potential in the strongest storms. A
north-south surface boundary is expected to lie from central NY into
east-central PA this afternoon, where low-level shear will be
locally enhanced to pose some risk of a few tornadoes.

The primary uncertainty for a more widespread severe event today is
the presence of considerable morning convection currently over
northwest PA and western NY. These storms are well-ahead of the
main forcing feature, and decrease confidence in significant
destabilization over the primary risk area this afternoon. These
early storms may pose a damaging wind and hail risk through the day,
especially after a few hours of heating.

...MT...
Scattered high-based thunderstorms are expected to develop over the
mountains of southwest MT this afternoon. Strong winds aloft and
steep low-level lapse rates will aid in the risk of damaging wind
gusts as the activity spreads northeastward through the early
evening.

...CO/WY...
Scattered afternoon thunderstorms are expected to develop over the
mountains of northern/western CO and southern WY. This activity
will spread northeastward into eastern WY/western NE where
inverted-v thermodynamic profiles are expected with 40-50 t-td
spreads. This may result in locally damaging wind gusts.

..Hart/Dean.. 09/02/2026


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SPC Sep 2, 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
1257 AM CDT Wed Sep 02 2026

Valid 021200Z - 031200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
AND CENTRAL MT AND FROM THE LOWER GREAT LAKES TO THE MID ATLANTIC...

...SUMMARY...
Severe thunderstorms are possible across portions of the eastern
Great Lakes to the Mid-Atlantic today and tonight. Damaging wind
gusts are the main threat, though some large hail and a few
tornadoes may also occur. Scattered severe gusts and more sporadic
occurrences of large hail appear possible from the northern Rockies
into northern High Plains Wednesday afternoon into night.

...Eastern Great Lakes, Mid Atlantic...
Several low-amplitude impulses embedded within a belt of moderate
mid-level northwest flow of 40-60 kt will move from the lower Great
Lakes into the northeast and Mid Atlantic today and tonight. A
surface low over James bay will trail a slow moving cold front to
the southwest across lower ON, the lakes and into MI/OH with a
second backdoor front stalled across the eastern Hudson Valley and
southern new England. Within the warm sector, a very moist air mass
will be in place over much of the Northeast contributing to large
buoyancy and broad, but uncertain potential for severe thunderstorms
much of the day.

A complex convective scenario is expected across the region
modulated by several rounds of thunderstorms beginning early this
morning. Convection associated with a lead shortwave trough exiting
southern ON will likely support scattered storms along the front
across the lower Great Lakes and NY this morning. Isolated large
hail and damaging winds are possible with these storms as they move
southeastward and encounter a gradually destabilizing air mass
across southern PA and possibly into VA/MD.

Air mass recovery is expected behind this initial condition as the
primary upper trough moves from WI and lower MI into western NY/PA
later in the afternoon. Steep mid-level lapse rates of 7-7.5 C/km
atop boundary layer dewpoints in the upper 60s to low 70s will aide
in destabilization with upwards of 2000-3000+ J/kg of MLCAPE by
afternoon from lower MI into western parts of NY and PA. Storm
development is expected ahead of the approaching trough and cold
front as well as on any residual outflow from the morning storms. A
mix of supercells and line segments is expected with all hazards
possible.

A greater tornado risk may evolve in the evening across southern NY
and central PA, contingent upon air mass recovery in the wake of the
prior storms and presence of a more supercellular mode. NAM/RAP
forecast soundings do show some elongation of low-level hodographs,
and any modifying old pool or outflow boundary could further enhance
low-level shear profiles favorable for tornadoes. Higher tornado
probabilities were considered, but uncertainty on the aforementioned
factors remains large.

...MT/ND...
A compact but strong shortwave trough is forecast to move rapidly
northeastward from the Great Basin to the northern Rockies today and
tonight. 35-50 kt mid-level flow will accompany this feature and
overspread a modestly moist, but warm and unstable air mass across
much of central and eastern MT. Ascent from the approaching
shortwave trough will aid in the development of thunderstorms across
the higher terrain of western MT through the afternoon. Despite
modest buoyancy, steep lapse rate profiles and a deep, well-mixed
boundary layer, will enhance severe-wind-gust potential with these
storms. 30-40 kt of deep-layer shear will promote organization and
clustering with some guidance showing a fast-moving line developing
and moving northeastward through the later afternoon/early evening.
Scattered severe gusts are likely, with peak intensity of 65-80 mph
possible.

Additional storms are possible across portions of eastern MT into
the evening within a zone of warm advection along a nocturnally
strengthening low-level jet. Isolated large hail appears to be the
primary hazard with those storms.

...WY...
Some model guidance shows high-based showers and thunderstorms
developing near the southern fringes of the northern Rockies trough
across WY this afternoon. Modest low-level moisture/buoyancy may
limit convective intensity, but sporadic strong outflow gusts are
possible given a very deeply mixed boundary layer.

...Mid MO Valley into IA and southern MN...
An intensifying low-level jet will likely support an increase in
thunderstorms late this evening/overnight across the MO valley and
parts of the Midwest. Moderate to strong elevated instability and
sufficient vertical shear may exist for a few stronger storms
capable of marginal severe hail. However, overall forcing for ascent
is modest and with building mid-level heights, confidence in a
broader organized severe threat is low.

..Lyons/Wendt.. 09/02/2026


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