SPC Sep 5, 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
0753 PM CDT Fri Sep 04 2026

Valid 050100Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE SOUTHERN GREAT LAKES INTO THE MID AND UPPER OHIO VALLEY...

...SUMMARY...
Severe storms capable of scattered occurrences of damaging wind with
gusts up to 70 mph are expected across the southern Great Lakes and
mid/upper Ohio Valley overnight. More isolated severe storms capable
of large hail and severe wind gusts may occur over portions of the
northern Plains. Strong to severe storms with a risk for damaging
wind gusts may persist for another couple of hours in the southern
Mid-Atlantic.

...Great Lakes into the Ohio Valley...

Forcing for ascent attendant to a weak mid-level disturbance
cresting the mid-level ridge is contributing to a couple of areas of
thunderstorm activity this evening over portions of eastern IA and
central WI. The 00Z DVN sounding is likely representative of the
inflow air mass for these storms, featuring a moist boundary layer
and relatively steep mid-level lapse rates with MLCAPE of around
4000 J/kg. It remains unclear whether a subset of the current storms
will grow upscale into a cold-pool-driven MCS overnight, or whether
additional storms will develop farther to the east across portions
of southern Lake MI and southwest Lower MI in the next few hours.
Either way, there is a consistent model signal for a bowing
convective system to evolve across portions of northeast IN into OH,
along the cool side of a composite surface boundary extending from
central WI through central IN into eastern KY.

Regional VWPs and 00Z soundings indicate the presence of 30-35 kt
northwest winds in the mid levels along the axis of the prospective
MCS track, which will contribute to sufficient deep-layer shear for
cold-pool organization. As such, a corridor of more concentrated
wind damage appears possible along with severe gusts up to 70 mph.

...Northern Plains...

A cluster of mainly elevated thunderstorms is ongoing this evening
over north-central SD, with that activity likely rooted above a warm
capping inversion observed by the 00Z ABR sounding. Additional
storms are expected to develop overnight along a nocturnally
strengthening low-level jet, where warm advection and moisture
transport will be maximized. Mid-level flow and resultant vertical
shear are forecast to weaken overnight owing to the proximity of the
mid-level ridge. However, the presence of steep mid-level lapse
rates and associated moderate to strong instability suggests the
potential for isolated severe storms capable of large hail and
severe wind gusts. As such, 5% wind and hail probabilities have been
included in this forecast update.

...Southern Mid-Atlantic...

Clusters of strong to severe thunderstorms ongoing over portions of
southeast VA into north-central and northeast NC will remain capable
of mainly damaging wind gusts for the next hour or two. Thereafter,
storms are expected to gradually weaken as the boundary layer
stabilizes.

..Mead.. 09/05/2026


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SPC Sep 4, 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
0755 AM CDT Fri Sep 04 2026

Valid 041300Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
GREAT LAKES INTO THE MID-ATLANTIC STATES...

...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.

...Southern Great Lakes into Mid Atlantic...
Early-morning satellite imagery shows a deep cyclone over the
Pacific Northwest and upper ridging covering the majority of the
CONUS east of the Rockies. A belt of enhanced mid-level flow
persists between these two features, arcing anticyclonically from
southern CA through the central Rockies and northern Plains into the
Upper Midwest/Upper Great Lakes and eventually through the
Northeast. Recent surface analysis shows a reservoir of low-level
moisture beneath the upper ridging, to the south and east of this
belt of stronger mid-level flow. Much of this area is void of
notable surface features, but a weak front does extend from southern
New England through southern NY, central Lower MI, and central WI to
a weak low over southern MN. A large cluster of showers and
thunderstorms to the south of this front from southern WI into
southern Lower MI. This cluster, which was initiated by warm-air
advection across MN and WI is forecast to continue southeastward
today, likely encountering a diurnally destabilized airmass.

The steeper mid-level lapse rates will remain displaced west of this
region, but ample low-level moisture (i.e. upper 60s/low 70s
dewpoints) coupled with afternoon temperatures from the mid 80s to
mid 90s will still support moderate to strong buoyancy. As such,
reintensification and/or new development is anticipated as the
ongoing cluster continues southeastward. Much of this region will be
on the southern fringe of the stronger deep-layer shear, with bowing
line segments as the predominant storm mode. The best overlap
between buoyancy and shear is expected across central and eastern
OH, where a corridor of greater potential for damaging gusts exists.

The threat for damaging gusts will extend into the Mid-Atlantic this
afternoon and evening amid a very warm and moist airmass. Vertical
shear will be weak, but ample moisture (i.e. PW values from 1.8" to
2"), strong buoyancy, and steep low-level lapse rates will support
the potential for strong outflow capable of wind damage. Bowing line
segments will be the primary storm mode here as well.

...Central Plains...
Weak lee troughing could contribute to modest low-level convergence
from western KS across western/central NE into southwest SD.
Dewpoints will likely be in the low to mid 60s within this
convergence zone, and steep mid-level lapse rates will contribute to
moderate/strong buoyancy. Even so, warm mid-levels may prevent the
airmass from completely destabilizing. The remaining convective
inhibition, coupled with the presence of large-scale height rises
across the region, casts doubt to whether successful convective
initiation will occur. Any mature updrafts could result in strong
downdraft, but uncertainty is too high to introduce any
probabilities with this outlook.

..Mosier/Lyons.. 09/04/2026


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SPC Sep 4, 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
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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SPC Sep 4, 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
0800 PM CDT Thu Sep 03 2026

Valid 040100Z - 041200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS PART OF THE MID ATLANTIC INTO MIDDLE OHIO VALLEY...AND ACROSS
PARTS OF THE UPPER MIDWEST...

...SUMMARY...
Scattered strong thunderstorm development, posing mainly a risk for
severe wind and hail, remains possible into the overnight hours
across parts of the Mid Atlantic and Upper Midwest into the Great
Lakes.

...01Z Update...

...Mid Atlantic...
A convectively generated or augmented mid-level perturbation
continues to migrate east-southeastward across the upper Ohio
Valley, toward the northern Mid Atlantic, along the southern fringe
of broadly cyclonic flow overspreading the Northeast. This
continues to provide support for a clustering of stronger convective
development currently in a corridor across east central Ohio into
south central Pennsylvania. Although this activity appears to have
waned some in intensity from earlier, updraft inflow emanating from
a more moist environment, along and south of a diffuse remnant
outflow boundary across the central Maryland through Delmarva
Peninsula vicinity, might reinvigorate activity later this evening
into the overnight hours.

...Upper Midwest into Great Lakes region...
Convective evolution into and through the overnight hours remains a
bit unclear. An initial cluster of convection, supported by a short
wave impulse now progressing toward the Minnesota/Ontario border
vicinity and Lake Superior, is undergoing substantial weakening as
inflow becomes more stable to the cool side of a quasi-stationary
frontal zone, which roughly extends from the Red River Valley
through southern Great Lakes region.

Upstream, near the crest of building mid/upper ridging,
lower/mid-tropospheric warm advection is supporting scattered
renewed thunderstorm development across northwestern and west
central Minnesota. Closer to the frontal zone, where the inflow
environment is characterized by moderate to strong instability,
there still appears potential for the evolution of a small
organizing cluster across the Brainerd MN vicinity through mid to
late evening. As this progresses eastward, it is not clear that
this will be maintained overnight. A strengthening southwesterly
low-level jet may focus additional upscale growing thunderstorm
development downstream, across parts of northeastern Wisconsin into
Lower Michigan, but, elevated to the cool side of the frontal zone,
it is not clear that the environment will support more than very
limited potential for severe hail and wind.

..Kerr.. 09/04/2026


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