SPC AC 042003
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0303 PM CDT Fri Sep 04 2026
Valid 042000Z - 051200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
GREAT LAKES INTO THE MID-ATLANTIC STATES...
...SUMMARY...
A couple of organized thunderstorm clusters are expected to develop
across the southern Great Lakes and mid/upper Ohio Valley through
tonight, accompanied by the risk for damaging wind gusts. More
widely scattered strong thunderstorms east of the Blue Ridge may
also produce damaging wind gusts this evening.
...20Z Update...
The northern portion of the Marginal Risk was expanded westward into
portions of northeastern Iowa to account for recent convective
development associated with a mid-level perturbation visible on
water vapor satellite imagery. An unstable airmass and modest
deep-layer shear will support loosely organized convection, capable
of producing isolated occurrences of 60 MPH winds and 1-inch hail.
Elsewhere, the western portion of the Slight Risk area was expanded
across Illinois, Indiana, and portions of Ohio, where thunderstorms
have developed along a surface boundary and may pose an increased
threat for 55-70 MPH wind gusts and 1-inch hail. See MCDs #2234 and
#2235 for more detail.
Further downstream across North Carolina, the severe wind
probabilities were extended southward to account for recent
convective trends. A corridor of higher wind probabilities was
considered across portions of Virginia, but uncertainty in the
longevity of the convection moving across the Appalachians and
overall convective organization precluded adding additional
highlights at this time.
The 30% wind threat area is expected to see convective development
later this evening, as storms move from the Great Lakes into the
region. There is some uncertainty in the northward extent of the
area owing to the drop off in buoyancy, but continued spread in the
high-resolution forecast guidance regarding the timing and placement
of convection precludes additional adjustments at this time.
Convection is also anticipated to develop across portions of
north-central Nebraska into South Dakota during the early morning
hours. These storms could produce isolated occurrences of hail,
though uncertainty in the timing of convective initiation and
maturation suggests this will primarily pose a threat in the Day 2
time frame.
..Halbert/Weinman.. 09/04/2026
.PREV DISCUSSION... /ISSUED 1146 AM CDT Fri Sep 04 2026/
...Midwest/southern Great Lakes to Mid-Atlantic States...
As large-scale pattern amplification occurs, a belt of moderately
strong northwesterly flow aloft will tend to overlie a frontal zone
that extends from southern portions of Minnesota/Wisconsin
east-southeastward to Pennsylvania/New Jersey. That said, ongoing
convection has effectively modified/southward-shunted the effective
front in several areas, and this will be the primary focus for storm
intensification/redevelopment this afternoon, as well into the
evening/late night.
The steeper mid-level lapse rates will remain displaced west of the
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 near/south of
the effective boundary. General storm re-intensification and/or new
development is anticipated this afternoon, particularly south/ahead
of currently ongoing clusters. Bowing line segments will be the
predominant storm mode, with damaging winds as the most common
hazard.
The threat for damaging wind gusts will extend southeastward into
the Mid-Atlantic this afternoon and evening amid a very warm and
moist airmass. Vertical shear will be weaker with southward extent,
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.
...Southern Wisconsin/southern Lake Michigan vicinity...
The same general meteorological thematic scenario as described in
the prior section applies to this region, and severe probabilities
have been extended westward regionally, albeit for a somewhat
conditional/uncertain scenario. A robust reservoir of
moisture/locally extreme buoyancy will exist particularly to the
south of ongoing midday convection. The region will be influenced by
the amplifying upper ridge, but there is at least some possibility
that storm redevelopment/intensification could occur near/east of
the surface triple point and/or near outflow, with some related
severe potential. Development could also occur toward the southern
Lake Michigan vicinity later tonight as isentropic ascent increases
near/northeast of the surface boundary.
...North-central Plains/Dakotas...
While perceived severe probabilities remain below 5%, some
strong/sporadic severe potential may exist also South Dakota, far
northern Nebraska and/or southeast North Dakota later today through
late tonight, although confidence in specific meteorological
scenarios remains low.
Weak lee troughing will contribute to modest low-level convergence
from western Kansas across western/central Nebraska into southwest
South Dakota. Dewpoints will likely be in the low to mid 60s F
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 remains high. Other storm
development could occur tonight, potentially as a byproduct of a
subtle mid-level wave/ongoing convection ongoing across South Dakota
this morning.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
SPC AC 041703
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1203 PM CDT Fri Sep 04 2026
Valid 051200Z - 061200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
VALLEY AND APPALACHIANS TO THE CAROLINAS...
...SUMMARY...
Severe thunderstorms capable of damaging gusts are possible across
portions of the central Appalachians and Carolinas on Saturday
afternoon and evening. Isolated occurrences of large hail and severe
wind gusts also appear possible over parts of the northern Plains
and vicinity Saturday afternoon into night.
...Eastern Carolinas...
A mid-level trough across the western Atlantic is forecast to
retrograde slightly on Saturday with an associated surface front
expected to move slowly southward from the Mid-Atlantic to the
Carolinas. South of this cold front, a very moist airmass will be in
place with strong instability, particularly across the eastern
Carolinas. Farther west, downslope flow off the mountains may result
in a more stable environment in the western half of the Carolinas.
This signal varies within the guidance, and confidence is not high
enough to lower probabilities across this area, but the greater
threat should remain farther east where mid to upper 70s dewpoints
and around 30 knots of shear amid a front and height falls aloft
should support scattered strong to severe storms capable of mostly
damaging winds.
...Ohio Valley...
Strong heating across eastern Kentucky and vicinity should provide
an unstable and uncapped airmass by Saturday afternoon. Mid-level
flow will be relatively weak across this region (~20 knots) and
therefore, effective shear and storm organization is expected to be
weak. However, strong heating and steep lapse rates will support
some damaging wind threat Saturday afternoon/evening. Some guidance
shows these storms clustering and traversing the Appalachians and
continuing into western Virginia and western North Carolina. The
relatively weak shear, and potential for lesser instability due to
downslope flow across the eastern Appalachians casts significant
doubt on this potential.
...Central to northern Plains...
Most guidance shows ongoing thunderstorms within a warm-air
advection zone across southeast South Dakota Saturday morning.
Isolated large hail is possible with this activity during the
morning hours before the low-level jet weakens and backs and these
thunderstorms weaken by late morning.
As the mid-level ridge strengthens during the day Saturday, height
rises will be present across much of the Plains. Despite this,
upslope flow will develop across the central High Plains. Within
this region, forecast soundings show moderate instability but weak
mid-level flow. This will support some isolated large hail and
severe wind gusts, but the lack of shear should limit the overall
severe weather threat.
A more organized cluster of storms may develop across southwest
Nebraska, but do not expect storm intensity to warrant higher severe
weather probabilities.
After 00Z, the low-level jet is forecast to strengthen across the
central/northern Plains. This could result in some isolated storm
development during the overnight period into the Dakotas. Given the
strong instability forecast across this region, these storms could
contain large hail or damaging wind gusts.
...North-central Montana...
A mid-level jet streak on the eastern periphery of a mid-level
trough across the Northwest will remain across Montana for much of
the period on Saturday. Weak instability may develop as temperatures
warm into the 70s across west-central Montana Saturday afternoon.
Overall, moisture will be lacking (30s F dewpoints) which should
limit the severe weather threat. However, there is some instability
within a zone of moderate to strong shear. Therefore, one or two
fast-moving strong storms may develop within this zone, but the
overall lack of moisture/instability precludes severe weather
probabilities at this time.
..Bentley.. 09/04/2026
WUUS02 PTSDY2
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
SPC AC 041929
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0229 PM CDT Fri Sep 04 2026
Valid 061200Z - 071200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE SOUTHEAST...
...SUMMARY...
Strong wind gusts are likely across the Southeast Sunday afternoon
and early evening. A more uncertain risk for severe wind and hail is
expected across parts of the northern Plains.
...Southeast...
Most guidance shows a weak mid-level shortwave trough moving across
the Southeast during the day on Sunday. Moderate to strong
instability is forecast south of a cold front across the region. The
greatest instability is anticipated near the coast where low to mid
70s dewpoints are likely. Mid-level flow will be quite weak, which
should limit overall storm organization. However, the combination of
the mid-level shortwave trough and the frontal forcing amid an
uncapped and strongly unstable environment should result in a
cluster of storms capable of water-loaded downbursts. A Slight Risk
has been added for the region where the greatest storm coverage is
expected.
...Northern Plains...
The ridge across the Plains will start to break down on Sunday with
a lee cyclone developing across eastern Montana. Moderate to strong
instability will be present across the northern Plains, potentially
with some stronger mid-level flow as the ridge breaks down. Storms
will be possible along the trough from eastern Wyoming into northern
Colorado, along the warm front near the Canadian border and into
northern North Dakota, and extending into western Minnesota, and
northwest of the low across eastern Montana where some instability
is expected to develop. Within this broader area, there will likely
be a few preferred zones that will eventually need a Slight Risk.
However, at this time, it is unclear where these preferred zones
will be. Greater resolution of the pattern evolution should make
these regions more clear in later outlooks.
..Bentley.. 09/04/2026
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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