Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0742 AM CDT Fri Aug 21 2026

Valid 211300Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS...MIDWEST...AND CAROLINAS...

...SUMMARY...
Scattered severe thunderstorms capable of producing large hail (some
2+ inches) and severe winds may occur over parts of the central
Plains into the Midwest this afternoon and evening. Damaging winds
will also be possible with scattered to numerous thunderstorms
across portions of the Carolinas and Southeast.

...Central Plains into the Midwest...
Elevated and widely spaced thunderstorms have developed this morning
from far southwest SD into central NE, and separately across eastern
OK. Weak low-level warm/moist advection is aiding this activity, and
ascent associated with a northwesterly mid/upper-level jet may also
be supporting the central Plains convection. Evolution of the
ongoing thunderstorms across NE remains unclear, as the airmass
downstream into southeast NE/northern KS will gradually destabilize
through the day. One possibility is for convection to slowly
strengthen and eventually develop into a bowing cluster this
afternoon across these areas, with an associated risk for
severe/damaging winds.

Another scenario is for this morning activity to weaken, and then
for isolated supercells to potentially develop later today in a
rather unstable airmass and strongly sheared mid/upper-level
northwesterly flow regime along/south of a front. Large hail (some
2+ inches) would be a threat with any sustained supercells, and
severe gusts could also occur as lapse rates become steepened.
Either scenario appears plausible, with recent high-resolution
guidance varying on possible solutions, including the potential for
one or more clusters to develop and persist tonight. Have therefore
maintained the Slight Risk across the central Plains with minimal
changes.

Thunderstorms are also occurring this morning over parts of WI to
the east of a weak surface low and associated mid-level
perturbation. While effective bulk shear is forecast to remain
fairly modest (around 20-30 kt), a mix of multicells and marginal
supercells is expected to develop later this afternoon across parts
of southern WI into northern/central IL along and ahead of a weak
front. Severe hail may occur with any persistent cells, while the
threat for damaging winds should increase as small clusters form and
spread east-southeastward through the early evening. While low-level
flow is not forecast to become overly strong, sufficient veering
with height through low/mid levels should exist to support modest
low-level hodograph curvature and some risk for a brief tornado.

...Carolinas into the Southeast/Lower Mississippi Valley...
Convection continues this morning along/ahead of a surface cold
front from central AL northeastward into the western NC. Modest
large-scale ascent associated with a weak mid-level shortwave trough
over the TN Valley is likely aiding this activity. Around 20-30 kt
of mid-level flow should be present today over parts of the
Carolinas, with similar values of deep-layer shear forecast.
Moderate to locally strong instability is expected to develop this
afternoon ahead of the front across the central/eastern Carolinas,
as a rather moist low-level airmass remains over these areas.
Thunderstorms should gradually increase in both coverage and
intensity this afternoon, with sufficient deep-layer shear for some
updraft organization. Multicell clusters capable of producing
isolated to scattered damaging winds should be the main threat as
low-level lapse rates become steepened with filtered daytime
heating. Still, some of the stronger cores could produce occasional
hail as well, even though lapse rates aloft appear poor. This
convection will spread towards the Atlantic Coast through the
afternoon/early evening before eventually weakening with the loss of
daytime heating.

Farther south across the Gulf Coast states into the lower MS Valley,
mid-level flow and related deep-layer shear are forecast to be
weaker (generally less than 20 kt). Even so, at least an isolated
threat for damaging winds should exist with scattered thunderstorms
that develop along/south of the front and spread southward through
the afternoon, as the airmass should become quite unstable with
robust diurnal heating.

..Gleason/Broyles.. 08/21/2026

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0354 AM CDT Fri Aug 21 2026

Valid 241200Z - 291200Z

...DISCUSSION...
A mid-level trough will move across the Northeast on Monday and the
surface front will be mostly offshore, reducing the severe weather
threat. As this trough departs, ridging will build across the
Rockies. This will eventually set up a pattern featuring individual
mid-level shortwave troughs within northwesterly flow from the
northern Plains to the Midwest. Some severe weather will likely
occur with mid-level shortwave troughs within this flow, but these
details likely will not become more clear until the short term. 

Model consensus indicates a stronger mid-level shortwave trough
traversing the Pacific Northwest on D7/Thursday. This pattern would
be favorable for some severe weather threat across Montana, but at
this time, it appears moisture will stay farther east. Therefore, no
severe weather is anticipated.