519
ACUS01 KWNS 212002
SWODY1
SPC AC 212000

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Fri Aug 21 2026

Valid 212000Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS...MIDWEST...LOWER MS VALLEY...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
also remain possible with scattered to numerous thunderstorms across
portions of the Carolinas and northern Gulf Coast states.

...20z Update...

...Lower MS Valley and Carolinas...
The forecast generally remains on track with only a minor eastward
expansion of the 15% wind probabilities in southern Alabama and the
far western Florida Panhandle. Modestly stronger low-to-mid level
flow (evident in the MOB VWP) and favorable thermodynamic profiles
(steep low-level lapse rates and high PW) should support stronger
downbursts and scattered damaging wind gusts, similar to areas
farther east. See Mesoscale Discussion #2069 for additional
short-term details.

...Midwest...
The Level 1/Marginal risk and Level 2/Slight risk areas were
expanded slightly northwestward based on observed convective
development ongoing across as of 1945 UTC across southwestern
Wisconsin. Some consideration was given to adding a targeted 5%
tornado probability area along the remnant outflow boundary
extending from southeast of Rockford, IL, into southwestern
Wisconsin; however, uncertainty regarding the longevity of a
supercellular storm mode (owing to the potential for cell
mergers/interactions) and the presence of only modest low-level
hodograph curvature/SRH precludes a 5% area at this time. See
Mesoscale Discussion #2070 for additional short-term details.

...Central Plains...
Latest high-res guidance has poorly captured the evolution of
morning and ongoing convection across portions of central and
eastern Nebraska through early this afternoon, which lends
uncertainty to the evolution of the severe threat through the rest
of the period. Given the continued potential for ongoing convection
to intensify and/or for additional redevelopment through the
evening, however, severe probabilities have been maintained with
only minor expansions made to the CIG1 wind and hail areas.

...Northern Great Basin into the Snake Valley...
Convective development is ongoing across portions of central/eastern
Nevada, with thunderstorms forecast to evolve northward through the
afternoon. The 5% wind probabilities and CIG1 area were expanded
westward and northward based on the placement of ongoing
thunderstorm activity and the latest HRRR/RRFS runs.

..Chalmers/Moore.. 08/21/2026

.PREV DISCUSSION... /ISSUED 1124 AM CDT Fri Aug 21 2026/

...Central Plains into the Midwest...
A northwest flow regime will result in a weakly forced and in a
limited confidence severe setup across the central Plains.  Ongoing
widely scattered storm activity may persist and reinvigorate during
the afternoon, or new development occurs along residual outflow as
the airmass becomes moderately to strongly unstable.  Forecast
sounding profiles show moist low levels beneath steep 700-500 mb
lapse rates amid veering and strengthening flow with height.  Large
hail (some 2+ inches) would be a threat with any sustained
supercells along with severe gusts (60-75 mph).  If a small cluster
can eventually develop, the severe-wind hazard would likely focus
with these potential storms.

A small west to east oriented band of storms is moving south across
southern WI to the east of a weak surface low and immediately
downstream of an 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...
Weakened shower/thunderstorm activity associated with an MCV over
the western Carolinas will likely dissipate during the early
afternoon.  However, renewed storm development is forecast in
proximity to this upper disturbance, as well as near residual
outflow from the earlier convection and a surface cool front draped
from the GA/SC Piedmont northeastward into the coastal plain of
eastern NC.  Strong heating of a seasonably moist boundary layer
will result in strong instability by mid afternoon.  Sufficient
deep-layer shear for some organized multicell potential will be
greatest near the upper-level feature.  Farther southeast near the
SC Low Country, weaker flow will result in a pulse thunderstorm
mode.  Scattered damaging gusts are possible with the stronger
thunderstorms through the early evening before nocturnal stability
weakens storms and ends the severe threat.

...North TX east into northern Gulf Coast states...
Antecedent outflow from overnight storm clusters over the lower MS
Valley and AL will serve as a focus for storm development this
afternoon.  Farther west, a more pronounced decaying MCS and
associated southward-moving MCV over east-central OK will also focus
storm activity across east TX into western LA.  The 12 UTC Little
Rock raob showed a belt of enhanced flow around the 4-5 km layer
(35-40 kt).  Other than a localized corridor where moderate
northerly flow will overspread a strongly destabilizing boundary
layer, slightly weaker northerly to northeasterly flow will
encompass this larger region from north TX to Mobile Bay.
Nonetheless, the development of very steep 0-3 km lapse rates (9 deg
C/km) by early to mid afternoon and high PW (1.75-2.0 inches) will
support scattered wind damage with the more intense downdrafts (most
likely and concentrated from east TX through southern MS).

...Northern Great Basin into the Snake Valley...
A mid-level vorticity max rotating northward around the western
periphery of the Four Corners upper high, will move into northern
NV/UT by late afternoon.  Deep inverted-V profiles will develop by
mid afternoon with a dry sub-cloud layer featuring large surface
temperature-dewpoint spreads.  A linear cluster of storms is
expected to evolve and move north across the NV/UT/ID vicinity
during the late afternoon and early evening.  Evaporatively cooled
downdrafts will be potentially capable of severe gusts 60-75 mph.

$$