046
ACUS02 KWNS 171712
SWODY2
SPC AC 171710

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1210 PM CDT Thu Sep 17 2026

Valid 181200Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ...

...SUMMARY...
Isolated severe storms will be possible across parts of Idaho/Utah,
Nebraska/Iowa, and the Piedmont of the Carolinas into north Georgia.

...Great Basin...
A closed midlevel low now over northern CA will move slowly eastward
over northern NV/southern ID tomorrow.  Ascent immediately
east-through-north of the midlevel low, in combination with daytime
heating in cloud breaks and low-level moisture on the northwest edge
of the monsoonal plume, will support scattered thunderstorms Friday
afternoon.  While MLCAPE will likely remain near or below 1000 J/kg,
midlevel lapse rates near 8 C/km and deep-layer southerly shear will
favor some organized/supercell structures capable of producing
isolated large hail and strong outflow gusts.

...IA/NE area...
Low-level warm advection is expected to support clusters of elevated
thunderstorms into Friday morning from northeast NE into northern
IA/southern MN along and north of a slow-moving baroclinic zone.
The potential remains for an MCV to emerge from the overnight storm
clusters, though its phasing with the surface warm sector and the
formation of additional storms along the surface wind shift Friday
afternoon are in question.  If storms form along this boundary,
there will be a narrow zone where curved low-level hodographs and
moderate-strong buoyancy could favor isolated severe storms.
Farther southwest, storm development is uncertain given (at best)
very weak forcing for ascent.  While an isolated downburst could
occur with a high-based storm, the overall threat for severe gusts
appears too low to maintain a MRGL into KS.

...Piedmont...
Lingering overnight convection in the vicinity of the Appalachians,
around the east/northeast periphery of the persistent midlevel high
over the south central U.S., could combine with terrain circulations
to provide weak convective outflow and/or differential heating zones
to help focus thunderstorm development Friday afternoon.  Storms are
expected to move generally southward into an environment with strong
surface heating/steep low-level lapse rates/moderate buoyancy with
the potential for precipitation-loaded downbursts with isolated wind
damage.

..Thompson.. 09/17/2026

$$