451
ACUS01 KWNS 181943
SWODY1
SPC AC 181941

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0241 PM CDT Fri Sep 18 2026

Valid 182000Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
CAROLINA PIEDMONT INTO NORTHERN GEORGIA...NORTHERN IOWA...PARTS OF
THE CENTRAL HIGH PLAINS...AND PARTS OF THE INTERMOUNTAIN WEST...

...SUMMARY...
An isolated severe risk continues for portions of the Carolinas into
northern Georgia and parts of the Intermountain West. Isolated
severe storms are also forecast later today across portions of
northern Iowa and parts of the central High Plains.

...20z Update...
Only minor adjustments were made to the existing outlook as the
forecast remains generally on track. See the discussion below and
MCDs #2306 and #2307 for additional information.

...Central High Plains...
As a mid-level vorticity maximum progresses north-northeastward
across the central High Plains later this evening, some modest
enhancement of deep-layer shear may support an isolated risk for
small to marginally severe hail in addition to isolated severe
gusts. This risk appears conditional on a more cellular storm mode
persisting farther northeastward where it can interact with more
favorable low-level moisture, however. Thus, while some
consideration was given to the additional of hail probabilities
within the existing Marginal Risk, the overall hail risk appears to
be generally less than 5%.

..Chalmers/Wendt.. 09/18/2026

.PREV DISCUSSION... /ISSUED 1129 AM CDT Fri Sep 18 2026/

...Carolina Piedmont into Northern Georgia...
Recent surface analysis places a wavy stationary front from southern
IL through southern IN and southern OH into southwest PA. Decaying
showers and thunderstorms currently precede this boundary from
southern IL into northern KY. This boundary is forecast to shift
southward today in response to a modest surge of cooler air in the
wake of a shortwave trough moving through southern Quebec and the
Canadian Maritimes. This front will be relatively weak, but
thunderstorm development is still anticipated this afternoon as the
front interacts with the warm, moist, and diurnally destabilized
airmass across the Carolina Piedmont and northern GA. Vertical shear
will be weak and a largely outflow-dominant storm mode is expected.
Even so, the strong buoyancy and ample moisture (i.e. PW values over
2 inches) will support the potential for occasionally strong
downbursts.

...Central High Plains...
Water-vapor imagery continues to show a convectively enhanced
vorticity maximum moving north-northeast from north-central NM into
southern CO. This vorticity max is forecast to continue
northeastward along the periphery of the upper ridging centered over
east TX, contributing to thunderstorm development from eastern WY
through eastern CO this afternoon/evening. Much of this activity
will occur in regions of cooler surface temperatures and/or more
limited low-level moisture. However, surface-based buoyancy could
exists in the CO/NE/KS border intersection vicinity, where a
combination of strong heating, and lingering post-frontal low-level
moisture will exist. Potential exists for initially isolated to
widely scattered storms to grow upscale into a small,
eastward-moving cluster this evening. Isolated severe gusts may
accompany the stronger outflow surges with this activity.

...Intermountain West...
Continued thunderstorm development is anticipated across the region
today, with overall coverage and intensity increasing as a shortwave
trough continues to move eastward into southern ID and northern UT.
Some moderate, filtered daytime heating is possible, but the overall
region is expected to remain relatively cool (i.e. high temperatures
ranging from the upper 60s across southern ID to the low to mid 70s
across northern UT). Even so, cold temperatures aloft will support
enough buoyancy, which will combine with strong deep-layer vertical
shear to support occasionally strong/organized updrafts. Strong to
severe gusts will be possible with any stronger, more persistent
storms. Some instances of small hail are possible as well.

...Northern Iowa into Far Southern MN...
Elevated thunderstorm development is still anticipated tonight,
supported by warm-air advection associated with a moderate low-level
jet that extends through the region. Highest storm coverage will
likely be displaced north and east of the strongest buoyancy. Even
so, a few of the southernmost storms could occur where moderate
vertical shear and buoyancy are in place, supporting the potential
for an isolated supercell or two. Primary risk with any stronger
storms is hail, but a strong gust or two is possible if any more
linear structures develop.

$$