ACUS02 KWNS 170533
SWODY2
SPC AC 170530

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1230 AM CDT Thu Sep 17 2026

Valid 181200Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY INTO
FRIDAY NIGHT ACROSS PARTS OF THE NORTHERN INTERMOUNTAIN WEST...THE
CENTRAL GREAT PLAINS INTO SOUTHERN PORTIONS OF THE MIDDLE MISSOURI
VALLEY...AND PIEDMONT OF CAROLINAS INTO GEORGIA...

...SUMMARY...
Areas of scattered strong thunderstorm development posing at least
some risk for severe hail or wind appear possible across parts of
the northern Intermountain West into the central Great Plains and
southern middle Missouri Valley, and portions of the Carolina into
Georgia Piedmont Friday afternoon and evening.

...Discussion...
Latest model output continues to indicate that larger-scale
mid-level troughing, with a vigorous lead embedded short wave
impulse, will dig across the northern Atlantic Seaboard accompanied
by significant surface cyclogenesis near and east of the Canadian
Maritimes through this period. In the wake of the cyclone, it
appears that a cold front will continue advancing offshore and
through the southern Mid Atlantic Seaboard, before becoming
quasi-stationary beneath the northern periphery of persistent
mid-level ridging, across the lower Ohio through lower and middle
Missouri Valleys.

Upstream of the mid-level ridge, a mid-level trough and embedded low
are forecast to slowly progress across the Intermountain West
through Rockies vicinity, preceded by a couple of more subtle
perturbations migrating around the northwestern through northern
periphery of the ridge.

...Piedmont of Carolinas into Georgia...
Low-level lapse rates may become rather steep by Friday afternoon,
within pre-frontal surface troughing to the lee of the southern
Appalachians, where a relatively moist and mixed boundary-layer
might become characterized by CAPE on the order of 1000-2000 J/kg. 
Perhaps aided by forcing for ascent associated with a convectively
augmented perturbation, storms may increase off the higher terrain
and pose a risk for localized downbursts.  It appears possible that
activity could eventually consolidate into a southward/southwestward
propagating cluster, with the cold pool strengthening sufficiently
to maintain a risk for potentially damaging wind gusts into Friday
evening, despite the weakness of the ambient deep-layer mean flow.

...Northern Intermountain West and adjacent Rockies...
Beneath the leading edge of the cold core of the mid-level low, cool
thermodynamic profiles, with at least modestly steep mid-level lapse
rates, may contribute to scattered strong storms capable of
producing severe hail Friday afternoon, in the presence of strong
deep-layer shear and difluent mid/upper flow.

...Great Plains into middle Missouri Valley...
Convective potential remains uncertain, with the timing of the short
wave perturbations impacting the region unclear.  

The latest model output, including convection-allowing and related
guidance, suggest that forcing for ascent with a secondary impulse
may not begin to emerge from the Raton Mesa vicinity until Friday
evening.  However, the remnants of a very warm and deeply
mixed-boundary layer within the lee surface troughing may still be
conducive to a few strong downbursts near convection overspreading
southeastern Colorado through at least portions of western Kansas
before weakening later Friday night.

Closer to a weak frontal wave/warm frontal zone across parts of
eastern Nebraska into western Iowa and northwestern Missouri, a
corridor of moderate to large CAPE will contribute to an environment
conditionally supportive of organized strong thunderstorm
development.  However, forcing for ascent to support boundary-layer
based thunderstorms remains unclear through late Friday afternoon. 
By mid to late evening, if not earlier, warm advection along a
nocturnally strengthening boundary-layer jet, beneath an
increasingly divergent upper regime, may support an evolving
supercell structure and small upscale growing cluster.  This may
still occur mostly above a stable and/or stabilizing boundary-layer,
but the environment might still be conducive to the development of a
few strong surface gusts.  Relatively warm thermodynamic profiles
seem likely to minimize the risk for severe hail.

..Kerr.. 09/17/2026

$$
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