SPC Sep 16, 2026 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0745 AM CDT Wed Sep 16 2026

Valid 161300Z - 171200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDWEST/OHIO VALLEY AND UTAH INTO FAR NORTHWEST COLORADO...

...SUMMARY...
Isolated strong to severe thunderstorms appear possible today across
parts of the Midwest/Ohio Valley and Utah/far northwest Colorado.

...Mid Mississippi Valley/Midwest into the Ohio Valley...
In between upper troughing over Canada and upper ridging over the
Southeast, a convectively augmented mid-level vorticity maximum over
IL/northwest IN evident on radar imagery will track eastward today
across the OH Valley/southern Great Lakes. While mid-level westerly
winds will remain fairly modest across this region (generally 20-30
kt or less), this feature should aid additional convective
development this afternoon across parts of IN into OH and vicinity
as a moist low-level airmass gradually destabilizes. Poor lapse
rates aloft should tend to limit overall updraft strength, but
locally damaging winds may occur with any loosely organized clusters
that can form and spread eastward through the early evening before
weakening with the loss of daytime heating.

Most guidance continues to show thunderstorms developing late this
evening (mainly after 17/03Z) over portions of IA/northern IL in a
modest low-level warm advection regime. While MUCAPE will gradually
increase across this region as low-level moisture streams northward,
the potential for severe/damaging winds should tend to remain low
since convection will remain elevated and well north of a stalled
surface front. Cloud-layer shear also appears marginal to support
supercells with hail potential. Given these limiting factors, have
not included low severe probabilities at this time.

...Southwest into the Great Basin...
On the southeast periphery of a closed upper low centered over
northern CA, around 35-45 kt of southwesterly mid-level flow will
persist today across parts of the Great Basin. Ongoing thunderstorms
across eastern UT/northwest CO are occurring in a strongly sheared
but weakly unstable environment. While occasional hail could occur
with the stronger cores, current expectations are for renewed
thunderstorm development later this afternoon as the rather moist
low-level airmass gradually destabilizes with filtered diurnal
heating. If any cells/small clusters can form, they would pose an
isolated threat for severe hail/gusts. But, the limited
heating/instability should temper the overall severe risk.

Farther south across AZ/NM, numerous to widespread thunderstorms are
expected to develop and spread northward through the period as a
weak mid-level perturbation moves northward from the Baja California
vicinity across the Southwest/Four Corners. Above-average low-level
moisture (50s/60s surface dewpoints) is already in place over these
areas, but modest lapse rates aloft and limited daytime heating due
to widespread cloud cover suggest that instability will remain weak.
Nearly unidirectional/southerly flow and modest strengthening with
height through mid/upper levels should foster only marginal
deep-layer shear to support updraft organization. While occasional
gusty winds could occur with the stronger cores that develop, the
threat for severe gusts appears too limited to include any
probabilities with this update.

..Gleason/Mead.. 09/16/2026

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