SPC Sep 17, 2026 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1247 AM CDT Thu Sep 17 2026

Valid 171200Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE INTERMOUNTAIN WEST AND IN THE CENTRAL HIGH PLAINS...

...SUMMARY...
Thunderstorms with isolated severe wind gusts and hail will be
possible in parts of the Intermountain West late this afternoon and
early this evening. A few strong gusts may also occur in parts of
the central High Plains.

...Intermountain West...
An upper-level low will move inland into the Intermountain West
today, as southwest flow remains at mid-levels over much of the
region. At the surface, a trough will deepen from southern Idaho
into western Utah. To the east of the trough, dewpoints in the 50s
F, will contribute to weak instability by afternoon. As surface
temperatures warm, thunderstorms will develop in the higher terrain.
RAP forecast soundings to the east of the trough at 00Z have 0-6 km
shear in the 30 to 40 knot range. In addition, low to mid-level
lapse rates are forecast to be in the 6.5 to 7.5 C/km range. This
environment will likely support an isolated threat for severe gusts
and hail. The threat should be concentrated during the late
afternoon and early evening, as cell coverage maximizes near the
instability axis.

...Central High Plains...
An upper-level ridge will move eastward today across the
north-central U.S, as a shortwave trough embedded in the ridge moves
through the central High Plains. At the surface, a warm front is
forecast to move slowly northward across southern and western
Nebraska this afternoon. An axis of moisture, with surface dewpoints
in the 60s and 70s F, will be oriented north of the front from the
mid Missouri Valley west-northwestward into the central High Plains.
During the late afternoon, scattered thunderstorms are expected to
develop near the shortwave trough, with storms moving gradually
northeastward across the central High Plains. Forecast soundings
near the area of greatest expected convective coverage have moderate
deep-layer shear suggesting an isolated severe threat will be
possible. However, lapse rates are forecast to be poor, which should
keep any severe threat marginal. If storms near the front can remain
nearly surface-based, then an isolated wind-damage threat could
develop, mainly during the early to mid evening, as low-level flow
increases.

..Broyles/Thornton.. 09/17/2026


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SPC Sep 17, 2026 0100 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 0100Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 PM CDT Wed Sep 16 2026

Valid 170100Z - 171200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE OHIO VALLEY AND IN NORTH-CENTRAL UTAH...

...SUMMARY...
Isolated strong to severe thunderstorms will be possible early this
evening across parts of the Ohio Valley and in north-central Utah.

...Ohio Valley...
The latest water vapor imagery shows a distinct low-amplitude
shortwave trough in southwest Ontario extending southward toward the
Ohio Valley. At the surface, a quasi-stationary front is located
from central Illinois east-northeastward into central Ohio. The
shortwave trough is providing large-ascent, supportive of scattered
thunderstorms ongoing near the front mainly across Ohio. South of
the front, surface dewpoints are in the mid 70s F, which is
contributing to moderate instability with MLCAPE estimated by the
RAP in the 1500 to 2000 J/kg range. The Wilmington, Ohio 00Z
sounding has 0-3 km lapse rates near 7.5 C/km, and the latest
WSR-88D VWP from Wilmington has 0-6 km shear in the 30 to 35 knot
range. This should be sufficient for a marginal severe threat for a
couple more hours this evening, with isolated wind damage possible.

...North-central Utah...
An upper-level low-pressure system is currently located near the
West Coast. Water vapor imagery shows a dry slot along the
southeastern periphery of the system from southern California into
western Utah. Thunderstorms are forming along the eastern edge of
the dry slot across north-central Utah, where large-scale ascent
appears to be maximized. Surface dewpoints in the 50s F with 500 mb
temperatures near -8 C are contributing to weak instability in
north-central Utah, with MLCAPE estimated by the RAP around 1000
J/kg. RAP forecast soundings suggest that low to mid-level lapse
rates are near 7 C/km. This should be steep enough, along with
moderate deep-layer shear, for isolated severe wind gusts and hail
early this evening.

..Broyles.. 09/17/2026


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SPC Sep 16, 2026 1630 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1112 AM CDT Wed Sep 16 2026

Valid 161630Z - 171200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
NORTHERN UTAH...AND PARTS OF OHIO AND VICINITY....

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

...OH and Vicinity...
Morning visible satellite imagery shows broken cloud cover across
much of OH, which will allow pockets of heating/destabilization and
lead to moderate CAPE values by mid-afternoon. Widely scattered
thunderstorm development is expected, in a regime of relatively weak
westerly flow aloft and poor lapse rates. PWAT values approaching 2
inches and rather steep low-level lapse rates could result in
precip-loaded downdrafts capable of strong or occasionally damaging
winds.

...UT...
Moisture has increased across UT over the past 24 hours, with
dewpoints now in the low-mid 50s and PWAT values over 1 inch. This
along with ample heating will lead to scattered afternoon
thunderstorms. A band of 35-45 knot southwesterly mid-level winds
across this area will provide sufficient deep-layer shear for a few
rotating storms capable of hail and gusty winds.

..Hart/Chalmers.. 09/16/2026


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SPC Sep 16, 2026 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... 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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