SPC Sep 18, 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
0741 PM CDT Thu Sep 17 2026

Valid 180100Z - 181200Z

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

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

...Intermountain West...
An upper-level low is currently located over northern California,
evident on water vapor imagery. Mid-level flow is southwesterly over
much of the Intermountain West with a dry slot located from southern
Nevada northeastward into northern Utah and southeast Idaho.
Scattered thunderstorms have developed within the nose of the dry
slot from north-central Utah into eastern Idaho. Within this zone,
the RAP has a pocket of instability with MLCAPE in the 1000 to 1200
J/kg range. In addition, the WSR-88D VWP near Pocatello, Idaho has
0-6 km shear near 40 knots. RAP forecast soundings in the vicinity
have low to mid-level lapse rates around 8 C/km. This environment
should support a threat for hail and isolated severe gusts for a
couple more hours this evening.

...Central High Plains...
On water vapor imagery, a mid-level shortwave trough is currently
located in the central Rockies. This feature will move into the
central High Plains this evening. At the surface, a warm front is
located from northern Kansas into southwest Nebraska. The front will
move northward into west-central Nebraska this evening. To the north
of the front, a moist axis is present with surface dewpoints from
the mid 60s to the lower 70s F. Near the moist axis, the RAP has
MLCAPE in the 1500 to 2000 J/kg range. In addition, the regional
WSR-88D VWP near North Platte has 0-6 km shear around 45 knots,
which will support an isolated wind-damage threat for a few more
hours this evening. Lapse rates are poor which will keep any severe
threat marginal.

..Broyles.. 09/18/2026


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SPC Sep 17, 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
1110 AM CDT Thu Sep 17 2026

Valid 171630Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
AND EVENING OVER PARTS OF IDAHO/UTAH...AND A SMALL PART OF THE
CENTRAL HIGH PLAINS....

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

...ID/UT...
Morning water vapor imagery shows an upper low over northern CA,
with a band of strong flow aloft with associated embedded shortwave
troughs extending across NV into UT/ID. Strong heating across this
area will aid in the development of scattered thunderstorms from
southern ID into northern UT by mid-afternoon. Sufficient vertical
shear is present for rotating updrafts capable of large hail and
gusty/damaging winds. While coverage of storms will likely be
limited, one or two severe cells are expected later today - mainly
over the eastern Snake River Plain.

...CO/KS/NE...
The remnants of a weak tropical low are tracking northeastward
across the four-corners region this morning. Ample moisture and
weak ascent associated with this feature will lead to considerable
clouds and scattered thunderstorms today over the mountains of CO
and southern WY. This activity will spread eastward into eastern CO
and western NE/KS with high-based convection posing a risk of
locally damaging wind gusts. The extent of this severe threat will
be modulated by daytime heating, which is uncertain at this time due
to lingering cloud cover.

..Hart/Chalmers.. 09/17/2026


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SPC Sep 17, 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
0730 AM CDT Thu Sep 17 2026

Valid 171300Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
UTAH/IDAHO INTO SOUTHWEST MONTANA...AND THE CENTRAL HIGH PLAINS...

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

...Utah/Idaho into Southwest Montana...
A closed mid/upper-level low over northern CA this morning will
slowly develop eastward today across the northern Intermountain
region. A 40-50 kt southwesterly mid-level jet and difluence aloft
will overspread parts of the northern Great Basin through this
afternoon. Large-scale ascent will likewise further increase through
the day across this region, with additional thunderstorm development
anticipated. The primary uncertainty regarding the severe risk
remains how much instability will develop given the prevalence of
clouds and ongoing precipitation this morning. With upper 40s to low
50s surface dewpoints already in place, some guidance suggests
sufficient diurnal heating in tandem with cool temperatures aloft
will support up to 1000-1250 J/kg of MLCAPE over southeast
ID/northern UT and vicinity this afternoon. If this occurs, then a
focused corridor of greater severe hail/wind potential may exist
across these areas, as deep-layer shear will be strong enough to
support supercells. Otherwise, a broader risk for isolated
hail/gusty winds will exist across the northern Great Basin with any
cells/small clusters that can develop.

...Central High Plains...
Between a mid/upper-level low over the West Coast and upper ridging
over the Southeast/southern Plains, multiple minor mid-level
perturbations should move northeastward from the Southwest/southern
Rockies towards the central High Plains by this evening. One leading
mid-level vorticity maximum aiding showers and isolated
thunderstorms across NM this morning should support additional
convective development across northeast CO into western NE and
vicinity by late afternoon. While low-level moisture and related
instability should gradually increase across this region through the
day, mid-level lapse rates should remain modest. This will probably
tend to limit updraft intensity, but sufficient deep-layer shear
should be present for some convective organization. A small cluster
or two could eventually evolve and pose some risk for isolated
severe gusts as they spread east-northeastward across the central
High Plains through the evening.

...Midwest/Ohio Valley into the Mid-Atlantic...
Ongoing convection across the Midwest has remained slightly elevated
to the north of a surface front through the early morning. Current
expectations are for this activity to move east-southeastward
through the rest of the morning in a weakly unstable environment.
Various observed 00/12Z soundings downstream across the OH Valley
and southern Mid-Atlantic show very poor lapse rates aloft (i.e.,
around 4.7-5 C/km in the 700-500 mb layer), which will likely hinder
robust updraft intensities. Furthermore, visible satellite imagery
shows extensive cloudiness present across these regions. This will
slow/dampen diurnal heating and related steepening of low-level
lapse rates. While strong/gusty winds may still occur with
convection that develops/spreads southeastward through the day, the
overall risk for severe/damaging winds appears too limited for 5%
probabilities at this time.

..Gleason/Mead.. 09/17/2026


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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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