Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0102 AM CDT Mon Aug 17 2026
Valid 171200Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL AND NORTHERN PLAINS...AND IN THE SOUTHERN
APPALACHIANS...
...SUMMARY...
Thunderstorms with severe wind gusts and hail will be possible this
afternoon and evening across parts of the central and northern
Plains. Severe gusts will also be possible in parts of the southern
Appalachians. Isolated severe gusts may occur in parts of Oklahoma
and Montana.
...Central and Northern Plains...
At mid-levels, a subtle shortwave trough will move across the
northern Plains today, within west-northwesterly flow. Ahead of this
feature, a broad corridor of low-level moisture will be in place
over the central and northern Plains. A moist axis, with surface
dewpoints in the upper 60s and lower 70s F, will setup from
northwest Kansas north-northeastward into central Nebraska and
eastern South Dakota. Along and near the moist axis, moderate to
strong instability will develop by midday with MLCAPE likely
increasing into the 2000 to 3000 J/kg range. At the surface, a cold
front will move southeastward across the Dakotas during the day.
Low-level convergence will become maximized ahead of the front
across central Nebraska and southeast South Dakota. This will lead
to scattered convective initiation, with thunderstorms forming and
moving southeastward into the stronger instability during the late
afternoon and early evening.
RAP forecast soundings near the instability axis at 00Z from
northeastern Nebraska into eastern South Dakota have 0-6 km shear
near 40 knots with low to mid-level lapse rates in the 7 to 7.5 C/km
range. This will support supercell development and isolated large
hail production in areas that have the best overall environment.
However, a mixed mode is expected. Supercells and multicells will be
capable of severe wind gusts. The severe threat will likely continue
into the mid evening, as a somewhat large convective cluster moves
southeastward into the mid Missouri and upper Mississippi Valleys.
...Southern Appalachians...
A mid-level shortwave trough will move east-southeastward across the
Ohio and Tennessee Valleys today, reaching the southern Appalachians
by early evening. Ahead of this feature, a moist and unstable
airmass will be in place. Surface dewpoints in the 70s F will lead
to the development of moderate to strong instability by midday. At
the surface, a cold front will advance southeastward into the
southern Appalachians. Low-level convergence along the front, along
with topographic forcing, will result in scattered thunderstorm
development in the afternoon. These storms are expected to move
east-southeastward across the higher terrain of the southern
Appalachians and into the lower elevations by early evening. The
very moist and unstable air, along with 0-6 km shear in the 20 to 30
knot range will support a wind-damage threat. Severe gusts will be
most likely with short organized line segments. The severe threat
could persist into the early evening.
...Southern Plains...
At the surface, a quasi-stationary front will remain in place across
southern and western Oklahoma today. Within the post-frontal air,
surface dewpoints will be from the mid 60s to the mid 70s F. As
surface temperatures warm, moderate to strong instability will
develop along and near the most axis. The instability, combined with
sufficient deep-layer shear and 0-3 km lapse exceeding 8 C/km will
be favorable for isolated severe wet downbursts.
...Northern High Plains...
West-northwest mid-level flow will be in place in the northern High
Plains over the top of a post-frontal airmass. Surface dewpoints in
parts of central and eastern Montana will be around 50 F. MLCAPE
will increase into the 500 to 1000 J/kg range over parts of the
northern High Plains. As temperatures warm during the day,
thunderstorms are expected to form in the higher terrain of central
Montana, with isolated cells moving eastward across the upper
Missouri Valley. Very steep low to mid-level lapse rates could
support an isolated potential for severe wind gusts during the late
afternoon and early evening.
..Broyles/Thornton.. 08/17/2026
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