Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0747 AM CDT Tue Aug 18 2026
Valid 181300Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
KANSAS INTO CENTRAL MISSOURI...
...SUMMARY...
Thunderstorms with severe wind gusts and isolated large hail will be
possible this afternoon and evening from the central Plains into the
lower Missouri Valley. Isolated severe gusts and hail will also be
possible from the Northern Rockies into the central High Plains, and
eastward into the Midwest and southern Lower Michigan. Damaging
gusts could also occur across parts of Mississippi and Alabama.
...Central Plains into Lower MO Valley...
Warm-air advection showers and thunderstorms are currently ongoing
across south-central/southeast NE. This activity is likely
reinforcing an outflow boundary from an earlier MCS that extends
from northwest KS into the NE/KS/MO border vicinity. These showers
and thunderstorms are expected to continue southeastward over the
next few hours, while gradually diminishing in coverage and
intensity. How this outflow modifies will influence the thunderstorm
potential across northern KS this afternoon. If the boundary does
not wash out, there could be a region of notable convergence that
develops across in the northwestern/north-central KS between the
outflow (reinforced by an approaching cold front) and a heat-driven
surface low that develops across western KS. Even with this
potential convergence, convective initiation is uncertain. Most
guidance maintains warm low/mid level temperatures, with the
resultant capping suppressing any thunderstorm development. Steep
lapse rates, moderate deep-layer vertical shear, and strong buoyancy
are expected north of the boundary, and there is a conditional risk
for large to very large hail and strong downdrafts if any updrafts
can mature.
A more certain scenario is expected farther east across eastern KS,
where evening thunderstorm development is anticipated as the
low-level jet increases. Steep lapse rates and moderate vertical
shear support the potential for thunderstorms capable of large hail
during the initially more cellular mode. These storms will likely
cluster quickly, with a trend towards upscale growth into a
forward-propagating MCS which then moves into MO. Damaging gusts
will become the primary risk once this occurs.
...Northern Rockies through the Central High Plains...
A shortwave trough is forecast to progress southeastward from
British Columbia/Alberta into the northern Rockies. Thunderstorm
development is anticipated across the northern Rockies as this wave
interacts with the destabilized and buoyant airmass across the
region. Moderate westerly flow will accompany this wave as well,
supporting the potential for more organized storm structures and the
development of several line segments. These widely scattered
thunderstorms are forecast to progress eastward/southeastward this
afternoon/evening, with additional development possible from WY into
the central High Plains. The moderate westerly flow aloft, high
storm bases, and steep low-level lapse rates support the potential
for strong to severe wind gusts as these storms progress
eastward/southeastward.
...Southern WI/northern IL into Lower MI...
Low-level moisture is expected to increase across the Midwest ahead
of an approaching cold front, resulting in moderate buoyancy by the
late afternoon. Convergence along the front will be weak but still
sufficient for convective initiation, with the combination of
moderate buoyancy and moderate westerly flow aloft supporting strong
to severe storms. An initially more cellular mode could yield large
hail within the strongest storms. A quick transition towards more
linear modes is anticipated, with damaging gusts becoming the
primary severe risk within any strong line segments.
...MS/AL...
Afternoon thunderstorm development is anticipated across MS and AL
as a weak vorticity maximum progresses southeastward into the warm,
moist, and unstable environment in place across the region. Vertical
shear will be weak, and an outflow-dominant, multicellular mode is
expected. Even so, some clustering into one or more line segments
appears probable, resulting in scattered thunderstorm coverage.
Steep low-level lapse rates and relatively high cloud bases support
the potential for strong downdrafts with any more robust convection.
..Mosier/Bunting.. 08/18/2026
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