ACUS01 KWNS 181412

SWODY1

SPC AC 181410



Day 1 Convective Outlook CORR 1

NWS Storm Prediction Center Norman OK

0910 AM CDT Tue Aug 18 2026



Valid 181300Z - 191200Z



...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST

KANSAS INTO CENTRAL MISSOURI...



CORRECTED FOR WIND CIG1 LINE ORIENTATION



...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



$$