Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1219 AM CDT Sun Sep 20 2026
Valid 201200Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
OKLAHOMA AND FROM EASTERN COLORADO INTO FAR WESTERN KANSAS...
...SUMMARY...
Thunderstorms with severe wind gusts and large hail will be possible
this afternoon and evening across parts of Oklahoma and from eastern
Colorado into far western Kansas. Isolated severe gusts and hail
will also be possible in parts of the southern Plains, and from the
Ozarks eastward into the Ohio Valley.
...Southern Plains...
At mid-levels, southwesterly flow will be in place today over much
of the central U.S. A shortwave trough is forecast to move into
Kansas and Oklahoma this afternoon. At the surface, a low will
deepen over southwest Oklahoma today, as a cold front advances
southward into central Oklahoma. Near the front, surface dewpoints
will be in the mid to upper 60s F, which will allow moderate
instability to develop by afternoon. MLCAPE is forecast to peak in
the 2000 to 3000 J/kg range in much of central and eastern Oklahoma.
As surface temperatures warm and low-level convergence increases,
scattered thunderstorms are expected to develop in the afternoon,
with storms moving from the Low Rolling Plains and Red River Valley
northeastward into central and eastern Oklahoma.
RAP forecast soundings at 00Z near the instability axis in central
Oklahoma have MLCAPE around 3000 J/kg with 0-6 km shear near 30
knots, and 700-500 mb lapse rates in the 7 to 7.5 C/km range.
Although a mixed mode is expected, the environment will likely
support supercell development in areas that become locally
favorable. Large hail and severe wind gusts will be possible with
supercells. The potential for supercells may continue into the early
evening over east-central Oklahoma, but a gradual transition to
linear mode is expected to take place. The wind-damage threat could
become maximized in the early evening, if an organized line segment
can develop.
...Central High Plains...
A mid-level shortwave trough will move into the central High Plains
today. Ahead of this feature, a lee surface trough will deepen
during the day from northeast New Mexico into eastern Colorado.
Surface dewpoints near the surface trough will be in the 50s F,
which will enable moderate destabilization by afternoon. As surface
temperatures warm, convection will initiate in the higher terrain
during the early afternoon and move eastward into the lower
elevations. A small complex of storms will likely develop from this
convection over the central High Plains. RAP forecast soundings near
the instability axis in eastern Colorado at 00Z have MLCAPE near
1500 J/kg with 0-6 km around 40 knots, and 700-500 mb lapse rates
near 7.5 C/km. This environment should be capable of producing
supercells with large hail and severe wind gusts.
...Ozarks/Mid Mississippi and Ohio Valleys...
At mid-levels, a subtle anticyclonic flow pattern will be in place
from the Ozarks eastward into the Ohio Valley. At the surface, an
axis of moisture and instability will be located from central
Missouri eastward into southern Indiana and southern Ohio, along
which surface dewpoints will be in the 70s F. By mid to late
afternoon, MLCAPE is forecast to peak in the 2000 to 3000 J/kg range
along much of this corridor. Although large-scale ascent will remain
relatively limited, increasing low-level convergence near the moist
axis will result in isolated convective initiation. Any small
cluster that can develop and persist in the late afternoon and early
evening could produce isolated severe wind gusts.
..Broyles/Thornton.. 09/20/2026
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