Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0727 AM CDT Sun Sep 20 2026

Valid 201300Z - 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.

...OK and TX...
Southwesterly upper-level flow over the southern Great Plains will
be downstream of an eastward-migrating upper trough moving into the
central and southern High Plains by early evening.  A frontal zone 
modulated by convection overnight over the eastern part of the TX
Panhandle and OK will sag southward through tonight.  A moist
airmass will undergo appreciable heating amidst surface dewpoints
in the mid to upper 60s F, resulting in moderate buoyancy by mid
afternoon.  Sufficient deep-layer shear for storm organization is
expected across OK, where a risk for severe wind gusts and some hail
is expected to evolve during the afternoon into the early evening. 
The 20/00z HREF/REFS ensemble guidance showed agreement in
delineating the strongest explicit 10-m wind gusts across parts of
southern OK within a corridor characterized by very steep 0-3 km
lapse rates.  Have introduced an intensity level-1 area where
confidence in 60-80 mph gusts is greatest.  

...Central High Plains...
A mid-level shortwave trough will move into the central High Plains
today.  An easterly component to low-level flow north of the surface
front will maintain a fetch of moisture (50s deg F surface
dewpoints), and this moisture combined with heating will enable
moderate destabilization by afternoon.  As surface temperatures warm
and convective inhibition erodes, scattered storms are forecast by
mid-late afternoon.  Model forecast soundings show straight
hodographs with sizable CAPE in the -10 to -30 deg C layer.  As a
result, a few supercells are probable with the primary severe hazard
being large hail (1 to 2.5 inches in diameter) along with isolated
severe gusts.  Some lingering severe risk may eventually develop
over southeast CO late this evening and spread into the OK Panhandle
overnight. 

...Ozarks/Mid Mississippi and Ohio Valleys...
A series of low-amplitude perturbations will move generally east
across the Ozarks and OH Valley to the north of a weakened mid-level
anticyclone centered over the northwest Gulf Coast.  A reservoir of
seasonally rich low-level moisture (mid 60s to low 70s deg F surface
dewpoints) will exist south a cold front that was analyzed near the
I-70 corridor this morning.  This frontal zone is forecast to
gradually push southward during the period and serve as the northern
delimiter of strong/severe thunderstorm activity.  

As the boundary layer heats through the mid afternoon to the south
of more extensive cloud cover with north extent, moderate buoyancy
will likely develop.  Some modest enhancement to mid-level flow will
probably accompany the aforementioned convectively augmented
mid-level features.  Portions of eastern IL into IN could perhaps
yield a slightly more favorable environment for severe storms due to
hodograph structure.  Yet, it remains uncertain whether some
strengthening of low-level flow in vicinity of the effective frontal
zone occurs later today.  The 19/06z NAM differed substantially
versus recent RAP model runs.  Regardless, a few clusters of strong
to severe thunderstorms will probably evolve, posing mainly an
isolated threat for wind damage.

..Smith/Mead.. 09/20/2026