795
ACUS01 KWNS 131958
SWODY1
SPC AC 131957

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Sun Sep 13 2026

Valid 132000Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
OHIO VALLEY INTO CENTRAL NEW YORK...

...SUMMARY...
Isolated to widely scattered severe thunderstorms will be possible
across parts of the upper Ohio Valley into the Northeast this
afternoon and evening. Isolated strong to severe thunderstorms may
also occur across parts of the central and northern High Plains.

...20Z Update...
Minor changes where made to the ongoing forecast based on recent
observations and model guidance. The overall forecast reasoning
remains valid, however. See the previous discussion for additional
details.

..Wendt.. 09/13/2026

.PREV DISCUSSION... /ISSUED 1139 AM CDT Sun Sep 13 2026/

...Northeast and upper/middle Ohio Valley...
Have upgraded portions of the region to a categorical Slight Risk
with expectations of a semi-focused regional corridor of wind damage
later this afternoon through early evening. Within large-scale upper
troughing over eastern Canada, a strong west-southwesterly mid-level
jet will overspread the Great Lakes into the Ohio Valley and
Northeast later today into tonight. A surface cold front will
likewise track eastward across these regions through tonight. A
seasonably moist low-level airmass will be in place ahead of the
cold front, but poor lapse rates aloft (around 6-6.5 C/km) and cloud
cover should limit the degree of destabilization that can occur this
afternoon, although cloud cover has tended to thin/abate since early
this morning across the upper Ohio Valley. While the main influence
of the upstream upper-level trough will not arrive until this
evening, strengthening mid-level flow through the day will support
35-45 kt of deep-layer shear and the potential for organized bands
of convection.

At least widely scattered thunderstorms are expected to develop
along/ahead of the front by mid afternoon (around 19-22Z) from parts
of Ohio into western New York, and then spread quickly eastward
across the upper Ohio Valley into the Northeast. The deep-layer
shear will be strong enough for some supercells initially, with
perhaps a marginal/isolated hail threat even with the poor lapse
rates present aloft. But, clusters/bowing segments with an isolated
damaging wind threat should quickly develop given the linear forcing
of the front. This convection is forecast to weaken with eastward
extent this evening with the onset of nocturnal cooling, and as it
encounters a less unstable airmass.

...Wyoming and central/northern High Plains to Missouri Valley...
A closed mid/upper-level low over the Pacific Northwest this morning
will move eastward to the northern Rockies/High Plains through the
period. Diurnal destabilization will generally be limited ahead of
this low, though a narrow zone of weak instability may develop by
late afternoon across southern Wyoming, and across northeast
Colorado into the Nebraska Panhandle in a modest low-level upslope
flow regime. Isolated thunderstorm development is expected with
sufficient wind profiles for isolated severe hail/wind potential.

Elevated thunderstorms should again increase in coverage across
western/central South Dakota towards the mid Missouri Valley late
tonight into early Monday morning. Moderate MUCAPE and sufficient
cloud-layer shear could support an isolated hail threat with the
initial development across western/southern South Dakota, though
mergers/interactions and weakening buoyancy will likely limit the
longevity and eastward extent of this threat into the mid Missouri
Valley.

$$