263
ACUS01 KWNS 130600
SWODY1
SPC AC 130558

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Sun Sep 13 2026

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
OHIO VALLEY INTO THE NORTHEAST...AND ALSO ACROSS PARTS OF THE
CENTRAL/NORTHERN HIGH PLAINS...

...SUMMARY...
Strong to locally severe storms are possible across parts of upper
Ohio Valley and Northeast this afternoon and evening. Isolated
strong to severe storms are also possible across parts of the
central and northern High Plains.

...Parts of the Ohio Valley to the Northeast...
A mid/upper-level trough is forecast to amplify as it moves across
the Great Lakes region toward the Northeast through tonight. A
surface low will move across Quebec, as a trailing cold front moves
through the eastern Great Lakes and Northeast this afternoon and
evening. The strongest deep-layer flow and large-scale ascent will
tend to lag the cold front, but some strengthening of flow in the
700-500 mb layer is expected across the warm sector this afternoon,
resulting in favorable wind profiles for organized convection.

Moderate buoyancy is expected to develop by late afternoon as CINH
weakens, and widely scattered storm development is eventually
expected along/ahead of the front. Despite the favorable wind
profiles, weak midlevel lapse rates and modest ascent may tend to
limit updraft intensity. Guidance continues to vary regarding the
magnitude of severe potential, with the 00Z HRRR/RRFS more
aggressive in developing organized convection (and possible
supercells), while other HREF guidance depicts generally weak
convection.

Localized damaging wind and isolated hail may accompany the
strongest storms. If later observational and guidance trends support
the more aggressive scenario, then greater severe probabilities may
eventually be needed.

...Central/northern High Plains...
A mid/upper-level low/trough initially over the Pacific Northwest
will move toward the northern Rockies and High Plains through the
period. Diurnal destabilization will generally be limited ahead of
this trough, though a narrow zone of moderate buoyancy may develop
by late afternoon from northeast CO into southeast WY and the NE
Panhandle. Isolated storm development will be possible, with
sufficient deep-layer shear for at least transient storm
organization and isolated severe hail/wind potential.

While any diurnal storms may tend to weaken through the evening,
elevated convection is expected to increase in coverage across
western/central SD tonight. Moderate elevated buoyancy and
sufficient effective shear could support an isolated severe threat
with the initial elevated storm development across western SD,
though storm interference and weakening buoyancy may tend to limit
the longevity and eastward extent of the threat.

...Parts of MT into northwest ND...
Increasing ascent associated with the approaching mid/upper-level
low/trough will result in elevated storm development this evening
across MT, which will spread into northwest ND overnight. Generally
weak buoyancy is currently expected to limit organized severe
potential, though small hail and locally gusty winds could accompany
the strongest storms.

..Dean/Halbert.. 09/13/2026

$$