793
ACUS01 KWNS 131246
SWODY1
SPC AC 131244

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0744 AM CDT Sun Sep 13 2026

Valid 131300Z - 141200Z

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

...SUMMARY...
Strong to locally 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.

...Ohio Valley into the Northeast...
Within large-scale upper troughing over eastern Canada, a strong
west-southwesterly mid-level jet will overspread the Great Lakes
into the OH Valley and Northeast by this evening. A surface cold
front will likewise track eastward across these regions through the
period. While a seasonably moist low-level airmass will be in place
ahead of the cold front, poor lapse rates aloft (around 6-6.5 C/km)
and cloud cover should limit the degree of destabilization that can
occur this afternoon. Still, even with the thermodynamic environment
remaining marginal, strengthening mid-level flow through the day
will support 35-45 kt of deep-layer shear and the potential for
organized convection.

Current expectations are for isolated to scattered thunderstorms to
develop along/ahead of the front by mid afternoon (around 19-22Z)
from parts of OH into western NY, and then spread quickly eastward
across the upper OH Valley into the Northeast. The deep-layer shear
will be strong enough for 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. Confidence in a corridor of greater damaging
wind potential remains too low for higher severe wind probabilities
at this time.

...Central/Northern High Plains into the Mid 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 from northeast CO into southeast WY and the NE
Panhandle in a modest low-level upslope flow regime. Isolated
thunderstorm development appears possible across this area, with
sufficient deep-layer shear for transient updraft organization and
isolated severe hail/wind potential.

While any diurnally developing convection will likely weaken through
the evening with the loss of daytime heating, elevated thunderstorms
should increase in coverage across western/central SD towards the
mid MO 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 SD, though
mergers/interactions and weakening buoyancy will likely limit the
longevity and eastward extent of this threat into the mid MO Valley.

...Long Island/Southern New England...
Bands of precipitation with embedded thunderstorms are ongoing this
morning across NJ into southern NY/New England. This activity is
being aided by ascent associated with a low-amplitude mid-level
shortwave trough. As this feature develops northeastward through the
early afternoon, continued low-level warm/moist advection will occur
across Long Island into southern New England. Most guidance
continues to show minimal surface-based instability over land, with
generally elevated thunderstorms expected. Still, given the modestly
enhanced low-level flow/shear forecast, trends will be monitored for
signs of surface-based instability/thunderstorm potential.

..Gleason/Lyons.. 09/13/2026

$$