420
ACUS01 KWNS 060543
SWODY1
SPC AC 060541

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1241 AM CDT Sun Sep 06 2026

Valid 061200Z - 071200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE SOUTHERN APPALACHIANS INTO THE SAVANNAH RIVER VALLEY AND OVER
PARTS OF WESTERN AND CENTRAL MONTANA...

...SUMMARY...
Widely scattered damaging wind gusts are likely across portions of
the Southeast Sunday afternoon and early evening. Widely scattered
large hail occurrences are expected across portions of western and
central Montana Sunday afternoon and evening. Additional areas at
risk for severe wind and hail are across parts of the Interior West,
over the northern and central High Plains, and from the eastern
Dakotas and western Minnesota into the Ozark Plateau and Gulf Coast
states.

...Synopsis...

A prominent mid-level ridge over the central U.S. is forecast to
weaken during the latter half of the period in response to the
progression of two distinct short-wave troughs and associated  wind
maxima through the Interior West. Separate, weaker perturbations
will move through the ridge axis over the northern Plains/mid-MO
Valley region on Sunday, contributing to thunderstorm development in
those areas. Elsewhere, a mid-level disturbance over the OH Valley
Sunday morning is forecast to move into the Cumberland Plateau
vicinity by afternoon, also likely serving as a focus for
thunderstorm development.

At the surface, a lee cyclone will persist over the northern High
Plains, with that feature potentially deepening Sunday night in
response to increasing height falls aloft. High pressure will build
across the Great Lakes, OH Valley, and Northeast with a baroclinic
zone present between those surface features from the mid-MO Valley
through the Ozarks and TN Valley into the Southeast.


...Southern Appalachians into the Savannah River Valley...

Temperatures in the 90s will coincide with boundary-layer dewpoints
in the 70s to yield a moderately to strongly unstable air mass
(i.e., MLCAPE of 2000-3000+ J/kg) by afternoon with steepening
low-level lapse rates. Aided by forcing attendant to the mid-level
disturbance mentioned above, that thermodynamic environment will
support an increase in thunderstorm coverage and intensity through
the afternoon along and ahead of the surface front.

Some increase in mid-level winds may accompany the disturbance with
up to 30 kt of deep-layer shear forecast in the vicinity of the
frontal zone. As such, the potential will exist for longer-lived
multi-cells and line segments capable of damaging wind gusts and
perhaps some large hail into evening.


...Ozark Plateau into the Gulf Coast States...

A similar thermodynamic environment to that previously described is
anticipated ahead of the surface front Sunday afternoon. Generally
weak forcing for ascent and vertical shear are expected to limit the
potential for a more organized severe weather threat. However, the
degree of instability will support briefly intense pulse-type storms
capable of locally damaging wet microbursts during the afternoon and
early evening hours.


...Northern Great Basin into the northern Rockies...

Increasing height falls and strengthening mid/upper-level flow will
overspread the region Sunday afternoon into night ahead of a
vigorous short-wave trough pivoting through the base of the Pacific
Northwest upper low. The strongest instability (i.e., MLCAPE up to
1000-1500 J/kg) is forecast across portions of western into central
MT with stronger capping with eastward extent. The presence of 40-50
kt of deep-layer shear will support supercells capable of mainly
large hail through Sunday evening. While forecast hodographs exhibit
considerable curvature/veering winds in the lowest 1-2-km AGL,
stability concerns in the boundary layer may limit severe-wind-gust
and tornado potential.

Weaker instability is forecast from northeast NV and northern UT
into central and eastern ID. However, the presence of steep lapse
rates and kinematics mentioned above may yield a few severe storms
capable of severe wind gusts.


...Northern and central High Plains...

Stronger forcing for ascent is expected to remain to the west and
east of the region through the daylight hours, leading to
uncertainty in storm coverage in the vicinity of the surface low and
lee trough. The 00Z models indicate an increasing potential for at
least isolated thunderstorms from mid-afternoon into evening along
the lee trough. RAP-based forecast soundings show steep lapse rates
and resulting MLCAPE of 1000-2000+ J/kg. The strongest deep-layer
shear of 40-50 kt is forecast across eastern MT into ND with
decreasing magnitudes with southward extent along the lee trough. As
such, a conditional risk for supercells capable of large hail and
severe wind gusts exists. While Marginal Risk wind and hail
probabilities will be maintained with this forecast, an upgrade to
level 2/Slight Risk is possible in subsequent updates.


...Eastern Dakotas and western Minnesota into the lower Missouri
Valley...

Clusters of mainly elevated thunderstorms may be ongoing at 12Z
Sunday, aided by forcing associated with the weak disturbance(s)
cresting the mid-level ridge axis. A subset of the early-day storms
is expected to persist into afternoon with additional storms forming
on the leading edge of more persistent cloud cover, where pockets of
stronger heating and boundary-layer dewpoints in the low/mid 70s
will yield MLCAPE of 1500-2500 J/kg. The 00Z models suggest that
storms will eventually grow upscale into an MCS that tracks south
along or to the immediate cool side of the surface boundary through
portions of the middle and lower MO Valley Sunday afternoon into
evening. It currently appears that  deep-layer shear of generally
less than 30 kt and marginally steep mid-level lapse rates may limit
the degree of cold pool organization and a greater/more continuous
damaging-wind threat. Nonetheless, the setup appears supportive of
sporadic damaging wind and severe hail occurrences.

..Mead/Chalmers.. 09/06/2026

$$