Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0726 AM CDT Fri Sep 11 2026
Valid 111300Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MIDWEST...
...SUMMARY...
Scattered severe thunderstorms capable of producing large hail,
(some 2+ inches), damaging winds, and a couple of tornadoes should
occur late this afternoon into tonight across parts of the Upper
Midwest. Thunderstorm development is more uncertain farther south
into the central Plains, where a conditional risk for large hail and
severe gusts will exist late this afternoon into the evening.
...Upper Midwest into the Central Plains...
Primary large-scale upper troughing will remain over central Canada
today, with an embedded mid-level shortwave trough forecast to eject
eastward over the northern Plains into the Upper Midwest through the
period. A modest surface response will occur across SD as the
shortwave trough ejects eastward, with most guidance suggesting a
sub-1000 mb low will develop into eastern SD by 12/00Z. A surface
cold front attendant to this low and the primary surface low over
central Canada will move east-southeastward across parts of the
Upper Midwest into the northern Plains, with a dryline extending
southward across the central Plains. A narrow corridor of 60s
surface dewpoints will be in place ahead of the cold front/dryline,
with diurnal heating aiding moderate destabilization along with
steepened mid-level lapse rates. Most guidance, including recent
NAM/RAP runs, show minimal MLCIN along/ahead of the front in far
northeast SD/western MN by 22-01Z. Convective development appears
likely in this time frame across this region, owing to sufficient
low-level convergence along the front coupled with forcing for
ascent associated with the mid-level shortwave trough.
Various NAM/RAP forecast soundings show strongly veering and
gradually strengthening winds with height through low/midlevels, and
35-45 kt of deep-layer shear will easily support organized
convection. Initial supercells should pose a threat for large hail
(isolated 2+ inches possible), but convective mode will probably
trend towards clustering fairly quickly given the presence of the
cold front and strengthening low-level jet this evening. Any
supercells that can remain at least semi-discrete into the early
evening may also have a tornado threat with greater low-level shear
forecast in this time frame. But, confidence in this scenario
occurring remains fairly low due to the mode transition expected.
Scattered severe/damaging winds should occur with any clusters or
bowing line segments that can develop and spread eastward through
the evening. However, the wind threat will likely wane with eastward
extent across MN into western WI by late this evening given the
narrow zone of destabilization forecast.
Convective initiation and overall thunderstorm coverage from
southeast SD/southwest MN into the central Plains are highly
uncertain and conditional this afternoon/evening, as the better
forcing for ascent with the shortwave trough will likely remain
across western/northern MN along and northeast of the surface low.
Still, a favorable thermodynamic environment and sufficient (25-35
kt) deep-layer shear would conditionally support severe hail/wind
with any thunderstorms that can develop and be sustained. There is
some signal in model guidance for successful convective initiation
across southern NE into northern KS late this afternoon/evening
where hotter surface temperatures are forecast. The southern extent
of the Marginal Risk has been adjusted to account for this
possibility, and the Slight Risk has generally been confined to
where greater confidence exists in robust thunderstorm development
(far northeast SD into western/northern MN).
...Mid-South into the Tennessee Valley/Carolinas and Virginia...
Two weak mid-level perturbations are evident in water vapor
satellite imagery this morning across the Southeast: one over AR,
and the other along the central Gulf Coast. These features will
generally track east-northeastward through the day, and should aid
additional thunderstorm development this afternoon. A stalled
surface front extending from the ArkLaTex into the TN Valley and
northeastward to VA should also provide a focus for thunderstorms.
Current expectations are for generally disorganized/pulse-type
convection to pose a threat for occasional damaging winds as diurnal
heating destabilizes the boundary layer and steepens low-level lapse
rates. But, modestly enhanced mid-level flow across parts of the
Mid-South and VA could promote loosely organized clusters with some
damaging wind threat as well.
..Gleason/Lyons.. 09/11/2026
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