Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1226 AM CDT Fri Sep 11 2026
Valid 111200Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE UPPER
MISSISSIPPI VALLEY INTO THE MID MISSOURI VALLEY...
...SUMMARY...
Scattered severe thunderstorms capable of large hail, potentially in
excess of two inches, a few tornadoes, and damaging wind gusts are
expected over portions of the upper Mississippi Valley Friday
afternoon into night. Storm development is more uncertain with
southward extent into the central Plains, where a conditional risk
for mainly large hail and severe wind gusts exists late Friday
afternoon through evening. Isolated occurrences of damaging wind
gusts appear possible from the Mid-South into the Carolinas and
Virginia.
...Synopsis...
A low-amplitude short-wave trough moving onto the Pacific Northwest
coast late this evening will progress through the northern Rockies
before reaching the ND/SK/MB border region by Friday evening.
Meanwhile, a preceding, lower-latitude disturbance is forecast to
move through SD into MN on Friday with strengthening mid/upper-level
winds and modest height falls accompanying these perturbations over
the northern Plains into the upper MS Valley. Elsewhere, a vorticity
maximum/weak upper low will drift east from the Ozark Plateau into
the mid/lower MS Valley.
At the surface, an area of low pressure over western SD at 12Z
Friday is forecast to deepen slightly while developing into
northeast SD by afternoon, before subsequently weakening while
moving through central MN Friday night. The surface cyclone will
coincide with a cold front that will advance through the northern
Plains and the upper MS Valley. The trailing extension of the
boundary will move more slowly south into the mid MO Valley and
central High Plains. A dryline will precede the cold front with that
feature extending from eastern SD through central NE into western KS
by late afternoon. Elsewhere, a synoptic front modulated by
convective outflow is expected to stretch from the Mid-South into
the southern Mid-Atlantic on Friday afternoon.
...Upper Mississippi Valley into the mid Missouri Valley...
A low-level jet (LLJ) is forecast to strengthen through the day from
the mid MO Valley into the upper Midwest, enhancing the poleward
flux of an increasingly moist air mass ahead of the surface low and
attending frontal system. The moisture increase will occur beneath a
plume of steep mid-level lapse rates with MLCAPE increasing to
1500-2500+ J/kg by mid to late afternoon. Initial storm development
is expected at that time across portions of northern MN along or
ahead of the front, on the northern fringe of stronger capping.
Vertically veering wind profiles with 40-45 kt of deep-layer shear
will support supercells as the initial storm mode with the primary
hazard being large hail, some of which could exceed two inches. A
few tornadoes appear possible with any sustained supercells from
late afternoon into evening when the strengthening LLJ enhances
low-level shear with effective SRH increasing to 250-300 m2/s2.
Storms are expected to gradually grow upscale along the cold front
during the evening, at which point, the risk for damaging winds
should increase.
Severe weather potential becomes more conditional with southward
extent along the front and dryline in the mid MO Valley owing to
stronger capping and weaker height falls/forcing for ascent. The 00Z
models (convection-allowing and parameterized) indicate a relative
minimum in thunderstorm chances over eastern SD and southwest MN
with increasing probabilities from northeast NE into south-central
NE and north-central KS. Given surface-based storm initiation and
sustenance, CAPE-shear parameter space will favor supercells capable
of all hazards from eastern SD and southwest MN into northeast NE
and northwest IA, with generally a wind and hail threat farther
south along the NE-KS state line.
...Mid-South into the Carolinas and Virginia...
Areas of thunderstorms are expected to be ongoing at 12Z Friday from
the Ozark Plateau into the southern Mid-Atlantic. Stronger heating
on the southern fringe any lingering cloud cover will combine with
boundary-layer dewpoints in the low to mid 70s F to yield MLCAPE of
1500-3000 J/kg by afternoon. Aided by forcing for ascent associated
with the mid-level trough approaching the mid/lower MS Valley,
thunderstorms are expected to increase in coverage and intensity
through the afternoon along and ahead of the composite surface
boundary. Weak vertical shear will limit storm organization with
mainly pulse storms expected. Nonetheless, the presence steep
low-level lapse rates and abundant moisture will be supportive of
wet microbursts capable of locally damaging wind gusts.
..Mead/Halbert.. 09/11/2026
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