Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1252 AM CDT Mon Jul 27 2026

Valid 271200Z - 281200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF THE UPPER MIDWEST/UPPER GREAT LAKES INTO THE OHIO VALLEY...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
SOUTHWEST SOUTH DAKOTA...WESTERN NEBRASKA...NORTHEAST COLORADO...AND
FAR NORTHWEST KANSAS...

...SUMMARY...
Severe storms capable of strong to severe wind gusts and large hail
are possible across the Great Lakes into the Ohio Valley Monday into
Monday night. More sporadic occurrences of damaging wind appear
possible in the Mid-Atlantic, Tennessee Valley, central High Plains,
and southeast Arizona.

...Upper Midwest/Great Lakes into the OH/TN Valleys...
A very moist airmass is in place from the Upper Midwest into the OH
and TN Valley. This airmass is exists south of a diffuse cold front
that extends from a surface low over far southeast Manitoba
southeastward to far eastern Upper MI. One thunderstorm is currently
ongoing near this boundary over eastern Upper MI. Most of the
thunderstorms are ongoing just northeast another surface boundary
demarcating the very moist (i.e. 70+ dewpoints) to it southwest. How
this warm-air advection activity evolves early this morning will
have a large impact on the severe potential farther downstream from
the Mid MS Valley into the OH and TN Valleys through the late
morning into the afternoon and evening. 

Much of the guidance is beginning to suggest the warm-air advection
activity clusters early this morning over the MN Arrowhead vicinity
before then tracking southeastward within the moisture/buoyancy
gradient and organizing/intensifying significantly. Synoptically,
the overall setup matches many characteristics of scenarios with
strong, forward-propagating MCSs, including a surface boundary
parallel to the deep-layer shear, at least modest mid-level warm
advection, and very strong to extreme buoyancy. Given the trend
within the guidance and favorable synoptics, confidence in the
development of a strong forward-propagating MCS is high enough to
adjust the 30% wind probabilities westward while also introducing a
CIG1 area. There is a chance that both higher wind probabilities and
a CIG2 may be needed, but predictability regarding convective
evolution is too low at this time.  

...Central High Plains into western/central NE and SD...
Moist, post-frontal surface flow is expected across much of NE and
SD, shifting from northerly early in the day to more easterly by the
afternoon. Dewpoints will initially be in the mid to upper 70s,
although strong boundary-layer mixing will likely result in
dewpoints ranging from the upper 50s/low 60s across the NE Panhandle
to the low 70s across eastern NE. This reservoir of low-level
moisture coupled with strong heating and steep mid-level lapse rates
will result in a corridor of moderate to extreme buoyancy from
eastern WY/northeast CO/southwest SD eastward across south-central
SD and much of NE.

Most of the guidance indicates a subtle, convectively augmented
vorticity maximum will progress eastward through the northern
periphery of the Four Corner upper ridge. This should contribute to
thunderstorm development across the high terrain, which would then
progress downstream into a more moist and unstable airmass. One or
more clusters could evolve, but the overall predictability of the
convective evolution is low. That being said, environmental
conditions support the potential for strong to severe gusts,
including the potential for some over 75 mph. Eastern extent of the
wind threat will likely be limited by building convective inhibition
associated with nocturnal cool, unless a  more coherent and
organized MCS were to evolve. If that occurs, the wind threat could
extend farther east into more of eastern NE and north-central KS,
and 5% wind probabilities were expanded eastward/southeastward to
account for this potential. 

Depending on the strength of the MCS, the wind threat could extend
eastward into more of OH and PA, and also farther southward into
more of TN, during the late afternoon/evening. 

...Mid-Atlantic States...
Some wind threat could exist during the afternoon/evening across the
Mid-Atlantic, where marginal buoyancy and deep-layer shear could
support a few stronger updrafts.  

...Southeast Arizona...
Isolated severe gusts are possible over southeast AZ as mid-level
moisture and daytime heating leads to scattered storms over
the higher terrain, particularly far southeast AZ. Cells are
expected to move westward into warmer temperatures and deeper
boundary-layer mixing, with PWAT over 1.25" and steep low-level
lapse rates supporting strong outflows.

..Mosier/Squitieri.. 07/27/2026