Going all in. If it happens I’ll start the first winter storm thread of the season. Potential for a destructive windbag/derecho Monday. SPC outlining a large Enhanced Risk area with SIG1 hatching. Potential upgrade to CIG2.
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.