Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0102 AM CDT Mon Jul 20 2026
Valid 201200Z - 211200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE UPPER MIDWEST AND GREAT LAKES...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTH
CAROLINA AND FAR SOUTHERN VIRGINIA...
...SUMMARY...
Severe thunderstorms are expected across portions of the Upper
Midwest and Great Lakes vicinity, especially late this afternoon and
tonight. Swaths of damaging winds, large hail, and a few tornadoes
will all be possible. Isolated damaging wind gusts may also occur
over parts of the Carolinas and southern Virginia.
...Upper Midwest/Great Lakes...
A potentially active severe-weather scenario is expected later today
into tonight, although some key uncertainties persist related to the
potential impacts of early day convection and associated cloud
debris.
A substantial shortwave trough over southern Manitoba will continue
to gradually amplify and spread southeastward to the Lake Superior
vicinity through tonight, with a strengthening belt of
mid/high-level west-northwesterly flow overspreading the Upper
Midwest toward the Lake Michigan vicinity, highlighted by 50-70 kt
mid-level winds and 100 kt winds in the upper levels across
Minnesota/Wisconsin. An east/southeastward-advecting plume of steep
mid-level lapse rates will overspread a warm sector with upper 60s
to lower/middle 70s F dewpoints.
Initially, a few early day storms could produce hail and perhaps
some strong wind gusts across east/southeast Minnesota into western
Wisconsin and eastern Iowa, amidst ample elevated instability and
effective shear over 50 kt. This activity may continue to spread
southeastward this morning but tend to wane during the day, leading
to a potential regional break prior to additional/more vigorous
development by late afternoon along the cold front as it progresses
east-southeastward toward Wisconsin/Upper Michigan and
northern/eastern Iowa.
The initial storms should primarily be supercells given such strong
deep-layer shear. A corridor of large hail and tornado risk is
evident east of the instability axis from Iowa across Wisconsin into
Upper MI. Even while near-surface winds may tend to veer with time,
effective SRH may exceed 300 m2/s2, especially across Wisconsin
toward Upper Michigan as supported by the seasonally very-strong 2-3
km AGL winds (700 mb winds in excess of 50 kt). The degree of SRH
could support a couple strong tornadoes (EF2+), and somewhat higher
tornado probabilities could be warranted in subsequent outlooks as
early day convection details are resolved. While supercells will
persist for a time, several storm clusters will evolve this evening,
with a continued damaging wind and some tornado risk persisting
southeastward this evening prior to storm intensity eventually
waning overnight.
...Carolinas and southern Virginia...
Convection and related cloud debris may persist early today, but a
moist air mass will again diurnally destabilize this afternoon along
and south of a roughly west/east-oriented front. Daytime heating,
70s F dewpoints and surface convergence will aid storm formation and
intensification this afternoon. MLCAPE in excess of 2000 J/kg, PWAT
over 2.00", and mid-level westerly flow aloft of 15-20 kt will lead
to multicellular storm mode with isolated damaging wind gusts during
the afternoon until around sunset.
...Florida...
Tropical Depression Two may gradually strengthen across the
northeast Gulf of America today and tonight. Reference the National
Hurricane Center for the latest development/forecast details. While
various global models support the notion of a strengthening of
southerly winds in the lowest 2-3km AGL, especially across the
western Florida Peninsula, it currently appears that
supercell-related tornado potential should remain low, largely
attributable to the overall weakness of the Depression and weak wind
aloft.
..Guyer/Weinman.. 07/20/2026
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