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Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1256 AM CDT Fri May 20 2022

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL ILLINOIS AND NORTHERN INDIANA...

...SUMMARY...
A wind-damage and isolated large-hail threat is expected from late
Saturday afternoon into early evening over parts of central Illinois
and northern Indiana. A marginal hail and wind-damage threat will
also be possible Saturday afternoon over parts of the southern
Plains, Ozarks, lower Ohio Valley, lower Great Lakes and Northeast.

...Central Illinois to Northern Indiana...
An upper-level trough will move northeastward across the
north-central U.S. on Saturday, as southwest mid-level flow remains
from the central Plains to the Great Lakes. At the surface, a cold
front will advance southward across the mid Mississippi Valley and
southern Great Lakes. By 21Z, the front is forecast to be positioned
from near Springfield, Missouri northeastward to just south of
Chicago. South of the front, surface dewpoints in the upper 60s and
lower 70s F will result in strong instability by afternoon.
Thunderstorm development is expected along and to the north of the
front during the late afternoon. Although individual cells will move
east-northeastward, organized line segments will tend to move in an
east or east-southeasterly direction. Multiple line segments are
forecast to develop in the late afternoon and persist into the early
evening from parts of the mid Mississippi Valley northeastward into
the southern Great Lakes.

The strongest destabilization is forecast to take place from central
Illinois into north-central Indiana, where the models suggest MLCAPE
could reach the 3000 to 3500 J/kg range. RAP forecast soundings late
Saturday afternoon along the instability corridor have 0-6 km shear
in the 30 to 35 knot range. 700-500 mb lapse rates are forecast to
exceed 8.0 C/km, indicating isolated large hail may occur with the
stronger updrafts. Low-level lapse rates are also forecast to be
steep ahead of the front, suggesting a wind-damage threat will also
be possible. The severe threat will be most likely with storms that
can move off the boundary and into the unstable airmass. The severe
threat should concentrated between 22Z and 01Z when the low-level
jet is forecast to strengthen across the mid Mississippi Valley.

...Southern Plains/Ozarks...
An upper-level trough will move eastward across the central High
Plains on Saturday, as a cold front advances southeastward across
the southern Plains and Ozarks. Strong destabilization is expected
to the south of the front by afternoon, where MLCAPE could reach the
3000 to 4000 J/kg range. Although large-scale ascent is forecast to
be weak, low-level convergence along the front will be enough for
isolated to scattered thunderstorm development. Although an isolated
severe threat is forecast during the late afternoon, convective
development is expected to be tied to the front. This should keep
the storms relatively close to the boundary where instability will
be considerably less. For this reason, any potential for strong wind
gusts and hail will likely remain marginal.

...Lower Great Lakes/Northeast...
Southwest mid-level flow will remain in place across the
northeastern U.S. on Saturday, as a subtle shortwave ridge moves
northeastward into southeastern Canada. At the surface, a cold front
will advance southeastward into the lower Great Lakes. A moist
airmass will be in place ahead of the front with surface dewpoints
in the 60s F. In response, moderate instability will be in place by
afternoon. Isolated thunderstorm development is forecast along the
front during the afternoon. These storms will move eastward, having
trouble getting off the boundary and into the stronger instability.
For this reason, any severe threat is expected to be isolated.
Veered winds at low levels and steep low-level lapse rates will be
favorable for marginally severe wind gusts. Hail could also occur
with the stronger updrafts.

..Broyles.. 05/20/2022