Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1051 AM CDT Tue Apr 21 2026
Valid 211630Z - 221200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
OVER THE CA CENTRAL VALLEY...AND OVER PORTIONS OF NORTHERN IL/IN...
...SUMMARY...
Isolated strong thunderstorms are possible in the California Central
Valley, capable of gusty winds and perhaps a tornado or two. Other
strong storms are possible in parts of northern IN/IL where gusty
winds may occur.
...Central CA...
Morning water vapor loop shows a well-defined shortwave trough
approaching the coast of central CA. An associated mid/upper level
jet will nose into CA, with forcing for ascent in the left-front
quadrant of the jet aiding in the development of afternoon/evening
thunderstorms over parts of the Central Valley. Forecast soundings
show steep low and mid level lapse rates and sufficient CAPE for a
few robust updrafts. Vertical shear will be strong enough for
supercell structures, including a risk of a tornado or two, small
hail, and gusty winds.
...Northern IN/IL...
A fast-moving shortwave trough currently over IA/MN will track
quickly southeastward into WI/IL/IN this afternoon. Visible
satellite and radar imagery show a line of high-based thunderstorms
developing ahead of the trough over southern WI. As these storms
track into northern IL/IN, continued heating/weak destabilization
will increase the risk of gusty/locally damaging wind gusts and
small hail in the strongest cores this afternoon.
..Hart/Flournoy.. 04/21/2026
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