RSS Mesoscale Discussions from Storm Prediction Center
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0739 AM CDT Tue Apr 21 2026
Valid 211300Z - 221200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Organized severe thunderstorms are not currently forecast across the
contiguous United States through tonight.
...IL/IN...
Morning water-vapor imagery shows a subtle disturbance over the mid
MO Valley, which is forecast to quickly move southeast into the
southern Great Lakes by early evening. An associated surface trough
is forecast to develop from Lower MI into southern WI and northern
IL by late afternoon. Despite modest moisture (upper 40s to mid 50s
deg F surface dewpoints) returning northward into the Cornbelt, cold
mid-level temperatures (around -16 to -18 deg C at 500 mb) per
forecast soundings and heating will yield weak instability by
mid-late afternoon. Models continue to show isolated to scattered
storms late today into the evening. It remains uncertain whether a
couple of stronger cells will yield a threat of hail beyond a risk
for small hail. This activity will likely diminish by mid-late
evening as it moves southeast into central portions of IL/IN.
...Central CA...
Strong cyclonic flow associated with a mid-level low and associated
trough will move across central CA into the Great Basin during the
period. Cold temperatures aloft north of the midlevel jet will
support weak instability over parts of the central valleys. Given
early precipitation and clouds, as well as marginal low-level shear,
severe storms appear unlikely. However, a few strong storms may
occur late in the afternoon if sufficient heating occurs behind the
early day rain. Small hail appears most probable with the strongest
cells.
..Smith/Thompson.. 04/21/2026
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