RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Tue Apr 21 12:42:02 UTC 2026.
No Mesoscale Discussions are in effect as of Tue Apr 21 12:42:02 UTC 2026.
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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Day 4-8 Outlook
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Tue Apr 21 2026
Valid 241200Z - 291200Z
...DISCUSSION...
... An active severe weather pattern is expected through much of the
forecast period ...
Broadly cyclonic midlevel flow will persist through much of the
forecast period to the south of a closed upper low over
south-central Canada. This will place much of the Southern Plains in
westerly or southwesterly mid- and upper-level flow each day. At the
same time low-level pattern will support southerly flow from the
surface up through 850 mb across the same region. The result will be
an increasingly moist airmass to the east of a north-south dryline
across western Oklahoma and Kansas, and to the south of a remnant
west-to-east frontal boundary.
Diurnal heating of this moist airmass will result in afternoon
MUCAPE values around 2000-3000 J/kg Friday and Saturday beneath
30-40 knots of vertical shear. Model guidance continues to show
several perturbations within the midlevel flow traversing the
Southern Plains on Friday into Sunday morning. The result will be
multiple rounds of severe thunderstorms. The exact location and
dimensions of these daily severe threats will likely be augmented by
the prior days' convection, but the overall pattern supports near
daily severe potential across much of the Southern Plains.
On Sunday (Day 6) a stronger, yet compact, midlevel wave is forecast
to move northeast across Oklahoma. This wave is forecast to induce
cyclogenesis across western Oklahoma, which should act to sharpen a
dryline. To the east of the dryline, strong southerly winds will
support surface dewpoints increasing into the upper 60Fs to perhaps
low 70Fs. Diurnal heating of this airmass will result in MUCAPE
values nearing 4000 J/kg across central Oklahoma. Deep-layer shear
approaching 50 knots will overspread the region during the afternoon
as the main wave approaches. Although global models are struggling
to initiate convection along the dryline, pattern recognition would
support a significant severe weather threat Sunday evening. The lack
of model convective initiation results in enough uncertainty to
preclude the introduction of 30% unconditional severe probabilities.
All severe hazards will be possible on Sunday.
The severe threat will continue into Monday/Day-7 as the midlevel
low and surface cyclone translate east into the lower Mississippi
Valley. The severe threat may continue into Tuesday/Day-8 across
portions of the Southeast US, although numerous days of preceding
convection should use up the steep lapse rate reservoir to the west
resulting in too much uncertainty to introduce unconditional severe
probabilities at this time.
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