Sharpy
Member
Quite a few days marked with yellow blobs this far out by SPC. Seemingly active period looming ahead - let’s get into the details:
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.
..Marsh.. 04/21/2026
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.
..Marsh.. 04/21/2026
