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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1250 AM CDT Thu Apr 21 2022

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN AND CENTRAL PLAINS...

...SUMMARY...
A severe threat is expected to develop across parts of the southern
and central Plains this evening. Large hail, along with an isolated
tornado threat will be possible. A marginal severe threat may also
develop across parts of the lower to mid Missouri Valley.

...Southern and Central Plains...
A shortwave ridge will move east-northeastward across the central
Plains today, with southwest mid-level flow beco*ing established in
the wake of the ridge. At the surface, a warm front will advance
northward into southern Kansas with a dryline in place from the
eastern Texas Panhandle into northwest Oklahoma. To the east of the
dryline and to the south of the warm front, a moist and unstable
airmass will be in place. Surface dewpoints are expected to increase
into the into the lower to mid 60s F by late afternoon. This will
yield MLCAPE in the 1200 to 2000 J/kg range by late afternoon.
However, a capping inversion will likely prevent convective
initiation during the day. Isolated thunderstorm development will
beco*e possible in the early to mid evening, as low-level
convergence beco*es enhanced along the warm front, and as the
low-level jet strengthens. Isolated thunderstorm development could
take place across northern Oklahoma, central and eastern Kansas and
far southeast Nebraska.

Concerning the severe potential, moderate deep-layer shear will
exist across much of the southern and central Plains, where 0-6 km
shear is forecast to be in the 30 to 40 knot range. A plume of steep
mid-level lapse rates will also be in place from the Texas Panhandle
northeastward into southern Kansas. Storms that initiate in the
stronger instability and near the plume of steep mid-level lapse
will likely beco*e supercellular and produce large hail. The
low-level jet will markedly increase low-level shear during the
evening, which could result in an isolated tornado threat with any
supercell that can overco*e the cap. There is conditionality with
this forecast, due to a lack of large-scale ascent. As a result,
only two or three surface-based thunderstorms are expected to
develop in the central Plains, but the severe potential will be
considerable with any updraft that can beco*e rooted in the boundary
layer.

...Lower to Mid Missouri Valley...
Westerly mid-level flow will be in place today from the lower
Missouri Valley eastward into the mid Mississippi Valley. A
shortwave ridge will approach from the west, as moisture advection
takes place across the central Plains and lower Missouri Valley. The
nose of the low-level jet is expected to beco*e focused across
northeast Kansas and southeast Nebraska by early this evening. As a
result, warm advection-related thunderstorm development is expected
along the eastern edge of the low-level jet, from eastern Nebraska
into western Iowa. Although instability will be weak this evening in
most of the lower to mid Missouri Valley, strong deep-layer shear
will be in place. RAP forecast soundings south of Omaha have
effective shear in the 50 to 55 knot range, with 700-500 mb lapse
rates approaching 7.5 C/km. This environment will support a hail
threat with elevated storms that can develop in the weakly forced
environment. The hail threat could affect areas further to the
northeast across south-central Iowa and northeast Missouri as a
cluster of storms moves northeastward during the mid to late
evening.

..Broyles/Weinman.. 04/21/2022