SPC 1200Z Day 1 Outlook
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 becoming 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
become possible in the early to mid evening, as low-level
convergence becomes 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 become 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 overcome 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 become 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 become 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
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