Day 1 Severe Weather Outlook

Valid 181200Z – 191200Z


Scattered severe thunderstorms are expected late this afternoon and
evening with a severe risk continuing into the overnight across
parts of the southern and central Plains. Severe gusts, large hail,
and a few tornadoes are possible.

A large-scale mid to upper-level trough over the West will pivot
east towards the central U.S., as a mid-level low/trough moves east
and northeast through the base of the larger-scale feature and into
the central High Plains by daybreak Thursday. Farther east, a
mid-level disturbance will move from the lower MO Valley into the OH
Valley/southern Great Lakes during the day. In the low levels, a
surface low will deepen over the central High Plains while a lee
trough/dryline extends southward into the southern High Plains
during the late afternoon. A warm front will advance northward into
the central Great Plains/lower OH Valley.

…Southern Great Plains…
Southerly low-level flow will transport moisture northward into
parts of northwest TX and OK/KS during the day. Models indicate
lower to mid 60s F surface dewpoints and heating will contribute to
1000-2500 J/kg MLCAPE by mid-late afternoon across parts of west and
northwest TX near the dryline. A lead disturbance is forecast to
arrive in the Permian Basin as early as 21z with thunderstorm
development along the dryline expected by mid-late afternoon. Steep
low to mid-level lapse rates and strong mid to high-level flow
(effective shear 50-60 kt), which will move into west TX by early
evening, will support supercells as an initial storm mode. Large to
very large hail may accompany storms early in their convective life
cycle along with a supercell-tornado risk possibly developing. This
tornado risk will likely focus near the Caprock and the Low Rolling
Plains during the late afternoon/early evening.

Flow fields are forecast to intensify through the evening and into
the overnight as a southerly LLJ centered over north TX shifts
northward into OK and strengthens to 65 kt by late tonight.
Concurrent with this LLJ intensification, 700-500mb flow will
markedly increase across north TX into OK. This overall scenario
favors upscale growth during the evening across the TX Big Country
with a squall line moving into parts of western north-central TX and
OK during the overnight. Convection-allowing models are in
reasonable agreement regarding this scenario. Despite some
boundary-layer cooling during the evening, the risk for severe gusts
will probably increase during the evening into the overnight with a
risk for mesovortex tornadoes. A gradual weakening in the squall
line is expected as it reaches the eastern OK vicinity early
Thursday morning.

…Lower Ohio Valley Vicinity…
Ongoing showers/thunderstorms are forecast over MO and the lower OH
Valley during the morning in conjunction with strong low-level warm
air advection on the nose of a 50 kt LLJ. Uncertainty remains
regarding the extent of severe potential across the Lower OH Valley
vicinity. Forcing associated with this feature in conjunction with
40 kt of 850-700 mb southwesterly flow could support organized
cells/bowing segments. The main limiting factors will be generally
weak instability and poor midlevel lapse rates, but enough potential
exists given the expected strong shear parameters with some isolated
strong/severe possible.

..Smith/Bentley.. 03/18/2020


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