Valid 141630Z – 151200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE
CENTRAL/NORTHERN HIGH PLAINS…
…SUMMARY…
Scattered severe thunderstorms with very large hail, a couple
tornadoes, and damaging winds are possible across parts of the
central and northern High Plains from late afternoon into tonight.
…Northern/central High Plains…
Confidence in storm coverage and initiation corridors are lower
today compared to yesterday. Surface dew points are drier this
morning with 50s prevalent to low 60s in KS in the wake of
yesterday’s convective overturning. Nevertheless, persistent
mid-level west-northwesterlies will maintain very steep lapse rates
atop the residual boundary-layer moisture and should yield a plume
of MLCAPE from 1500-2500 J/kg at peak heating from the Black
Hills/eastern WY south across far eastern CO/western KS.
Forcing for ascent will be rather weak near the higher terrain and
southerly low-level flow dominates eastern CO at present. Convective
initiation should be delayed until late afternoon and may be sparse
in the central High Plains, with storm coverage beyond a cell or two
highly questionable within the corridor most favorable for
supercells. Still, effective bulk shear of 40-50 kt with relatively
straight hodographs will support the risk of a couple supercells
capable of producing isolated very large hail. The tornado threat
will likely depend on a discrete cell interacting with the somewhat
greater low-level shear/hodograph curvature expected near the
CO/KS/NE border area along the east edge of the greater buoyancy.
Somewhat greater confidence in convective initiation is across
southeast MT/northeast WY owing to peripheral influence of a minor
shortwave trough approaching from the Canadian Rockies. Isolated to
perhaps scattered storms should develop along the northern extent of
the buoyancy plume. There is some signal for upscale growth into a
small, increasingly elevated MCS downstream across portions of
western SD/NE tonight as a 25-35 kt nocturnal low-level jet develops
across the Panhandles to southwest NE. Isolated severe wind and hail
will remain possible into the early overnight.
…Central Gulf Coast to the Mid-Atlantic…
The effective surface boundary, modulated by convective outflow,
will continue to sag southward toward the Central Gulf Coast and
southeastward toward the South/Mid-Atlantic coasts. The richer
moisture (PW greater than 2 inches) and large buoyancy (MLCAPE of
2500-3500 J/kg) should be confined to the eastern Carolinas
southwestward into the central Gulf Coast. Vertical shear will be
very weak and boundary/storm mergers will largely drive isolated
downburst potential. Somewhat stronger deep-layer shear is expected
farther north toward Chesapeake Bay, which could compensate some for
the weaker buoyancy and poor mid-level lapse rates.
…Northern IN vicinity…
A diffuse surface front will provide a focus for thunderstorm
development this afternoon, as a minor mid-level impulse approaches
from southern WI. Lingering low-level moisture and surface heating
will support MLCAPE of 1000-1500 J/kg, while deep-layer vertical
shear will be at least marginally favorable for a couple
organized/supercell storms. Very weak low-level flow will greatly
limit hodograph size/SRH magnitude, but there will be modest
vertical vorticity along the surface boundary. A couple of storms
with hail/wind near severe criteria and a brief tornado are all
possible.
..Grams/Leitman.. 08/14/2019
$$