SPC AC 011937
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0237 PM CDT Sun Aug 01 2021
Valid 012000Z - 021200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON ACROSS PARTS OF THE CAROLINA COASTAL PLAIN...
Thunderstorm activity may continue to develop and organize across
the North Carolina coastal plain late this afternoon and pose a
risk for damaging wind gusts.
...20Z Outlook Update...
Adjustments have been made to the categorical and probabilistic
outlook lines, mostly to the account for the progression of a number
of synoptic and sub-synoptic perturbations and associated surface
Seasonably modest low-level moisture and boundary-layer warming are
limiting destabilization across the Northeast, as a vigorous short
wave trough gradually begins to turn east of the lower Great Lakes
region. However, there does still appear at least a window of
opportunity for some intensification of ongoing convective
development late this afternoon and evening, particularly across
parts of southwestern into central Pennsylvania, as a 50 kt 500 mb
jet streak propagates eastward out of central Ohio.
Across Texas, vigorous thunderstorm development is ongoing along a
weak southward advancing outflow boundary across the Edwards Plateau
and Hill Country vicinity. However, this is far removed from even
the weak to modest (10-20 kt) west-northwesterly mid-level flow on
the southern fringe of upper troughing across the Ark-La-Tex
vicinity into the Gulf Coast states. With thermodynamic profiles
not much, if any, more conducive to downburst potential, severe
weather probabilities appear comparatively weaker, and generally
less than 5 percent.
.PREV DISCUSSION... /ISSUED 1120 AM CDT Sun Aug 01 2021/
A few supercells have evolved into a small cluster along the surface
front across northeast NC. Additional convective development is
expected farther southwest near the surface cyclone across central
NC. Air mass ahead of the front/cyclone continues to destabilize in
the presence of mid to upper 70s surface dew points. While low-level
SRH should remain modest, slightly backed surface winds across far
eastern NC may support the threat for a tornado or two. The primary
hazard will likely be scattered damaging winds as the upstream
convection develops and evolves into an eastward-moving cluster
across eastern NC through this afternoon.
Lower-topped thunderstorms have developed along and just ahead of an
eastward-progressing cold front in the lee of the Lower Great Lakes.
More pronounced boundary-layer heating is underway across western to
northeast PA into southeast/east-central NY, which should aid in
some intensification of convection this afternoon. However,
boundary-layer temperatures and dew points will be seasonally subpar
with the bulk of destabilization occurring through steepening of
mid-level lapse rates with approach of the shortwave trough. In
addition, lower-level flow will remain relatively modest with faster
mid-level flow largely confined to the upper portion of the weak
buoyancy profile. As such, convection may struggle to become
substantially deep and organized, which may result in only sporadic
bouts of damaging winds and isolated marginally severe hail.
Scattered thunderstorms are expected along a trailing cold front
that will slowly slide south across the region this afternoon. Weak
deep-layer shear but large buoyancy will favor pulse to loosely
organized multicells. Wet microbursts capable of producing locally
damaging wind gusts will be the main hazard.
In what is otherwise a weak meridional flow pattern across the West,
a pair of MCVs, one over southeast NV and the other near the
OR/ID/WA border area, may help focus weakly organized severe
potential this afternoon. Relatively high PW values along with steep
low-level lapse rates will support a threat for microbursts capable
of isolated severe gusts.
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