Valid 131300Z – 141200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
ACROSS VA…AND THIS AFTERNOON/EVENING ACROSS THE CENTRAL HIGH
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS EXTENDING WESTWARD
FROM THE MID-ATLANTIC ACROSS TN…
Scattered severe thunderstorms with damaging winds are expected
across the southern Middle Atlantic into the Tennessee Valley.
Severe thunderstorms with very large hail and damaging winds should
also develop across the central High Plains.
The primary larger-scale features today are northern stream troughs
moving east-southeastward over Quebec and ND/MN, though a
separate/weaker belt of westerlies is located farther south from the
central Plains across the OH Valley to the Mid-Atlantic. Within
this southern flow belt, diffuse MCVs are progressing
east-southeastward over MO/IL and OH/WV, with ongoing convection in
multiple clusters through this corridor. The stronger storms along
the lower OH River are producing a cold pool and will likely persist
until at least late morning, with the southward extent of the
outflow likely demarcating the zone of afternoon redevelopment of
storms this afternoon across TN. A few damaging gusts will be the
main threats with multicell clusters/line segments in an environment
of rich low-level moisture and moderate buoyancy along the southern
edge of the 25-35 kt midlevel flow.
The ongoing convection from southern OH to WV has shown signs of
weakening slowly this morning. Still, residual clouds and some rain
will slow surface heating from roughly 15-19z across
central/northern VA, with the more probable zone of stronger
destabilization along the southern fringe of the morning clouds/rain
in the vicinity of southern VA. Upstream VWPs reveal 40 kt midlevel
flow as low as 4 km above ground level over southern OH/eastern
KY/WV, and this somewhat stronger flow will translate over VA this
afternoon with the remnant MCV. Will maintain the 30% wind/Enhanced
risk area in this update, though the influence of clouds on
destabilization through early afternoon will likely modulate
additional storm development this afternoon, and potentially reduce
the severe threat.
…Central High Plains this afternoon through early tonight…
A low-level upslope flow regime will establish today across eastern
CO, prior to a weak reinforcing frontal surge overnight. South of
an ongoing band of elevated storms driven by midlevel warm
advection/frontogenesis, the low levels will warm and MLCAPE is
expected to increase to 2000-3000 J/kg by mid-late afternoon.
Deep-layer vertical shear will be favorable for supercells from
northeast CO/northwest KS northward. Surface-based storm
development is expected 21-00z across northeast CO along a surface
trough on the northeast edge of the steeper low-level lapse rates
and deeper mixing. The initial storms will likely be discrete
supercells capable of producing isolated very large hail and perhaps
a tornado or two. Convection may grow into a larger cluster this
evening and propagate southward into a weak nocturnal low-level jet
across far eastern CO/western KS, with a continuing threat for
damaging winds into early tonight.
…Upper MS Valley area this afternoon…
A midlevel shortwave trough over eastern ND this morning will move
southeastward over MN/western WI by this evening. Ascent preceding
the midlevel trough will coincide with daytime heating and low-level
convergence along a weak northwest-southeast oriented front, which
will support thunderstorm development this afternoon.
Boundary-layer dewpoints in the 60s and afternoon surface
temperatures approaching 80 F will drive MLCAPE of 1000-1500 J/kg,
in an environment with effective bulk shear near 40 kt. The net
result will be the potential for a few organized/supercell storms
capable of producing isolated damaging winds/large hail. An
isolated tornado may also occur with storms moving southeastward
along the boundary, where low-level shear and vertical vorticity
will be larger.