Spc:
Northeast...
Scattered thunderstorms should develop later this morning into
afternoon, over the mid/upper Ohio Valley and Lower Great Lakes
regions. This activity should pose an increasing threat for hail,
damaging to severe gusts, and a few tornadoes as it moves eastward
across the outlook area, with the greatest threats in and near the
"enhanced" corridor.
This will occur as large-scale ascent, deep-layer wind profiles and
vertical shear all strengthen ahead of the Great Lakes shortwave
trough, and perhaps ahead of an eastward-moving MCV or convectively
enhanced vorticity lobe from morning activity over IL. These
processes, occurring along and ahead of the surface cold front, may
support multiple rounds of convection. Activity will impinge on a
diurnally destabilizing and favorably moist boundary layer, commonly
characterized by surface dewpoints in the upper 50s to upper 60s F.
In addition to heating, moist advection ahead of the convection
should help to:
1. Strengthen buoyancy over areas of PA/NY now containing more
modest theta-e than in the Ohio Valley, and
2. Offset vertical boundary-layer mixing enough to maintain or even
increase preconvective dewpoints farther west.
MLCAPE in the 1500-2000 J/kg range should become common, in a
supercell-supporting kinematic parameter space of 40-55-kt
effective-shear magnitudes. Though near-surface flow may be weak,
veering with height and hodograph curvature should be greatest near
the NY/PA border and into western NY, with effective SRH in the
150-300 J/kg range. Analog soundings and a 2-D hail model applied
to forecast soundings each suggest significant-severe hail may
occur, with the risk of a few such reports now appearing large
enough to draw an unconditional area. Otherwise, the wind and
tornado threats largely appear to be similar to those described in
the previous outlook, with minor adjustments made for more-recent
progs of convective trends.
