lfg
...NY/New England...
Surface-based thunderstorms are expected to develop by midday over
parts of western NY and/or adjoining ON, along and south of the
front. Activity should increase in coverage and move mostly
eastward across central/eastern portions of NY and south-central New
England through the afternoon, its movement aligned with an
instability gradient and boundary-layer moist axis. Damaging to
locally severe wind gusts will be the main concern. Confidence has
increased that enough large-scale lift (related to the MCV) and
diurnal low-level destabilization will occur to support maintenance
of the threat eastward into New England. The 15% wind area has been
extended accordingly.
Surface dewpoints generally in the low/mid 60s F will be common in
the preconvective environment across the region, with minimal
MLCINH. Accordingly modified RAOBs and forecast soundings suggest
that -- despite weak midlevel lapse rates -- MLCAPE around 500-1000
J/kg will develop (locally/briefly higher), atop a reasonably
well-mixed boundary layer with steep low-level lapse rates. A
roughly unidirectional deep-layer wind profile is expected, with
effective-shear magnitudes in the 30-40-kt range. Given the weak
capping and progressive regime of ascent preceding the MCV, some
cold-pool aggregation may occur in upscale growth of convection,
enabling forward propagation to impinge on the destabilized boundary
layer, potentially as far east as the MA and perhaps NH coastlines
given the westerly flow that can advect favorable boundary-layer
theta-e that far.