Valid 032000Z – 041200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS FAR
EASTERN OHIO INTO NORTHWEST PENNSYLVANIA THE REMAINDER OF THE
AFTERNOON…
…SUMMARY…
A couple of strong thunderstorms could produce strong gusts the
remainder of the afternoon across parts of far eastern Ohio and
western Pennsylvania.
…OH/PA…
Isolated showers and thunderstorms have developed across northwest
PA this afternoon ahead of a surface cold front draped across
central OH. 19z mesoanalysis showed a small area of MLCAPE
approaching 1000 J/kg overlapping an area of 35 kt effective shear
across eastern OH into northwest PA. The Marginal risk has been
confined mostly to northwest PA where better instability and shear
parameters are located and where a line of TCU was noted in visible
imagery. Given weak instability/poor lapse rates, a lack of
convergence along the front and weak upper forcing for ascent, the
severe threat should remain limited and quickly diminish with loss
of daytime heating. Still, a couple of strong wind gusts will be
possible with the strongest cells as they quickly track
east/northeast.
..Leitman.. 10/03/2019
.PREV DISCUSSION… /ISSUED 1115 AM CDT Thu Oct 03 2019/
…Synopsis…
Within the westerlies, large-scale mid-level troughing appears
likely to continue migrating inland of the Pacific coast, through
much of the Intermountain West by late tonight, accompanied by a
cold front. As this occurs, downstream ridging is forecast to build
east of the northern Rockies, and a remnant mid-level closed
low/troughing to the east is expected to turn east-southeastward
across southern Ontario/southwestern Quebec and the Great Lakes
region. It should continue to undergo deformation in a confluent
regime ahead of another short wave trough digging south-southeast of
Hudson Bay. However, models do suggest that some further deepening
of an associated modest surface frontal wave is possible east of the
lower Great Lakes, through New England by late tonight. While the
front advances across the Ohio Valley through the Mid Atlantic Coast
region and Tennessee Valley today through tonight, southward
advancement across the Ozark Plateau/southern Plains probably will
be slower, beneath mid-level subtropical ridging centered over the
Southeast.
In association with this regime, areas of scattered thunderstorm
development are possible today, aided by daytime heating within a
seasonably moist environment beneath the western flank of the
subtropical ridge, and beneath the core of the mid-level cold air
overspreading the Pacific Northwest and northern intermountain
region. A few thunderstorms could also develop in association with
the frontal wave migrating east-southeast of the lower Great Lakes
region.
…Parts of lower Great Lakes/upper Ohio Valley…
Models do continue to indicate that weak to moderate boundary layer
destabilization is possible this afternoon in the warm sector of the
frontal wave. CAPE may reach 500-1000 J/kg near the immediate
vicinity of the surface low, west of the Allegheny Mountains, across
parts of northeastern Ohio into western Pennsylvania. This will be
largely driven by daytime heating of seasonably moist boundary layer
air, with mid-level temperatures remaining relatively warm and lapse
rates weak. Still deep-layer shear beneath 30-50 kt westerly
850-500 flow may contribute to an environment marginally conducive
to severe wind potential (mainly 18-22Z), given storm development.
However, with mid/upper support for large-scale ascent remaining
generally well north of the region, even widely scattered to
isolated sustained storm development remains uncertain.
$$