Day 1 Severe Weather Outlook

Valid 241200Z – 251200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE CAROLINA PIEDMONT…

…SUMMARY…
Showers and a few thunderstorms are expected across the southern and
middle Atlantic coastal states Friday. A couple strong storms are
possible, and a damaging gust or a brief tornado cannot be ruled
out.

…Synopsis…
A stacked sfc-500 mb low will traverse the Ohio Valley through the
period, with a belt of 80 knot mid-level flow overspreading
portions of the Southeast into the Mid-Atlantic. The primary surface
low will drift northeast towards Lower Michigan. However, a
secondary surface low will develop across eastern portions of the
Deep South/Carolina Piedmont regions, as the aforementioned
mid-level trough intensifies atop a sharpening baroclinic zone
oriented along the leeward side of the southern Appalachians.
Cyclogenesis across the southeast will be accompanied by a northward
surge of a modified, moist low-level airmass originating from the
eastern Gulf of Mexico, ahead of a cold front. Increased low-level
warm-air/moisture advection and associated convergence along and
ahead of the front, beneath stronger flow aloft, suggest that
isolated to scattered thunderstorm development is possible, with the
possibility of a couple storms briefly reaching severe limits.

Elsewhere across the western CONUS, a mid-level ridge will begin to
develop, along with surface high pressure. As such, cooler
temperatures and large-scale subsidence will reduce the potential
for deep, moist convection in most areas. The one exception may be
northern Washington, where an embedded shortwave cresting the
developing ridge may promote enough deep-layer ascent, that along
with modest diurnal heating, may support a couple stronger updrafts.
Nonetheless, buoyancy is expected to be weak, with only a flash or
two expected.

…Portions of the Carolina Piedmont…
Though low-level clouds and showers will prevail throughout the day
across the southeast in the warm-air advection regime, some
insolation will promote 6-7 C/km low-level lapse rates ahead of the
cold front. Modest mid-level lapse rates (6 C/km) atop near 60F
dewpoints will promote 500-1000 J/kg MLCAPE values across portions
of the Carolina Piedmont through the later half of the period.
Increased convergence along the cold front will induce a broken band
of relatively strong convection, likely initiating around 21Z across
southeast Georgia, with convection progressing across central South
Carolina into southern/central North Carolina into the late
evening/overnight hours. 50 knots of deep-layer unidirectional
shear, with up to 30 knots of 0-1km shear (and some low-level
veering noted) suggest that a couple of the stronger, more sustained
storms may organize, with transient low-level rotation possible. As
such, a couple of damaging gusts may accompany a few of these
storms. The magnitude of the shear amidst relatively rich low-level
moisture suggest that a brief tornado is possible in the absence of
a stable boundary layer.

..Darrow/Squitieri.. 01/24/2020

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