Day 1 Severe Weather Outlook

Valid 091200Z – 101200Z


Severe thunderstorms are not expected on Monday.

A positively tilted large-scale 500 mb trough will progress across
the central and eastern CONUS, coincident with a rapidly deepening
surface low which will eject into the upper-Hudson Valley by the end
of Day 1/Monday, with multiple areas of thunderstorms possible
across the eastern third of the CONUS, where marginal buoyancy can
materialize. Elsewhere, a mid-level shortwave trough will traverse
the southwest CONUS, where deep-layer ascent and cold air aloft
(promoting marginal instability) may serve as a focus for isolated
thunderstorm development.

…Eastern parts of the Ohio Valley…
A strong cold front will accompany the aforementioned low, inducing
convergence/low-level lift to eastern parts of the Ohio Valley into
the northern Appalachians. Broad 850 mb WAA beneath steep (7.5
C/km) mid-level lapse rates will promote marginal buoyancy (150 J/kg
MUCAPE), with convective showers and a few lightning flashes
possible with the more intense cells, mainly within the 00-06Z time

…Portions of the mid-South…
Richer low-level moisture will be present ahead of the cold front,
with surface temperatures warming into the 60s/70s and dewpoints
exceeding 60 F through the day. Strong 850 mb WAA is also likely
atop and behind the cold front, driven by the approach of the
smaller 500 mb shortwave trough to the west. Marginally unstable air
parcels into the post-frontal regime will promote isolated
thunderstorm activity late in the period (03-12Z).

…North Carolina Coastline…
Isolated thunderstorms will also be possible along the North
Carolina Coast, along the western periphery of a low-level moist
axis of confluence ahead of the large-scale mid-level trough. The
best time for storms would be during the first half of the period,
as a small, embedded mid-level impulse briefly enhances deep-layer
ascent across the area.

…Portions of the Southwest…
500 mb temperatures dropping below -20C will contribute to a pocket
of steep mid-level lapse rates of 7.5 C/km, which will translate
eastward with the aforementioned 500 mb shortwave trough, supporting
isolated thunderstorm potential in southern parts of Arizona/New
Mexico during the day, and Far West Texas later in the period.

..Squitieri.. 12/09/2019


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