Day 1 Severe Weather Outlook

Valid 291200Z – 301200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
MS AND TN VALLEYS EAST TO THE SOUTHERN APPALACHIANS…

…SUMMARY…
Strong to locally severe thunderstorms may impact parts of the
Mid-South and central Gulf States Sunday afternoon and evening, with
at least some potential for damaging wind gusts and/or a tornado or
two.

…Synopsis…
While a northeastern Pacific upper low digs south-southeastward
toward/along the California coast through the second half of the
period, the more substantial feature with respect to deep convection
will be the large upper trough/low initially centered over the
Plains states, moving slowly eastward while deepening with time.
More specifically, an energetic short-wave feature — rotating east
across Texas early in the period — is progged to turn more
northeastward as it rounds the base of the larger-scale trough, and
then shift into the Midwest/Ohio Valley overnight.

As this system rounds the base of the main trough, weak cyclogenesis
is progged to begin over the western Tennessee vicinity during the
afternoon, along the eastward-moving cold front. The low is then
expected to deepen rapidly while shifting northward across the Ohio
Valley toward the Upper Great Lakes, in tandem with the parent upper
disturbance. Meanwhile, the trailing cold front should cross the
lower Mississippi Valley during the afternoon, and then accelerate
eastward across the central Gulf Coast states and Tennessee Valley
before reaching the Appalachian crest late in the period.

…Lower MS and TN valleys east to the southern Appalachians…
A band of showers and embedded thunderstorms will be ongoing at the
start of the period in the vicinity of the advancing cold front —
from the lower Ohio and Mid Mississippi Valley area, southwestward
into southeast Texas. Very weak lapse rates/instability across the
warm sector should largely hinder convective intensity through the
day, though very strong flow/shear will support local/occasionally
stronger storms, and attendant/low-end risk for wind and/or a brief
tornado. Severe potential may become maximized in the 22z to 02z
time frame, in the vicinity of the Mississippi/Alabama border and
eastward into central and northern Alabama, as cyclogenesis begins
in response to the northeastward ejection of the upper short-wave
trough across the mid Mississippi Valley area. However, despite
favorable low-level and deep-layer shear, and a relatively moist
boundary layer, sufficient CAPE development to support enhanced
severe weather coverage remains questionable. As such, will refrain
from a SLGT risk/5% tornado area upgrade at this time.

Overnight, as the front accelerates eastward, a narrow, forced
convective line will cross the eastern half of the MRGL risk area,
posing a continued/low-end severe risk through the end of the
period.

..Goss/Bentley.. 12/29/2019

$$

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