Valid 112000Z – 121200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS PARTS OF EAST CENTRAL ALABAMA…CENTRAL
GEORGIA…WESTERN AND CENTRAL SOUTH CAROLINA…AND CENTRAL AND
EASTERN NORTH CAROLINA…
Widely scattered strong storms may impact parts of the Alabama,
Georgia and South Carolina piedmont into northern Mid Atlantic
coastal plain late this afternoon and early evening, accompanied by
some risk for severe weather.
…20Z Outlook Update…
Latest observational data, objective analysis and forecast soundings
continue to suggest that the environment is becoming at least
conditionally supportive of organized severe thunderstorm potential
within pre-frontal surface troughing to the lee of the southern
Appalachians. Deep-layer and low-level shear is strong, beneath a
40-60 kt west-southwesterly 850 mb jet axis extending across the
Georgia piedmont into the northern Mid Atlantic coastal plain. And
at least weak boundary-layer destabilization is ongoing, as surface
dew points slowly climb through the lower/mid 60s, in the presence
of modest daytime heating.
Forcing to support thunderstorm initiation remains the primary
uncertainty. This seems likely to remain weak, with any
thunderstorm development resultant from continued destabilization
expected to remain isolated to widely scattered at most.
The most prominent attempts at sustained deep convective development
are currently ongoing near/west through northeast of LaGrange GA and
Auburn AL, where CAPE may be maximized (up to around 500 J/kg).
This appears near the southern fringe of neutral mid-level height
tendencies (to leading edge of northeastward spreading weak
mid-level height rises), with low severe weather potential appearing
to diminish in areas to the southwest.
.PREV DISCUSSION… /ISSUED 1030 AM CST Tue Feb 11 2020/
Split flow aloft will continue across the U.S. this period, with
northern-stream troughing to shift across the Great Lakes and into
the Northeast, while a second trough digs southeastward out of the
Canadian Rockies toward the north-central U.S. in its wake.
In the southern stream, a low/trough currently residing over the
southwestern deserts and adjacent northwestern Mexico will advance
slowly eastward to the southern Rockies/southern High Plains, while
downstream ridging amplifies in response over the Southeast.
At the surface, a cold front extending from a weak low over the Mid
Atlantic region west-southwestward to Deep South Texas will progress
steadily southeastward while weakening. Farther north, a
second/polar cold front is forecast to shift southeastward out of
the Canadian Rockies/Prairie Provinces into north-central portions
of the CONUS.
…Southeast Virginia to central Alabama…
Ahead of a cold front gradually shifting southeast of the
Appalachians, a moist warm sector is indicated — though weak lapse
rates aloft continue to limit available CAPE. This — combined with
weak convergence along the front and a general lack of appreciable
surface heating suggest that frontal convection will remain
generally limited in intensity despite amply
strong/west-southwesterly flow aloft.
As a very weak/subtle short-wave trough shifts across the Southeast
today, a modest/relative diurnal peak in convective activity is
expected. A few of the strongest updrafts may prove capable of a
locally stronger wind gust or two, and a brief/weak tornado cannot
be ruled out as well. However, any risk appears to remain limited,
and should diminish from west to east as the subtle upper feature
crosses the region and short-wave ridging — and associated
subsidence — increases in its wake.