Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Columbia SC
1154 PM EDT Sat Jul 21 2018
a deepening upper trough and surface boundary will lead to
chances of showers and thunderstorms, some possibly severe,
tonight and Sunday. The deep upper trough will then remain over
the east Continental U.S. Through late next week, providing a continued good
chance of showers and thunderstorms.
Near term /until 6 am Sunday morning/...
negatively tilted upper trough over the Ohio Valley into west
Carolina this evening. Convection developing upstream ahead in
the foothills of SC/NC this evening as suggested by high
resolution models. Storm Prediction Center has put the western portion of the County Warning Area in
a Severe Thunderstorm Watch until 2 am. Strong mid level short
wave over east Tennessee/northwest Georgia moving east-southeast and models
suggest increasing large scale ascent across the region this
evening into the overnight. The air mass appears to be capped at
the moment with limited cumulus across the area, especially in
the csra. However, model soundings indicate moderate to strong
cape thru the evening and given strong dynamics, the cap is
likely to break at some point. Increasing deep layer shear
associated with mid level jet advecting northeast from central
Georgia and dry air aloft support severe thunderstorms with damaging
wind main threat. Dcape is around 1500 j/kg. Large hail also
possible. Expect at least scattered convection late this evening
into the overnight well ahead of a surface cold front which is
expected to move into the area around daybreak. A watch may be
needed east of the current watch at some point and will monitor
trends as the storms move through the Piedmont. Overnight lows
will generally be in the low 70s.
Short term /6 am Sunday morning through Tuesday/...
on Sunday, the upper low over the Ohio Valley will continue to
drift southward as deep ridging over the Atlantic blocks the
eastward progression of systems. The main trof axis will be
close enough to the area that advection of vorticity should be
generally minimal, and the dry air that has been entrained on
the south and west side will move over central SC and the csra.
This will keep showers and thunderstorms spotty during the
afternoon despite supportive mid level tamps and lapse rates
for convection. A strong storm or two cannot be ruled out, but
coverage will be on the low side for July.
By Monday, the upper low will have dropped into southern Georgia,
and deep southerly to southeasterly flow will become established.
Model guidance has pretty high chances of rain, but it probably
won't be until late in the day with mid level dry air in place
during the morning.
Moistening will continue into Tuesday, and with little change in the
overall pattern to the continued strong Atlantic block, chances of
thunderstorms look higher than average once again.
Temps will be a couple of degrees below normal during the afternoons
with considerable cloud cover expected, while min temps will be near
normal in the lower 70s.
Long term /Tuesday night through Saturday/...
more of the same is expected Wednesday and Thursday as the upper low
moves little. Numerous afternoon and evening thunderstorms are again
expected to develop, with afternoon Max temps remaining around 90,
give or take a couple of degrees.
The upper low may weaken by the end of the week, allowing for a
little drying, but typical July afternoon/evening convection
would still be expected as modest instability develops each
Aviation /04z Sunday through Thursday/...
main near term concern is cluster of severe thunderstorm
activity currently to the north of dnl/ags, and west of cae/cub,
moving to the east-southeast. This activity could affect those taf sites
by around 0430z. Will indicate a tempo group to handle. Strong
gusty winds and hail will be possible with these storms.
Otherwise, will expect the convective activity to gradually weaken
as it moves across the forecast area later tonight. Some questions
regarding stratus development in its wake. For now, will indicate a
tempo group for MVFR cigs.
Some questions regarding extent of convective coverage Sunday as
drier air moves into the region.
Extended aviation outlook...scattered afternoon and evening
thunderstorms Sunday. Increased chance rain and possible
associated restrictions from Monday thru Thursday. Late
night/morning fog/stratus possible.