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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 181956

Area Forecast Discussion
National Weather Service Charleston SC
356 PM EDT Thu Jul 18 2019

Into early next week, the area will remain hot and humid
between an inland trough of low pressure and Atlantic high
pressure. A cold front is expected to stall over or close to
the region by the middle of next week, bringing higher rain
chances and somewhat cooler temperatures. 


Until Sunset: Radar shows thunderstorms far inland and along 
portions of the sea breeze. SPC Mesoscale Analysis continues to
show MLCAPEs getting up to 2,500-3,000 J/kg and DCAPEs 
approaching 1,200 J/kg. This could lead to some marginally 
severe pulse storms with damaging winds. Steering winds aloft
are fairly light, which is causing slow storm movements. With 
deep moisture in place (PWATs around 2"), very heavy rainfall is
a concern with local flooding possible in low-lying and poorly 
drained areas. CAMs continue to be in good agreement showing the
thunderstorms diminishing around sunset.

Tonight: Our area will remain between Atlantic high pressure 
and troughing inland. Both the synoptic models and the CAMs are
in good agreement showing land areas relatively dry while there
is a small risk of late night showers over the coastal waters. 
Temperatures will remain mild.


Friday through Sunday: Outside any thunderstorms, heat index values 
will top out in the 105-109F range at many locations, and heat index 
values could briefly top out around 110F at some locations near the 
coast/just inland from the beaches as the sea breeze pushes inland. 

Guidance depicts above normal PoPs Friday afternoon/early evening, 
especially across southeast GA, due in part to an enhanced weakness 
in the upper ridge over the region. capped maximum PoPs around 50 
percent across SE GA, but locally greater PoPs could eventually be 
required. In typical fashion for mid-July, a couple of pulse 
thunderstorms could briefly become severe with damaging wind gusts.

Saturday and Sunday: Per latest guidance, only subtle changes in the 
configuration of the upper ridge and inland surface trough could 
translate to reduced coverage of diurnal/afternoon into evening 
thunderstorms as compared with Friday afternoon/evening. The risk 
for brief/isolated damaging wind gusts will continue each 


Moderate confidence this period. The low-level lee-side trough looks 
to persist early in the week before deeper troughing likely moves 
into the area for mid week. This will mean increasing rain chances 
and lower temperatures, although hesitate to be too aggressive with 
rain chances so far out given the rarity of summertime cold fronts 
in this part of the country. Heat indices could still be near 110 
degrees through Monday but the risk for Heat Advisories will likely 
be over starting Tuesday.


18Z TAFs: VFR for much of the afternoon. Thunderstorms are
expected across portions of the area from late this afternoon 
through early this evening. The most likely times these will 
occur near the TAF sites is covered by VCTS. There is a high
level of difficulty determining precise flight restrictions and
timing. Amendments may be made later based on radar trends and 
possibly to add TEMPO groups. The thunderstorms will dissipate 
by later this evening, allowing VFR to prevail.

Extended Aviation Outlook: VFR much of this period. Brief flight 
restrictions and gusty/shifting winds could occur within/near 
thunderstorms, especially during the afternoon/evening hours. 
The chance for thunderstorms/associated flight restrictions could be 
greatest Friday afternoon/evening and starting Tuesday as a cold 
front approaches the region.


Tonight: The synoptic pattern will consist of high pressure in
the Atlantic and a trough inland. The surface pressure gradient
will become elevated the first half of the night, causing the 
low level jet to set up. Expect S to SW winds up to 15-20 kt 
with higher gusts through midnight. Winds will gradually ease
during the second half of the night, as the gradient lowers
slightly. Seas will be in the 2-4 ft range.

Friday through Tuesday: A typical summer pattern featuring a trough 
of low pressure inland and offshore high pressure will support a 
continuation of south/southwest winds through the period. Wind 
speeds will be enhanced near the coast during the afternoon/evening 
from the sea breeze and across coastal waters during the overnight. 
Through this weekend, winds should remain capped around 20 knots and 
seas should;d average 2-4 feet, below Small Craft Advisory levels.
Early next week, a cold front will approach the region, and the 
probability for local SCA conditions could increase.