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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 201700

Area Forecast Discussion
National Weather Service Charleston SC
100 PM EDT Sat Jul 20 2019

The area will remain situated between an inland trough and
Atlantic high pressure into early next week. A cold front is
expected to stall over or close to the region by the middle of
next week, then linger into late week. 


Afternoon Update: Minor tweaks made to the hourly temperatures
and dew points to take the current observations and blend into 
the next few hours. Also, did the same with the sky grids based 
on the satellite imagery. The CAMs continue to show virtually no
convective threat this afternoon and that's what the forecast 
continues to reflect.

Rest of Today: Mid and upper level ridging will expand into the
region from the Atlantic, while at the surface we're still near
the west and northwest edges of the oceanic high, with the 
Piedmont trough anchored about where it has been the past few 
days. Due to the lack of any forcing other than the sea breeze, 
PWat only around 1.75 inches and a mid level cap to the persist,
there doesn't look to be much if any convection this afternoon.
The overall consensus doesn't support anything more than 
isolated activity after 3 or 4 pm, and mainly across our GA 
zones. DCAPE is forecast as high as 1200-1500 J/kg, so there 
could be a strong or borderline pulse severe storm with strong 
winds as the hazard. H8 temps of 18-19C support max temps in the
lower and middle 90s inland from the immediate coast, where a 
modest south and southwest sea breeze will limit highs to "only"
the upper 80s.

Tonight: The synoptic pattern changes very little and once any 
isolated convection across far interior GA fades by mid evening,
the rest of the night will stay rainfree. There are presently 
no indications of fog, especially since there will be little if 
any prior rainfall. Low temps will be very similar to early this
morning, which will be at or near climo.


Sunday and Monday: Only subtle overall change to the synoptic 
pattern both at the surface and aloft. A continuation of hot and 
humid conditions will persist with mid 90s common each afternoon 
along with heat indices 105-107 degrees many areas. Convection 
potential each afternoon appears to be best along the coastal sea 
breeze corridor and we have maintained 20-30 POPs for isolated to 
scattered coverage. 

Tuesday: An erosion of upper ridging as mid level troughing sags 
into the southeast states. A cold front is forecast to advance from 
the eastern Tennessee Valley into northern GA and the western 
Carolinas by afternoon. Models were in good agreement that pre-
frontal convection will congeal off the mountains prior to mid 
afternoon, then advance east and southeast toward the coast late day 
and early evening into a mainly untapped atmosphere will decent mid 
level instability. We maintained 50-60 POPs area-wide. A few strong 
to severe tstms may be possible if enough cold pooling or upstream 
organization occurs, still plenty of time to follow-up on model 
trends at this point.


Likely POPs in order Tuesday night just ahead of the surface cold 
front and mid level short wave. The front is forecast to stall along 
the southeast coast during mid to late week. Broad upper troughing 
will deliver a favorable medium for unsettled weather across the 
forecast area during this period. Bouts of scattered to numerous 
showers and tstms are expected Wednesday and perhaps again Thursday. 
Model agreement on the frontal position wanes by late week with the 
boundary tending to wash out by early next weekend. We maintained 
POPs slightly greater than climo for this period. Temps will be 
tempered by a good bit of cloud cover along with chances for 
convective rains mid to late week.


18Z TAFs: VFR. Some gusts are expected this afternoon,
especially with the sea breeze. But no precipitation is

Extended Aviation Outlook: Brief flight restrictions could occur 
within thunderstorms, especially during the afternoon/evening hours 
Sunday and Monday. The chance for thunderstorms/associated flight 
restrictions are expected to increase Tuesday afternoon and evening 
ahead of a cold front. Scattered to occasionally numerous showers 
and tstms are expected in the vicinity of a stalled front during 
mid/late week.


Today and tonight: A typical mid-summer synoptic pattern remains
in place, featuring a trough inland over the Southeast and high
pressure offshore. Expect S-SW this afternoon, veering to the 
SW tonight. Speeds will become enhanced in Charleston Harbor 
and near the coast this afternoon and evening, and across the 
Atlantic waters tonight. Speeds will peak as high as 15 or 
15-20 kt and seas will average 2-3 ft, with maybe some 4-footers
far offshore.

Sunday through Thursday: South to southwest flow will prevail
Sunday into early afternoon on Tuesday. Wind speeds will 
continue to be enhanced at times, surging into the 15-20 knot 
range but remaining below SCA levels. Seas should be 2-4 feet. A
cold front is expected to stall out over or near the local 
waters mid to late week. A weak gradient should result in light 
winds and seas in the 2 ft range. We also expect showers and 
tstms to increase in coverage during this time frame.