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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 170203

Area Forecast Discussion
National Weather Service Charleston SC
1003 PM EDT Sun Jun 16 2019

Atlantic high pressure will prevail into Tuesday. An inland
surface trough will develop by mid week then persist over the
Southeast into next weekend. 


As of 10 PM: IR satellite indicates clear to mostly clear
conditions across the forecast area this evening. Overall, the
current forecast remains on track. However, I will adjust hourly
temperatures through the night, aligning with recent MOS cooling

As of 730 PM: The seabreeze is expected to exit the forecast
area over the next half hour. I will update the forecast to
decrease PoPs and cloud cover. In addition, I will warm the low
temperatures tonight a degree or two, aligning with recent
trends in observations and latest MOS.

As of 540 PM: KCLX detected the seabreeze tracking steadily
inland across the forecast area. Isolated showers were nearly
stationary about 5 mile east of the sea breeze. These showers
should rain themselves out over the hour. West of the seabreeze,
temperatures have managed to peak in the mid 90s in a few 
areas. I will update the forecast to warm the hourly
temperatures to align with recent observations.

Previous Discussion:
Through Sunset: Radar imagery is showing some convection along 
the sea breeze, with slightly better coverage and intensity 
across coastal GA. This matches up fairly well with the synoptic
models and the CAMs. SPC Mesoscale Analysis shows MLCAPEs 
approaching 1,500 J/kg, but the moisture still is somewhat 
lacking, which is helping to limit the areal coverage and 
intensity. The result will be convection dissipated by sunset.

Tonight: A weak mid-level low will be over FL, with general SW 
flow overhead. At the surface, high pressure will be in the 
Atlantic with weak troughing to our northwest. Late night marine
showers will make a run for the coast, only to get squashed by 
subsidence. The result is a dry forecast over land. With 
increasing dew points and light to calm winds, there should be 
some patchy fog inland late tonight. Lows will be near normal.


Monday through Wednesday: Overall, conditions will gradually become 
more conducive to convective development as we approach mid week. 
Aloft, the ridge will hang on Monday then weaken Tuesday and 
Wednesday as a shortwave ripples through. At the surface, the 
subtropical high will extend into the area Monday, followed by a 
surface trough that moves into the area through Wednesday. Monday 
convection should be isolated to scattered, with the best coverage 
across southeast Georgia. Rain chances on Tuesday and Wednesday 
certainly warrant higher values, but have kept them in the high 
chance range. Model differences are considerable regarding coverage, 
with some depicting virtually no coverage and others having coverage 
that could support 50-60 percent chances. Overall, there aren't any 
obvious features to latch onto for determining possible organization 
and any severe threat. Atmospheric flow is better by Wednesday, so 
perhaps the severe threat is marginally higher then. In general, the 
severe threat looks low each day but there could be an isolated 
stronger storm depending on how mesoscale boundaries interact. 
Temperatures should top out in the low 90s each day, with lows in 
the low to mid 70s.


A fairly robust mid level short wave is progged to pass through the 
southeast states Thursday into early Friday. This appears to be the 
most significant period for a potential risk of organized convection 
as 700 MB flow increases greater than 30 kt over much of the area. 
Timing and convective mode look tricky and global models continue to 
show moderate to strong instability at times late week. It still 
remains quite uncertain how convection will play out at this 
juncture. On Friday, the surface trough will mostly move offshore 
and POPs range from slight chance northern SC zones to chance GA. 
Upper ridging is expected to build over the weekend with hot and 
humid weather and at least a slight chance for afternoon/evening 
showers and tstms. Temps on average will run above climo by several 
degrees for highs and lows through most of the medium range.


00Z TAFs: VFR will prevail with clouds continuing to dissipate
this evening. Ground fog is expected to develop across the
terminals around 09Z and continue until just after sunrise 
Monday. VFR is expected throughout the night and into tomorrow 
with cumulus and cirrus present tomorrow afternoon with the 
arrival of the seabreeze. Along the seabreeze, isolated SHRA 
and/or TSRA could form but the chance of direct contact with 
either terminal is too uncertain to mention in the TAFs.

Extended Aviation Outlook: Mainly VFR. Brief flight restrictions 
are possible in afternoon showers/thunderstorms, especially by 
mid week.


Tonight: Atlantic high pressure will be the main driver of the
winds, generally from the S or SE this evening around 10 kt,
then veering to the SSW or SW and easing a few kt by daybreak 
Monday. Seas will be 2-3 ft.

Monday through Friday: Through the week, south to southwest flow is 
expected to prevail across the local waters as the area sits between 
high pressure to the east and a developing trough inland. Wind 
speeds will mainly top out in the 15-20 knot range, primarily along 
the land/sea interface in the afternoon and in surges during the 
overnight periods. Seas will average 2-4 feet, and could be as high 
as 5 feet at times over the outer waters in the mid to late week