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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 240132
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
932 PM EDT Sat Mar 23 2019

.SYNOPSIS...
High pressure will persist through early Monday. Low pressure
will cross the region Monday night followed by a strong cold
front Tuesday. Another low pressure will develop off the
Southeast coast and will gradually move away through midweek.
As the low departs, high pressure will build into the area and
will prevail into next weekend. 

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Very few changes were made for the evening update. 

GOES-E 1-minute Visible and Geo-Color satellite imagery shows 
an impressive smoke plume emanating from a controlled burn in 
the open areas of Fort Stewart. The plume orientation shows the
flow pattern quite well, initially moving west behind the sea 
breeze then corkscrewing clockwise with height as the plume 
encounters northwest flow aloft. Data suggest most of the smoke
is aloft, but is likely obscuring the late afternoon sun
somewhat with a hazy, brownish color. Some of this smoke may
work its way back to the surface closer to the burn site after
sunset with a slight westward drift through the night beneath 
the nocturnal inversion per latest output from the experimental 
H3R near surface smoke plume trajectory forecast. Will add 
patchy smoke for several hours in areas like Jennie and 
Glennville, but not anticipate widespread issues at this time.

Otherwise, high pressure will hold its influence on the region
tonight. The boundary layer will decouple later this evening,
first well inland, then closer to the coast once the sea breeze
circulation decays. Low dewpoints coupled with clear skies and
calm/light winds will support solid radiational conditions. A
band of mostly thin high cirrus will likely push through later
tonight, but do not anticipate this will have much of an
influence on the radiational setup. Lows will range from the
upper 30s across the Francis Marion National Forest into areas
north of Lake Moultrie to the lower 50s along the South Carolina
beaches and the Georgia coastal region, including Downtown
Charleston.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday: High pressure will provide another dry day. Onshore flow 
will hold temps in the 60s on the beaches, but high in the mid/upper 
70s will be common away from the immediate coast. High level clouds
will stream into the region from the west. 

Sunday night: Atlantic high pressure will maintain rain-free 
conditions. By early Monday temperatures will bottom out around 50F 
inland and in the mid-upper 50s on the coast. 

Monday:  Atlantic high pressure will retreat from the region, and 
low pressure will approach the region from the west. The morning 
should remain rain-free. Then, ahead of the advancing shortwave 
trough aloft and associated surface low, warm conveyor belt moisture 
should spread into the region during the afternoon. Latest afternoon 
PoPs are graduated from chance inland to slight chance closer to the 
coast, with lowest PoPs across far southern counties. 

Monday night: The lead shortwave trough aloft and associated surface 
low will translate east across the region. Deep-layered forcing for 
ascent/associated moisture will support scattered to numerous 
showers, with best precip coverage during the first half of the 
night. To address this scenario, evening PoPs range from likely 
north to chance south, then overnight PoPs settle back to 30-50 
percent across the region. 

Also of note, Monday afternoon and Monday evening, showers could 
also be accompanied by isolated thunderstorms. However, model 
instability remains weak and appears unfavorable for any severe 
weather. 

Tuesday: The low pressure will push offshore, and a strong cold
front will push through the region from north to south. This 
front will bring an abrupt wind shift to the northeast and will 
signal a rapid change to a below-normal temperature regime that 
will persist until late week. Also, persistent moisture within 
the associated baroclinic zone could support isolated/scattered 
showers through Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Low pressure will develop off the coast Tuesday night/Wednesday and 
will only gradually move away from the coast through Thursday. As a 
result, showers could remain over or close to the coast through 
midweek, and elevated northeast winds/below-normal temps could 
persist through Thursday. The, building high pressure will help push 
temps into the upper 70s/around 80 late next week into at least 
early next weekend.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
VFR.

Extended Aviation Outlook: Flight restrictions possible Monday 
night through Tuesday night.

&&

.MARINE...
Tonight: South/southeast winds will become more easterly through
the night. Winds 10 kt or less with seas 1-2 ft nearshore and
2-4 ft offshore.

Sunday through Thursday night: On the periphery of Atlantic high 
pressure, southeast winds will be enhanced by the sea breeze Sunday. 
Then, ahead of approaching low pressure, winds will turn to the 
south/southwest Sunday night and Monday, and a few gusts could 
exceed 20 kt Monday/Monday evening. Then, a strong cold front will 
cross the waters from north to south late Monday night into Tuesday, 
and winds will shift sharply to the northeast and will intensify. 
Then, due to the tightening gradient between high pressure building 
from the north and low pressure developing offshore, winds/seas 
could easily reach Small Craft Advisory levels most areas Tuesday 
through midweek, and gale force gusts could occur, especially beyond 
20 nm.

Rip Currents: There will be enhanced risk for rip currents
beginning Tuesday as elevated northeast winds and swell impact 
the beaches.

&&

.TIDES/COASTAL FLOODING...
Between strong high pressure building from the north and low 
pressure developing off the coast, strong northeast winds will 
create elevated tide levels along the coast Tuesday through 
Thursday. While astronomical factors do not favor tidal flooding, 
probabilistic guidance depicts a low chance for minor salt water 
flooding, especially Wednesday. We will continue to assess this 
scenario during the next several days.

&&

.EQUIPMENT...
The KCLX radar remains out of service. Repairs are expected to occur 
Monday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$