870 
FXUS62 KCHS 112206
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
606 PM EDT Sat Aug 11 2018

.SYNOPSIS...
Low pressure will persist near the region through the weekend.
A weak front could drift into the area during the middle of
next week. High pressure will then prevail during the second
half of the week before weak low pressure returns next weekend.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Isolated to scattered convection remains anchored in the higher
theta airmass in the wake of the sea breeze early this evening.
Sea breeze convergence remains fairly weak with SMC values 
averaging only 20-30 g/kg/12hr. This pattern will change little 
over the next few hours. Farther to the west, a line of 
convection moving across central Georgia is steadily weakening 
with time as it encounters a slightly less favorable 
thermodynamic environment that is in place across interior 
Southeast Georgia. Some remnants of this activity could breach 
the far interior Georgia zones around sunset, but should not 
amount to too much. Pops have been lowered by 10-20% for most 
areas with the early evening update. The risk for severe weather
remains quite limited as weak convergence will curtail the 
formation of robust updrafts. 

Isolated to perhaps low end scattered convection could redevelop
after midnight as H8-H7 shortwave energy draw closer and
interacts with higher moisture/coastal convergence in the wake 
of the sea breeze. Maintained lowish pops through the overnight 
period at the coast. Lows from the lower-mid 70s inland to the 
upper 70s at the beaches look on track.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday: Aloft we find a closed low spiraling near Lake Erie and over 
Ohio, with its associated deep cyclonic flow to extend across the 
local area. At the surface, a stationary front will remain just off 
to the W-NW of the CWA, with a trough just out ahead of the front, 
located over or near the forecast district. While there will be some 
showers/t-storms mainly across the Charleston tri-county and coastal 
Colleton and maybe Beaufort County to start the day in the region of 
the best convergence, most areas will remain capped through early 
afternoon. Given that much of the flow throughout the troposphere is 
from the SW, this maintains a moisture-laden air mass featuring PWat 
around 1.75 to 2.00 inches. MUCAPE is as great as 1500-2500 J/kg and 
with the resultant sea breeze, the nearby trough and the usual meso-
scale boundaries that form, we have chance to high end chance PoP in 
the afternoon. Coverage looks to be highest inland from US-17 to as 
far inland as near US-301. The overall severe weather threat is low 
given unimpressive thermodynamics and poor lapse rates. But with 
DCAPE as much as near 1000 J/kg, there could be one or two storms 
that produce strong or severe wind gusts. If convection from 
upstream is able to move in late, the severe coverage would be 
greater further inland. H8 temps are near 18-19C, a little above 
normal for mid-August, and this will support max temps in the lower 
90s inland from the coast. 

Sunday night: Lingering convection will generally fade during the 
mid evening hours, before the coverage of convection ramps up over 
the coastal areas, especially South Carolina during the overnight 
period due to increasing moisture convergence. PoP is capped at 
slight chance/chance, highest over the Charleston tri-county closer 
to daybreak. Areas of stratus and patchy fog could form in a few far 
inland locations if skies clear out enough. Lows will average in the 
lower and middle 70s most communities.

Monday and Tuesday: The cut off low eventually transitions into more 
of a closed low as it moves into the NE part of the nation Tuesday, 
while its associated mid and upper trough persist across the entire 
eastern third to quarter of the country. Meanwhile at the surface, 
there is still a nearby stationary front and trough, with the 
axis of the Bermuda High aligned across Florida. Monday looks to
be a little more active regarding convection than Tuesday, with
some support from the RRQ of the upper jet and its resulting 
divergence and the tail of a weak short wave moving through the 
South Carolina upstate and North Carolina. MUCAPE is around 
1500-2500 J/kg both days, but the elevated moisture on Monday is
less so on Tuesday as a deeper W-NW flow develops due to the 
parent low associated with the front to pull off the Delmarva 
and mid-Atlantic. We're carrying 40-50% poP Monday, mainly to 
"blend" better with our neighbors, thane mostly 30% Tuesday. 
There could be some multicell clusters that form Monday due to 
the support aloft, with damaging winds and heavy rainfall the 
main hazards. Any severe threat Tuesday is low due to more 
pulse- type activity. Temps both days will peak in the lower 90S
inland from the coast.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Drier conditions are anticipated mid week as high pressure builds 
over the region Wednesday/Thursday while sfc low pressure is less 
pronounced inland. Other than a few afternoon showers/thunderstorms, 
the pattern should support slightly warmer conditions with high 
temps peaking in the low-mid 90s. Higher precip chances could return 
next weekend as the sfc trough becomes more pronounced inland 
while a front shifts toward the Mid-Atlantic states.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
VFR.

Extended Aviation Outlook: Brief flight restrictions are possible at 
KCHS Sunday and Monday morning, and at both KCHS and KSAV each 
afternoon and evening due to SHRA/TSRA through Thursday. Otherwise 
VFR will prevail.

&&

.MARINE...
Tonight: Broad low pressure will remain across the east coast 
through tonight. Winds across the marine zones should continue 
from the southwest between 10-15 kts with seas 1-2 ft.

Sunday through Thursday: The sub-tropical ridge will remain 
positioned to the SE through the period, with occasionally 
strengthening of the gradient to occur with slightly lower pressure 
inland. There is the typical fluctuations in winds to the SSW with 
the sea breeze each afternoon and evening, then around to the WSW 
with the "cooling" land each night. On average winds will be no 
greater than around 15 kt (except occasional stronger gusts in 
Charleston Harbor during the day), and since there remains the lack 
of swell energy, seas won't be any more than 2-4 ft. The coverage of 
showers and t-storms will be highest each post-midnight period into 
the mid or late morning hours, although some organized convection 
with damaging winds could occur late Monday and early Monday night.

&&

.TIDES/COASTAL FLOODING...
Tides are expected to peak 7.0-7.2 ft MLLW in Charleston Harbor 
and 8.9-9.1 ft MLLW at Fort Pulaski. A Coastal Flood Advisory 
remains in effect for most of the South Carolina coastal zones 
until 10 PM. Trends are being monitored along the Georgia coast
and it is possible the advisory may need to be expanded.

Elevated high tide levels will continue into early next week 
due to lingering astronomical influences and occasional onshore 
winds. The evening high tides are the most problematic and could
result in coastal flooding. As a result, additional Coastal 
Flood Advisories are possible.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Coastal Flood Advisory until 10 PM EDT this evening for 
     SCZ048>050.
MARINE...None.

&&

$$