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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 181805
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
205 PM EDT Wed Sep 18 2019

.SYNOPSIS...
A cold front will shift south of the area this afternoon. High
pressure will then build across the region and persist into
early next week. 

&&

.NEAR TERM /THROUGH TONIGHT/...
This Afternoon: A backdoor cold front will continue to shift south 
over parts of Southeast Georgia into early afternoon hours. MLCAPE 
around 1500 J/kg and PWATs near 1.8 inches along and south of 
the front should support mainly isolated to scattered showers, 
but a few thunderstorms will also be possible during peak 
heating hours mid afternoon into early evening. The bulk of 
precip should come to an end across the area as the front 
shifts further south of the Altamaha River this afternoon. 
However, a few showers could linger well behind the front as 
high pressure builds across the region from the north. Temps 
will be noticeably cooler compared to the previous day. In 
general, high temps should peak in the lower 80s across Southeast
South Carolina and low/mid 80s before fropa in Southeast Georgia.

Tonight, a wedged ridge of high pressure is forecast to build 
southwest along the east facing slopes of the Appalachians 
tonight. The ridging should support steady NE winds across the 
CWA tonight. The NE winds will likely result in a gradually 
lowering of low level thicknesses and cooling H85 temps across 
the region. The combination of cooling llvl thermal profiles and
clearing sky will yield below normal low temperatures tonight. 
Using a blend of cooler MOS, I will forecast low temperatures to
range from the upper 50s across inland SC to the low to mid 60s
across SE GA.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday: Surface high pressure will dominate the eastern seaboard. 
Very dry air aloft will reside across the forecast area as Pwats 
will mainly be less than 1 inch. Dry weather is on tap plenty with 
abundant sunshine across most of the area. Atlantic stratocu and 
coastal afternoon cumulus are expected. There could be a potential 
for a few very light showers or sprinkles to brush far south coastal 
GA, but measurable rain potential looks quite low. Cooler temps are 
on tap with highs from the upper 70s north to lower 80s south. The 
coastal corridor will also see breezy conditions, especially closer 
to the beaches and barrier islands.

Friday: Models continue to hint at a weak coastal trough just off 
the GA coast. Latest data also progs a decent amount of isentropic 
ascent into southeast GA. Pwats will increase slightly over 1 inch 
and light patchy showers could certainly develop. Patchy showers 
further inland to the south of I-16 are also possible after mid 
afternoon. We have some slight chance POPs in that area with low-end 
chance POPs along the GA coastal corridor. We should see more clouds 
across the area although northern SC zones may still see a mostly 
sunny day, especially inland. 

Saturday: Deep layered ridging will continue to expand across the 
forecast area. We anticipate a dry day with scattered stratocu 
more prevalent along coastal GA with the onshore flow. Temps
will begin a warming trends with highs in the mid 80s with upper
80s to the west of I-95.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Deep layered ridging will persist into Monday and then tend to break 
down thereafter. Models hint at a weak front and stronger northwest 
flow aloft by mid-week, however the depth of dry-layered air was 
still enough to keep mentionable POPs out of the forecast. Temps are 
expected to run above climo each day with a return to some 90 degree 
high temps early next week inland and southern zones.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
A backdoor front will continue to shift south of the terminals early 
this afternoon with high pressure building in its wake. Low clouds 
should bring an hour or two of MVFR conditions at the SAV 
terminal, but a few showers could also develop across parts of 
Southeast Georgia, resulting in the need for an additional hour 
or two of TEMPO MVFR conditions. Winds have struggled to gust at
either terminal this afternoon due to cloud cover, but should 
eventually gust to 13-17 kts during peak heating this afternoon.
Otherwise, expect skies to become mostly clear or clear overnight
at both terminals. Northeast winds could become gusty approaching
18Z Thursday.

Extended Aviation Outlook: VFR conditions will prevail.

&&

.MARINE...
This Afternoon and Tonight: A backdoor cold front will slide south 
of the marine zones early this afternoon with high pressure building 
across the waters in its wake. Gusty northeast winds are expected 
across the waters behind the front as cold air advection occurs from 
the north and the pressure gradient tightens. Further south, 
convection has dampened wind fields and speeds have been slower to 
increase. However, these winds conditions should be temporary for 
the next hour to two before increasing from the northeast. The 
combination of wind and sea conditions remain highlighted with Small 
Craft Advisories for all marine zones outside of the Charleston 
harbor through tonight. In general, northeast winds will gust to 
20-25 kts. Long period swells near 11 seconds will also help 
seas build up to 5-7 ft in nearshore waters and 7-10 ft in offshore
Georgia waters (highest tonight). 

Northeast winds will dominate throughout the week as high 
pressure anchors to the north. Small Craft Advisory conditions 
for all coastal waters into Friday evening for the nearshore 
waters and well into Saturday night for the offshore Georgia 
waters. We may need to issue a SCA for the Charleston Harbor on 
Thursday as periods of near 25 kt wind gusts are possible. 

The pressure gradient is forecast to weaken during the weekend as 
the surface high bridges closer to the marine waters. Seas will 
gradually subside with time as well. By Monday, winds may become 
light and variable, before becoming south to southwest later in the 
day.

Rip Currents: A Moderate Risk of rip currents is in place today for 
all beaches due to lingering long period swells and increasing 
longshore currents due to strengthening northeast winds behind a 
departing front. The rip current risk will remain elevated through 
the end of the week as northeast winds and strong longshore currents 
continue.

&&

.TIDES/COASTAL FLOODING...
Low chances for minor coastal flooding around the times of high
tide through late week, especially along the South Carolina coast.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 8 PM EDT Friday for AMZ350-352-354.
     Small Craft Advisory until 4 AM EDT Sunday for AMZ374.

&&

$$
NEAR TERM...DPB
SHORT TERM...
LONG TERM...
AVIATION...DPB
MARINE...DPB
TIDES/COASTAL FLOODING...