Area Forecast Discussion
Issued by NWS Charleston, SC

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604
FXUS62 KCHS 210744
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
344 AM EDT Sat Oct 21 2017

.SYNOPSIS...
Strong high pressure will shift offshore this weekend. A cold
front will then move through Monday night into Tuesday with a
stronger but dry cold front to move through Tuesday night. High
pressure will then prevail into late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM: Ground fog is expected to dissipate within a half hour
to hour after sunrise this morning. Latest IR satellite images
indicated that thin cirrus was approaching the forecast area from
the west. Forecast soundings indicate that the cloud cover will
remain very thin through the day, but may thicken tonight as the H5
trough swings over the ArkLaTx. The center of a large sfc high will
shift off the coast of the mid Atlantic states by this afternoon,
then pushing NE through tonight. The pressure pattern across the
forecast area will remain under ridging, however, the pressure
gradient should increase slightly starting this evening. The surface
pattern is expected to support onshore flow today, then backing from
the ENE overnight. High temperatures are forecast to range in the
low 80s as low temperatures range from around 60 inland to near 70
across the beaches.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
A coastal trough will push inland across the area Sunday and the
associated isentropic ascent, low-level convergence and moisture
will lead to some showers. The trough should move well inland and
dissipate by Sunday night but strengthening low-level onshore flow
and deeper moisture moving in from the southwest ahead of an
approaching cold front/upper trough will cause an increase in rain
chances/amounts Sunday night and especially Monday/Monday night.
Although low-level shear/helicity will be on the increase Monday,
instability will likely be marginal and thus the risk for severe
thunderstorms is low. Temperatures will remain above normal through
the period, even through Tuesday given the downslope winds and
slacking cold advection.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
A strong cold front will move through Tuesday night as a broad upper
trough envelopes the eastern U.S. Dry, but cooler conditions will
then prevail through Thursday before some moderation occurs late in
the week as high pressure quickly shifts offshore allowing a milder
return flow to set up. Some uncertainty in the longer range model
guidance implies lower forecast confidence late next week but could
see some rain return to the area Saturday. Temperatures will be
mostly below normal through Thursday night before possibly rising
closer to or even above normal through the end of the week. Some
inland locales should get into the 40s each morning from Wednesday
through Friday.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions will prevail at both KCHS and KSAV through 06Z
Sunday. The environment will support patchy ground fog near the
terminals early this morning. Based on the latest 5-minute
observations, I will include a TEMPO for 6Z-10Z for MIFG.

Extended Aviation Outlook: Brief flight restrictions are possible
Sunday due to low clouds/light showers. Higher chances of flight
restrictions are expected Sunday night into Tuesday as a cold front
affects the area with heavier showers and potentially some
thunderstorms. Breezy/gusty winds also possible
Tuesday/Wednesday.

&&

.MARINE...
Today and Tonight: The center of a large sfc high will shift off the
coast of the mid Atlantic states by this afternoon, then pushing NE
through tonight. The pressure pattern across the coastal waters will
remain under ridging, however, the pressure gradient should increase
slightly starting this evening. The surface pattern is expected to
support ENE winds through tonight. Wave heights today are forecast
to range between 2-3 feet within 20 NM, around 4 feet across AMZ374.
Tonight, wave heights are expected to gradually increase, with 6 ft
waves reaching the outer portion of AMZ374 late tonight.

Sunday through Thursday: Conditions will deteriorate a bit this
weekend as a cold front approaches from the west and likely moves
through early Tuesday. Another stronger cold front will then move
through Tuesday night. A Small Craft Advisory will likely be needed
for the nearshore/offshore waters Monday into Tuesday and into
Wednesday morning beyond 20 nm as seas reach 6+ feet.

Rip Currents...Onshore winds, small swells, and lingering
astronomical influences will support a moderate risk of rip currents
at the GA beaches today. Conditions will be close to a moderate risk
on the SC beaches, but the wind speed is a little less than further
south, so a low risk is maintained for now.

&&

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

&&

$$
NEAR TERM...BSH/NED
SHORT TERM...RJB
LONG TERM...RJB
AVIATION...NED/RJB
MARINE...NED/RJB



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