Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 200742
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
342 AM EDT Fri Oct 20 2017

.SYNOPSIS...
Strong high pressure will continue over the area, then shift
offshore this weekend. A cold front will likely move through
Monday night into Tuesday before a stronger cold front moves
through Tuesday night ushering in much cooler weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 340 AM: Observations indicate that steam fog was occurring
near inland rivers and lakes and patchy ground fog in a few
spots near the coast. The fog is expected to dissipate within
one hour of sunrise. The rest of the day will feature building
high pressure, with the center of a 1025 mb high reaching the
SC/GA coast this afternoon. In the mid levels, a broad center of
a H5 590 DM ridge will build over the CWA this evening and
overnight. This pattern will support mostly clear sky, dry
conditions, and winds shifting from the ENE by this afternoon.
High temperatures are forecast to range in the lower 80s.
Minimum temperatures tonight should reach the lower 50s inland
to the low 60s along the coast. Much like this morning, I will
indicate patchy fog near inland water bodies during the predawn
hours.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
High pressure should keep conditions warm and dry through Saturday
but a few light showers will be possible Saturday night, mainly
along the GA coast, then moreso across the entire forecast area
Sunday as a coastal trough pushes inland. The trough should move
well inland and dissipate by Sunday night but strengthening low-
level onshore flow and deeper moisture moving in from the west ahead
of an approaching cold front/upper trough will cause an increase in
rain chances/amounts Monday. Although low-level shear/helicity will
be on the increase Monday, instability will likely be marginal and
thus the risk for thunderstorms, and especially severe
thunderstorms, appears to be low at this time. Temperatures will be
above normal through the period.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
A potent upper shortwave and/or closed low will affect the area
Monday night into Tuesday, pushing an initial cold front through the
area Monday night into Tuesday. Expect a good chance for showers and
some thunderstorms along and ahead of the cold front, followed by
drier and cooler high pressure. Tuesday should be mainly dry,
although some showers could linger, especially near the SC coast
early in the day. A secondary, stronger cold front will then move
through Tuesday night as the main 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 return flow to set up.
Temperatures should stay above normal through Tuesday before falling
at or below normal through Thursday night. Many inland areas should
get into the 40s Thursday/Friday mornings.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
At 5Z...KSAV 5 minute ASOS observations over the past hour
indicated a dewpoint depression between 0-2C with visibility
ranging between 2.5 to 10 SM. I suspect that patchy shallow
ground fog has developed across the terminal. The rest of
tonight should feature nearly calm winds with clear sky. I will
mention BCFG and TEMPO 3SM BR between 6Z-10Z. Otherwise, TAFs
will feature VFR conditions with light NE winds through early
this afternoon, then winds shifting from the east between 18Z to
21Z.

Extended Aviation Outlook: Brief flight restrictions are possible
Sunday due to low clouds/showers. Higher chances of flight
restrictions are expected Sunday night through Monday night,
possibly into Tuesday, as a cold front affects the area with heavier
showers and potentially some thunderstorms.

&&

.MARINE...
The center of sfc high pressure is expected to shift from the
southern Appalachians this morning to along the SC/GA coast by
this afternoon. Conditions across the marine zones are forecast
to improve through today into tonight. Gusty NE winds will
remain possible until early this afternoon, then winds should
shift from the ENE and weaken. Wave heights are forecast to
gradually subside over the next 24 hours, generally decreasing
by a foot. Small Craft Advisory for AMZ374 will remain in effect
until 2 pm this afternoon.

Saturday through Wednesday: 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 may be needed starting
Saturday night for seas reaching 6 feet beyond 20 nm, then likely
remain into Wednesday.

Rip Currents...Steady northeast winds, long period swell from the
east and astronomical influences associated with a recent new moon
should support an elevated risk of rip currents through late this
week, mainly along Georgia beaches. A moderate risk of rip currents
will continue for the Georgia beaches today.

&&

.TIDES/COASTAL FLOODING...
Persistent northeast winds and astronomical factors will lead to a
risk for minor coastal flooding during the morning high tides
through Saturday, mainly in Southeast South Carolina.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for AMZ374.

&&

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



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