Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 200548
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1248 AM EST Tue Nov 20 2018

.SYNOPSIS...
A cold front will move through late Tuesday, followed by high
pressure that will prevail through late in the week. An area of
low pressure will move through the region late this week and
this weekend, resulting in unsettled weather.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Although patchy fog will occur through the overnight, with
increasing and thickening mid and high level clouds associated
with the sub-tropical jet, conditions will not be a repeat of
the foggy weather 24 hours ago. These clouds will also prevent
temps from dropping more than about 1-3F the remainder of the
night.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
Tuesday and Tuesday night: A broad mid and upper level trough will
encompass the eastern half of the CONUS, with a surface cold front
poised to move through later in the day. Overall, the front will be
relatively moisture starved, primarily producing cloud cover across
the region. Model soundings show the bulk of the moisture between
700-850 mb, with much drier air above and below that layer. A few
models do generate some light precipitation, but it seems prudent to
maintain a dry forecast at this point. Instead, the expectation is
that the front and trough aloft will manifest as just cloud cover,
which will decrease from the west in the afternoon. The actual cold
front is not expected to reach the coast until the evening, so the
forecast area will be in the milder air mass out ahead of it. Highs
are forecast to range in the upper 60s for most areas, with some low
70s possible along the coast, especially the Georgia coast.
Overnight, the front will move quickly offshore and high pressure
will begin to nose in from the north. Mostly clear skies are
expected with lows ranging from the upper 30s well inland to the
upper 40s at the coast.

Wednesday through Thursday: Confluent zonal flow will prevail into
Thursday morning when a well defined shortwave approaches from the
west late in the day. Expansive Canadian high pressure will move
across the Great Lakes and almost to New England through Thursday
evening. This high will prevail across the forecast area, bringing
clear skies on Wednesday and increasing clouds Thursday.
Temperatures will be much cooler, with highs ranging from the upper
50s around Lake Moultrie to the low/mid 60s near the Altamaha.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Model guidance is becoming better aligned regarding formation of a
Gulf low near the western edge of the Gulf of Mexico late Thursday
as mid and upper level shortwave troughing exits the desert
southwest and enters the central U.S. Guidance diverges on the
evolution of the pattern aloft heading into the weekend, but low
pressure looks increasingly likely to move east or northeast near or
over the area through the weekend, bringing another round of
unsettled weather. An additional trailing shortwave trough could
transit near the region early next week, but it remains unclear how
much moisture will be available to work with. The 19/00Z GFS and
ECMWF depict widely different scenarios, increasing forecast
uncertainty late in the long term period.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Maybe a little ground fog prior to dawn, otherwise VFR ceilings
will prevail through Tuesday Tuesday in advance of a cold front
that passes through during Tuesday evening.

Extended Aviation Outlook: VFR conditions are expected to
prevail at both terminals into late week. Flight restrictions
will be possible this weekend as low pressure moves nearby.

&&

.MARINE...
Overnight: Other than a little fog slipping into Charleston
Harbor and within a few miles of the coast, conditions across
the maritime area will be relatively quiet overnight. Westerly
winds will be no more than about 10 or 12 kt, with seas 2-4 ft,
highest beyond 40 nm offshore.

Tuesday through Saturday: A cold front will approach the waters
on Tuesday and winds ahead of the front will be out of the
west-southwest mainly in the 10-15 knot range. Behind the front,
high pressure will begin building in and winds will shift to
more northerly and then northeasterly with time. By Thursday,
the northeast gradient will tighten significantly and wind
speeds will increase to the point where Small Craft Advisories
look increasingly likely. These advisories will likely be needed
through at least Friday. By Friday night and Saturday an area
of low pressure is expected to impact the region though there is
considerable model disagreement regarding the eventual track of
the low.

&&

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

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...


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