Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 271825
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
125 PM EST Mon Feb 27 2017

.SYNOPSIS...
High pressure will push off the eastern seaboard today, with a weak
coastal trough to develop nearby tonight. High pressure will remain
over the Atlantic through the middle of the week. A cold front will
move through Wednesday night into Thursday, followed by more high
pressure for the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
No changes with this update.

Fast moving W-SW flow will prevail aloft to the north of a
flattened mid and upper ridge from near the Yucatan, across Cuba
and the Bahamas, and into Atlantic north of the Caribbean
islands. At the surface an impressive region of high pressure
centered just off the Delmarva is strengthening and moving
offshore. Despite a southeasterly synoptic flow, it`ll take
awhile for the low levels to moisten. And with a decent
subsidence cap around 4-5k ft, there is little prospects for
rain before dark. Mid and high level clouds are on the increase
in association with upstream short waves, a coupled upper jet
structure and a developing warm front over the northern Gulf
coast states. The warm advection in place puts us back into the
70s for most places again this afternoon. The exceptions will be
shoreline communities, due to the onshore trajectories and the
sea breeze, that limits highs to the mid or upper 60s.

Tonight: Mid level perturbations will traverses the area,
allowing for the development of a subtle coastal trough in close
proximity to the area. Isentropic ascent (most especially on
the 295K surfaces) and moisture flux will combine with upper
difluence/divergence to generate at least potential for showers
to occur. Model solutions are not in agreement, but given better
moisture and forcing, we are showing at least chance PoP`s to
occur. There looks to be three potential mechanisms for how the
showers gets going. First is the nearby Atlantic trough, the
second is the energy aloft, and finally even the possibility
that sea breeze induced convection from the Gulf of Mexico will
ride in from the southwest. We won`t go anything more than
30-40% chances just yet, most especially since some credence has
to be given to the drier GFS. There is some elevated
instability, so isolated thunder can`t be ruled out, especially
near the immediate coast where surface based instability is a
little more prevalent. Considerable multi-layered clouds will
put a blanket on nocturnal cooling, and with ongoing warm
advection, temps will hold fairly steady or even rise a couple
of degrees overnight. On average temps will be as much as 15-20F
warmer than last night.

Fog will become a concern after midnight, due to wet grounds, the
lack of wind and favorable condensation pressure deficits. If there
is enough build-down of stratus involved in the mix, then coverage
might be more than just patchy, and dense fog may also be an
issue.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
Tuesday into Wednesday: The forecast area will remain under the
influence of Atlantic high pressure through Wednesday. Aloft, upper
ridging will extend northward from the Gulf of Mexico/Florida.
Perhaps the main item of interest is the impressive warm-up
expected. Temperatures will be around 15-20 degrees above late
February/early March normals. Highs Wednesday are currently forecast
to approach record values (see climate section below). Otherwise,
fairly quiet with a few diurnal showers/thunderstorms possible in
the afternoon. Slight chance PoPs seem appropriate. Winds will get a
bit breezy on Wednesday as the pressure gradient tightens ahead of
an approaching cold front. Southwest winds will gust to 25-30 mph in
the afternoon.

The aforementioned cold front will cross the area late Wednesday
into early Thursday. Showers and thunderstorms are expected to
accompany the front. Despite decent shear, the front will be passing
at a climatologically unfavorable time of day, so severe threat is
low. Temperatures will fall back to normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Cool and dry surface high pressure will build into the area late
week and then slide into the Atlantic by Monday. Lack of moisture or
any significant forcing will allow for a precip-free forecast.
Temperatures will be near normal early in the period, then slowly
warm early next week as southerly flow develops on the backside of
the high.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR for the daylight hours today. A weak coastal trough and
some energy in the mid and upper levels should cause flight
restrictions for portions of tonight with stratus, isolated to
scattered SHRA, and maybe fog/mist. Our current thinking for
flight restrictions is at least MVFR from 00-12Z at KSAV and
06-12Z at KCHS. Adjustments to the timing are expected in future
TAFs.

Extended Aviation Outlook: Flight restrictions possible in early
morning fog/stratus Tuesday and Wednesday. A cold front will move
through early Thursday with brief restrictions possible in
clouds/showers.

&&

.MARINE...
Today: Strengthening high pressure is moving east and away from
the Delmarva coast. Winds are expected to remain E-SE, peaking around
15 kt. Seas will build to 3-4 ft, highest across the outermost
GA waters.

Tonight: There is enough of a weakness in the ridging across the
maritime community, allowing for a subtle trough to develop over or
near the area. The flow slowly veers around to the SE and South at
speeds a little less so than during the daytime. Seas hold in steady
state, ranging from 2 ft within 5 or 10 nm of the coast, 3 ft most
elsewhere, except 4 footers beyond 30 nm offshore. There is enough
instability to produce at least isolated thunderstorms.

Elevated dew points point toward a risk for sea fog, but the
trajectories are probably still too much east of due south to cause
any major concerns in this regard. If stratus build-down occurs
and/or winds are a more favorable South to SW, then fog chances
would be greater.

Tuesday through Saturday: South/southwest flow will persist through
midweek as the coastal waters remain on the backside of surface high
pressure. Speeds 10-15 knots on Tuesday will increase on Wednesday
ahead of an approaching cold front. Conditions may flirt with small
craft advisory criteria late Wednesday into Thursday, especially in
the Charleston county waters and outer Georgia waters. The front
will cross early Thursday with conditions to slowly improve through
the day. North/northeast winds will then prevail through the end of
the week as high pressure builds in from the west. Another brief
uptick in wind speeds could occur Saturday morning.

Sea fog: Warm southerly flow moving over the cooler shelf waters may
result in patchy sea fog developing late Tuesday into Wednesday.

&&

.CLIMATE...
Record high temperatures for March 1
CHS: 82 degrees last set in 1997
CXM: 79 degrees set in 1918
SAV: 86 degrees set in 1918

Record high minimum temperatures for March 1
CHS: 61 degrees set in 2012
CXM: 63 degrees set in 2012
SAV: 65 degrees last set in 2012

&&

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

&&

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


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