Area Forecast Discussion
Issued by NWS Charleston, SC

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534
FXUS62 KCHS 231218
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
718 AM EST Thu Feb 23 2017

.SYNOPSIS...
Low pressure will pass to the southeast through Friday. A cold front
will cross the region early Saturday, followed by cooler high pressure
through Monday. The high will then shift offshore bringing unseasonably
warm temperatures and some rain back to the area for mid week. Another
cold front could move through Wednesday night into Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: A closed mid level low will shift through south-central
Florida early on, across the northern Bahamas by this afternoon
and northeast over Atlc waters tonight. The surface low will
follow a similar path, displaced somewhat north of it`s mid
level reflection. Across the forecast area, models in agreement
that deep layered moisture is on the wane, and this is noted in
both PWAT progs and time/height moisture analysis displays.
Isolated showers are possible today, but the potential for
measurable amounts looks meager although the 4KM NSSL WRF and
HRRR both show some spotty inland-moving showers associated with
the sea breeze this afternoon. Since 850 MB to 500 MB
condensation pressure deficits are quite high prior to 18Z, we
think the activity will indeed be spotty and isolated with
mainly dry weather for the afternoon. With increasing potential
for sunshine, we maintained very warm high temps in the upper
70s most areas away from the beaches and barrier islands.

Tonight: Upper level ridging builds in, while complex surface
low pressure lifts north of the Bahamas. Dry weather is expected
with mainly clear skies resulting in slightly improved
radiational cooling. Models show that many areas will reach
cross-over temps late, resulting in stratus and fog development.
We have widespread patchy fog, but areas of fog may develop with
some patchy dense fog not out of the question. We lowered
minimum temps a couple degrees in many of our normally cooler
spots.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Low pressure well off the Southeast U.S. coast Friday will slowly
shift northeast farther into the Atlantic Friday night as a cold
front near the Mississippi Valley begins to move east into the Deep
South. The front will move through the area Saturday but limited
moisture and instability will prevent significant rain
chances/amounts. Some dense fog will be possible Saturday morning.
Temperatures will be well above normal through Saturday, with record
highs/high mins possible Friday/Saturday (see Climate section
below), then fall closer to normal Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A chilly air mass will remain in place into early Monday but
temperatures should moderate quickly as return flow sets up as high
pressure shifts offshore. This will allow temperatures to get back
above normal, possibly record warmth, which will persist through
Wednesday before a cold front likely moves through Wednesday night
into Thursday. Some showers possible Monday with some
showers/thunderstorms Tuesday/Wednesday, mainly northern and inland
areas, as instability increases and some upper disturbances move
over or just north of the area. The better rain chances/coverage
will likely come later Wednesday into early Thursday as a cold front
moves through. At this point the timing of the frontal passage is
not favorable for strong storms given the limited instability. A
much cooler air mass is then expected Thursday.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
VFR conditions are likely today with isolated showers around the
coastal corridor this morning. Tonight, attention turns to a
favorable environment for late night fog and stratus development.
At this juncture, we opted for MVFR vsbys and scattered lower
clouds but there is a good chance the trend toward IFR conditions
nearing dawn on Friday will continue during later cycles.

Extended Aviation Outlook: Flight restrictions likely Saturday
morning due to low clouds/fog. Low risk for restrictions
Monday/Tuesday due to low clouds/showers.

&&

.MARINE...
Low pressure around Florida and Bahamas will enhance a southeast
swell component through tonight. The main quest for the marine
forecast are near-shore sea heights along shallow waters and
specifically within 20 NM. We maintained a SCA across near shore
GA waters, however seas closer in to the Savannah River Entrance
were likely only in the 3-4 ft range. Solid SCA conditions will
continue over outer GA waters through tonight. Ne flow averaging
15 KT with occasional 15-20 KT flow offshore will persist today.

Tonight: Various wave height guidance indicates building seas
across near shore South Carolina waters and marginal SCA
conditions are possible in the 10-20 NM waters. We opted to
delay any SCA issuances at this time to gather more information
and trends from the Charleston Pilot and future model runs
today.

Friday through Tuesday: A cold front will move through Saturday
followed by cooler high pressure into Monday before the high shifts
farther offshore and winds turn more southerly. Persistent northeast
winds will lead to Advisory conditions Friday beyond 20 nm and
possibly into the Charleston County nearshore waters. Some
improvement is then expected until after the cold front passes later
Saturday when Advisories are likely for at least the offshore
waters. Increasing southerly winds Mon could lead to additional
Advisories, mainly beyond 20 nm.

&&

.CLIMATE...
Record Highs for Feb 24:
KCHS: 81 set in 2012/1996.
KCXM: 81 set in 1930.
KSAV: 86 set in 2012.

Record Highs for Feb 25:
KCHS: 80 set in 1949.
KCXM: 80 set in 1930.
KSAV: 82 set in 1985/1930.

Record High Minimums for Feb 24:
KCHS: 60 set in 1992.
KCXM: 61 set in 1901.
KSAV: 64 set in 1980.

Record High Minimums for Feb 25:
KCHS: 62 set in 1992.
KCXM: 59 set in 2011.
KSAV: 63 set in 1992.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 11 AM EST Sunday for AMZ374.
     Small Craft Advisory until 1 PM EST this afternoon for AMZ354.

&&

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



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