Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 240307
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1007 PM 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 /UNTIL 6 AM FRIDAY MORNING/...
Inland, elevated dewpoints, mainly clear skies and light
winds/radiational cooling should support fog formation
overnight. Close to the coast, persistent winds will delay the
onset of fog. However, winds near the coast should slacken
sufficiently to allow to at least patchy fog toward daybreak.
Also of note, recent high resolution model runs are generally
backing away from widespread dense fog formation. Thus,
maintained the ongoing generic mention of areas of fog away from
the immediate coast with no mention of dense fog/low
visibilities.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday and Saturday: Low pressure centered over Florida will
gradually shift offshore and northeast over the western Atlantic,
leading to quiet but warm conditions as deep layer ridging occurs
over the Southeast ahead of a cold front approaching from the west.
Expect temps to soar into the upper 70s/lower 80s away from the
immediate coast Friday afternoon and around noon Saturday, until the
cold front shifts through the area. These temps could break previous
records (see climate section below). Low temps will also remain mild
ahead of the front, ranging in the mid/upper 50s Friday night.
Noticeably cooler temps will be in place behind the cold front. In
general, temps will dip into the upper 30s inland to low/mid 40s
closer to the coast Saturday night.

Moisture levels will not be all that impressive as the front pushes
through the area, suggesting that only a few showers will be
possible during cold fropa Saturday morning into early Saturday
afternoon. However, there will be risk of fog Friday morning and
Saturday morning while sfc dewpts approach the low/mid 50s and winds
remain decoupled each night ahead of the front. By noon Saturday,
stronger low-lvl winds will cross the region, resulting in breezy
conditions with significant warming ahead of the cold front.

Sunday: High pressure will become centered over the Southeast,
leading to quiet/dry conditions under a zonal flow aloft. Overall
temps will be closer to normal for this time of year. In general,
high temps will range in the low/mid 60s, highest in away from the
coast in Southeast Georgia.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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 /03Z FRIDAY THROUGH TUESDAY/...
VFR until at least 06Z-10z. Then, elevated dewpoints, mainly
clear skies and light winds will eventually support fog/
stratus over or just inland from the terminals, especially
during the 10Z until 14-15Z time frame. 00Z TAFs advertise
IFR vsbys and LIFR CIGS during this time frame. However, recent
high resolution guidance has backed away from coverage of dense
fog, perhaps due to persistent NE winds. Thus, forecast
confidence in flight restrictions is not high. In any event,
VFR conditions will return by late Friday morning.

Extended Aviation Outlook: Flight restrictions are likely Saturday
morning due to low clouds/fog. Another low risk for restrictions
will be possible Monday/Tuesday due to low clouds/showers.

&&

.MARINE...
Overnight: An enhance pressure gradient between inland high
pressure and offshore low pressure will only gradually relax,
and elevated seas will persist. While NE winds should remain
below 20 knots, seas of 6-7 feet will continue to push into
nearshore waters near the 20 nm benchmark, and seas as high as
8-9 feet will persist beyond 20-40 nm. As a result, Small Craft
Advisories remain valid to all zones outside Charleston Harbor
through the night.

Friday through Tuesday: Small Craft Advisories will be in effect
for offshore Georgia waters and nearshore South Carolina waters
through much of Friday morning. However, winds/seas will slowly
improve Friday afternoon as low pressure conditions to drift
well offshore. Expect conditions to fall below Small Craft
Advisory levels over all nearshore South Carolina waters by
Friday evening when northeast winds veer to the south. However,
high seas will likely linger in offshore Georgia waters. Some
improvement is expected across all waters Friday night into
Saturday until cold air advects over the waters behind a passing
cold front Saturday afternoon. A Small Craft Advisory will
likely be ongoing in offshore Georgia waters at the time, but
marginal Small Craft Advisories could be needed over a portion
of the nearshore waters Saturday night. Conditions should then
improve to below Tonight: Low pressure east of Florida will
generate NE winds, generally no more than 15 KT by late this
evening and overnight. However, stronger winds closer to the low
and further offshore are generating swell that is propagating
into our waters. The latest NOAA buoy observations have been
running 1-2 ft higher than current wave model runs. The wave
heights were raised to account for this. As a result, Small
Craft Advisories will remain in place for all of the coastal
waters. Additionally, the advisory for the nearshore GA waters
has been extended for a few hours. Given the ongoing trends, the
wave heights may need to be raised further later tonight and
for the Advisory in the nearshore GA waters to get extended yet
again.t terminals, so forecast confidence is not high. In any
event, VFR conditions will redevelop by late Friday
morning.Small Craft Advisory levels over all waters by daybreak
Sunday. However, increasing southerly winds could lead to
additional Small Craft Advisories on Monday, 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 Friday for AMZ352.
     Small Craft Advisory until 11 AM EST Sunday for AMZ374.
     Small Craft Advisory until 11 PM EST Friday for AMZ350.
     Small Craft Advisory until 5 AM EST Friday for AMZ354.

&&

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


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