FXUS62 KCHS 211600

Area Forecast Discussion
National Weather Service Charleston SC
1100 AM EST Wed Feb 21 2018

A large area of high pressure will remain across the region
through the weekend. A cold front will likely impact the area
early next week, followed by cooler high pressure into the
middle of next week.


Late this morning, the radar is resolving enhanced
reflectivities relative to yesterday. While it is uncertain how
much of this precipitation will survive to the surface, some
observations indicate the potential for brief periods of light
rain through this afternoon.

Today: It will be another warm, late winter day with the region
remaining along the immediate western flank of a deep-layered
anticyclone centered just offshore. Modest southerly breezes
will keep elevated dewpoints in place and help drive 850 hPa
temperatures up another 2-3C compared to Tuesday. Despite the
warm start this morning and a steady warming of the lower
troposphere due to subsidence, a thick cumulus deck will likely
develop by mid-morning as surface heating commences and parcels
rise to their respective LCLs. This coupled with a weak-
moderate onshore flow from off the cold Atlantic shelf waters
will limit temperatures somewhat, especially across the coastal
counties. Still, expect highs to reach the lower 80s inland, but
coastal areas will be quite a bit cooler, especially within a
few miles of the Atlantic. The beaches could easily remain the
mid to perhaps upper 60s. The record highs at both the
Charleston and Savannah Airports could be challenged, but the
record in Downtown Charleston/Riley Waterfront Park is likely


Tonight: Warm and humid conditions for late February will remain
in place as subtropical high pressure holds offshore. Another
round of low-stratus and fog are likely within the ongoing
stagnant synoptic pattern, but the details of the stratus and
fog distribution is still somewhat uncertain. SREF probabilities
and forecast soundings suggest the greater risk for dense fog
will be roughly along and east of the I-95 corridor where there
could be a bit of a sea fog component, but areas well inland
could see some locally dense fog where stratus build-down
occurs. Unlike this morning where southeast winds have limited
parcel residence times over the cold shelf waters, surface winds
are forecast to have a more southerly component, especially
along the lower South Carolina coast. This could increase the
sea fog risk in the Charleston-Beaufort corridor after midnight.
Opted to go about 1-2 degrees above the warmest statistical
guidance for lows Thursday morning with lows only bottoming out
in the lower to mid 60s.

Thursday through Saturday: A large ridge of high pressure
centered over the western Atlantic will maintain a hold over the
Southeast United States into the weekend, favoring unseasonably
warm temps. 1000-850mb thicknesses support temps roughly 15
degrees above normal with highs generally in the upper 70s to
lower 80s each afternoon. Temps could approach record highs away
from the immediate coast each day (see climate section below)
within a light southeast flow that gradually turns more
southerly over the weekend. The expansive ridge will also be
responsible for producing a fairly strong inversion through late
week, helping maintain precip-free conditions over much of
Southeast South Carolina and Southeast Georgia into the weekend.

Fog remains the main issue during late night/early morning hours as
a light southeast wind drives moisture onshore under ridging aloft.
Given the setup, at least patchy fog will be possible as temps dip
into the upper 50s to lower 60s Thursday night and Friday night. Sea
fog drifting onshore could become a concern during the weekend as
sfc winds gradually turn southerly. Patchy fog remains in the
forecast for most locations each night, but could need to be
expanded in coverage this weekend, especially near the coast.


A large ridge of high pressure extending from the western Atlantic
late weekend will begin to retreat southeast early next week as a
mid/upper trough of low pressure advances toward the Mid Atlantic
and Northeast United States. A southward extending cold front
associated with this trough is expected to slowly advance through
the Southeast United States Sunday and Monday, bringing at least
chances of showers to most areas. PWATs up to 1.75 inches and
favorable upper-lvl divergence associated with a passing h25 jet
aloft also suggest a period of moderate showers late Sunday into
Monday. Despite increasing cloud cover and shower activity, temps
will likely remain warm through much of Sunday ahead of cold front,
peaking in the upper 70s to lower 80s away from the coast during the
afternoon. Showers and cold fropa should lead to noticeably cooler
temps on Monday with afternoon highs peaking in the low/mid 70s.
High pressure should then build over the area from the north into
the middle of next week under a zonal flow aloft, favoring even
cooler temps each day over Southeast South Carolina and Southeast
Georgia. In general, temps should peak in the upper 60s to lower 70s
Tuesday, then mid/upper 60s Wednesday. Overnight lows could dip into
the upper 40s/lower 50s Tuesday night.


Surface and satellite observations indicate that VFR conditions
should prevail through the remainder of the afternoon. Moisture
profiles do support broken ceilings periodically lowering to
MVFR levels, but probabilities of prevailing MVFR conditions are
too low to include a group in the TAFs. For now, a TEMPO group
showing MVFR ceilings at SAV has been introduced through 16Z.
Fog/stratus probabilities will increase again late tonight.
Limited conditions to MVFR for now, but lower conditions may be

Extended Aviation Outlook: Flight restrictions are possible with low
stratus and/or fog during late night into early morning hours each


Today: Southeast winds will persist today with speeds around 10
kt. Seas will average 2-3 ft nearshore waters with 3-4 ft
offshore waters. Could still see some patchy sea fog linger
through late morning, but no major impacts are expected.

Tonight: Winds will veer more southerly tonight as Atlantic high
pressure maintains its influence over the region. This slightly
more southerly component could support a higher risk for sea fog
as parcel residence times will increase slightly. Will show
areas of fog after midnight, especially within 5 NM of the
coast. Speeds will generally remain near 10 kt with seas 2-3 ft
nearshore waters and 3-4 ft offshore waters.

Thursday through Monday: High pressure will dominate the weather
pattern over the coastal waters through the weekend. The pattern
favors fairly quiet conditions in regards to winds/seas with
conditions expected to remain below Small Craft Advisory levels.
However, sea fog will potentially be an issue while lower 60 dewpts
spread across slightly cooler nearshore waters, especially when
light southeast winds gradually turn south this weekend. Marine
Dense Fog Advisories are possible. In general, southeast winds
should remain at or below 10 kt under the influence of strong high
pressure, then gradually turn more south and increase to 10-15 kt
ahead of a cold front approaching the waters early next week. A
northerly wind should then develop on Monday behind the cold front.
Seas will range between 2-4 ft in nearshore waters and peak near 4-5
ft in offshore Georgia waters.


Record highs for February 21:
KCHS: 82/1991
KSAV: 83/1991
KCXM: 80/2001

Record high minimums for February 21:
KCHS: 61/1989
KSAV: 62/1939
KCXM: 61/1939

Record highs for February 22:
KCHS: 82/1991
KSAV: 83/1991 and previous
KCXM: 77/2011

Record high minimums for February 22:
KCHS: 60/1990
KSAV: 64/1897
KCXM: 61/1991 and previous

Record highs for February 23:
KCHS: 81/2012 and previous
KSAV: 84/2012
KCXM: 78/1980

Record highs for February 24:
KCHS: 81/2017
KSAV: 86/2012
KCXM: 81/1930


The Downtown Charleston observation site (KCXM) is reporting
intermittently. Please use the data with caution.




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