Area Forecast Discussion
Issued by NWS Charleston, SC

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534
FXUS62 KCHS 192021
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
321 PM EST Mon Feb 19 2018

.SYNOPSIS...
A large area of high pressure will remain across the region for
much of the week. A cold front should approach the area early
next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
The weak coastal trough has shifted inland this afternoon with S
to SSE flow developing in most locations. Sfc dewpoints are now
in the low to mid 60s. A weak onshore flow through tonight will
maintain a positive moisture flux beneath a strengthening
nocturnal inversion. This favors the redevelopment of low
stratus late this evening, with gradual lowering as the boundary
layer flow weakens. Models are in fairly good agreement on the
potential for widespread fog after midnight, potentially dense.
We continue to show areas of fog developing overnight and will
maintain a mention of dense fog in the Hazardous Weather
Outlook. Lows will drop into the upper 50s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
The short term period will be dominated by a large ridge centered
between the Carolinas and Bermuda. In fact, GEFS normalized anomaly
of H5 and H7 heights will remain two standard deviations above
normal Tuesday through Thursday. To the west, a longwave trough will
remain over the western CONUS through the period. This pattern
should keep deep moisture generally limited to Mississippi basin.
Forecast soundings across the CWA indicate a very strong subsidence
inversion centered around H85, the strength of the inversion is
forecast to range from 4-6 degrees C. Below the inversion, southeast
winds will supply marine moisture across the forecast area,
especially near the coast. At night, the moisture will likely
support the formation of widespread stratus, with lowering cloud
bases through the night. The development and lowering of stratus
will be possible each night, resulting in late night to early
daytime fog. Daytime mixing may allow cloud cover to scatter during
the afternoon. However, cloud cover will be slow to dissipate from
morning stratus. Despite the cloud cover, a very warm thermal
profile should result in high temperatures to reach the low to mid
80s inland, in the upper 70s near the coast. These temperatures will
be near record levels, see climate section below. The strong capping
and lack of forcing will result in dry conditions through the short
term period.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A large ridge of high pressure centered over the western Atlantic
will be the primary contributor to the weather over the Southeast
United States, allowing warm conditions to persist through the
weekend. In general, temps will be well above normal, peaking into
the upper 70s/lower 80s Friday, Saturday and Sunday. Overnight lows
will be mild, ranging in the upper 50s to lower 60s. The next chance
for more substantial shower chances should arrive late Sunday or
Monday as a mid/upper trough passes to the north with a southward
extending cold front that shifts through the Southeast. Once fropa
occurs, temps should be slightly cooler, peaking in the mid/upper
70s on Monday.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
The stratus and fog gradually burned off this morning. Mainly
scattered cumulus deck expected this afternoon into early
evening. However, abundant low-level moisture and weak wind flow
combined with the loss of daytime heating should facilitate
extensive stratus development this evening. MVFR conditions will
quickly take hold, lowering to IFR by late evening at KSAV and
early Tue morning at KCHS. Fog potential looks a bit greater
tonight than last night given weaker low-level winds so we have
visibility also dropping considerably later tonight. Climatology
favors worse conditions at KSAV so we included LIFR late tonight
into Tue morning. Conditions should gradually improve through
late Tue morning.

Extended Aviation Outlook: Fog and low ceilings may develop across
the region Tuesday night into early Wednesday morning. Patchy fog is
possible late Wednesday night. Otherwise, VFR conditions should
prevail.

&&

.MARINE...
Fairly weak winds/seas expected through tonight. Fog will again
be a possibility due to southeast flow bringing higher dewpoint
air across the cooler nearshore waters. Additionally, we expect
stratus to develop along the coast this evening and gradually
lowering. Marine fog is likely within 15 NM of shore, including
harbors and inlets. Dense fog is also possible, especially after
midnight. We are showing patchy fog this evening, becoming areas
of fog overnight.

Monday through Saturday: Strong high pressure will remain over the
western Atlantic through late week. Warming dewpoints and a strong
low level inversion should yield marine stratus with fog over the
shelf waters through Thursday. Otherwise, the marine area should see
steady southeast winds and wave heights between 2-3 feet nearshore
and 4-5 feet across the outer GA waters.

&&

.CLIMATE...
Record Highs

Wednesday 2/21 CHS   82 1991
               SAV   83 1991
               CXM   80 2001

&&

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

&&

$$
NEAR TERM...JRL
SHORT TERM...NED
LONG TERM...DPB
AVIATION...JRL/NED
MARINE...JRL/NED
CLIMATE...



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