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000
FXUS62 KCHS 290801
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
401 AM EDT Thu Jul 29 2021

...HOT AND HUMID CONDITIONS WITH EXCESSIVE HEAT POSSIBLE
THROUGH SUNDAY...

.SYNOPSIS...
High pressure will build over the area through Saturday. A cold
front will stall over or just north of the area Sunday through
the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Through Sunrise: Patchy to areas of fog will gradually expand
across the interior through sunrise. Condensation pressure
deficits are only marginally favorable for significant fog
formation, but vsby 2-4 miles are likely with some localized
patches of dense fog with vsby 1/4 mile or less possible near
bodies of water and other low-lying areas.

Today: Mid-level heights will steadily rise today as the large
anticyclone centered over the Central Plains builds into the
Southeast U.S and Deep South. An expansive area of dry air noted
on GOES-E water vapor imagery will remain across the area
through the afternoon. This dry air will essentially limit the
convective potential as any moist updrafts that area able form
ahead of the afternoon sea breeze will quickly get choked off
due to dry air entrainment. There is a weak signal in a few of
the CAMs that enough low-level moisture and H8 theta-e could be
present to allow for a shower or two to spark across far
interior Southeast Georgia in the Millen-Metter-Reidsville-
Ludowici corridor during peak heating, but any such shower
activity will be likely very short lived due to the reason noted
above. The risk for any measurable rainfall in this area is
likely to low to justify a mentionable pop.

Highs will range from the lower-mid 90s inland to the mid 80s
at the beaches. Dewpoints are expected to mix out into the lower
70s across the interior, but should hold in the mid-upper 70s
across the coastal counties as the sea breeze moves inland.
Would not be surprised to see a few spots in the coastal
corridor from Beaufort to Charleston see dewpoints briefly hit
the 80 degree mark. Heat index values are expected to peak
103-107 (highest across the coastal counties inland from the
beaches) which is below the local July Heat Advisory criteria of
110.

Tonight: Clear skies and dry conditions will prevail. While
winds across the interior are likely to decouple, winds may stay
up a bit across the coastal counties through the night as the
pressure gradient is expected to tighten a bit as lee-side
troughing develops to the west. Lows will range from the mid 70s
inland to the lower 80s at the beaches and Downtown Charleston.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
The mid-levels will consist of a long-wave trough to our north and a
strong and broad ridge to our west on Friday. The trough will
strengthen/amplify with time, pushing the ridge further to the west.

Friday: High pressure will prevail across our area during the day
with fair weather clouds. A cold front will approach from the
north/northwest at night, but it`s not expected to reach our area.
Models are in great agreement, keeping the area dry during the day.
Some of them hint at weakening convection maybe making it into the
Charleston Tri-County during the evening/overnight, then
dissipating. But given the dry air, we leaned towards a dry forecast
at night. Thickness values and 850 mb temperatures will yield
temperatures well above normal. High temperatures are forecasted to
be the hottest of the summer. Most locations will be in the upper
90s with several spots inland expected to hit the 100 degree mark.
Even the beaches won`t be much lower, generally being in the lower
90s. Dew points will vary across our area. Far inland, they`ll be in
the lower 70s as some drier air mixes in from the northwest. Closer
to the coast, they`ll rise to at least the mid 70s in the afternoon.
They`ll be even higher along the immediate coast upper 70s to near
80 degrees) where a pinned sea breeze will allow them to pool. The
combination of the heat and humidity will result in the highest heat
indices so far this summer. Heat indices above 110 degrees are
expected for our coastal counties and the CHS and SAV metro areas.
Heat Advisories would be needed for these locations. Farther inland,
if more dry air mixes in both the dew points and heat indices would
be a few degrees lower, which would be just short of Advisory
criteria. Even the night will be steamy, with some locations not
falling too far below the 80 degree mark. Temperature records for
the hottest nights could be in jeopardy.

Saturday: The cold front will stall over or just north of our area.
But moisture will increase with time. Most of the models have dry
conditions persisting across our area during the morning and the
early afternoon. Then, they have convection developing along the
front and the sea breeze late in the day and into the evening. It
appears the best convective potential will be across our SC
counties, aided by the proximity of the front and the sea breeze. A
few pulse severe thunderstorms are possible with damaging wind
gusts. But these details will need to be refined in future forecast.
Highs again will be well above normal, in the mid to upper 90s. Lows
will also be a few degrees above normal.

Sunday: There is the potential for another day with above normal
temperatures. But this will all depend on the afternoon convection
or lack of. Models differ on the convective potential and its
placement. For now, we stayed consistent with our neighboring
offices and all went with the NBM.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
The models have been persistent showing a mid-level trough
amplifying/strengthening across the eastern half of the country next
week. The surface pattern forecast from the WPC has a front just to
our north. As a result, the NBM has a wet pattern for our area next
week. The wettest conditions should be during the daytime hours.
High temperatures are forecasted to be below normal.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Fog is the main concern at all three terminals through sunrise.
Shallow ground of is already in progress at a number of
locations early this morning and will likely thicken to at least
MVFR at KCHS, KJZI and KSAV over the coming hours. Prevailing
MVFR vsbys will be highlighted roughly 08-09z through 1130z.
There are signals that a low cloud deck with cigs around 2000 ft
could briefly develop and mainly impact KCHS and KJZI just
before sunrise. The cloud deck is not as likely to impact KSAV.
The fog and low clouds will quickly burn off after sunrise
leaving only a shallow cumulus field which will get cleared out
during the afternoon with the passage of the sea breeze.

Extended Aviation Outlook: Flight restrictions are possible in
showers and thunderstorms late Saturday through Monday.

&&

.MARINE...
Today: Northeast winds this morning will veer to the southeast
this afternoon a sea breeze develops and moves inland. Winds
will generally remain 10 kt or less with seas 1-2 ft.

Tonight: South to southwest winds will pick up to 10-15 kt
overnight in response to lee-side troughing that develops well
to the west. Seas will average 1-2 ft.

Friday through Monday: Winds are expected to increase Friday
and Friday night as a cold front approaches from the
north/northwest. Wind gusts could hit 25 kt in the Charleston
Harbor Friday afternoon and evening, so a Small Craft Advisory
may be needed for them. Wind gusts across the rest of our
coastal waters appear to be just short of 25 kt through Friday
night. But if they rise a few kt, then Small Craft Advisories
will also be needed in these zones. The front should remain over
or just to our north this weekend into early next week. During
that time frame, each afternoon expect slight backing of the
winds and higher gusts associated with the sea breeze along the
land/sea interface and in the Charleston Harbor. Each night,
expect slight veering of the winds.


&&

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

&&

$$