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000
FXUS62 KCHS 060747
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
347 AM EDT Thu May 6 2021

.SYNOPSIS...
A cold front will advance through the region today. Weak low
pressure will develop near the Southeast coast tonight and will
move away through Friday. Drier high pressure will then prevail
through this weekend. Another cold front is expected to push
into the region early next week. The front could stall just
south of the area, allowing low pressure to track over the
Southeast around the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: The cold front is poised to move across the local
counties from the northwest prior to daybreak, eventually
pulling off most coastal sections by 12Z. The front will only
make it so far southeast and south of the region through the
day, stalling out across Florida as it becomes somewhat aligned
to the flow aloft. A short wave dropping east-southeast from
middle Mississippi Valley and into the Tennessee Valley will
cause a wave of low pressure to form along the front about
150-200 nm east of Charleston. There are even indications that a
secondary wave could develop closer to the Charleston region by
late in the day, as a mid level trough over the eastern states
amplifies with time, causing heights to gradually fall across
the region.

Our potential for any convection is limited, given weak
forcing, minimal instability and CAPE and considerable dry air
above the boundary layer. We show just slight chance PoPs across
coastal Georgia and also over McIntosh County where the better
moisture profiles will exist. We can`t rule out a few showers
further north into coastal South Carolina along the sea breeze
this afternoon, but there is just too much dry air in place, so
we held off any mention in the gridded forecast.

A deep offshore flow will prevail across most communities near
and west of I-95, while a slackened pressure pattern allows for
sea breeze circulations, albeit rather weak, to form elsewhere
in the afternoon. This will cause a rather large spread in max
temperatures, which look to range from the lower 70s across
shoreline sections of Charleston County, to as warm as 80-85F
across the vast majority of the region outside of there.

Tonight: A broad mid and upper level trough will cross the area
will cause the Atlantic low to deepen a bit as it shifts further
offshore. There might be just enough moisture within the
cyclonic flow around this feature to produce a few showers
across parts of Charleston and Berkeley County. But rain
probabilities are held at less than 15%, so do not require any
mention in the forecast. There is good cool advection in wake
of the departing area of low pressure, as 850 mb temperatures
drop from 11-12C at 00Z Friday down to 7-8C by 12Z Friday.
Within a dry air mass, temperatures look to get down into the
lower and middle 50s inland from US-17, with upper 50s or lower
60s closer to the immediate coast and in the Charleston metro
region.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
This period will feature rain-free conditions.

Friday: Between low pressure northeast of our area and dry high
pressure building from the west/northwest, west to northwest winds
could gust to around 30 mph from late morning into early evening.
Expect highs in the middle to upper 80s, warmest near the coast due
to downslope/offshore flow.

Friday night: High pressure will expand east over the region, and
clear skies, light winds and dry air will promote excellent
radiational cooling. This will be the coolest night of this forecast
cycle, with lows ranging from the middle/upper 40s inland to the
middle/upper 50s close to the coast, and lower 50s across a wide
swath of territory in between.

Saturday: The surface high will shift offshore, and a ridge of high
pressure will build through 850 mb over the Southeast. This will
support a slightly warmer temperatures, with highs in the upper
70s/lower 80s at most locations, except lower/middle 70s on the
beaches due to the sea breeze.

Lake winds: West-northwest winds could gust around 25 knots on Lake
Moultrie Friday. A Lake Wind Advisory could be required.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Sunday: Rain-free conditions will continue for one more day. The
surface high will shift over the Atlantic, and deep layered ridging
will prevail across the region. This scenario will support a return
to above-normal temperatures middle/upper 80s common, and a few
inland GA locales could top out around 90F. On the beaches, the sea
breeze should hold temperatures in the 70s.

Monday and Tuesday: Another cold front will cross the region. Ahead
of the front, guidance depicts at least scattered showers/
thunderstorms Monday into Monday night. Medium range depictions of
limited instability suggest a low chance for severe weather.
Tuesday, the front is expected to push through then stall just south
of the region, and possible scenarios range from lingering moisture
and isolated/scattered showers to stronger high pressure pushing
most moisture/precipitation south of the region. The latest forecast
settled on slight chance PoPs north/chance PoPs south, but
adjustments will almost certainly be required within subsequent
forecasts. Temperatures in the middle/upper 80s Monday should cool
slightly into the lower/middle 80s Tuesday.

Wednesday and Thursday: The stationary front/associated baroclinic
zone will persist over the southeast CONUS, and moisture transport/a
series of shortwaves should support a more general chance for
showers/thunderstorms. The main upper trough should advance through
the region with a continued chance for showers/thunderstorms
Thursday. The potential for severe weather may remain low, as a weak
wedge regime could hold instability south of the region. Also, due
to uncertainty regarding timing/coverage of precipitation, PoPs are
capped at chance for this period, but high PoPs could be required
for at least part of the time. Due to clouds/precipitation, high
temperatures should remain below normal in the 70s, and cooler
temperatures are possible within the wedge over northern/inland
counties.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
VFR will prevail through 06Z Friday. Winds will shift to the NW
and N behind a cold front prior to 12Z, with a forecast
challenge of whether or not the sea breeze can push through the
terminals this afternoon.

Extended Aviation Outlook: Expect gusty WNW winds Friday afternoon.
VFR through Sunday. Flight restrictions are possible early next
week.

&&

.MARINE...
Today: A cold front will slide across the coastal waters early
this morning, progressing south and southeast through the day. A
weak wave of low pressure will form along the front about
100-150 nm east of the local waters. This pattern will allow
for winds to clock around to the N and NE on the South Carolina
waters and to the NW on the Georgia waters during this morning.
Then as the gradient slackens this afternoon, sea breeze
influences will turn winds around to a more E or SE direction.
On average wind speeds will be at or below 15 kt through the
entire day, with seas of 2 or 3 ft.

Tonight: The aforementioned low will deepen a few millibars as
it lifts east and northeast, allowing for a decent climb in
pressure overnight, along with increasing cool advection. This
will generate winds that eventually shift to the W and NW,
increasing quite a bit after midnight, peaking at 15-20 kt on
the Georgia waters late, and generally 15 kt or less elsewhere.
The offshore flow will limit how large seas can get, so 3 or 4
ft looks to be the maximum at this stage.

Friday through Tuesday: Between low pressure northeast of our area
and dry high pressure building from the west/northwest, west to
northwest winds could gust around 25 knots Friday/Friday evening,
and Small Craft Advisories will likely be required for most/all
coastal waters. Seas of 3-5 feet will prevail Friday into Friday
night, and seas as high as 6 feet cannot be ruled out beyond 20 nm.
As high pressure shifts over the waters later Friday night through
Saturday, NW winds should back to SW and diminish below SCA levels.
Seas will subside to 1-3 feet. Then, high pressure will shift into
the Atlantic, and S/SW winds will increase to at least 15-20 knots,
with gusts to 25 knots and associated SCAs possible. Seas will build
to at least 3-5 feet. These conditions will persist until a cold
front crosses the waters Monday night/early Tuesday, and winds
shift to the N. After cold fropa, seas should subside to 2-3
feet.

&&

.FIRE WEATHER...
Friday: West-northwest winds will likely gust to around 30 mph
during the afternoon, and afternoon relative humidity values are
expected to drop to 25-30 percent at many locations, leading to
increased fire potential. However, recent rainfall has raised fuel
moisture in many areas, and this could limit the overall fire danger.

Saturday: Relative humidity could fall into the 20-25 percent range
inland, but wind gusts should remain capped at 15-20 mph.

Sunday: Atlantic high pressure could contribute to south-southwest
winds gusting around 25 mph, and inland relative humidity could fall
into the 25-30 percent range.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
FIRE WEATHER...