Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 061754
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
154 PM EDT Wed Jul 6 2022

.SYNOPSIS...
High pressure will prevail across the region most of this week.
A front will shift across the area late weekend, then stall
south of the region. High pressure should then return early
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Rest of Today: Low and mid level ridging will prevail across
the entire region, while at the surface the local counties
remain between an inland trough and sub-tropical ridging that
extends across the western Atlantic.

It`ll be a typically hot and humid summer day with 850 mb temps
as high as near 20C, resulting in max temps in the lower and
middle 90s away from the effects of the sea breeze near the
coast. These values combined with dew points as great as the mid
and upper 70s will yield max heat indices of 105-108F most
communities. There could even be a few pockets of 110F heat
index values, but not enough to raise a Heat Advisory.

The coverage of convection through the day looks fairly limited
given the large scale subsidence in place with the low and
mid level ridging. However, MLCAPE in excess of 3000 J/kg and
meso-scale boundaries such as the sea breeze and a remnant
outflow from overnight convection, plus the proximity to the
inland trough, will produce at least isolated to scattered
showers and t-storms this afternoon.

Since DCAPE reaches as high as 800-1000 J/kg, there might be
isolated instances of strong or marginally severe downbursts of
wind, while the strength of the updrafts and Hail CAPE around
1000 J/kg can cause a little large hail to occur in isolated
storms. In addition, PWat of 2.0-2.3 inches and limited storm
motion can result in locally heavy rainfall.

Tonight: The low and mid level ridging looks to weaken a tad,
allowing for a short wave ride and maybe an associated MCS to
ride in from the northwest. This produces 30-50% PoPs across
much of South Carolina and 20-30% chances in Georgia. These PoPs
might prove to be too conservative, especially north and west,
and the greatest coverage will generally be between 9 PM and 1
AM. The strength of the updrafts as indicated by the HREF and
risk for cold pooling to occur, will yield a low end chance of
strong or marginally severe winds in isolated storms. Should an
MCS indeed occur, given elevated PWat, locally heavy rains will
be likely. Even with rain-cooled air to occur, it`ll still be a
warm night with min temps in the mid and upper, except for some
lower 70s where the heavier rains occur.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday and Friday: Mid-lvl ridging will persist across much of the
Deep South and Southeast United States, but will gradually weaken
while retreating west as a series of h5 shortwaves traverse along
the southern periphery of a broad trough extending across the
Northeast. Each day should start off typical of summertime, with
onshore winds and a sea breeze circulation being the primary driver
of convection across the local area during peak diurnal heating.
Heading into late afternoon and early evening hours, precip trends
should become more focused on upstream convection across the Mid-
Atlantic states potentially making a run toward north/inland
locations. Strong diurnal heating (highs in the low-mid 90s), ample
moisture characterized by PWATS greater than 2.25-2.50 inches along
with weak shear suggest marginally organized convection potentially
reaching the local area during evening hours. A few thunderstorms
could be strong and/or marginally severe with damaging winds. Some
thunderstorms could also produce heavy rainfall given a moist
environment and weak steering flow. Low temps will remain mild,
generally in the mid-upper 70s away from the immediate beaches each
night.

On Saturday, the longwave trough across the Northeast United States
becomes slightly more amplified, shifting the focus of h5 shortwave
energy across the Carolinas for much of the day. Given a warm and
moist airmass in place (highs in the low-mid 90s and PWATs
approaching 2.5 inches), scattered to numerous showers/thunderstorms
are probable, some of which could produce a period of heavy
rainfall. A few strong and/or marginally severe thunderstorms can`t
be ruled out during afternoon/evening hours.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Broad mid-lvl ridging will continue to retreat west while a weak
cold front advances toward the region from the north, eventually
traversing the local area Saturday night through Sunday, producing
periods of showers and thunderstorms capable of heavy rainfall
within a warm and moist environment marked by PWATs in excess of
2.25 inches. A few strong and/or severe thunderstorms can not be
ruled out with fropa. Once fropa occurs, temps should be noticeably
cooler (5-10 degrees) for a few days (highs in the mid-upper 80s).
Low temps should also be cooler, generally ranging in the low-mid
70s. Latest guidance suggests high pressure to return across the
Southeast United States while the previously mentioned front remains
stalled just south of the region early next week. Given the setup,
convective patterns should be more typical of the summer with
afternoon/early evening showers and thunderstorms driven by inland
moving seabreeze circulations under large scale ridging aloft.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
18Z TAFs: The sea breeze should bring increased winds this
afternoon. Though, probabilities of flight restrictions from
SHRA or TSRA are too low to include in the TAFs. Another round
of SHRA or TSRA could move in from the northwest this evening,
most likely bringing some impacts to CHS, then maybe JZI. We
added VCSH in the CHS TAF for a few hours to account for this,
but more changes will be needed based on future radar trends.
Further south at SAV, no impacts are expected in the evening and
overnight.

Extended Aviation Outlook: Brief flight restrictions are possible
during afternoon/evening showers and thunderstorms through late
week. Periods of flight restrictions are possible this weekend as
shower/thunderstorm coverage increases with an approaching cold
front. Otherwise, VFR conditions should prevail.

&&

.MARINE...
Rest of Today and tonight: The local marine community will lie
within the western extension of sub-tropical Atlantic ridging
and a NE-SW oriented trough inland. Sea breeze circulations and
nocturnal low level mixing will produce S and SW winds as high
as 15 or 20 kt, with seas on average 3 or 4 feet.

Mariners are to remain alert for isolated to scattered t-storms
tonight, some of which could result in heavy rains with reduced
visibilities, gusty winds and larger seas.

Thursday through Monday: High pressure will remain the dominant
weather feature across the western Atlantic while weak troughing
occurs inland for much of this week. However, a series of low
pressure waves will approach the region from the north-northwest
late week, resulting in some enhancement of the pressure gradient
across local waters through at least Friday. Southerly winds should
increase to 15-20 kt, with the potential of slightly higher winds
supporting the need of marginal small craft advisory conditions
across portions of the coastal waters. Seas should also build from 2-
4 ft to 3-5 ft late week. A cold front is then expected to shift
across local waters late Saturday into Sunday, resulting in a brief
surge of offshore winds that eventually turn more northeast-east
early next week. However, winds and seas are expected to gradually
decrease/subside Monday as the front stalls south of the region and
the pressure gradient becomes more relaxed across local waters.

Rip Currents: Nearshore buoy observations indicate a 2 ft swell
around 9 seconds. This combined with modest onshore winds at
the beaches this afternoon will generate a Moderate Risk of rip
currents. A few rip currents have already been reported at
Tybee Island and more are possible at other beaches.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...DPB
LONG TERM...DPB
AVIATION...
MARINE...


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