093
FXUS62 KCHS 091757
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
157 PM EDT Thu May 9 2024

.SYNOPSIS...
A cold front will approach the area tonight, then move offshore
Friday. High pressure will prevail for the weekend into early
next week. A storm system could affect the area by the middle
of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Radar indicates a line of strong to severe thunderstorms over
our area and moving towards the coast. Temperatures ahead of the
line have peaked in the mid to upper 80s, which is a bit lower
than the expected highs, owing partially to stratus hanging
around a little longer this morning. But even with this, there
is plenty of instability in place. SPC Mesoscale Analysis
indicates MLCAPE values peaking in the 1,500-2,000 J/kg with
effective bulk shear 45-50 kt. DCAPE values have trended a
little lower, but combined with the shear, this will continue to
bring us an enhanced wind threat. An tornado also cannot be
ruled out into late this afternoon given the hodographs.

We continue to adjust the POPs/weather grids based on the radar
trends. The CAMs continue to indicate the southern end of the
line that will move across our GA counties will be slower to
reach the coast by about 1-2 hours, followed by stratiform
precipitation across our area for about 1-2 hours beyond that.
The rainfall will dissipate and move east of the forecast area
by mid-evening. The rest of the night should remain generally
dry. However, a second MCS will arrive from the west after the
pre- dawn hours Friday morning. Rain-cooled temperatures are
expected to remain nearly steady around 70 degrees tonight.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Friday: We remain focused on Friday with another potential severe
weather day ahead. By morning, the cold front will be positioned
across the SC/GA Midlands. The front is not expected to clear the
area until late, therefore we could see another round of convection
moving in from the west some time between late morning and afternoon
as the boundary presses toward the coast. This is another highly
uncertain event with a range of possibilities, noted by differing
solutions for nearly each model. Most models do show some sort of
line/cluster of showers and thunderstorms moving through the
forecast area at some point during the day however. One possibility
is that lingering showers/thunderstorms in the morning could delay
destabilization, which will inhibit deep convection later in the
afternoon. There are also signals of an upstream MCV propagating
across southern AL/GA and northern FL, which could advance into
southeast Georgia and portions of southeast South Carolina. However
these southerly systems have the potential to greatly alter the
downstream environment by cutting off southerly flow/moisture across
the forecast area, thus inhibiting destabilization. On the other
hand, a moderate break from the previous night`s convection and
perhaps a slight break in clouds would destabilize the environment
early on, allowing for a rich, untapped environment for
strong/severe storms to develop. Overall, it is unclear how the
severe threat will pan out Friday, and there is a degree of
dependence on the evolution of Thursday`s event. With that said, any
severe storms that develop would be capable of producing damaging
wind gusts, large hail, and/or an isolated tornado. Outside of
severe weather, showers and even general thunderstorms could result
in locally heavy downpours with PWATS in the 1.6-1.8" range.
Guidance hints towards the greatest rainfall amounts falling south
of the Savannah River. Showers and thunderstorms should push
offshore by the evening with conditions rapidly clearing behind the
front. Max temperatures will be slightly cooler due to ongoing or
afternoon convection, with highs in the mid 80s. FROPA and clearing
skies will cause temperatures to significantly drop Friday night,
with lows in the mid to upper 50s inland and lower 60s along the
coast.

Saturday and Sunday: Quasi-zonal flow will exist aloft and general
high pressure will gradually build. A cool, dry air mass will move
into the area behind the cold front bringing rain-free conditions.
Mostly sunny skies are expected both days with highs peaking in the
upper 70s to low 80s Saturday and low to mid 80s Sunday. A
relatively cool night is expected Saturday, with lows in the mid to
upper 50s inland and lower 60s along the coast.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Early next week will briefly start off quiet before a warm front
extending across the Deep South lifts north. Conditions look quite
unsettled beginning late Monday night into Wednesday. Rain chances
were increased into the likely range (55-70%) during this period due
to the consensus of deep moisture moving in, in addition to
plentiful forcing aloft with a shortwave traversing the Central U.S.
Near normal temperatures are expected to rise through the middle of
next week owing to southerly flow.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
18z TAFs: Radar indicates a line of thunderstorms moving
towards the coast. The highest probability of impacts is noted
with TEMPO groups, with remnant thunderstorms persisting
afterwards, and then stratiform precipitation. The precipitation
should end by this evening, with VFR persisting into part of
the night. MOS and some of the ensembles then indicate IFR
ceilings developing over the terminals late tonight, which we
kept in the TAFs. Finally, another round of showers and
thunderstorms is expected to bring impacts to the TAF sites late
in the TAF time period.

Extended Aviation Outlook: Scattered to numerous showers and
thunderstorms could continue into Friday afternoon with flight
restrictions and gusty winds possible within convection. VFR
conditions will return for the weekend into early next week.

&&

.MARINE...
Southwest winds will range between 15-20 kt the rest of this
afternoon. A few periods of gusts around 25 kt are possible
across the Charleston County nearshore waters, but no Small
Craft Advisories are planned at this time. Seas should favor
values between 3-4 ft, with 5 ft seas possible across portions
of the Charleston Co. nearshore. Otherwise, the primary concern
remains the passage of a squall line of thunderstorms late this
afternoon into early this evening. These storms could produce
gusts in excess of 50 kts and possibly a waterspout. Convection
should end over the marine zones this evening. Winds tonight
will return from the southwest between 15 to 20 kts. Wave
heights of 2-4 ft will be common tonight.

Friday: A strong cold front will push offshore late, causing SW
winds to shift out of the north. Marginal Small Craft Advisory
conditions are expected Friday afternoon through Friday night with
gusts ranging between 20-25 kt. At this time, the Charleston County
nearshore waters out to 20nm and the outer Georgia waters from 20-
60nm look the most promising for any advisories that could be
needed. Seas will be slightly elevated with 2-4 ft in the nearshore
waters and 5 ft seas beyond 20nm. Another concern for the local
waters will be the potential for strong thunderstorms Friday
afternoon. There is still a large degree of uncertainty; however,
any storms that do develop and move across the waters will be
capable of producing strong wind gusts.

Saturday through Tuesday: Marine conditions will improve Saturday
morning as high pressure builds in from the west. Northerly winds
will shift out of the south with speeds dropping to 10 kt or less
and seas averaging 1-3 ft through Monday. Monday night into Tuesday
winds and seas look to increase/build ahead of the next storm
system.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...BRM
LONG TERM...BRM
AVIATION...BRM
MARINE...BRM