809
FXUS62 KCHS 090613
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
213 AM 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 /UNTIL 6 AM THIS MORNING/...
At 210 AM, a line of severe thunderstorms was pushing east
across the upstate of SC. These storms should continue an
eastward motion, passing just north of the forecast area early
this morning.

It`ll be another warm night for May, with most areas not falling
below 70F. As of right now the low temperature at KCHS for May
8th has been 73F, which should it hold, would tie it for the
record high for the date set in 2003.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/...
Thursday and Friday: The mid-levels will consist of zonal flow
over the Southeast U.S. Thursday morning. A shortwave will be
embedded in the flow, moving over our area Thursday afternoon or
evening. Troughing will strengthen over the Great Lakes Region
on Friday, with amplification expected down towards our region
by late Friday. At the surface, Low pressure will be near the OH
Valley Thursday morning. This Low will gradually shift eastward
with time, moving off the Mid-Atlantic coast by late Friday. A
cold front attached to the Low will approach from the northwest
Thursday. It`ll be located just to our northwest early Friday
morning. The front should slowly move through our area from
northwest to southeast Friday afternoon, shifting offshore
Friday evening. The main focus will be the severe potential
Thursday, followed by possibly a second round on Friday.
Thursday morning should be dry, with any convection going on
well to our west. This line is expected to shift eastward during
the day, and into our area. There will be a deep plume of
moisture ahead of this line with PWATs rising to ~2". This is
well above normal for this time of year, above the 90% mark for
CHS per the SPC Sounding Climatology. In addition to this
moisture will be above normal temperatures. Highs will peak in
the lower to middle 90s, which is near record values for this
date. So there will be plenty of moisture and heat in place
across our area, which will be supportive of severe
thunderstorms. MLCAPE values should peak in the 1,500-2,000 J/kg
range. Lapse rates will be steep, especially in the lower
levels, Additionally, nearly unidirectional 0-6 km shear should
be in the 40-50 kt range. So the main threat will be damaging
winds, possibly widespread, large hail, and maybe even an
isolated tornado. The SPC has upgraded portions of our area to
an Enhanced risk, and this seems reasonable given the
environmental setup. The main question will be the timing and
evolution of the storms. The CAMs have a MCV moving through our
area, ranging from the very late morning through the afternoon.
The synoptic models also hint at this, more towards the later
afternoon. Since any lines of convection tend to move faster
than the models, we`re anticipating it to reach our far inland
counties early in the afternoon, making it to our coastline by
later in the afternoon, then offshore by the evening. The line
will be moving at a decent speed, so the severe threat at any
one location should only be around for maybe an hour or two. In
addition to the already mentioned hazards, locally heavy
downpours are expected, with flooding possible in the typical
low-lying and poorly drained areas. But the risk of widespread
areal flooding is low. Once the convection moves through, their
should be some remnant showers persisting into the evening, with
a potential lull for a brief time overnight. Then, another
round of convection is possible Friday morning into the
afternoon. The models are starting to hint that the instability
and moisture setup could be similar on Friday compared to
Thursday. But this doesn`t mean that we`ll have identical severe
impacts on Friday. What happens on Friday will depend partly on
what happens Thursday. The SPC has our area under a Marginal
Risk for severe weather on Friday, and this seems reasonable. We
wouldn`t be surprised if it got upgraded further. Otherwise, we
have likely POPs for most of the day Friday with high
temperatures near normal. Convection will finally end from
inland to coastal locations Friday evening, as the front moves
through. Friday overnight is expected to be dry. Clearing skies
will yield temperatures from the mid 50s far inland to the
lower/middle 60s along the immediate coast.

Saturday: Mid-level troughing will persist over the East Coast.
High pressure will build in from the west, bringing much drier
conditions. Expect mostly sunny skies with highs in the upper
70s to lower 80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
High pressure will bring dry conditions and seasonal
temperatures this weekend through early next week. Models then
suggest that a storm system could move across our area starting
late Monday and possibly lasting through Wednesday. There
remains uncertainty in the models, so we didn`t stray away from
the blend, which has a period of likely POPs. But this aspect of
the forecast will need to be adjusted with future updates.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
VFR conditions are expected to prevail at KCHS, KJZI, and KSAV
into early this afternoon. A line of thunderstorms will approach
from the west this morning. Based on radar trends and recent
HRRR runs, the leading edge of the thunderstorms is expected to
reach KCHS, KSAV, and KJZI by 18Z. The TAFs will feature gusty
west winds and TSRA by 18z. The environment may support severe
wind gust and possibly hail. Each TAF will also include a TEMPO
from 18-21Z for VFB20G30kts and MVFR conditions during TSRAs.
High resolution guidance indicates that the thunderstorms will
push east over the Atlantic by late this afternoon, with
generally stratiform rain with isolated lightning remaining into
the early to mid evening.

Extended Aviation Outlook: A front will bring periods of flight
restrictions Thursday night through Friday. VFR will return for
the weekend.

&&

.MARINE...
Tonight: There remains a fairly decent gradient between high
pressure centered to the east-southeast, and strong low pressure
in the middle Mississippi Valley. The end result will be for S
and SW winds as high as 15 or 20 kt throughout, even in
Charleston Harbor. Seas will increase, becoming 2-4 feet on
average, and up to 5 feet in the outer Georgia waters.

Thursday through Friday: A strong cold front will approach
Thursday causing SW winds to increase. Marginal Small Craft
Advisory conditions are expected across our Charleston waters
Thursday afternoon and evening due to gusts around 25 kt, and
again Friday night behind the front. Additionally, there will be
the potential for strong thunderstorms Thursday afternoon and
evening, following by a second round Friday late morning or
afternoon. The timing of thunderstorms remains unclear, but any
storms that do develop and move across the waters will be
capable of producing strong wind gusts.

Saturday through Monday: Marine conditions will rapidly improve
this weekend as weak high pressure builds in from the west. By
Saturday, winds will drop to 10-15 kt and seas to 3 ft or less
through Monday.

&&

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

&&

$$

NEAR TERM...NED
SHORT TERM...
LONG TERM...
AVIATION...NED
MARINE...