Severe Thunderstorm Warning 43, NWS Charleston, SC

Area Forecast Discussion
National Weather Service Charleston SC
335 PM EDT Sat Jun 8 2019

.SYNOPSIS...
Low pressure and unsettled conditions will prevail through the
first half of next week. A cold front will advance into the
Southeast starting around midweek, but this front could be slow
to push through the region. Drier high pressure should build
over the area late week or early next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Latest RAP analysis shows the strongest moisture transport
centered across interior Southeast South Carolina and this is
where the largest concentration of convection is ingoing.
Instability remains plentiful and moisture levels remain high
with PWATS 2.0-2.25 inches. Convection should remain centered
across the interior for the next few hours before additional
convection, possibly in the form of a line, moves north out of
northern Florida and far Southeast Georgia this evening.

Tstm activity has been pretty sparse across northern Florida so
far where deep convection stretching from the eastern Gulf of
Mexico into central Florida is likely having some sort of
impact. However, analysis tools do show both moisture transport
and deep layered convergence is building so expect showers/tstms
to initiate across far Southeast Georgia soon. This is likely
the activity at the various HREF members are grabbing onto and
pushing it north across Southeast South Carolina and Southeast
Georgia later this evening. Pops will be held at 70% for most
areas this evening with chance pops for the early morning hours
Sunday given the warm, moist and weakly unstable atmosphere will
linger. Lows will range from the lower 70s inland to the upper
70s at the beaches.

A few strong to briefly severe tstms will be possible with
torrential rainfall, cloud-to-ground lightning and damaging wind
gusts being the primary threats. The severe threat will be
greatest where updrafts become augmented by mesoscale boundary
collisions.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Sunday through Monday: Low pressure at the surface and aloft and
associated moist environment will dominate conditions. Primarily in
response to a shortwave trough advancing through the northern
Plains/Great Lakes, the Southeast Conus upper low will gradually
open and weaken Sunday through Monday, transitioning to a positively
tilted trough over the region by early week. Sustained moisture
transport will maintain PWAT values around 2 inches. Within this
environment, the combination of instability and modest forcing for
ascent provided by weak shortwave troughs aloft and various
mesoscale surface boundaries will support periods of
showers/thunderstorms. While precipitation could occur at any time,
best coverage of convection should occur from late morning/midday
into the evening hours. This convective regime will belie accurate
portrayal of hourly PoPs beyond a few hours into the future, but
most/all areas should receive measurable rainfall Sunday and Monday.

Locally excessive rainfall could occur either day. However, the
probability for widespread flooding rainfall should remain low, and
most rainfall should be beneficial given our moderate to severe
drought conditions.

Sunday, clouds/precipitation could limit instability, so the
potential for any pulse severe thunderstorms with damaging wet
microbursts should remain quite low. However, latest guidance
consistently depicts somewhat stronger diurnal instability Monday,
so the potential for pulse severe thunderstorms could be somewhat
greater.

Otherwise, hourly and maximum temperatures will depend greatly on
convective trends both days. Where conditions remain rain-free for a
few hours and/or where some sunshine manages to break through cloud
cover, temperatures could push into the upper 80s. Conversely,
temperatures will fall back into the 70s when/where thunderstorms/
heavy rain occur. Low temperatures should remain mainly in the 70s,
as high as upper 70s on the beaches.

Tuesday: The upper trough will continue to weaken but along with
surface low pressure will persist over the region. Most
significantly, guidance depicts high pressure over the Ohio
Valley/Great Lakes attempting to expand and push a cold front/drier
air toward our area. Feel that cold fropa/stronger drying over
northern counties as depicted by the 08/12 UTC GFS20 is too
optimistic, and the NAM12/European solutions are preferred. The
latter scenario suggests that the cold front/drier air will remain
north of our region, and deep layered moisture featuring PWAT values
around 2 inches will remain draped over our region with periods of
showers/thunderstorms.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Tuesday night and Wednesday will likely remain quite wet due to
a surface low moving through the area, accompanied by upper
shortwave energy. The upper trough finally starts to shift northeast
late in the week with drier high pressure building over the area
Thursday into the weekend.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Update from earlier thinking. Convection now looks to remain
north and inland of the terminals through mid-afternoon with
convection potentially moving through both KSAV and possibly
KCHS this evening. Highest confidence is at KSAV where MVFR
conditions will be highlighted. VCTS seems appropriate at KCHS
for now with this second area of convection.

Extended Aviation Outlook: Periods of showers/thunderstorms will
produce flight restrictions and gusty winds at both terminals,
especially from late morning into each evening when
precipitation coverage will be greatest.

&&

.MARINE...
Tonight: Southerly flow regime will persist. Conditions look to
favor a bit of a nocturnal surge, especially across the central
and southern waters. Speeds look to peak 15-20 kt in this region
with 10-15 kt elsewhere. Seas will average 2-4 ft.

Saturday through Wednesday: Outside showers/thunderstorms, south to
southwest winds will average 10-20 knots, with highest winds during
the diurnal sea breeze and during each night. Seas should average 2-
4 ft. Thunderstorms will frequently produce locally hazardous
conditions through this period.

&&

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

&&