Severe Thunderstorm Warning 9, NWS Charleston, SC

Area Forecast Discussion
National Weather Service Charleston SC
105 PM EST Tue Jan 9 2024

.SYNOPSIS...
A strong storm system will impact the region today into
tonight. High pressure will briefly return for mid week, before
the next system arrives Friday. High pressure should rebuild
later in the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
QLCS continues to progress eastward and will reach the far W/SW
portion of the CWA in the next 30 minutes. Lots of small bowing
segments/circulations noted along the line suggesting a high
potential for damaging winds and spin-ups. Tornado watch covers
the entire CWA through 6 pm. Interesting afternoon ahead...

Previous discussion...
No substantial changes were made to the going forecast. Initial
strong warm/moist advection surge is currently underway,
manifesting as fairly solid batch of heavier showers lifting up
through the southeast South Carolina. Already getting decent
wind gusts with that batch of showers with speeds pushing 50 mph
(see most recent PNS issued before 10 am), and the strongest
low level winds are yet to develop per latest RAP13 data.

Rest of the day: Initial batch of isentropic ascent driven
showers will be lifting northward out of the CWA over the next
few hours...with a bit of a clear slot spreading into the area
ahead of the main upstream convective line. Upstream QLCS has
been producing quite a bit of severe weather, several confirmed
(TDS) tornadoes and reports of severe winds/wind damage along
and ahead of the convective line.

Severe parameters across our area just ahead of the line remain
very impressive through the afternoon. Effective bulk shear
values in excess 65 knots, 0-3KM effective SRH around 500
m2/s2, SCP values increasing to in excess of 8 units and STP
(sig tor parameter) greater than 2 suggesting a strong tornado
potential. The one question mark continues to revolve around
instability. That said, most recent SPC mesoanalysis/forecast
does show an axis of >500 J/Kg MLCAPE spreading up through the
entire CWA by early-mid afternoon ahead of the line.

Winds: A very impressive and anomalous wind field will spread
across the forecast area today, producing very strong wind
gusts. Forecast soundings continue to indicate 50+ knots of flow
just a few thousand feet off the surface. With temperatures
warming into the upper 60s and low 70s, we should see enough
boundary layer mixing to produce wind gusts of 45 mph everywhere
and a Wind Advisory remains in effect. There also still remain
an enhanced wind threat along the coast where frequent gusts
into the 50-60 mph range are expected and a High Wind Warning
remains in effect. Winds are expected to peak beginning around
noon and continuing just ahead of the approaching squall line
into the evening.

All told, the table remains set for a very impactful afternoon
with very gusty/potentially damaging winds outside of the
convective line and a severe QLCS rolling eastward through the
CWA between noon and 8 pm.

Tonight: As the early evening begins, the strong line of
thunderstorms will push off the coast and the severe threat will
end. In the wake of the front, winds will turn southwesterly
and remain quite gusty especially in the evening hours while the
Wind Advisory is still in effect. Even after midnight winds are
still expected to frequently gust to at least 25 mph and even
up to 30 mph at times. Cold air will quickly rush in behind the
front and lows are forecast to reach the upper 30s inland and
the low 40s along the coast.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
The forecast area will be positioned between strong low
pressure to the north and high pressure to the south on
Wednesday. Tight pressure gradient between these two features
will lead to gustiness persisting through the morning hours,
before winds ease through the afternoon. Precipitation will be
long gone with a dry forecast in place. Temperatures will be
cool with highs topping out in the low to mid 50s. Lows
Wednesday night will span the 30s.

High pressure and dry weather on tap for Thursday. Cloud cover
and rain chances increase late Thursday night as the next system
approaches and a coastal trough develops. Highs will be in the
upper 50s to around 60, with lows mainly in the upper 30s to mid
40s.

Potent shortwave will eject out of the Southern Plains Friday,
with an associated surface low to deepen while lifting into the
Great Lakes region later in the day and into Friday night. As
this occurs, a warm front will lift north through the region,
followed by the trailing cold front Friday evening/night. It's
another strong, dynamic system bringing yet another round of
gusty winds and potential for severe weather.

PWats are expected to surge to over 1.5 inches and rain chances
increase quickly through the day. Certainly will have shear
present, and models are indicating some degree of instability.
SPC currently highlights the area with 15% probabilities for
severe weather in their extended outlook. Damaging wind gusts
and isolated tornadoes will be the main threat within any
stronger storms. Rainfall totals through this event are
currently forecast to average in the 0.50- 0.75 inch range, with
locally higher amounts possible. No flooding is anticipated at
this time given the progressive nature of the system.

Winds are not expected to get to the levels of today/Tuesday's
system, but it will still be notably breezy. At the least, a
Lake Wind Advisory will likely be needed. Temperatures are
expected to reach the upper 60s to around 70 as the area becomes
positioned in the warm sector.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
High pressure will build in through the weekend behind
departing low pressure and associated cold front. Aside from
gusty west winds on Saturday, quiet and dry weather conditions
are expected. Temperatures will be cooler than normal. Rain
chances return on Monday as a cold front potentially impacts the
area but still a lot of inconsistencies between models.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Line of strong to severe thunderstorms will be crossing through
southeast Georgia and southeast South Carolina this afternoon.
Current timing suggests the line and the worst conditions will
be felt at the KSAV terminal between 20Z and 23Z...KCHS/KJZI
between 21Z and 00Z.

IFR conditions are expected as the line comes through, as well
as very strong gusts from the west with the passing storms. Peak
gusts could be near 50 knots with the main line. Once the
storms pass, VFR conditions are expected to return with
southwest winds still gusting into the 25-30 knot range this
evening, and then around 25 knots through the end of the TAF
period.

For winds outside of thunderstorms, frequent gusts up to around
45 knots are expected at KSAV, while peak gusts could approach
50 knots at times at KCHS and KJZI. The peak time period for
gusts will be through mid to late afternoon, prior to the
arrival of the line.

Extended Aviation Outlook: Gusty winds will linger into
Wednesday. Flight restrictions and gusty winds are possible on
Friday with the next storm system.

&&

.MARINE...
Today: Extremely dangerous conditions are expected across the
local waters today. A strong cold front will steadily draw
closer to the waters from the west through the day, likely
reaching the coast and beginning to move offshore by around
sunset. A tight pressure gradient and impressive low-level
jetting will spread across the area, producing uncommonly strong
winds. The peak time period for winds will be just ahead of the
front during the afternoon hours. There are no changes to the
headlines, with Storm Warnings in effect for Charleston Harbor,
the Charleston County waters, and the outer Georgia waters where
frequent gusts to 50 knots are expected this afternoon. Gale
Warnings remain in effect elsewhere and frequent gusts are
expected to peak in the 40-45 knot range. The line of storms
will track eastward across the local waters during the late
afternoon and early evening hours, and the waters should be
rain- free by around midnight and remain that way thereafter.
From the late evening on the storm force winds will diminish
but solid gales will continue through sunrise for most of the
waters. Once the Storm Warnings come down they will need to be
replaced by Gale Warnings. Seas will be quite impressive as
well, peaking in the afternoon and into the early evening.
During this time, the Charleston County waters and outer Georgia
waters are forecast to experience 10-15 ft. For the southern
South Carolina waters the forecast is a bit lower in the 8-12 ft
range and in the 7-11 ft range in the nearshore Georgia waters.
Also of note, waterspouts will be possible as the line of
thunderstorms passes through.

High Surf: Due to uncommonly strong winds and rapidly
increasing seas, large breaking waves are expected at all
beaches through tonight. Though the highest breaking waves are
still anticipated for the Charleston and Colleton County coasts,
breaking waves of 5-7 feet are expected for all beaches.
Therefore, the High Surf Advisory has been expanded to include
the entire coast.

Wednesday through Sunday: Improving conditions are expected
through the day on Wednesday. All headlines should be down by
late Wednesday evening. No marine concerns for Thursday.
Conditions will again deteriorate on Friday as the next storm
system impacts the region. Small Craft Advisories are likely
across all waters which will continue into Saturday. There is
also a chance for gale force gusts, and Gale Watches/Warnings
could eventually be needed. The worst conditions appear to occur
Friday evening through Saturday morning. Vast improvement for
Sunday as high pressure rebuilds.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Wind Advisory until 10 PM EST this evening for GAZ087-088-
     099>101-114>118-137>141.
     High Surf Advisory until 7 PM EST this evening for GAZ117-119-
     139-141.
     High Wind Warning until 10 PM EST this evening for GAZ119.
SC...Wind Advisory until 10 PM EST this evening for SCZ040-042>045-
     047.
     High Wind Warning until 10 PM EST this evening for SCZ048>052.
     High Surf Advisory until midnight EST tonight for SCZ048-051.
     High Surf Advisory until 7 AM EST Wednesday for SCZ049-050.
MARINE...Storm Warning until 7 PM EST this evening for AMZ330-374.
     Storm Warning until 1 AM EST Wednesday for AMZ350.
     Gale Warning until 6 AM EST Wednesday for AMZ352-354.

&&

NEAR TERM...Adam
SHORT TERM...ETM
LONG TERM...ETM
AVIATION...Adam/ETM
MARINE...BSH/ETM

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