-- Discussion containing changed information from previous version are highlighted. --
710
FXUS62 KCHS 171810
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
210 PM EDT Fri May 17 2024

.SYNOPSIS...
A storm system will bring impacts to our area this weekend.
High pressure returns to our region next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 2 PM: KCLX detected a stream of showers tracking across SE
GA into lower SC. Based on radar trends and recent HRRR runs,
PoPs have been increased through this evening. In addition,
given the arriving rainfall and thick cloud cover, high
temperatures will be reduced by 1 to 2 degrees.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
Saturday: The mid-levels will consist of a trough over the
Middle/Lower MS Valley in the morning. It will shift eastward and
take on a positive tilt, becoming located over the OH/TN Valleys by
the afternoon, and over the Southeast U.S. late at night. At the
surface, a warm front will be located north of our area in the
morning, attached to a weak Low over NC. This weak Low will
gradually move offshore with time, dragging a cold front with it.
The cold front is expected to move through our area late at night.
There will be deep moisture across our region. A band of nearly 2"
PWATs originating in the Gulf of Mexico will overspread our area in
the afternoon. These values are above the 90% mark per SPC sounding
climatology for CHS. They`re also 2 standard deviations above normal
per NAEFS. What`s more impressive is the NAEFS IVT is from the SW
and is 4-5 standard deviations above normal over southern portions
of our area in the afternoon and evening. So there`s plenty of
moisture to rain out of the atmosphere. But the day may start out
mostly dry with the main focus in the afternoon. It is likely a MCS
will be ongoing in the vicinity of the central Gulf Coast in the
morning. It`s expected to track east into our area during the
afternoon. Some of the synoptic models differ on the timing. Though
the consensus along with the long-range CAMs points towards the
afternoon. There should be plenty of instability in place with highs
in the 80s. MLCAPEs could approach 2,500 J/kg with decent mid-level
lapse rates. There will also be plenty of shear with 0-6 km bulk
values 40-50 kt, with hodographs mostly unidirectional. So any
organized line of thunderstorms moving through our area could easily
become severe, with the main hazard being damaging winds. But a
brief tornado also can`t be ruled out along the edge of the line and
bowing segments. SPC has upgraded our entire area to a Slight Risk,
and this seems reasonable given the synoptic and mesoscale
parameters. Locally heavy rainfall is also expected with the storms.
Though, the widespread flood potential should be limited, mainly
because the storms should be moving at a decent speed. Once the line
moves through, stratiform precipitation should persist afterwards,
followed by scattered thunderstorms into the evening and overnight.
Low temperatures should be a few degrees above normal.

Sunday: A positively tilted mid-level trough will be over the
Southeast U.S. in the morning. It`ll slowly shift offshore into the
evening and overnight. A cold front will be located just offshore in
the morning, and moving away as time progresses. Surface troughing
is expected to form over our region in the afternoon, and persist
into the overnight. Even though the cold front will have crossed
through our area the previous night, the deep moisture will be very
slow to decrease. PWATs will remain in the 1.5-2.0" range, which is
above normal per SPC sounding climatology for CHS and per NAEFS.
Given all of the moisture and synoptic lift, models are in good
agreement indicating scattered showers in the morning increasing to
numerous or widespread showers by the afternoon. Temperatures should
peak in the lower 80s, limited by the aforementioned showers. This
will also lead to less instability than the previous day. But there
should be enough instability in place for some thunderstorms.
However, shear will be much less than the previous day. So while
there should be some thunderstorms, the severe risk is much lower
than on Saturday. Locally heavy rainfall will be a bigger concern
given the high PWATs and slower storm motions. We can`t rule out
flooding in some areas, especially considering the potential for
saturated soils from Saturday`s heavy rains. Showers will decrease
in coverage and intensity from west to east during the evening and
overnight hours. Most locations should be dry by daybreak Sunday,
except maybe the immediate coast.

Monday: The mid-levels will consist of a positively tilted trough
just off the Southeast U.S. coast in the morning, and a ridge just
to our west. The ridge will slowly build into our area into the
afternoon. At the surface, High pressure centered well to our north
will build down the coast, making its way into our area. The high
should bring lowering POPs than the previous two day. Though, a few
showers cannot be ruled out along a pinned sea breeze. Northerly
surface winds will bring below normal high temperatures, ranging
from the upper 70s to around 80 degrees.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Mid-level ridging will be over our region through Wednesday,
followed by southwest flow on Thursday. Surface High pressure
centered to our north Monday night will shift over our region by
Wednesday, then offshore on Thursday. A cold front could approach
from the northwest later Thursday, possibly bringing showers.
Temperatures will be trending higher, reaching into the 90s by
Thursday.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Prior to the 18Z TAFs, KCLX detected scattered showers streaming
across SE GA, with showers passing over and near KSAV. Showers
and thunderstorms should gradually increase across SE GA through
mid-evening. The KSAV TAF will feature a TEMPO between 0-3Z for
VFB10G15kt during TSRA. KCHS and KJZI may see passing showers
this evening into the late night hours. MOS and forecast
soundings indicate that MVFR ceilings are expected to develop
over the terminals late tonight remaining into mid Saturday
morning. Conditions are expected to become VFR by 14Z Saturday.

Extended Aviation Outlook: A storm system will bring periods of
flight restrictions this weekend. VFR returns later Monday.
-- End Changed Discussion --

&&

.MARINE...
Today and Tonight: Weak sfc high pressure will prevail across local
waters for much of the day while a mid-lvl ridge axis is positioned
near the Southeast Coast. This will support quiet marine conditions
into late afternoon or early evening with south/southeast winds
generally no higher than 10 kt. Seas will range between 1-2 ft.
Heading into overnight hours, there should be an uptick southerly
wind speed (10-15 kt) as a warm front lifts north across the region.
Seas will also build during the night, approaching 2-3 ft by
midnight. Shower and thunderstorm chances will also increase
overnight as the warm front advances north. A few thunderstorms
could become strong displaying gusty winds and it`s not out the
question for a few Special Marine Warnings if that becomes the case.

Extended Marine: Conditions are expected to remain below Small Craft
Advisory criteria. Southerly flow will persist through Sunday, then
the winds turn northerly behind a cold front early next week. Wind
gusts could briefly approach 25 kt late Sunday night into Monday
morning with an initial burst of cold advection, mainly over the
Charleston County nearshore waters.

&&

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

&&

$$

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