859
FXUS62 KCHS 170852
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
452 AM 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/...
Prior to Daybreak: Latest satellite imagery and sfc obs indicate
patchy to areas of fog across parts of the Tri-County Area, where
temps have cooled into the mid 60s, near sfc dewpt levels. There
could be a 1-2 hour period of patchy dense fog for some locations
just prior to high clouds entering across the region ahead of
overnight MCS shifting across parts of south-central Alabama/Georgia
and the Florida Panhandle. Once these clouds arrive, visibilities
should improve.

Today and Tonight: The previously mentioned MCS will make a run
toward locations south of I-16 across southeast Georgia in a
decaying state, but for the most part is anticipated to remain south
of the Altamaha River while encountering a substantial amount of dry
low-mid level air displayed in model soundings and seen on water
vapor imagery. Nevertheless, a slight chance of showers will remain
in the forecast across southeast Georgia and far inland locations of
southeast South Carolina through late morning. Heading into the
afternoon, weak sfc high pressure and a mid-lvl ridge axis
positioned near the coast aloft will shift across the western
Atlantic as low pressure takes shape across the Deep South and is
driven eastward by a series of h5 shortwaves in advance of a
longwave trough crossing the Mississippi River Valley. Clusters of
showers/thunderstorms, perhaps in the form of another MCS should
approach far southern zones late day, and more likely early to mid
evening as a warm front begins to lift north across the local area.

In advance of the warm front, sfc temps are still expected to peak
in the mid-upper 80s this afternoon, with moisture advection and
isentropic lift supporting few to scattered showers and
thunderstorms by late day, mainly west of the I-95 corridor across
southeast Georgia and perhaps southeast South Carolina. However,
precip chances are likely to increase as the warm front lifts north
across the local area starting early to mid evening tonight, and
there is some indication that sufficient instability and shear could
support a few stronger and/or severe thunderstorms, mainly across
southeast Georgia and perhaps far inland locations across southeast
South Carolina. Much will depend on the evolution of the potential
MCS upstream in regards to severe thunderstorm chances, but should a
few severe thunderstorms occur, damaging winds, hail and even a non-
zero risk for a tornado near/along the warm front is not out of the
question. Temps will remain mild during the night as the area
becomes warm-sectored, with lows only dipping into the upper 60s to
lower 70s.

&&

.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 /09Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected to prevail at CHS/JZI/SAV terminal
through 06Z Saturday. However, the remnants of an MCS will impact
the area, with the potential for SHRA/TSRA at the terminals (highest
chances at SAV). For now, VCSH remains in the TAF for SAV starting
around 15Z. Adjustments will likely be needed with later TAF
issuances to account for timing/occurrence of the event.

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

&&

.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...DPB
SHORT TERM...
LONG TERM...
AVIATION...DPB
MARINE...DPB