851
FXUS62 KCHS 050227
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1027 PM EDT Sat May 4 2024

.SYNOPSIS...
Atlantic high pressure will remain across the Southeast U.S.
through much of next week. A cold front will approach the area
on Friday.

&&

.NEAR TERM /THROUGH SUNDAY/...
The bulk of showers/thunderstorms have decreased substantially
across the local area, either dissipating or shifting north with the
first round of H5 vort energy rounding the periphery of a mid-lvl
trough positioned to the west/northwest. Additional h5 shortwave
energy should traverse northwest zones after midnight, pressing mid-
upper ridging further east across the western Atlantic through
daybreak. Latest guidance suggests the bulk of deeper moisture
sliding northeast with time, favoring few to scattered showers along
with isolated thunderstorms across parts of southeast South Carolina
within a few hours of daybreak. This aligns with the potential for a
few showers and thunderstorms developing across the Atlantic making
a run toward locations along Charleston County closer to daybreak.

Outside of shower/thunderstorm activity the main concern will be the
potential for fog late. Despite some clouds, light winds and recent
rains could help produce some patchy fog away from the coast while
condensation pressure deficits are favorable a few hours prior to
daybreak. There is a potential for greater fog coverage across parts
of southeast Georgia if drier air off the sfc results in less cloud
cover late. Overnight lows should remain mild, ranging in the mid
60s inland to upper 60s/lower 70s near the coast.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
Sunday: The mid-level weakness that was aligned along the
Southeast U.S. coast Saturday will shift offshore as shortwave
ridging builds in behind it. This feature will dominate for
Sunday with forecast soundings and model time sections showing a
distinct lowering of mean moisture values with quite a bit of
drying occurring in the mid- levels. PWATs will lower about a
quarter of an inch, but will still remain rather elevated with
values holding around 1.50". Convection will be mostly driven by
the afternoon resultant sea breeze along with mesoscale
boundary collisions. Most of the convection looks to concentrate
along the climatologically favored I-95 corridor and chance
pops around 50% still look reasonable for the afternoon/early
evening hours. Localized corridors of higher pops may eventually
be needed as mesoscale trends become more apparent. Mid-level
drying will help enhance the risk for gusty winds with modified
soundings supporting DCAPE values around 800 J/kg. Although
0-6km bulk shear will be limited in the absence of any
meaningful forcing mechanism passing by aloft, any convective
updrafts that can be enhanced by mesoscale boundary collisions
could yield a few strong to locally severe convective wind
gusts. Freezing levels and WBZ heights look to remain seasonably
high, but some small hail can not be ruled out. There will also
be a potential for some localized flooding of low- lying and
poor drainage areas with fairly weak steering winds in place.
Convection will gradually wind down during the evening hours
with the best focus for showers/tstms refocusing over the
Atlantic overnight. Some of this activity could make a run for
the coastal counties during the early morning hours Monday.
Highs will warm into the lower-mid 80s with overnight lows
ranging from the mid 60s well inland to the lower 70s at the
beaches and Downtown Charleston.

Monday: Monday could be a convectively more active day as shortwave
ridge aloft dampens and shifts offshore as a modest southern stream
shortwave crosses the Southeast U.S. during the afternoon hours. The
pattern will favor yet another modest resultant sea breeze moving
inland within a moderately unstable environment and fairly low
convective temperatures. Convection could get going fairly quickly
Monday morning, first initiating along the developing resultant then
shifting and/or refocusing inland and potentially interacting with
additional convection firing over the Midlands, CSRA and east-
central Georgia. There are signals that a large amalgamation of
shower/tstms will occur over inland areas mid-late afternoon as a
number of significant boundary collisions occur within a warm/moist
environment. With the approaching shortwave providing modest forcing
for ascent during the diurnal maximum, a healthy coverage of
showers/tstms is expected, especially away from the coast. Pops 60-
70% were held for now, but the introduction of categorical pops may
eventually be needed as confidence on the placement/timing of
mesoscale features increases. A few strong tstms could occur with
wet microbursts if updrafts can become enhanced in the vicinity of
boundary collisions. Convection will gradually wind down across the
interior Monday evening with the focus for showers/tstms shifting
into the Atlantic. A southwest steering flow should keep most of
this marine-based convection over the Atlantic, possibly brushing
the middle/upper Charleston County beaches early Tuesday morning.
Highs will warm into the lower-mid 80s with lows Tuesday morning
ranging from the mid 60s well inland to the lower 70s at the beaches
and Downtown Charleston.

Tuesday: Mid-level heights will begin to build Tuesday as Monday`s
shortwave pushes offshore. Modified soundings show the atmosphere
becoming increasing capped through the day in response to increasing
subsidence aloft, but there may still be enough mixed-layer
instability and convergence along the afternoon resultant sea breeze
to initiate a few showers/tstms. Slight chance pops look reasonable
for Tuesday afternoon. Highs will warm into the upper 80s/near 90
away from the beaches.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
*** THE FIRST HEAT WAVE OF THE SEASON TO BRING NEAR RECORD HEAT
 NEXT WEEK ***

Subtropical ridging will dominate the Southeast U.S. for much
of next week bringing with it a risk for building heat and the
first real heat wave of the year. The NWS defines a heat wave as
a period of abnormally hot weather that generally lasts for 2
days or more. As the heat builds next week, a number of record
highs and record high minimums could be challenged. Forecast
soundings show pronounced subsidence inversion just below 700
hPa prevailing for much of the period and while an isolated
shower/tstm could still pop along the sea breeze each afternoon,
the probabilities for anything measurable look to remain below
20 percent for both Wednesday and Thursday. The hottest day
looks to occur Thursday as compression heating and deep westerly
flow occur ahead of an approaching cold front prevails. 850 hPa
temperatures could warm as high as 19-20C by this time with
mid- level temperatures between 850-500 hPa running about +1 to
+2.5 standard deviations depending on the layer. Highs look to
warm into the lower 90s by Wednesday with mid 90s possibly by
Thursday, which is about 12-15 degrees above normal. It will
remain rather warm during the overnights with lows only cooling
to around 70 well inland to the mid 70s at the beaches and
Downtown Charleston.

Although dewpoints will likely mix out into the 60s each afternoon
yielding maximum heat indices in the mid 90s to near 100 (below the
new Heat Advisory criteria of 108-112), the experimental NWS Heat
Risk tool is highlighting much of the area in a "moderate (cat 2)
heat risk" Wednesday through Friday given how abnormal this level of
heat is for the time of year and the lack of any meaningful
nighttime recovery. Precautions should be taken, especially given
this will be the first real heat wave of the year. Rain chances
could increase Friday as a cold front moves through the region.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Prevailing VFR conditions are expected at CHS/JZI/SAV terminals
through much of the night into Sunday morning. However, some
guidance suggests the potential for MVFR conditions due to patchy
fog and/or low cigs, mainly between the 09-13Z time frame Sunday.
Confidence remains too low to include at the terminals in the
latest TAF issuance. Another round of flight restrictions could
come late morning/early afternoon Sunday as showers and/or
thunderstorms develop, then shift inland. For now, VCSH has been
introduced at CHS/JZI between 15-19/20Z and 19-23Z at SAV. TEMPO
MVFR cigs/vsbys could eventually be needed for showers or thunderstorms
that directly impact the terminals late Sunday morning and/or
afternoon.

Extended Aviation Outlook: Flight restrictions possible in
overnight/early morning fog and stratus. Isolated to scattered
showers and thunderstorms are possible Saturday through Monday.

&&

.MARINE...
Tonight: Quiet marine conditions are expected locally between
high pressure across the western Atlantic and weak low pressure
across southeast Georgia. Outside a few early morning thunderstorms,
the surface pattern will yield southeast winds around 10 kt or
less through the night. Seas should range between 1-2 ft across
most nearshore waters and 2-3 ft across waters off the Charleston
County coast and offshore Georgia waters.

Sunday through Thursday: There are no concerns. Southerly winds will
prevail through the period. While some nocturnal surging and sea
breeze enhancements could occur each day, winds should largely
remain 15 kt or less. Seas will average 2-4 ft.

&&

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

&&

$$

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