862
FXUS62 KCHS 042227
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
627 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/...
This Evening: H5 shortwave energy rounding the periphery of a mid-
lvl trough positioned west/northwest of the local area will continue
to support a few showers/thunderstorms that drift north, mainly near
the I-95 corridor across southeast South Carolina during the next
few hours. Modest instability, characterized by SBCAPE near 1500-
2000 J/kg and PWATs around 1.7 inches suggest a thunderstorm could
produce a brief heavy downpour away from the coast, but severe
weather is not expected. Expect this activity to slowly wane
across southeast South Carolina during the next few hours due to
the loss of diurnal heating around sunset, but a few showers
and/or thunderstorms can not be ruled out across far inland
areas for the next several hours. The greatest potential for
additional showers/thunderstorms should arrive across inland
areas of southeast Georgia early evening, where outflow from
previous convection across southeast Georgia provides a boost in
lifting and moisture convergence ahead of showers/thunderstorms
approaching from the west. This activity is likely to remain in
a sub-severe state given the lack of stronger instability and
shear across the local area, but will likely provide the most
precip coverage locally through the night and the greatest
potential for gusty winds during evening hours.

After Midnight: H5 shortwave energy continues to traverse across
northwest zones and will press mid-upper ridging east across the
western Atlantic, suggesting some potential for few to scattered
showers/thunderstorms into late night hours, particularly across
inland areas of southeast South Carolina. Additional convection is
possible in the Atlantic coastal waters later tonight as well, some
of which might skirt the South Carolina coastal counties starting a
few hours prior to daybreak Sunday morning. Despite some clouds,
light winds and recent rainfall could produce some patchy fog away
from the coast. Overnight lows will remain mild, generally 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 /22Z SATURDAY THROUGH THURSDAY/...
Showers will be moving through the terminals over the next few
hours. A few thunderstorms are possible, although most of the
thunderstorm activity should remain a bit more inland.
Otherwise, VFR conditions will be the rule this afternoon and
tonight. A touch of fog is possible later tonight through
sunrise Sunday, although fog probabilities are too low to
include in the terminal forecasts at this juncture.

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...
This Evening and 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 south-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...Adam
MARINE...DPB