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069
FXUS62 KCHS 041906
AFDCHS

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

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

.NEAR TERM /THROUGH TONIGHT/...
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Convoluted pattern lingers across the region this afternoon
with broad mid-level troughiness across the southeast CONUS and
some semblance of a short-wave circulation moving through
north-central Georgia. Morning band of showers and
thunderstorms have long since diminished but with a fresh round
of convection taking off across central and southern Georgia.
Here at home, "heating of the day" convection has pressed
inland to some degree, but aligned along some semblance of a
differential heating induced low level convergence axis running
from near Savannah up through the Lake Marion/Moultrie area.

Tonight: Short-wave trough will slowly pass through the region
tonight through Sunday morning. Showers and some thunder
currently aligned through the forecast area will persist for the
next several hours before weakening during the early to mid
evening timeframe. Meanwhile, upstream convection through
central Georgia will be making inroads into the far western/
southwestern part of the forecast area later this evening
before continuing up through the South Carolina counties during
the overnight hours. Additional convection is possible in the
Atlantic coastal waters later tonight as well, some of which
might skirt the South Carolina counties overnight into Sunday
morning. Lots of little things to account for and we have
tweaked/adjusted pop/weather trends accordingly. But further
adjustments are likely through tonight.

Severe storms are unlikely. But given weak wind profiles and
resultant slow moving convection, we will need to keep an eye on
rainfall rates and amounts, particularly through the evening.
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&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
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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.
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&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...

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*** 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.
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&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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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.
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&&

.MARINE...
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The surface pattern will yield south-southeast winds between 5-10
kts through tonight. Wave heights are forecast to favor values
around 2 ft, with 3 ft seas possible beyond 40 nm late tonight.

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.
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&&

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

&&

$$

NEAR TERM...Adam
AVIATION...Adam
MARINE...Adam