771
FXUS62 KCHS 261109
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
709 AM EDT Wed Jun 26 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while weak
cold fronts linger near our area through the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early morning update: Small batch of cloud cover has developed
over parts of Colleton and Dorchester counties in the last hour
or two along with patchy fog across parts of the forecast area.
Updated the forecast to reflect that. Otherwise, no significant
changes were made to the forecast.

Upper level ridging encompasses much of the western CONUS with
more or less zonal flow through the eastern U.S. save for a
couple of convectively induced short-wave troughs (and decaying
convection) moving through the mid Mississippi River Valley. A
wavy stationary boundary/trough cuts through the Carolinas into
southern Georgia separating some drier air well inland from the
very humid air mass that remains in place across our region.
Some semblance of a weak surface low (thermally induced) lingers
over southeast Georgia. Quiet conditions prevail for the moment
with temperatures in the middle 70s to around 80.

Stronger northern stream short-wave energy will dig into the
Great Lakes region later today and begin to drive upper level
troughing across the Appalachians with upper level height falls
beginning to edge into the southeast region later this afternoon
through tonight.

Today: Coastal southeast will remain within the broader scale
surface low pressure pattern lingering across the region with
another day of very warm temperatures coupled with a very humid
air mass wedged along the eastern Carolinas and southeast
Georgia coast. Ample instability (MLCAPE values are running over
2K J/Kg early this morning although capped at the moment. But
with heating, high-res guidance suggest instability will tick up
into the 2500-3500 J/Kg range this afternoon. But with the lack
of any larger scale forcing mechanism, afternoon convection will
be driven by the inland sea breeze push and any old boundaries.
But showers and thunderstorms are a good bet to develop inland
off the coast this afternoon and forecast will continue to
advertise isolated to scattered pops. With ample instability
along with fairly decent DCAPE values to work with, a few strong
to severe storms are a possibility.

Heat index values: Similar to the last few days, surface
dewpoints well inland (west of the I-95 corridor) will tend to
mix/lower this afternoon, keeping heat index readings in check
despite temperatures approaching the hundred degree mark. Along
and east of the I-95 corridor and especially along the coast,
middle 70s to near 80 dewpoints will lead to heat index values
at or above 108F once again this afternoon. A Heat Advisory has
been issued for area along and east of the I-95 corridor.

Tonight: Diurnally driven convection will run its course
through the evening hours. As mentioned, upper level troughiness
will edge into the southeast region through the course of the
night with enhanced QG-forcing for ascent working across the
Appalachians and into the western Carolinas. It does appear at
this juncture that any associated shower activity will remain
well upstream through the night and plan to maintain a dry
forecast. Low temperatures once again will only dip into the
middle 70s to around 80.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Thursday: Mid-level longwave troughing initially over the East Coast
will gradually shift offshore as time progresses. More notably, a
shortwave embedded in the overall flow is expected to move over our
region during the late afternoon or evening, then stall overhead
overnight. A cold front located to our northwest at daybreak should
very slowly move into our area late in the day, likely stalling
across our area overnight. There will be a plume of deep moisture
ahead of the front. PWATs could exceed 2.25", which is above the 90%
mark for CHS per SPC Sounding Climatology. The heat will be the main
concern due to 850 mb temperatures, low-level thickness values, and
compression near the front. Highs are expected to reach the mid to
upper 90s across most of our area, except cooler at the beaches. Dew
points well into the 70s near the coast will cause heat indices to
rise to 108-110 degrees. So Heat Advisories may be needed, most
likely for our coastal counties. Forcing from the front, the
afternoon sea breeze, and the shortwave will generate convection in
the afternoon. The synoptic models and long range CAMs are in good
agreement, indicating scattered to numerous coverage. MLCAPEs should
approach 1,500 J/kg across portions of our area with some shear.
With DCAPEs exceeding 1,000 J/kg, a few marginally severe storms
with damaging winds are possible just about anywhere. Hence, the SPC
has our area under a Marginal Risk for severe thunderstorms, which
seems reasonable. Additionally, there will be the potential for
locally heavy rainfall underneath the thunderstorms due to fairly
weak steering flow and the potential for training. Convection should
gradually decrease during the evening. But isolated remnant
convection should persist everywhere overnight. Lows will be in the
70s.

Friday: The mid-levels should consist of a shortwave hovering over
our region in the morning. It is expected to dissipate into the
afternoon, followed by weak zonal flow during the evening and
overnight. At the surface, a stationary front should be spread
across our area in the morning. It`s expected quickly lift north as
a warm front into the afternoon, becoming located well north of our
area by the evening hours. Deep moisture will persist across the
region. PWATs should stay ~2.25", which is well above normal.
Similar to Thursday, high temperatures are expected to reach well
into the 90s for most areas. Dew points well into the 70s near the
coast will cause heat indices to rise as high as 108-110 degrees,
which would prompt Heat Advisories, most likely for our coastal
counties. Forcing from the remnant shortwave, departing front, and
the afternoon sea breeze will generate convection. Models point to
another round of scattered to numerous coverage, especially in the
afternoon. Instability should be similar to Thursday. However,
shear and DCAPEs appear to be lower. This would lower the severe
risk. But given the atmospheric setup and time of year, a strong or
marginally severe storm with damaging winds is possible just about
anywhere. There will also be the potential for locally heavy
rainfall underneath the thunderstorms due to weak steering flow and
the potential for training. Convection should gradually decrease
during the evening. But it`s most likely to persist closer to the
coast overnight. Lows will be in the 70s.

Saturday: Weak mid-level zonal flow will initially be over our
region, with broad High pressure building later into the day.
Surface High pressure will be in the western Atlantic, while weak
troughing develops over the Southeast U.S. later in the day. Deep
moisture will continue to prevail across the region. Similar to the
previous two days, high temperatures are expected to reach well into
the 90s for most areas. Dew points well into the 70s near the coast
will cause heat indices to rise as high as 110 degrees along the
coast. So more Heat Advisories may be needed. Instability from the
afternoon heat and humidity will generate convection along the sea
breeze as it moves inland during the afternoon. Strong or marginally
severe storms are possible.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Surface troughing or weak fronts will be impacting the Southeast
U.S. during the long term, while High pressure is located in the
western Atlantic. Expect the typical diurnal convection with the
highest POPs each afternoon and evening, then trending lower
overnight. High temperatures will be well into the 90s each day.
Additionally, heat indices could approach 108 degrees along the
coast through Monday.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
KCHS/KJZI: Small area of cloud cover has developed near the
Charleston tri-county area early this morning and could lead to
a brief period of MVFR ceilings at KJZI and possibly KCHS.
Otherwise, VFR through the morning into the afternoon. Scattered
showers and thunderstorms are possible this afternoon into
early evening. However, indications are that most of the
activity will occur a bit inland from the Charleston County
coast and may not impact the terminals. Still too much
uncertainty to include an explicit mention in the terminal
forecasts, but will carry VCSH at KCHS during the afternoon.

KSAV: A similar story, with some cloud cover around the area
this morning followed by showers and thunderstorms possible this
afternoon into early evening. Recent guidance trends suggest
KSAV will have the higher probabilities for showers and storms.
12Z terminal forecast will carry VCTS at the terminal during the
mid to late afternoon period.

Extended Aviation Outlook: Mostly VFR. However, convection could
bring brief flight restrictions, mainly each afternoon and
evening.

&&

.MARINE...
Persistent southerly flow lingers across the coastal waters
through tonight, generally 10 to 15 knots with some gusts to
around 20 knots. Seas 2 to 3 feet through today building to 2 to
4 feet tonight.

Extended Marine: A typical summertime pattern is expected with High
pressure in the western Atlantic and occasional surface troughing or
fronts over the Southeast. Each day, expect gradually backing winds.
They`ll be strongest along the land/sea interface and across the
Charleston Harbor with the formation of the afternoon sea breeze.
Each night, winds will gradually veer, possibly surging closer to
the coast. Seas will be 2-3 ft.

Rip Currents: Today, increasing 1-2 foot swell energy to around
9 seconds is expected to begin impacting the South Carolina
beaches later today and into the southeast Georgia coast
tonight. With that, internal guidance suggests a moderate rip
current risk developing along the coast, particularly the South
Carolina beaches as we go through the day.

Thursday a 1-2 ft SE swell around 7 seconds and
another SE swell around 9 seconds will be impacting the beaches.
Per internal calculations, this would increase the rip current risk.
We opted to maintain a Low risk for our SC beaches, but added a
Moderate Risk at our GA beaches, where rip currents are most likely
at Tybee Beach.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening
     for GAZ101-116>119-138>141.
SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening
     for SCZ043>045-047>052.
MARINE...None.

&&

$$

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