640
FXUS62 KCHS 270829
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
429 AM EDT Thu Jun 27 2024

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

&&

.NEAR TERM /THROUGH TONIGHT/...
Overnight composite analysis reveals larger scale northern
stream troughing through the Great Lakes into New England.
Trailing positive tilt short-wave trough axis is advancing
through the Appalachians with a couple of convectively induced
vorticity centers (MCVs) noted along the trough axis, one
moving into Alabama and second across eastern Tennessee. Surface
boundary oriented along and ahead of the upper trough cuts
across the western Carolinas into central Georgia. Quiet weather
across our immediate region, with the most active weather
currently ongoing from the mid Atlantic into New England.

Advancing upper trough axis moving through New England into the
mid Atlantic will help drive the surface cold front deeper into
the southeast region today. That, in tandem with modestly
increasing QG-forcing for ascent, local sea breeze interactions
and perhaps some support from the remnant MCV eventually moving
into Georgia should drive a better coverage of showers and
thunderstorms this afternoon into the evening, with convection
kicking off largely after 2 pm. Early morning forecast will
advertise scattered-numerous precip chances with the best
coverage anticipated late afternoon through the early evening
timeframe. A further increase in rain chances may eventually be
needed once convective evolution becomes clear.

Severe weather parameters/possibilities: Forecast instability
is sufficient although not super impressive, owing to subtle mid
level warming that develops this afternoon into this evening
(1-2 J/Kg MLCAPE off the coast and a bit higher in a narrow
corridor along the coast where boundary layer moisture is
greatest). Antecedent larger scale 0-6 Km shear values are
unimpressive for organized severe storms, 20 knots or less but
strongest in the tri-county region and points north. That said,
there may be some localized enhanced low level shear values to
tap along the coast (or in the vcnty of any local boundaries)
with locally backed and increased low level flow and coincident
with where the better instability will be found. In fact, high-
res guidance does forecast 1 to 2 units of positive Supercell
Composite Parameter along the coast as a result of the stronger
backed flow/instability. Upshot, while a well organized severe
weather threat does not appear likely, given some favorable
parameters, a few strong to severe storms producing damaging
winds will be possible across the forecast area as depicted in
the latest SPC Day One outlook, with the higher threat perhaps
across the SC counties and along the coast.

Otherwise, a slight cool down in thermal profiles is anticipated
(H8 temps dipping off around 2C cooler compared to Wednesday)
along with increasing convection/cloud cover during the
afternoon. That should result in slightly "cooler" max temps
today...93-98F across the forecast area and cooler right along
the coast. But with the envelope of enhanced surface dewpoints
still situated along the coastal corridor, still getting heat
index values running 107-110F before arrival of convection and
basically along and east of the I-95 corridor to the Savannah
River. A bit more on the fence regarding heat advisory
headlines. But upon collaboration with surrounding WFO`s, a Heat
Advisory has been issued for the above mentioned areas.

Tonight: Upper level troughiness lingers through the night and
it`s unclear if the surface boundary actually pushes through or
simply stalls/washes out across the region. As mentioned above,
convection is looking to linger through the evening hours,
moving off the coast and diminishing late evening and overnight.
Overnight lows should dip into the middle 70s most areas
(73-78F), warmer along the coast of course, with some fog
possible particularly in areas that do receive decent rainfall.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Friday: The mid-levels should consist of a shortwave hovering over
our region in the morning. It is expected to dissipate into the
afternoon. Weak High pressure is forecasted to form over the
Southeast during the evening and overnight. At the surface, a
stationary front should be spread across our far inland counties 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 and overnight hours. Deep moisture will persist across
the region. PWATs should stay ~2.25", which is above the 90% mark
for CHS per SPC Sounding Climatology. The heat won`t be as intense,
with highs expected to reach the lower to mid 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 as high as 105-108
degrees, which is borderline for Heat Advisories. If any are issued,
they would be most likely for our coastal counties. Forcing from the
remnant shortwave, departing front, and the afternoon sea breeze
will generate convection. The synoptic models and long range CAMs
are in good agreement, indicating scattered to numerous coverage.
We`ll note that the NBM was an outlier, having POPs up to 80%. This
seemed way too high, so we capped them at 50%, which is still
decent. There doesn`t appear to be as much instability as previous
days. MLCAPEs may struggle to reach 1,000 J/kg across portions of
our area. Even DCAPEs may only be a few hundred J/kg with weak
shear. So a strong storm with gusty winds is possible just about
anywhere, but marginally severe storms appear less likely with this
setup. There will also be the potential for locally heavy rainfall
underneath the thunderstorms due to very weak steering flow and the
potential for training. Convection should gradually decrease during
the evening and overnight. But it`s most likely to persist closer to
the coast overnight. Lows will be in the 70s.

Saturday: Weak mid-level High pressure initially over the Southeast
U.S. will strengthen and build westward as time progresses. It`s
eastern periphery will be over our region overnight. Surface High
pressure will be in the western Atlantic. Meanwhile, weak troughing
is expected to develop over the Southeast U.S. later in the day,
then persist into the night. Deep moisture will prevail across the
region. PWATs should stay ~2.25", which is well above normal.
Similar to Friday, 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.
Models point to another round of scattered to numerous convective
coverage, especially in the afternoon. Once again, the NBM was the
high outlier, so we went below it and kept chance POPs. Instability
and DCAPEs are similar to Friday. So again, a strong storm with
gusty winds is possible just about anywhere, but marginally severe
storms appear less likely with this setup. There will also be the
potential for locally heavy rainfall underneath the thunderstorms
due to very weak steering flow. Convection should gradually decrease
during the evening and overnight. But it`s most likely to persist
closer to the coast overnight. Lows will be in the 70s.

Sunday: The mid-levels will consist of strong High pressure over the
Southern Plains, with its eastern periphery reaching into our
region. At the surface, High pressure will be in the western
Atlantic, while weak troughing prevails over the Southeast U.S. Deep
moisture will continue to persist 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 closer to the
coast will cause heat indices to rise as high as 112 degrees, which
would prompt Heat Advisories. Instability from the afternoon heat
and humidity will generate scattered to numerous convective coverage
along the sea breeze as it moves inland during the afternoon. Strong
or marginally severe storms are possible along with locally heavy
rainfall.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Weak fronts or surface troughing will continue to impacting the
Southeast U.S., while High pressure is located in the western
Atlantic. This will lead to diurnal convection with the highest POPs
each afternoon and evening, then trending lower overnight.
High temperatures will be well into the 90s each day and drop into
the 70s each night. Additionally, heat indices could approach 108
degrees along the coast on Monday.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
KCHS/KJZI/KSAV: VFR conditions prevail through early afternoon
Thursday. However, precipitation chances appear likely during
the afternoon after around 19Z with the possibility of TSRA
impacting all terminals between 22Z and 04Z Friday. 06Z terminal
forecasts will have VCTS mentioned 22Z and after through early
mid evening. Further timing refinements will be made with later
forecasts.

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

&&

.MARINE...
Stout south to southwesterly flow (gusts to around 20 knots) lingers
in the coastal waters through early morning but should weaken
some as we go through the morning hours. Showers and
thunderstorms are likely to impact the coastal waters late this
afternoon through this evening with briefly higher winds and
waves expected. Seas 2 to 4 feet this morning subside slightly
to 2 to 3 feet.

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 2-4 ft.

Rip Currents: A lingering 2 ft, 9 second swell coupled with some
astronomical influences and typical sea breeze enhancements along
the beaches support a moderate risk for rip currents for all beaches
today and Friday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Heat Advisory from 11 AM this morning to 6 PM EDT this evening
     for SCZ044-045-048>052.
MARINE...None.

&&

$$

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