303
FXUS62 KCHS 272047
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
447 PM 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 /UNTIL 6 AM FRIDAY MORNING/...
Quick update to cancel the Heat Advisory as convection
overspreads the forecast area.

A trough axis will push through the New England through the day
today, while along the southern periphery an associated
shortwave trough will swing through the southeastern states.
According to 12Z upper air analysis, this shortwave is
positively tilted and rather elongated, extending from the
southern Mid-Atlantic into the Florida Panhandle. Ongoing
convection across southwestern GA and the Florida Panhandle can
be attributed to this shortwave feature. As the feature
progresses eastward, convection is forecast to begin
overspreading the local forecast area. Some weak returns are
already being picked up by KCLX as of 1630Z across Tattnall and
Long counties in southeast GA. CAMs have really struggled today
to resolve the ongoing convection to the SW, with most models
depicting the ongoing convection over GA dissipating before it
reaches the local forecast area. This convection has in fact
held together and as of 19Z has entered Tattnall County. SPC
mesoanalysis depicts a region of higher ML CAPE values (roughly
2000 J/kg) as well as DCAPE values around 1000 J/kg across far
southeast GA. A strong to marginally severe thunderstorm is
certainly possible this afternoon. After convection moves into
southeast GA further convective initiation is likely across the
remainder of the forecast area, and numerous showers and
thunderstorms remain mentioned in the forecast.

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 /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday: A rather fragmented mid-level pattern will be overhead as a
weak mid-level ridge centers across Texas. Toward the Carolinas,
vorticity will be elongated from the Atlantic southwest to the
southeastern United States. The vorticity will start to get torn
apart as it exists on the periphery of the aforementioned ridge.
Looking down at 700/ 850 MB actually has the vorticity retrograding
back west underneath the  mid-level ridge and being picked up in the
next wave. Towards the SC coast, the secondary weakness will remain
though with forecast soundings advertising widespread instability
(MLCAPE around ~1500 J/kg). Given this, have PoPs at likely for
Friday with most of the convection being favored in the afternoon to
evening hours. Expect high temperatures again in the low 90s as 850
MB temperatures remain around 19 degrees C. The other concern over
the last couple of days has been the chance for another Heat
Advisory Friday. Current thinking is that dewpoints will be a few
degrees lower Friday compared to Thursday as enough convective
overturning occurs for slightly more mixing. So the widespread 78/
80 dewpoints of Thursday will be a degree or two less Friday. This
coupled with high temperatures a degree or two lower will keep max
heat index values around 105 degrees (or just shy of 108 degrees/
Heat Advisory criteria).

Saturday and Sunday: This weekend looks rather active with multiple
rounds of afternoon into evening showers and thunderstorms likely.
In the mid-levels of the atmosphere, weak PV will continue to decay
with mid-level ridging retreating west as a trough axis begins to
amplify across the Eastern United States. Simultaneously, PWATs are
forecast to climb to between 2.25" and 2.4". Instability will also
be impressive, with MLCAPE values around 1800 J/kg Saturday and
around 2000 + (J/kg) by Sunday. Likely PoPs are advertised for both
Saturday and Sunday afternoon. High temperatures for both days are
currently advertised to be in the low to mid 90s (thanks to 850 MB
temperatures warming to 21 degrees C), but this could be moderated
due to ongoing afternoon convection. Max Heat Index values are
currently advertised to reach Heat Advisory criteria in places both
Saturday and Sunday. A Heat Advisory might be required for the
coastal zones this weekend.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Ensemble guidance is in fairly good agreement for the extended with
a rather active period forecast Monday as a weak cold front
approaches from the northwest. Tuesday into Wednesday the GEFS/
GEPS/ and EPS all indicate that mid-level ridging will slide east
slowly building over the southeastern United States. WPC Cluster
Analysis shows good agreement of this, with only slight differences
in the strength and expanse of the 594 dam ridge.

Sunday night into Monday: A cold front will approach the area from
the northwest on Monday with showers and thunderstorms initiating
across the Midlands of SC and Piedmont of NC. High temperatures
Monday will be only around 90 degrees in most places given the
likely coverage of storms.

Tuesday: There is uncertainty on Tuesday with a weak backdoor cold
front that is forecast to slide down the east side of the
Appalachians. Guidance is indicating that the front makes it through
the coastal plain of SC, before washing out and heading north by
Wednesday. Synoptically, a mid-level ridge over the Southern Plains
of the United States will nudge east Tuesday with a mid-level trough
quickly exiting the east coast. This type of setup generally does
allow a weak cold front to temporarily push south before retreating
north. Most of the time though, convective enhancement to the front
(via a reinforcing cold pool) is needed to really get the front
through. Either way, this will bring a chance of showers and
thunderstorm to the region Tuesday afternoon (less coverage compared
to Monday) with highs only in the upper 80s.

Wednesday: Mid-level ridging will nudge east and center across MS/
AL/ GA with air rapidly drying in the 500 - 750 MB level. This will
really start to limit convective development with temperatures again
warming back into the low to mid 90s.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
KCHS/KJZI/KSAV: Flight restrictions are likely at all three
terminals this afternoon with showers and thunderstorms. Storms
should first begin to impact KSAV, before progressing northward
and impacting KCHS/KJZI. A TEMPO group has been included for
each terminal, beginning earlier at KSAV. Precipitation should
end around 04 or 05Z tonight, however lingering clouds could
possibly cause additional vis and cig restrictions. However,
confidence in those impacts is not high enough at this juncture
to include mention in the 18Z TAFs.

Extended Aviation Outlook: Prevailing VFR conditions through the
period. Brief flight restrictions are possible each afternoon due to
showers and thunderstorms. The highest chances of thunder will be
Friday, Saturday, Sunday, and Monday afternoons thanks to the
proximity of an upper level disturbance. By Tuesday, a weak cold
front will wash north with mid-level high pressure taking control of
the region. This will likely limit shower and thunderstorm
development Tuesday and Wednesday.

&&

.MARINE...
South to southwesterly flow at 10 to 15 knots will persist
across the coastal waters this afternoon and into tonight.
Showers and thunderstorms are likely to impact the coastal
waters late this afternoon through this evening with briefly
higher winds and waves expected. Seas are forecast to average 2
to 3 ft.

Extended Marine: Surface high pressure will remain anchored across
the western Atlantic with southerly flow generally expected through
the period. Each afternoon, a gradual backing of the winds to
southeast is expected as a sea breeze forms, with winds strongest
along the land/sea interface. A weak cold front will ooze southwest
over the waters Monday into Tuesday, but the wind shift will be
transient with a quick return of southerly winds forecast. Seas will
be 2 to 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
Friday and Saturday.

&&

.FIRE WEATHER...
The South Carolina forestry commission reported low fuel moistures
across portions of the area today. Widespread coverage of showers
and thunderstorms Saturday and Sunday will help to alleviate some of
the low fuel moisture values.

&&

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

&&

$$

NEAR TERM...CPM
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...CPM/Haines
MARINE...CPM/Haines