FXUS62 KCHS 210537
Area Forecast Discussion
National Weather Service Charleston SC
137 AM EDT Fri Jul 21 2017
Atlantic high pressure will extend west into the southeast
coast through this weekend as a surface trough remains inland.
Unsettled weather will ensue toward the early to middle part of
next week as a cold front approaches the area.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Dry conditions will prevail overnight. A few high clouds
rotating around the northeast periphery of the upper low
spinning near Jacksonville, Florida, will move overhead from
time to time, but expect mostly clear skies to prevail through
daybreak. Some shallow ground fog will be possible early Friday,
mainly in areas that saw rain earlier today. Lows lower-mid 70s
inland with mid-upper 70s coast look on track.
.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/...
Familiar summer pattern should prevail through the weekend with
upper level ridge building eastward over the forecast area
while the upper low to the southwest further weakens. Despite
large scale subsidence, there will remain enough atmospheric
moisture to combine with the sea breeze to support isolated
diurnal convection along the sea breeze. Temperatures will push
into the mid 90s away from the coast Fri/Sat under plenty of
sunshine while the sea breeze will limit max temps to around 90
to the lower 90s. This will result in heat indices in the 100 to
105 range during this period.
The upper ridge will begin to break down on Sunday as upper
heights start to fall in response to a digging trough over the
Great Lakes into the Ohio Valley region. This will result in an
increase in pops with increasing moisture advection into the
region and with increasing clouds, temperatures will moderate a
bit back near normal values.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A more active and synoptically driven weather pattern expected
during the extended forecast period. Slow moving positively
tilted upper trough will settle over the east coast early next
week combining with increasing atmospheric moisture with a
continued southerly circulation associated with the Bermuda
high. Precipitable water values will be at or above 2 inches
resulting in increasing pops each day through Wednesday. Expect
highest chances of pops on Tues/Wed as a surface boundary will
push into the area and stall.
There is some uncertainty towards the end of the extended
period as the GFS is showing some drier air pushing in from the
north while the ECMWF keeps much deeper moisture over the
forecast area with a lingering upper trough axis along the
Temperatures during this period will generally be near normal
for max temperatures but slightly above normal for min
temperatures due to extensive cloud cover.
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
VFR. Isolated convection possible along the sea breeze corridor
but the chances will be lower today and thus no mentions in the
Extended Aviation Outlook: VFR conditions will prevail.
The Atlantic surface ridge will tend a bit tonight with winds
10-15 KT at times. Seas through tonight will range from 1-2 ft
nearshore to 2-3 ft offshore.
The weekend will feature a typical summer pattern with Bermuda
ridge holding strong and influencing the coastal waters.
Generally light to moderate southwesterly winds backing during
the afternoon near the coast due to the sea breeze. Incoming
swell is low and expected seas 2 to 4 ft through the weekend
into early next week, mainly due to the local wind.
Elevated tide levels due to the lunar perigee and new moon will
result in the possibility for minor coastal flooding during the
evening high tides this weekend into early next week,
especially along the SC coast.
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