Scientific Forecaster Discussion
fxus62 kchs 261039
Area forecast discussion
National Weather Service Charleston SC
639 am EDT Mon Jun 26 2017
a cold front will linger just offshore through Tuesday. High
pressure is forecasted to pass to our north Wednesday, then move
into the Atlantic during the second half of the week.
Near term /until 6 PM this evening/...
no major changes were made for the sunrise update.
26/10z surface observations and various rap mass fields suggest
the cold front is bisecting southeast South Carolina and
southeast Georgia. The boundary will ooze ever so slowly to the
south today, reaching a position roughly along a Reidsville-
Savannah-buoy 41033-buoy c line this afternoon as surface high
pressure tries to nudge in from the northwest. Although low-
level winds will shift to the north and northeast ahead of the
front in response to weak cyclogenesis taking place off the
Charleston County coast, model mass fields clearly slow
definitive moisture and surface-based instability gradient in
the aforementioned corridor across the leading edge of the cold
Expect scattered to numerous showers/tstms to develop south of
the front as early as late morning and persist in the Savannah-
Darien-Ludowici corridor through late afternoon as a weak 700
hpa shortwave ripples across southeast Georgia and interacts
with moderately unstable warm sector. Convection will steadily
decrease by late afternoon as the pre-frontal airmass becomes
increasingly overturned. Pops will range from 50-70% south of a
Glennville-Savannah line, to 20-30% along a Reidsville-Beaufort-
Kiawah Island line, with 0% pops for the counties bordering the
csra and the southern South Carolina midlands. Similar to Sunday,
precipitable waters in excess of 2 inches and the potential for convective
training could yield pockets of flooding, mainly in urban and
low-lying/poor drainage areas. An isolated severe tstm could
also occur with modified rap soundings at Darien, Hinesville and
Jesup showing SBCAPE 2600-3000 j/kg with Li's as low as -8c
embedded within a belt of 0-6km bulk shear near 30 kt. Highs
will warm into the mid 80s for most locations while a few upper
80s could occur well inland where some decent breaks in the
cloud canopy are possible.
Short term /6 PM this evening through Thursday/...
tonight: convection across the far south will quickly wind down
during the early evening hours. Another weak area of low
pressure is expected to develop along the cold front overnight,
which could push isolated shower activity back onshore along
the beaches early Tuesday. Will show slight chance pops across
the various beach communities to account for this. Lows will
range from the mid-upper 60s inland to the upper 70s along the
Tuesday through thursday: a cold front will linger just
offshore Tuesday. At the coast: chance pops remain in place for
our coastal counties due to their proximity near the
moisture/lift associated with the front. The highest instability
is far offshore, so we're not expecting any significant storms
across the area. Inland: pops are slight chance as drier air
from a surface high to our northwest builds into the area. The
front will be pushed away from our area Tuesday night as the
high moves closer. The center of the high is forecasted to pass
to our north Wednesday. Most of the area should be dry at that
time, but models hint at some moisture/instability across our
southernmost counties in the afternoon/evening hours as some
convergence takes place along the sea breeze. We have slight
chance pops to account for this. The high shifts offshore
Thursday, allowing S to southeast flow to develop late. This will bring
more moisture into our southern counties and further increase
the threat of showers/thunderstorms. High temperatures will be
within a few degrees of normal each day.
Long term /Thursday night through Sunday/...
nearly zonal flow will persist aloft with surface high pressure in
the Atlantic. Southerly flow around the high will advect moisture
into the southeast as an inland trough develops into the weekend.
The result will be the typical summertime shower/thunderstorm
pattern with the coverage and intensity appearing to increase each
day into the weekend.
Aviation /12z Monday through Friday/...
VFR. Risk for showers and tstms will be greatest south of the
ksav terminal this afternoon along a weak cold front.
Probabilities for impacts are too low justify a mention of thunderstorms in the vicinity
or thunderstorms and rain at this juncture.
Extended aviation outlook: brief flight restrictions are possible
due to showers/thunderstorms Tuesday afternoon/evening and then
again on Friday.
today: north to northeast winds will prevail today as weak low
pressure exits the local marine area. Winds will remain 10 kt or
less with seas 2-3 ft.
Tonight: a light northeast flow regime will hold in place with
speeds around 5 kt. Seas 2-3 ft during the evening hours will
subside to 1-2 ft after midnight.
Tuesday through friday: a cold front will linger just offshore
Tuesday, bringing changing wind directions. High pressure is
forecasted to pass to our north Wednesday, causing an increase in
the pressure gradient, which will lead to slightly higher winds and
seas Wednesday and Thursday. Conditions will improve as the high
moves into Atlantic during the second half of the week, allowing the
gradient to decrease.
tides could once again approach shallow coastal flooding
thresholds in the Charleston Harbor with the late evening high
tide cycle. Tide levels at fort Pulaski look to peak just shy of
shallow coastal flooding levels. A coastal flood advisory may be
needed for parts of the lower South Carolina coast, especially
for Charleston County.