Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
939 PM EDT Wednesday may 27 2015
high pressure will extend across the region through early next
Near term /until 6 am Thursday morning/...
tonight...large Atlantic high pressure will be the prominent
feature as it extends across the local zones...while aloft we/ll
lie on the west/northwest edge of deep-layered ridging. This will allow
for quiet weather conditions to prevail as skies average out to be
partly cloudy with light/calm winds. The onshore synoptic flow
and elevated dew points will limit overnight minimums to middle or
upper 60s most communities. The outliers will be immediate
shoreline places with 70-72 more common.
Cross-over temperatures will be obtained across parts of the west/northwest
locations...and given earlier rainfall this will lead to patchy
fog formation late. However...soil temperatures are quite warm and
upstream convective debris clouds will linger much of the night.
These factors will limit the areal coverage/visibility reduction.
Thus we continue to refrain from adding fog to the forecast...but
will amend if necessary since there is at least another update
cycle before any fog starts forming.
Short term /6 am Thursday morning through Saturday/...
with deep layered high pressure in place through
Saturday...conditions should be seasonably warm into the first
half of the weekend with temperatures ranging from the upper 70s at the
beaches to the upper 80s inland. With general subsidence in
place...sea breeze boundary will not generate too much convection
as it moves inland on Thursday and Friday afternoon/evening. Right
now...just some isolated showers/thunderstorms are expected away
from the coast with many places remaining dry.
Saturday...a very weak surface wave will move in from the Atlantic
on Saturday...increasing the chances of showers and thunderstorms a
bit with an slight increase in surface convergence...but with
ridging still in place aloft...low end chance category looks like
the best forecast for now due to lacking synoptic support. Temperatures
will again be within a couple of degrees of normal for the end of
Long term /Saturday night through Wednesday/...
upper level ridging will extend over the region through most of the
long term period...although an upper level trough will begin to
encroach on the southeast U.S. Toward the middle of next week. At
the surface...Atlantic high pressure will generally prevail into
early next week. There is then some indication that high pressure
will try to build from the north toward the middle of next
week...causing a weak coastal trough to develop just offshore.
Overall...moisture advection from a synoptic onshore flow and low
level convergence with the sea breeze should support isolated to
scattered showers and thunderstorms each day...with the greatest
coverage Tuesday and Wednesday with the nearing upper trough and
development of the weak coastal trough just offshore. Temperatures
will be near to slightly above normal through the period.
Aviation /02z Thursday through Monday/...
VFR is expected to prevail.
Extended aviation outlook...VFR conditions are expected to prevail
Thursday through the period with only a small chance of lower
ceilings/visibilities in rain showers/thunderstorms and rain this weekend.
tonight...an extensive sub-tropical ridge will maintain its grip
on the marine community...maintaining east/southeast winds at less than
10 or 12 knots and seas of no more than 2 or 3 feet. A few showers are
possible out near the warmer Gulf Stream waters...but the risk for
thunder/lightning is zero.
High pressure will continue over the waters through early
next week...generally maintaining an onshore flow with speeds of
around 15 knots or less. Despite the weak wind speeds...favorable
trajectories will result in seas of 2-4 feet across the waters...with
some seas to 5 feet in the outer Georgia waters Saturday as a weak
surface trough passes through the waters.