Area forecast discussion
National Weather Service Charleston SC
135 am EDT Tuesday may 21 2013
Synopsis...
an upper level disturbance over the area will dissipate through
middle week while Atlantic high pressure prevails until late week. A
cold front will drop through the area Friday...followed by high
pressure through next weekend.
&&
Near term /until 6 am this morning/...
we have expanded slight chance of showers eastward of I-95 across a
larger portion of southern South Carolina overnight...otherwise
few changes on the update early this morning. Debris clouds have
decreased but areas of stratus and stratocumulus expected to
increase over southeast Georgia into southern South Carolina.
It/ll be another warm and very humid night...and thus restricting
lowest temperatures only in the middle and upper 60s away from the beaches.
&&
Short term /6 am this morning through Thursday/...
Atlantic high pressure will be the dominant feature at the surface
Tuesday and Wednesday. The persistent upper shortwave meandering
over the southeast states will gradually become absorbed by a trough
axis to the west middle week. The upper trough will then continue to
swing toward the area on Thursday...with a cold front approaching
the western zones by the evening hours.
Deep moisture and precipitable water values will be highest
Tuesday under the influence of the lingering shortwave
energy...before synoptic scale forcing diminishes a bit by
Wednesday. Expect scattered coverage of mainly diurnal showers
and thunderstorms both Tuesday and Wednesday...highest during the
favored afternoon and evening periods. Convection will mainly be
driven by a combination of daytime heating/instability...seabreeze
convergence...and any boundary interactions. Will thus advertise
best thunderstorm potential along and inland of the
seabreeze...however there are still some indications that
isolated showers/weak thunderstorms could push from the marine
zones locally onshore each night and early morning. The
approaching front could support better convective coverage on
Thursday...yet prefer to maintain persistence by keeping rain
chances in the 30 percent range to account for some timing
differences seen in forecast model solutions.
Expect a steady warming trend Tuesday through Thursday. High
temperatures will range from the low to middle 80s for the majority
of the forecast area on Tuesday...with the exception of the far
southwest counties where temperatures could climb into the upper
80s. High temperatures will then peak in the upper 80s most inland
locations for Thursday...while being suppressed in the low to middle
80s closer to the coastline.
&&
Long term /Thursday night through Monday/...
fairly good model consistency regarding an upper trough shifting
southeast and a cold frontal passage Friday or Friday night. Dry and
slightly cooler Canadian high pressure looks to build in for the
weekend before shifting offshore early next week.
&&
Aviation /05z Tuesday through Saturday/...
kchs...isolated showers and brief MVFR ceilings possible overnight...
otherwise VFR until daybreak. A rich tropical-like feed of
moisture and coastal convergence will interact with the sea breeze
during the late morning and afternoon hours today...producing
scattered rain showers and possible thunderstorms and rain. For now we maintained a prob30
group for rain showers and MVFR conditions from 15-21z until trends can be
better defined.
Ksav...we anticipate a few hours of MVFR conditions in light
low stratus/stratocumulus overnight and continue to indicate that
trend. Isolated to scattered convection will form along the sea
breeze boundary during late morning through middle afternoon...thus
a prob30 group from 16-21z was maintained.
Extended aviation...the main concern will be sporadic reductions
in ceilings and visibilities...mainly associated with scattered
showers and thunderstorms through the period. The greatest chances
will be in the afternoon hours Wednesday and Thursday...although early morning
flight restrictions cannot be ruled out each day.
&&
Marine...
tonight...a strong ridge of high pressure centered over the
Atlantic will extend west across the coastal waters...generating southeast
and S winds at or below 10 or 12 knots and seas in the 2-4 foot
range. Could see some stronger storms moving in from the south
overnight.
High pressure will remain over the western Atlantic through
Thursday night...maintaining a general southerly flow and
allowing seabreeze circulations to develop each afternoon. A cold
front will drop through the region early Friday...with a northeast
flow developing as Canadian high pressure builds in its wake.
Winds and seas will likely increase over the weekend as a result.
&&
Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...none.
&&
$$
Synopsis...
near term...
short term...wms
long term...jrl
aviation...
marine...
