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Area forecast discussion 
National Weather Service Charleston SC
1122 am EDT Tuesday Jul 22 2014

Synopsis...
a trough of low pressure will linger over the area today before
dissipating tonight. Atlantic high pressure will then build over
the region through the weekend. A cold front will approach from
the northwest early next week.

&&

Near term /through tonight/...
an inverted surface trough across the region this morning will
gradually shift to the northwest through this afternoon. Extensive
cloud cover this morning has thus far limited insolation...with
temperatures still in the upper 70s to lower 80s. Partial breaks in the
clouds expected through early afternoon though we did lower high
temperatures by about two degrees based on the expectation that mostly
cloudy will be the rule. The upper low to our west will slowly
retrograde today though deep...moist southerly flow will remain in
place. 12z radiosonde observation showed a shallow wedge of northeast flow at the
surface though this should mix out as the sea breeze gets going
this afternoon. The ongoing showers across Charleston and Berkeley
counties will likely continue...then the best coverage shifts into
inland SC as the 850-700 mb convergence axis lifts north. Some
shortwave energy is prognosticated to rotate into inland southeast Georgia
later this afternoon so we bring in some moderate probability of precipitation in that
region later in the day. Given precipitable waters above 2 inches...fairly slow
boundary layer flow and decent low-level convergence...heavy
rainfall could again be a concern today. Fortunately...many of
the areas that picked up substantial heavy rainfall on Monday may
be on the dry side today.

Tonight...the upper low will continue to shift slowly west toward
New Orleans with the trough over the area dissipating. Any evening
showers and storms should diminish pretty quickly with convection
shifting offshore where the greater instability will be found.
Lows in the lower to middle 70s inland and closer to the upper 70s at
the coast.

&&

Short term /Wednesday through Friday/...
Wednesday and Wednesday night...a closed middle and upper level low
over the Delta of the Mississippi will open as it slowly
retrogrades...allowing ridging over the Atlantic to expand over the
southeast United States. At the surface...Atlantic high pressure
will prevail while a Lee side trough develops inland. This is a more
typical summertime pattern for the region...thus expect mainly
scattered afternoon/evening showers and thunderstorms across the
area. A southerly low level flow with slight veering of the flow
aloft should support highs in the lower to middle 90s inland from the
immediate coast. Lows at night should be in the lower to middle 70s.

Thursday and Thursday night...an upper level trough will begin to
dig into the eastern United States...causing the inland trough to
strengthen while Atlantic high pressure continues its influence over
the region. A westerly flow aloft will result in drier
conditions...at least across southeast Georgia...but increasing low
level convergence later in the day in vicinity of the inland trough
and channeled vorticity aloft could result in a better chance of
convection across parts of southeast South Carolina. Thus...the
forecast indicates a low chance for showers and thunderstorms across
much of the Charleston quadrant-County area with a slight chance
elsewhere to the south. The downslope flow will also support warm
temperatures...with highs solidly into the middle 90s away from the
immediate coast where the sea breeze should remain pinned. Lows will
once again be in the lower to middle 70s at night.

Friday...the middle and upper level trough axis will shift farther east
while at the surface the inland trough will shift closer to the
coast. Precipitable water values will rise as well...and this should
result in an increased potential for convection with the forecast
indicating a good chance of showers and thunderstorms...especially
in the afternoon and evening. Less of a downslope flow and increased
cloud cover should result in highs in the lower to perhaps middle 90s
away from the coast.

&&

Long term /Friday night through Monday/...
the middle and upper level trough will weaken over the eastern United
States over the weekend...as ridging tries to expand south of the
region. The upper trough will then get reinforced and expand
southward early next week from energy dropping across the Great
Lakes region. At the surface...Atlantic high pressure with a weak
trough of low pressure inland will prevail through the
weekend...before the strengthening upper trough drives a cold front
toward the area from the northwest early next week. Expect mainly
diurnal scattered showers and thunderstorms over the weekend...but
coverage could increase early next week as the front nears and
moisture increases. Temperatures should be near normal for most of
the long term period.

&&

Aviation /15z Tuesday through Saturday/...
kchs...abundant low level moisture has resulted in low ceilings
and reduced visibilities at the start of the forecast period...but
prevailing conditions should improve to VFR by around 17z. Given
the potential for numerous showers to impact the terminal...have
included a tempo group for showers with some flight restrictions
through 17z. Then...have vicinity thunderstorms in the forecast
from 17-21z as confidence in coverage/timing is somewhat reduced.
The greatest focus for convection should then shift inland late
this afternoon...likely bringing and end to convection at the
terminal.

Ksav...abundant low level moisture has resulted in low ceilings
and reduced visibilities at the start of the forecast period...but
prevailing conditions should improve to VFR by around 15z.
Scattered showers and thunderstorms are possible late this morning
through mid-afternoon...but confidence of any direct impact at
the terminal is low and have kept mention out of the forecast
until trends become better established.

Extended aviation outlook...VFR conditions expected to prevail.
Brief flight restrictions possible within scattered mainly
afternoon/early evening showers and thunderstorms. The best coverage
is expected Friday and Saturday.

&&

Marine...
today and tonight...a trough of low pressure near the coast this
morning will dissipate through tonight. The weak pressure gradient
will lead to winds mainly 15 knots or less...generally peaking near
the coast this afternoon with the sea breeze...and possibly along
the Charleston County waters this evening. Seas mostly 3 feet or
less but possibly reaching 4 feet offshore tonight.

Wednesday through Sunday...Atlantic high pressure will build over
the waters through Sunday while a trough of low pressure lingers
inland. As a result...a general south/southwest flow is expected to
prevail. The strongest winds will occur during the afternoon/early
evening hours along the land/sea interface due the sea breeze...and
as a nocturnal surge develops over the coastal waters during the
evening/late night hours...pushing winds as high as 15-20 knots with
the potential for higher gusts. Seas will generally range from 2-4
feet.

&&

Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...none.

&&

$$

Near term...rjb
short term...jaq
long term...jaq
aviation...jaq
marine...jaq/rjb

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