Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
350 am EDT Monday Jul 6 2015
Atlantic high pressure will prevail with an inland trough of low
pressure lingering through the weekend.
Near term /through tonight/...
today...the upper closed low over the lower Ohio Valley will weaken
and lift northward while trailing shortwave energy over Alabama
this morning weakens and shifts into Georgia this afternoon. Overall
weaker forcing should lead to less convective coverage than recent
days...although scattered showers and thunderstorms are still
expected inland as the lazy sea breeze kicks in. Southeast
Georgia could see numerous showers and storms closer to the
deeper moisture and possible influence from convective outflow
farther south. Expect a very low severe storm risk given limited
instability/shear...most likely where any mesoscale boundaries
enhance updraft strength...particularly over southeast Georgia.
With decent cloud coverage highs should be limited to around 90
away from the coast to lower 90s inland.
Tonight...lingering convection early should weaken and
dissipate...with most of it shifting offshore late. Low
temperatures should be in the lower to middle 70s...with some upper
70s along the SC coast.
Short term /Tuesday through Thursday/...
Tuesday and Tuesday night...the remnant axis of an upper level
trough will be located over the Appalachians to start the day...but
will dissipate as the day progresses allowing upper level ridging to
begin expanding westward into the region. At the surface...high
pressure will continue to build in from the Atlantic while a weak
trough persists inland.
There could be some showers over the adjacent Atlantic in the
morning...with a few potentially advecting onshore and impacting the
beaches due to a favorable low level trajectory. Then...a weak
disturbance along the southeast periphery of the dissipating upper
trough combined with low level convergence associated with the sea
breeze and inland trough should be sufficient for scattered shower
and thunderstorm development...mainly in the afternoon and early
evening. Temperatures away from the immediate coast should reach
highs around 90 or in the lower 90s...with nighttime lows in the
lower to middle 70s.
Wednesday and Thursday...the upper level ridge will continue to
expand westward over the region...while the Atlantic surface high
gradually retrogrades closer to the coast. Despite increased
subsidence...there appears to be sufficient low level moisture and
instability for scattered showers and thunderstorms to develop
along/ahead of the sea breeze during the afternoon and early evening
hours each day. Rising heights aloft will support increasing
temperatures...with highs reaching the middle 90s across most inland
areas by Thursday.
Long term /Thursday night through Sunday/...
medium range guidance is in good agreement with the overall synoptic
pattern through the long term period. Upper level ridging will
continue to retrograde...shifting over the region...then eventually
becoming centered west of the region by late in the weekend. At the
surface...Atlantic high pressure will retrograde as well...with its
axis taking on a west-east orientation just south of the region.
Overall...this pattern will favor more typical summertime conditions
with isolated to scattered showers and thunderstorms in the
afternoon/early evening each day...although coverage should be a bit
lower by late weekend as a drier northwest flow develops aloft.
Temperatures will gradually warm each day beneath rising heights
aloft...staying above normal through the long term period.
Aviation /07z Monday through Friday/...
mostly VFR through 06z Tuesday...although LIFR ceilings will impact ksav
this morning...possibly through around daybreak. Showers and
thunderstorms off the SC coast this morning should remain there but
chances will increase toward afternoon around the terms as the sea
breeze begins to meander inland. Coverage should be less than
previous days though and storms should not be as intense given
Extended aviation outlook...brief flight restrictions are possible
in mainly scattered afternoon/early evening showers and
today and tonight...south to southwest winds 15 knots or less with
seas 2-3 feet near shore and 3-4 feet beyond 20 nm will prevail.
Tuesday through Saturday...south to southwest winds will prevail
through the period as the region remains along the western periphery
of Atlantic high pressure. Winds will generally average 10-15
knots...possibly a bit higher at night with weak nocturnal surging and
along the land/sea interface with the afternoon sea breeze. Seas
will average 2-4 feet. Both winds and seas look to remain below Small
Craft Advisory thresholds.
Rip currents...we upgraded to a low-end moderate risk along the
Charleston County coast due to recent activity...lingering swells
and gusty winds this afternoon with the sea breeze.