Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
740 am EDT Wednesday may 27 2015
high pressure will extend across the region through early next
Near term /through tonight/...
the upper ridge axis will remain just off the southeast United
States coast today while an elongated shortwave stretches from SW
to NE across central GA/SC. At the surface...weak Atlantic high
pressure will remain in place but a weak Lee side trough will
setup in the midlands. The cap will hold fairly strong across
coastal areas today. Farther inland...the combination of Lee
trough convergence...upper jet divergence...deeper moisture and
shortwave energy will support scattered showers and thunderstorms. We
maintained the highest probability of precipitation across inland areas during the middle afternoon.
Very little 0-6 km shear will be present and convective available potential energy only top out
around 1,000 j/kg...thus severe weather is not a primary concern.
High temperatures will top out in the upper 80s.
Any diurnal convection will die off after sunset. Low chances for
shallow ground fog in areas where precipitation occurs...
especially farther inland where the boundary layer will decouple
late tonight. Lows will range from the lower 70s near the coast
where winds stay up...to middle 60s inland.
Short term /Thursday through Saturday/...
Thursday and Thursday night...the region will remain along the
western periphery of deep ridging centered over the western
Atlantic. The combination of weak channeled vorticity and the
inland progressing sea breeze should support isolated to scattered
showers and thunderstorms in the afternoon generally along and west
of a Moncks Corner...Walterboro...Clyo to Reidsville line.
Convection will then quickly dissipate by early evening with the
loss of diurnal heating and as the sea breeze pushes west of the
area. Highs will be in the middle and upper 80s inland of the immediate
coast...with nighttime lows in the middle 60s.
Friday and Friday night...the upper level ridge will extend farther
west over the region...with strong subsidence resulting in rain-free
conditions for the area during the day. The development of a weak
coastal trough Friday night could result in isolated showers and
thunderstorms over the coastal waters...but will not indicate any
advecting onshore at this time although it is possible given onshore
wind trajectories. Highs will once again be in the middle and upper 80s
inland of the immediate coast. Lows should be in the middle to upper
Saturday...despite continued ridging aloft...models indicate the sea
breeze becoming a bit more active with respect to convection and the
forecast shows isolated to scattered showers and thunderstorms
across the area as a result. No significant changes in temperatures
are expected from previous days.
Long term /Saturday night through Tuesday/...
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 /12z Wednesday through Sunday/...
VFR conditions are expected to prevail at kchs and ksav through
12z Thursday. Scattered showers and thunderstorms are expected to
develop late this morning into this afternoon...but the greatest
coverage will be inland of the terminals. As a result have kept
mention out of the forecast...but as trends become better
established a mention of thunderstorms may be needed in the
Extended aviation outlook...mainly VFR through the period.
winds today and tonight will be at or below 15 knots with seas no
higher than 3 feet as high pressure persists.
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.