Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1035 PM EDT Monday Jul 6 2015
Atlantic high pressure will prevail with an inland trough of low
pressure lingering through the weekend.
Near term /until 6 am Tuesday morning/...
late Monday evening...showers/thunderstorms over southern/coastal
locations were diminishing in coverage...while only isolated
showers were developing/dissipating along the sea breeze well
inland. Expect this gradual decrease in convection coverage to
continue over land...and the focus for at least isolated/scattered
thunderstorms should shift over coastal waters overnight.
Short term /6 am Tuesday morning through Thursday/...
Tuesday...a remnant upper trough axis will weaken across the SC
midlands and a broad upper ridge will rebuild. In the lower levels a
steady southerly flow will be in place...bringing moisture off the
western Atlantic. We may see some showers moving onshore during the
morning due to weak convergence off the coast and the landward storm
motion. The sea breeze will develop and push inland fairly early in
the afternoon given the synoptic scale flow. Although middle-levels
will be warming and the cap will strengthen...surface dewpoints in
the lower 70s and temperatures in the lower 90s will yield 1500-2000 j/kg
convective available potential energy. Such a thermodynamic environment combined with forcing along
the sea breeze should be sufficient to produce isolated to scattered
showers and thunderstorms Tuesday afternoon and early evening.
Wednesday and Thursday...a fairly similar pattern will persist
Wednesday and Thursday though the upper ridge will continue to
strengthen. This will result in high temperatures pushing into the middle
90s by middle week. Middle- level capping will also strengthen but a
robust afternoon sea breeze and considerable surface-based
instability will still allow for 20-30 percent rain chances mainly
during the afternoon/evening. Although we are lacking appreciable
shear or upper synoptic scale forcing mechanisms...given the
surface-based buoyancy and convective outflow boundaries...
isolated severe thunderstorms will be possible each day.
Long term /Thursday night through Monday/...
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 /03z Tuesday through Saturday/...
VFR. Low probability for flight restrictions around daybreak
Tuesday...especially at ksav. The probability for thunderstorms
near the terminals Tuesday afternoon remains too low to justify a
mention within 00z tafs.
Extended aviation outlook...brief flight restrictions are
possible in mainly scattered afternoon/early evening showers and
overnight...S/se winds 10-15 knots with a few gusts to 20 knots will
veer toward the SW overnight. Seas will average 2-3 feet within
nearshore waters and as high as 4 feet beyond 20 nm.
Isolated/scattered thunderstorms could locally alter winds/seas.
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.