Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
426 am EDT Friday Oct 9 2015
high pressure will weaken today. A weak cold front will approach
from the northwest tonight...then cross through the region on
Saturday. A weak low will develop off the South Carolina coast on
Sunday...then move to the northeast on Monday. A weak cold front
will move through on Tuesday followed by high pressure through
Near term /through tonight/...
pre-dawn...high pressure extends across Georgia and the Carolinas
while a weak coastal trough persists off the far S Georgia and North
Florida coasts. High clouds had thickened a bit from Atlanta to
Columbia but our region only seeing areas of thin high cloud
cover. The forecast problem through daybreak is fog formation and
low stratus development...especially across southeast Georgia where Atlantic
moisture is copious in the boundary layer. As of 4 am...it appears
the widespread dense fog may remain just to the SW and S of the
Altamaha river area given the synoptic alignment of the coastal
trough. Despite this some locally dense fog is possible along and
S of I-16. We have maintained patchy fog mentions in most all of
our zones this mornings as temperatures remain steady in the low/middle 60s.
Today a weak middle level short wave ridge over our region will slide
offshore while an advancing upper trough digs from the Great Plains
toward the Missouri Valley area. Models continue to show quite a
bit of drier air with weak subsidence in the middle levels across
much of the region. While model consensus suggests a gradual
atmospheric destabilization along and west of I-95 this afternoon...
convective parameters are weak in the middle layers. We have trimmed
areal extent of mainly slight shower chances this afternoon out of
the Charleston metropolitan area and confined 20/30 probability of precipitation inland from the
sea breeze corridor...mainly in southeast Georgia. There could be
isolated brief thunderstorms in southeast Georgia but confidence pretty low and
thus not included in the forecast products.
Another warm day on tap after early morning fog/stratus dissipates
inland. Maintained plenty of middle 80s away from the beaches and
barrier islands. Clouds confined to diurnal cumulus/SC along with
periods of high cloudiness today.
Tonight should be mainly dry this evening outside of isolated showers
lingering across parts of inland Georgia. Clouds will thicken from
the west overnight as the middle/upper wave approaches from the Tennessee
Valley and upper Gulf Coast region. Convective rains are expected to
break out across north Georgia and the South Carolina upstate and
midlands after midnight. We continued to forecast increasing probability of precipitation
late...especially inland. There may be patchy fog in some spots but
the increase in deeper moisture and cloudiness should preclude a
risk for widespread fog issues.
Short term /Saturday through Monday/...
an upper low will swing through the deep south on Saturday...
allowing a surface low to develop off the SC coast before lifting
northeast away from the area. Expansive upper jet divergence
combined with ample vorticity advection and precipitable waters approaching 1.75"
will support widespread showers with some thunderstorms on Saturday.
Although the best forcing shifts offshore Saturday evening... wrap
around moisture will maintain isolated to scattered showers across
the coastal waters through Sunday night or even Monday.
Over land areas...cooler air will shift in from the northwest on
Sunday...and gradual drying will scour the clouds during the day.
Highs will only be in the lower to middle 70s due to cold advection.
A dry and warmer day expected Monday as high pressure builds in.
Highs will reach the middle/upper 70s.
Long term /Monday night through Thursday/...
a shortwave will clip the area Tuesday...pushing a weak and mainly
dry cold front through the region. Behind it...a zonal upper pattern
and surface high pressure will produce dry weather with high temperatures a
bit above normal in the lower 80s and lows in the 50s/60s.
Aviation /08z Friday through Tuesday/...
there is the potential for some low stratus and/or patchy fog to
develop late tonight...especially at ksav where there will be better
low level moisture with a weak coastal trough positioned nearby.
As a result...the forecast indicates MVFR/IFR conditions at ksav
from into middle morning with the potential for even lower flight
categories to occur. At kchs...have maintained VFR conditions on
the 06z taf cycle given lower confidence in fog/stratus formation.
VFR conditions are then expected to prevail at kchs and ksav
during the day Friday.
Extended aviation outlook...VFR conditions expected through Friday
evening. Increasing chances of MVFR or lower ceilings and possibly
visibilities late Friday night through Saturday with showers and thunderstorms. Low
ceilings possible Saturday night into Sunday morning. Mainly VFR
through tonight...light winds and seas 1 to 3 feet
prevailing within 20 nm. Seas well offshore closer to 3 feet on
average. Directions should veer from a light onshore component this
morning to more of a S to SW component by late tonight.
North to north-northeast winds increasing Saturday night into Sunday
behind a departing surface low. Fairly good chances for Small Craft
Advisory conditions during this period...at least from 25 knots gusts.
Conditions settle down early next week though a brief surge is
expected out of the west-southwest on Tuesday as a cold front pushes
flood waters in most areas will gradually recede...though slightly
worsening conditions possible along some main Stem rivers as upstream
water gets routed through.
a coastal Flood Advisory in effect through 800 am this morning
for Charleston/coastal Colleton counties. The 610 am high tide
will likely peak between 7.0 to 7.2 feet mean lower low water in
the Charleston Harbor.
High tides are expected to approach...or slightly eclipse...7
feet mean lower low water for Charleston Harbor for the next
several days. Any expected levels above 7 feet would require
coastal flood advisories.
SC...coastal Flood Advisory until 8 am EDT this morning for scz049-