Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
428 am EDT Tuesday Aug 4 2015
a weak area of low pressure will move northeast away from the region
today. An inland trough will develop Wednesday and persist through
Friday. A cold front will affect the area over the weekend.
Near term /through tonight/...
pre-dawn...the center of the surface low was passing just south
of North Charleston at 4 am. The low level cyclonic flow helped
focus intense moisture convergence overnight along coastal SW
Charleston County as precipitable waters close to 2.4 inches were noted on
analysis. The intense rains failed to make it into downtown
Charleston and conditions should improve the next couple of hours
as the low moves along NE Charleston County. Radar rainfall
estimates in the 3-4 inch range were common between Johns Island
SC to Seabrook Island SC...east to Kiawah Island SC. Torrential
downpours will continue around McClellanville SC through 10z. In
the wake of the low...widespread low clouds and patchy build down
fog was developing along and west of I-95. This has been added to the
Middle level shortwave energy moving through the Carolinas this
morning will continue to eject the surface low to the NE with
focus for heavier rains sliding into southeast North Carolina as the core
of the deep moisture pulls out. Through late morning...we
maintained chance probability of precipitation in the Charleston tri-County area as
convergence and weak upper difluence brush the central South
In the wake of low elsewhere today...widespread low clouds will
erode after middle morning giving way to partly cloudy skies and warming
temperatures. A residual surface trough will bisect the forecast area this
afternoon with some building subsidence aloft. Along our northwest tier of
zones...diurnal convection chances look very slim this afternoon
with isolated afternoon and evening showers and thunderstorms possible over
eastern...far southern...and coastal zones. Much drier 850-500 mb
air will continue to press SW today and this should keep
convection coverage fairly sparse for the most part. Highs will
rebound to the middle 90s well inland with afternoon heat indices in
the 103-105 degree range.
Mainly quiet conditions overnight with partly cloudy to mostly
clear skies and perhaps isolated showers just off the beaches
last with the land breeze.
Short term /Wednesday through Friday/...
a quasi-zonal flow will briefly setup on Wednesday...yielding hot
temperatures in the middle/upper 90s. Increasing southwest flow in the
lower levels during the latter half of the day will evoke a surge in
precipitable waters with values back above 2" across southeast Georgia by afternoon.
Isolated showers/thunderstorms will pop during maximum heating though better
coverage is likely across southern Georgia where moisture is deeper.
An upper trough will develop over the eastern United States Thursday
into Friday...causing a surface trough to develop just inland. Low
level moisture will increase during the period with precipitable waters above 2"
on Thursday and close to 2.3" by Friday. Given less middle-level
capping and ample low-level Theta-E...we expect better coverage of
showers and thunderstorms especially Friday. Decreasing upper heights and
greater sky cover will produce a cooling trend with highs middle 90s on
Thursday and lower 90s Friday.
Long term /Friday night through Monday/...
the upper trough will push east Friday night with a cold front
pushing toward the SC/Georgia coast late Saturday. Decent convective
coverage expected on Saturday. Drier high pressure may attempt to
build from the northwest on Sunday. However...given the models' dry
bias behind warm season cold fronts we maintained slight chance probability of precipitation
on Sunday. Better convective coverage possible Monday into Tuesday
as some shortwave energy drops through the area.
Aviation /08z Tuesday through Saturday/...
kchs...light rains should impact the terminal through 09z. Brief
MVFR ceilings expected. After the low passes later this morning...lower
clouds could fill in a bit around dawn and will continue to
monitor. There is still a chance for showers and thunderstorms into this
afternoon...but chances will be decreasing as some subsidence
begins to take hold aloft.
Ksav...conditions have tanked in the wake of the surface low now
along the South Carolina coast. Widespread LIFR ceilings and areas
of build-down fog should persist until middle morning...likely
breaking up just prior to 14z as temperatures warm. Otherwise...VFR
with only low chances of an afternoon thunderstorm.
Extended aviation outlook...main concerns are occasional reductions
in visibility and/or ceiling due to showers and thunderstorms. Although
impacts cannot be ruled out any day...greater coverage is expected
Thursday and Friday.
south winds have surged to around 20 knots off the Charleston County
coast and seas were in the 4-5 feet range...perhaps locally higher.
With the low moving out this morning...winds should resume a SW
component with a typical late day uptick in speeds...a more
typical type regime. Over Georgia waters...conditions were
improving as the flow has shifted offshore but seas still in the
5-6 feet range beyond 20 nm. We are hanging onto a Small Craft
Advisory in that leg until 8 am.
Another SW nocturnal surge is anticipated tonight...briefly
near 20 knots over some of our near shore waters through late
evening...then speeds decreasing late. While winds and seas
will be elevated...cannot rule out a period of Small Craft
Advisory conditions across the outer Georgia waters.
Marine...Small Craft Advisory until 8 am EDT this morning for amz374.