Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1252 am EDT Wednesday Jul 30 2014
a stationary front will remain offshore tonight through Thursday
before moving back toward the coast Friday through early next week.
Near term /until 6 am this morning/...
forecast looking fine overnight. Areas of middle level clouds at times
with clear to partly cloudy skies persisting. No change to our forecast
outside of very minor initialization tweaks. Readings falling into
the 60s most areas west of U.S. 17 with some lower to middle 60s in
cooler well inland spots where clouds can remain few to scattered.
Short term /6 am this morning through Friday/...
on Wednesday...with the upper trough axis just to our west we will
retain a zonal flow while dry high pressure remains at the surface.
Due to the middle-level subsidence...model soundings show a pronounced
cap around 600 mb which should preclude much in the way of precipitation.
Nevertheless...some of the models are indicating some rain showers
developing during the afternoon due to weak convergence with a
coastal trough. With dewpoints mixing into the low/middle 60s this does
not seem likely so we are maintaining a dry forecast. High temperatures
will be in the lower 90s inland with middle/upper 80s near the coast
where the sea breeze drops temperatures in the afternoon.
Thursday the upper trough deepens...with middle-level flow becoming
southwesterly and some shortwave energy moving into the forecast
area. However in low-levels a ridge will remain just off the
middle-Atlantic coast with east-northeast flow across the area. The middle-level cap
will weaken considerably on Thursday while precipitable waters increase. The sea
breeze should get going earlier in the day with isolated showers and
thunderstorms possible by the afternoon. Highs will be in the lower 90s.
On Friday the upper trough further deepens while the stationary
front just offshore pushes toward the coast. Increasing SW flow
above 850 mb and easterly flow below that will support precipitable waters
increasing to around 2 inches. Model soundings show the cap
essentially gone...so as the boundary layer destabilizes we should
see increasing coverage of showers/storms. The sea breeze will also
come into place...in addition to the convergence along the surface
front. We maintained 40 probability of precipitation with highs in the upper 80s to lower
Long term /Friday night through Tuesday/...
the latter portion of the forecast period looks to be rather
unsettled with the mean long wave trough position aloft to shift a
hair further west...and the sub-tropical Atlantic ridge to nose in
from the east. This allows for the stationary front at the surface
to set up over or near the forecast area this weekend and early
next week. Moisture will continue to stream in courtesy of a southeast
and south flow in the low levels and a rich SW feed in the middle and
upper reaches of the troposphere. Forcing due to the proximity of
the stationary front will provide the necessary lift to generate
at least a solid chance of precipitation coverage throughout.
Temperatures will be held in check due to plenty of clouds and the higher
There are fortunately still no indications that any sort of tropical
or sub-tropical low will form on the front...especially since it
looks to have too much interaction with the nearby land mass of the
southeast. However...the tropical wave in the eastern Atlantic has a high
probability of developing into a tropical cyclone. But this feature
looks to curve out in the Atlantic...turning away from Continental U.S. Before
it gets much further west than about 70-75 degrees and to the NE of
the Bahamas. Should it become a named system it would be Bertha. In
2008 Bertha was both the longest lived and easternmost developing
July tropical cyclone on record.
Aviation /06z Wednesday through Sunday/...
VFR through the 00z taf period at both kchs/ksav. Isolated convection
mainly in the form of spotty showers possible this afternoon or early
evening but potential for any one area getting rain is quite low.
Extended aviation outlook...occasional flight restrictions are
possible late week and next weekend as a stationary front meanders
a relatively weak pressure pattern will translate to a tranquil
night across the coastal waters. Variable winds including the
early sea breeze should give way to more uniform northeast winds
10 knots or less tonight...although guidance differs regarding the
overnight wind direction. Seas will generally range from 1-2 feet
within nearshore waters to 2-3 feet beyond 20 nm.
A modest east to NE flow will persist over the waters through Friday.
Speeds will be increasing Thursday into Friday due to a tightening
gradient though winds/seas will remain well below advisory
Saturday through Sunday...the stationary front looks to slide into
the waters...perhaps even moving onshore. Winds will veer in
response...but still nothing more than about 12-18 knots and 3 or 4 feet