Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1235 am EST Thursday Mar 5 2015
Atlantic high pressure will extend across the region overnight. A
strong cold front will approach from the northwest Thursday and
will pass off the coast early Thursday evening. Colder high
pressure will build over the area Thursday night into Saturday. A
coastal trough will develop offshore late in the weekend. A storm
system could impact the area early next week.
Near term /until 6 am this morning/...
dry weather overnight. Low clouds with origins from the Gulf of
Mexico will reach the Savannah River over the next few hours...but
guidance is split on how far north it GOES from there. Adjusted
sky cover grids to be a bit more optimistic for southern South
Carolina zones. Widespread sea fog continues just off the beaches
and has show signs of buffeting coastal communities over the past
hour...mainly along the Charleston County coast where low-level
trajectories are the most favorable for fog to reach land. A dense
fog advisory is not expected at this time given the small area
that will be impacted. It will be warm night with a well mixed
boundary layer helping to keep temperatures up. Nudged overnight
lows up a degree or so most areas and adjusted hourly temperatures
to match. Lows will bottom out in the Lower-Middle 60s with upper 50s
at the beaches.
Short term /6 am this morning through Saturday/...
Thursday...surface high pressure will be centered over the Atlantic
while a cold front approaches from the west...and eventually passes
through the forecast area in the afternoon into the evening.
Tightening pressure gradient will allow for breezy conditions to
develop with southwest winds expected to gust up to around 25 miles per hour.
Compressional heating ahead of the front and deep southwest flow
will allow temperatures to soar well above normal again. Highs will
will be in the upper 70s/around 80 with current records expected to
stay safe. Given upper forcing and increasing
moisture...precipitation will accompany the front. Weak instability
and unimpressive lapse rates will keep thunder to a
minimum...however could not rule out a couple rumbles in the
afternoon. Thursday night...north/northeast flow will help usher
much colder air into the region. Low temperatures will drop to the
middle 30s/low 40s. Favorable mixing profiles will allow for gusty
winds over Lake Moultrie. A lake Wind Advisory may be needed late
Thursday night into Friday.
Friday...high pressure will build in from the northwest while the
front remains nearly stationary well off the southeast coast. Given
forecast area is situated in the favorable right entrance region of
upper jet and forcing from weak middle level disturbance embedded
within southwest flow aloft...precipitation will be possible. One
forecast concern will be p-type as early as late Thursday night
in inland Berkeley County and perhaps spreading into the
Charleston tri-County region Friday morning into early afternoon.
Surface wet bulb forecasts show the freezing line nudging down into
our northern SC zones. Moisture will be one of the bigger
questions...but forecast soundings do hint at a window where
freezing drizzle/light freezing rain will be possible. Will
certainly need to continue to monitor trends. Temperatures will be
well below normal with highs expected to be 30-40 degrees colder
than previous days. Friday night...moisture will quickly start to
dry out with temperatures expected to drop around freezing. A
freeze watch may eventually be needed.
Saturday...high pressure will remain the dominant weather feature at
the surface...while nearly zonal flow remains aloft. Lack of
significant forcing and moisture will keep a dry forecast in tact.
Temperatures will be moderate a bit although still be below normal.
Highs will be in the upper 50s.
Long term /Saturday night through Wednesday/...
there remains a good bit of uncertainty in the long term period
as an active baroclinic zone is expected to waver from the
northern Gulf Coast region and Florida late in the weekend to
Georgia and the Carolinas during early to middle week. Global models
differ on timing and strength of these impulses moving through the
southeast states during this time. With periods of clouds and showers
possible from time to time...temperatures will probably be near or
slightly below climatology.
Aviation /06z Thursday through Monday/...
watching low clouds spreading northeast out of the Gulf of Mexico.
These are on target to impact ksav 08-9z with ceilings dropping to
low-end MVFR and possibly high end IFR. Guidance suggests these
clouds will not reach kchs at this time and will trend the 06z tafs in
that direction. At ksav will show ovc012 tempo ovc008 08-12z to
cover. VFR at kchs. Fog appears unlikely given the well mixed
boundary layer that is in place. Low-level wind shear /llws/ will
be an issue at both terminals through sunrise with as much as 40
knots of wind at 1500 feet off the deck. VFR for much of the day before
ceilings/visibilities crash late afternoon/early evening as a cold front
pushes through the terminals. IFR or lower conditions are likely
and will trend the tafs in that direction.
Extended aviation outlook...flight restrictions likely Thursday
night into Friday along with gusty north to NE surface winds. A low
probability for light freezing rain/freezing drizzle will exist
at kchs especially Friday morning. Conditions expected to improve
over the weekend with high pressure and VFR.
as S/SW winds as high as 15-20 knots continue to advect dewpoints in
the 60s over the chilly Atlantic shelf waters...conditions will
remain very favorable for sea fog development over near shore
waters overnight. Maintained the ongoing dense fog advisory for
all near shore zones outside Charleston Harbor. While fog could
occasionally push into Charleston Harbor...SW winds should hold
the most persistent dense fog over amz350...thus no dfa has been
issued for amz330. Will continue to assess. Seas overnight will
range from 2-4 feet within nearshore waters to 4-5 feet beyond 20 nm.
Thursday through Monday night...marine conditions are expected to
deteriorate early in the period as a cold front approaches and
passes through the water Thursday evening. Warm moist flow ahead of
the front will be favorable for sea fog development... thus have
maintained mention in the forecast. As front passes through the
waters...strong cold advection will ensue providing favorable mixing
profiles. This will allow for stronger winds aloft to be mixed to
the surface. Have issued a gale watch for nearshore Charleston
County waters and outer Georgia waters late Thursday night into Friday
morning...and small craft advisories for the remaining coastal
waters including the Charleston Harbor. Conditions will subside on
Friday afternoon as high pressure builds in and the pressure
gradient relaxes. Marine conditions will remain fairly benign the
remainder of the weekend into early next week with winds/seas below
Small Craft Advisory criteria.
ksav tied the record high of 84 degrees for March 4.
Record highs for 5 March...
Record low maximums for 6 March...
Marine...Small Craft Advisory from 10 PM this evening to 1 PM EST
Friday for amz330.
Dense fog advisory until 11 am EST this morning for amz350-352-
Small Craft Advisory from 10 PM this evening to 4 PM EST
Friday for amz352.
Gale watch from this evening through Friday morning for amz350.
Gale watch from late tonight through Friday morning for amz374.
Small Craft Advisory from 1 am to 4 PM EST Friday for amz354.