Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
756 PM EDT Wednesday Mar 12 2014
a strong cold front will move through the region this evening...
followed by unseasonably cool high pressure through Friday.
Another cold front will push into southeast South Carolina and
southeast Georgia Sunday. The front will either stall over the
area or continue pushing south into Florida early next week. At
least one wave of low pressure will develop along this stationary
Near term /until 6 am Thursday morning/...
a Wind Advisory remains in effect for all areas until 2 am.
The cold front is expected to push offshore around 10 PM. Ahead of
the front there will be a few showers but the main impact with the
front will be strong and gusty winds which will be near 40 miles per hour at
times...especially on elevated surfaces such as bridges and
overpasses. The highest winds should come prior to midnight when
the greatest pressure rises will occur...likely on the order of 6
mb per 3 hours. Skies will clear after the frontal passage as
downslope flow takes hold. Temperatures should bottom out in the
middle/upper 30s inland and closer to 40 at the coast. There is a
very low probability for temperatures well inland to reach
freezing around daybreak but chances are too low to warrant freeze
warnings. Persistent winds and dry conditions will prevent frost
Short term /6 am Thursday morning through Saturday/...
the longwave trough axis will be shifting off the coast Thursday
morning with strong high pressure settling into the region. The
Canadian airmass overspreading the area will yield temperatures
about 20 degrees colder than 24 hours prior. Low-level downslope
flow will result in modest compressional heating but high temperatures on
Thursday will still only reach the middle to upper 50s.
The surface high will settle overhead Thursday evening...allowing
the boundary layer to decouple shortly after sunset. Model time
sections show a deep dry profile which supports strong radiational
cooling overnight. Friday morning lows expected to be in the upper
20s to lower 30s away from the coast. Thus we issued a freeze watch
for all zones except the Georgia coastal areas where lows in the middle
30s are anticipated. Even if a freeze does not occur in some locales
there is a good chance for scattered frost development.
Low-level ridging and warm advection on Friday will result in a
quick rebound in temperatures into the middle/upper 60s under mostly
sunny skies. As the surface high shifts off the coast and a
southerly flow develops...Friday night will be quite a bit warmer
with lows in the 40s.
An upper shortwave lifts into central Georgia/SC on Saturday with a
backdoor cold front sinking into the midlands and Pee Dee region.
Some weak isentropic ascent will develop during the afternoon across
inland areas so we maintained a slight chance for rain showers.
Highs will reach the lower 70s with continued warm advection.
Long term /Saturday night through Wednesday/...
conditions look unsettled through early next week as a cold
front is expected to push south into southern South Carolina Sunday
and then either stall out or continue to push south into Florida
Sunday night into Monday. High pressure should then build in through
Wednesday with generally dry conditions and moderating temperatures.
Aviation /00z Thursday through Monday/...
mainly VFR conditions with just a very small chance of brief MVFR
ceilings...and a few showers...from about 01-03z as a cold front
passes through. The main impact will be winds which could gust
near 35 knots through about 06z...shifting from west-southwest to west-northwest with the frontal passage.
Winds will slacken toward daybreak as the pressure gradient
subsides but then pick back up again slightly once better mixing
commences...although not nearly as strong.
Extended aviation outlook...VFR Thursday night through Saturday.
MVFR ceilings and/or visibilities likely Saturday night into at least
early Monday along with showers due to a cold front. Gusty winds
expected into Thursday afternoon.
strengthening winds in advance of a cold front late this
afternoon/early this evening and especially due to strong cold
advection/sharp surface pressure rises in the wake of cold frontal passage
this evening justifies gale warnings for all coastal waters.
As winds diminish to some degree overnight...the Gale Warning
should transition to a Small Craft Advisory over Charleston
Harbor...but gales will continue across other coastal waters
through the night. Hazardous seas will range from 6-7 feet within
nearshore waters/highest beyond 10 nm given the offshore flow...
to 7-10 feet beyond 20 nm...highest beyond 40 nm.
Conditions will improve drastically Thursday as the pressure
gradient...low-level jet and cold advection wane. All headlines for
the nearshore waters should come down in the morning with the outer
waters following in the afternoon. Generally tranquil conditions
then expected Thursday night through Saturday before things likely
go downhill early next week as a cold front pushes into the area
from the north Sunday with the worst conditions likely Sunday night
and/or Monday as low pressure pushes offshore and high pressure
builds from the north.
critical relative humidity is expected Thursday. However...winds
will fall below critical levels before critical relative humidity
is attained. Given widespread rainfall/near term impact on fuel
moisture...per collaboration with partners we did not issue a Fire
Danger Statement for Thursday.
Georgia...freeze watch from late Thursday night through Friday morning
Wind Advisory until 2 am EDT Thursday for gaz087-088-099>101-
SC...freeze watch from late Thursday night through Friday morning
Wind Advisory until 2 am EDT Thursday for scz040-042>045-
Marine...Gale Warning until 8 am EDT Thursday for amz350-352-354-374.
Gale Warning until 2 am EDT Thursday for amz330.