Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
732 PM EST Friday Feb 5 2016
inland high pressure will prevail tonight. A coastal trough
will develop offshore and strengthen Saturday. Low pressure will
track north and deepen off the southeast coast Saturday night
through Sunday....then will move away toward the northeast Sunday
night. A cold front will cross the area Monday. Then...a deep
trough will remain in place through the middle of next
week...bringing unseasonably cool conditions to the area.
Near term /until 6 am Saturday morning/...
as of early evening...no major changes for tonight/S forecast.
High pressure will prevail...centered over central NC. Pretty
decent radiational cooling conditions...especially inland...will
allow temperatures to drop to around 30 inland...near freezing
around coastal metropolitan areas and upper 30s at the immediate coast.
Short term /6 am Saturday morning through Monday/...
this forecast period includes a particularly challenging
precipitation event...and most attention focuses on the potential
for a period of wet snow late Saturday night into Sunday morning.
Low pressure will be tracking north/northeast and deepening rapidly
off the southeast coast...while an impressive upper low will
traverse southern counties of the forecast area. As the upper low
trends toward a negative tilt...strong forcing for ascent will
develop across the region. Initially...the response will include an
expansion deep layered moisture and rain across much of the forecast
area as Saturday night progresses. Then...late Saturday night into
Sunday morning cold advection will push toward the coast in concert
with dynamic cooling. The big question is whether sufficient cooling
will occur while deep comma cloud moisture remains over the region
to support non-liquid precipitation. 12z models have certainly
trended farther west with a longer duration comma feature north of
the upper low...and we have accordingly raised probability of precipitation to categorical
most areas except far inland Saturday night...followed by a longer
period of precipitation Sunday. However...models have offered an
uneven thermal evolution...and much of the forecast uncertainty
hinges on the uncertain degree of cooling. The most likely scenario
suggests that rain will mix with or change to a period of wet snow
late Saturday night into Sunday morning...with temperatures above
freezing preventing any significant accumulation/impacts. However...
in a worst case but less likely scenario...strong forcing for ascent
will support local convective enhancement...and rain/mixed
precipitation could give way to localized/heavier bursts of wet snow
which could briefly but quickly accumulate on roads...tree limbs and
power lines. While the past couple runs of the NAM support a
significant snow event...this model appears to convert too much rain
to snow and could well be placing the critical comma head
moisture/critical temperatures for snow much too far inland. As of late
Friday afternoon...the probability for the worst case scenario
remains too low to justify a Winter Storm Watch...but will address
the within the hazardous weather outlook.
Backing up in time...Saturday will turn out mostly cloudy with below-
normal high temperatures in the 50s. With the possible exception of south
coastal counties...most areas should remain rain-free until after
Looking ahead...expect a chilly and dry night Sunday
night...followed by a cold frontal passage Monday. Moisture appears too meager
to support any measurable precipitation. Temperatures 55-60f should
Long term /Monday night through Friday/...
overall the long term period looks rather steady state and cool. The
deep and cold trough in the middle/upper levels will persist and even
get reinforced by additional energy diving out of the northern
plains into middle week. This set up will keep temperatures cool and
well below normal with breezy conditions each afternoon. High
pressure will settle into the region from the central Continental U.S. By about
Thursday. For much of the period highs will struggle to get out of
the 40s with overnight lows into the 20s away from the coast.
Also...there are no significant opportunities for rain.
Aviation /00z Saturday through Wednesday/...
VFR to prevail through 00z Sunday...although clouds and light
rain chances will be on the increase Saturday as a coastal trough
develops offshore and strong upper trough approaches from the
west. Very small risk of ceilings dropping to MVFR levels toward the
end of the taf period.
Extended aviation outlook...there will be a chance for restricted
ceilings Saturday night into Sunday morning. Otherwise VFR
conditions will prevail.
tonight...high pressure will build across the southeast U.S.
Northerly winds will be around 10-15 knots in the evening. Then, they
will transition to the northeast and increase to around 15-20 knots
overnight in response to the surface pressure gradient increasing
between the high and a coastal trough beginning to form. Seas will
be 3-4 feet within 20 nm and 5-6 feet across the outer Georgia waters.
The Small Craft Advisory will remain up for the outer Georgia
waters due to seas.
Saturday through Wednesday...due to the deepening low pressure
off the southeast coast...raised a gale watch for amz374 Saturday
night through Sunday...and there exists a low probability for
gales to spread into near shore waters during this time.
Otherwise...elevated winds/seas and Small Craft Advisory
conditions will remain common through this period. Another period
of gales is possible in the wake of a cold front Monday
night/Tuesday...especially beyond 20 nm.
Marine...gale watch from Saturday evening through Sunday evening for
Small Craft Advisory until 10 PM EST Saturday for amz374.