Scientific Forecaster Discussion
fxus62 kchs 082315
Area forecast discussion
National Weather Service Charleston SC
615 PM EST Thu Dec 8 2016
colder high pressure will extend over the area through the
first half of the weekend. A weak trough of low pressure is
expected to develop over the Atlantic coastal waters Saturday
night and Sunday. By next week, a series of cold fronts are
expected, with the first one arriving by Monday night, then
potentially a stronger cold front by mid week.
Near term /until 6 am Friday morning/...
tonight: a deep mid and upper level cyclone moving through
eastern Canada, and it's associated and trailing short wave will
trek through the northeast quadrant of the country. At the
surface, the leading edge of the Arctic air is overspreading
much of the nation east of The Rockies, including the local
Winds are already north and northwest and dew points are down in
the 40s, but even colder and drier air is not far upstream, and
will pass through later this evening in association with the
passage of the 850 mb front, that pushes the 850 mb 0c isotherm
to as far south as near I-16 in Georgia late tonight.
Although there is too much mixing to prevent pure radiational
cooling, there is plenty of cold advection as the Arctic air
mass builds from the Great Plains, and drops lows around 7-8 am
Friday to generally the mid or upper 30s. Skies will be a mix of
few-scattered stratocumulus with the 850 mb front, plus sct-
broken mid and upper clouds with a potent and coupled jet
Short term /6 am Friday morning through Sunday/...
overview...this period will be marked by much colder temperatures
and little or no chance of precipitation.
Friday...the area will be just in the wake of a strong cold front
with polar high pressure building from the northwest. Even with
mostly sunny skies, strong cold advection will hold high
temperatures to around 50 north to the lower 50s south. Winds will
not be more than 5-10 mph, thus the wind chill effect will be
minimal. Friday night...expect some of the coldest temperatures so
far this season as high pressure continues to settle over the area.
The pressure gradient weakens allowing winds to drop to calm/near
calm under mostly clear skies. Expect temperatures to reach a solid
freeze in most areas away from the immediate coast. Still going for
mid 20s well inland upper 20s to lower 30s elsewhere.
Saturday...high pressure moves to just north of the region with
light northeast winds. Given models not showing much warm advection,
expect highs will struggle to reach back into the lower to mid 50s.
Saturday night...not quite as cold as Friday night, but still
freezing temperatures likely from I-95 west and mid to upper 30s
closer to the coast. The one factor that could keep temperatures
from getting this cold, especially closer to the coast, will be the
potential for a developing coastal trough of low pressure over the
near shore waters as low and mid level flow veers to east-southeast.
Some models actually trying to produce some light qpf, but have kept
slight chance pops for the coastal waters, possibly reaching extreme
coastal areas of South Carolina counties toward day break.
Sunday...although models differ on the strength and position of the
developing coastal trough, they seem to agree that it will weaken
and move northward through the day. Surface high continues moving
northeast into the Atlantic ahead of a developing storm system over
the central U.S. By late in the day. Have kept slight chance/low end
chance pops mainly over the water with again slight chance scrapping
the immediate SC coast, mainly Charleston County. The presence of
the coastal trough offshore most of the day and a departing high to
the north will hold a weak wedge with low level northeast winds and
likely mostly cloudy skies. Thus, although temperatures will be
warmer, they will still likely stay just below normal in the upper
50s to lower 60s.
Long term /Sunday night through Thursday/...
a zonal flow will prevail over much of the United States early week
through mid week, setting up a period of quick moving systems and
associated fronts shifting across the southeast. Expect the first of
two fronts to push through the area on Monday with potentially some
showers over parts of the area. Tuesday will be relatively quiet and
dry while a light southerly wind develops ahead of the next
approaching front. On Wednesday, a more significant cold front will
sweep through the area with showers. Dry and cooler high pressure
will then extend across the region on Thursday.
Overall high temps should range in the upper 60s to lower 70s
Monday, then low/mid 60s Tuesday and Wednesday. By Thursday, high
temps should only peak in the upper 40s to lower 50s. Overnight lows
will generally range in the mid/upper 40s away from the coast Monday
and Tuesday nights. Wednesday night lows should range in the
mid/upper 30s inland to low/mid 40s near the coast.
Aviation /23z Thursday through Tuesday/...
Extended aviation outlook: mainly VFR.
tonight: conditions will continue to deteriorate on the coastal
waters, as a humongous region of Arctic high pressure builds
from western Canada and the Great Plains. Cold advection, steady
isallobaric pressure rises and geostrophic winds of 25 or 30 kt
will produce Small Craft Advisory conditions over amz350 and
amz374, and near advisory thresholds elsewhere. Looking at
soundings from various model guidance we certainly could expand
on the coverage of the two pre-existing small craft advisories,
but will wait until trends become better defined to be certain.
Friday...marginal small craft conditions expected to end by
afternoon as cold high pressure continues building from the
Saturday...no highlights as high pressure builds just north of the
waters. North-northeast winds of generally 15 knots or less and seas
4 feet or less.
Sunday...a weak coastal trough of low pressure is expected to slowly
move up the coast and then dissipate by late day. Other than the
potential for scattered showers, no highlights expected as winds
veer to east-southeast. By Sunday night, models are showing winds to
increase from the south, but not thinking they will reach small
Monday...southwest winds of 15 to 20 knots possible ahead of the
next cold front, expected to move through by late afternoon/evening.
Not much moisture again with this front, with slight chance for
Tuesday...high pressure returns north of the area with north-
northeast winds of mainly 15 knots or less and seas 2 to 4 feet,
Marine...Small Craft Advisory until 2 PM EST Friday for amz374.
Small Craft Advisory until 11 am EST Friday for amz350.