Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
416 PM EST sun Feb 14 2016
a surface ridge extending through the forecast area today will
shift off the coast tonight. A warm front will develop south of
the forecast area tonight. The front will lift northward and into
the area Monday ahead of a cold front. The cold front will move
through the region late Monday night and early Tuesday.
Near term /until 6 am Monday morning/...
cold and dry high pressure centered over New England continues to
ridge into the southeastern states with dewpoints in the single
digits across the forecast area. Increasing clouds through the day
have limited temperatures this afternoon. Clouds expected to
continue to increase through the night as low level flow becomes
more southeasterly off the Atlantic after 00z and weak isentropic
upglide overspreads the cold dome of high pressure in place. The
cloud cover will actually help temperatures remain somewhat steady
overnight although persistent northeasterly flow will usher in
some cooler air across the northern midlands as an in situ cold
air damming wedge develops. Moisture will remain very shallow in
the lowest 4000-5000ft with dry air aloft and no moisture in the
snow growth area. No dynamical forcing overnight with the only
lift occurring from isentropic upglide. Think much of any
precipitation overnight will fall as virga and go into saturating
the near surface layer with little if any reaching the ground.
Probability of precipitation increase after 06z into the chance range by early morning and
soundings indicate predominate ptype would be freezing
rain/drizzle but minimal impacts expected.
Short term /6 am Monday morning through Monday night/...
model forecast thermal profiles continue to support very light
freezing rain/drizzle mainly along and north of a line from
Manning to Aiken to McCormick during the 12z-15z time frame
before surface temperatures begin to warm above freezing from southeast
to northwest as strong warm advection ahead of the approaching
system erodes The Wedge. Cannot rule out a trace of ice
accumulation across the northern midlands and after collaboration
with neighboring offices decided to Post a Freezing Rain Advisory
for Lancaster and Chesterfield counties ending at 17z. Think
impacts will be minimal with any icing occurring on elevated
surfaces and there is a possibility that little accumulation
occurs at all given the lack of deeper moisture available.
Chances of rain increase through the afternoon into evening as the
upper trough amplifies to our west and upper forcing/ascent
increase from west to east. Generally expect a lull in precipitation from
middle morning through late afternoon and then probability of precipitation ramp up to
categorical overnight. Potential for periods of heavy rain as
strong southerly 50-55kt low level jet provides ample moisture
transport into the region. Cannot rule out an isolated elevated
thunderstorm as lapse rates become steep and cross totals remain
high...although surface based instability is relatively
non-existent. Average rainfall amounts could range from a quarter
inch to as much as 0.75 inches due to increased forcing as the
upper trough takes a negative tilt.
Non Standard temperature trend expected with temperatures rising late
afternoon and overnight Monday night due to warm advection ahead
of the surface low. Breezy conditions also likely and a lake Wind
Advisory may be needed.
Long term /Tuesday through Sunday/...
a shortwave trough embedded in the upper trough over the eastern
part of the country will eject east across the forecast area Tuesday
morning. This will drive a cold front east through the forecast area
early Tuesday. The GFS moves the moisture out of the area more
quickly than the NAM and is warmer with high temperatures on
Tuesday. Leaned toward the GFS and have probability of precipitation gradually decreasing
after 12z and probability of precipitation less than 15 by 18z. The models continue to show
much of the moisture and lift associated with another middle-level
shortwave trough remaining north of the forecast area Tuesday
night. Weak high pressure will build into the southeastern US
behind the front with a much drier airmass returning through the
end of the work week. Surface low pressure over southeastern
Canada is expected to bring the next frontal boundary near the
area this weekend. Temperatures will generally be near to above
normal through the long term period with highs in the upper 50s to
60s and lows in the 30s and 40s.
Aviation /21z Sunday through Friday/...
MVFR ceilings developing across the taf sites this evening.
Surface high pressure ridging into the region from the northeast
will move off the coast tonight. Moisture and isentropic lift
will increase across the area late tonight with a slight chance
of rain at ags/dnl/ogb and freezing rain at cae/cub beginning
just before daybreak Monday. The chance of rain will increase
through the morning hours but as temperatures rise at cae/cub...
the threat of any frozen precipitation will diminish. Have left out
mention of precipitation due to low confidence in timing and minimal if
any visibility impacts.
Clouds are expected to increase and lower to MVFR this evening
as onshore flow promotes wedge development. The hrrr is more
pessimistic than most of the other guidance and takes the ceilings
down to IFR overnight. Winds will be easterly 10 knots or less.
No fog expected to develop late tonight due to wind and clouds.
Extended aviation outlook...cig/vsby restrictions possible Monday afternoon
into Tuesday morning as a southern stream low pressure system crosses
the region. Strong gusty winds also expected Monday night into Tuesday.
SC...Freezing Rain Advisory from 1 am to noon EST Monday for scz015-