Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
140 PM EST Sat Feb 28 2015
Canadian high pressure will build into the area over the weekend
with temperatures remaining below normal. A warming trend is
expected next week with southerly flow developing. A series of
fronts affecting the region will bring periods of showers and
possibly some thunderstorms.
Near term /through tonight/...
water vapor imagery continues to show a very broad upper trough
extending across the entire country with shortwave energy digging
southward along the West Coast with weak cyclonic southwesterly
flow across the southeastern states. At the surface a 1044mb high
was centered over the eastern Great Lakes and building eastward and
starting to ridge down the East Coast on the east side of the
Satellite imagery shows a blanket of high clouds streaming from
southwest to northeast across the Gulf of Mexico and covering the
eastern midlands and lower csra and this will likely remain in place
through the day. Clouds are expected to increase later today as
isentropic lift over the region increases due to northeasterly flow
in the lowest 3000 feet with increasing southerly flow above that
layer. Despite some early sunshine the increasing clouds and
persistent northerly flow should keep temperatures down a bit cooler
than yesterday with highs generally in the middle/upper 40s to around
50. As the isentropic lift begins late afternoon there is a slight
chance of light rain across the southern midlands and csra.
A cold air damming wedge becomes established over the forecast area
tonight with strengthening isentropic lift as low level southerly
flow increases to near 40 knots atop the shallow near surface layer
with northeasterly winds. The best isentropic lift develops over the
csra and shifts northward over the western midlands late tonight and
then northeastward over the entire forecast area Sunday before
shifting away from the region late Sunday. Probability of precipitation become likely late
tonight with mainly light precipitation expected.
Model forecast soundings continue to indicate a threat of possible
freezing rain late tonight into Sunday morning as the drier air
advecting in from the north may be enough to support some diabatic
evaporative cooling which could keep surface temperatures at or slightly
below freezing for a period of time. While the threat exists...the
light nature of the precipitation and uncertainty that the temperatures
will actually be at or below freezing lead to low confidence for any
headlines and prevent anything more than a mention in the forecast
and will include a brief mention in the severe weather potential statement product. Precipitation should
turn to all rain after 15z as the atmospheric column saturates and
warms due to warm advection.
Temperatures tonight will be limited by thickening and lowering
clouds but expected to fall into the lower 30s north to middle 30s
Short term /Sunday through Sunday night/...
model forecast soundings continue to indicate a threat of
possible freezing rain late tonight into Sunday morning as the
drier air advecting in from the north may be enough to support
some diabatic evaporative cooling which could keep surface temperatures
at or slightly below freezing for a period of time. While the
threat exists...the light nature of the precipitation and
uncertainty that the temperatures will actually be at or below freezing
lead to low confidence for any headlines and prevent anything more
than a mention in the forecast and will include a brief mention in
the severe weather potential statement product. Precipitation should turn to all rain after 15z as the
atmospheric column saturates and warms due to warm advection.
Temperatures not expected to move too much on Sunday with strong
wedge conditions in place and precipitation across the region.
Well below normal temperatures with highs in the upper 30s northern
midlands to Lower/Middle 40s csra. Precipitation will shift out of
the area late Sunday The Wedge will begin to break down Sunday
night as a cold front pushes into the area from the west...and may
actually see temperatures rise a bit as the cold air retreats. Low
chances of light rain or drizzle continue Sunday night with lows
in the upper 30s to lower 40s.
Long term /Monday through Friday/...
medium range models continue to point to a change in the upper
pattern from the persistent East Coast trough to a progressive
upper ridge shifting out of the west across the country and
bringing warmer temperatures but unsettled weather to the forecast
area by middle week.
Shortwave energy moving off the New England coast on Monday will
push a front through the forecast area on Monday which will stall
to the south. Transient surface high pressure will move across the
Ohio Valley to the middle Atlantic coast Monday into Tuesday with
generally low probability of precipitation. Increasing southwesterly flow over the stalled
front will result in chance probability of precipitation across the region Monday night
into Tuesday due to the overrunning of the moist warm air over the
cool surface layer. The stalled cold front to the south will
return northward as a warm front Tuesday night and lift north of
the area on Wednesday with increasing southerly flow and
temperatures becoming above normal. A long wave trough will move
out of the inter mountain west and push eastward while a cold front
approaches and crosses the region sometime Wednesday night into
Thursday. Have bumped up probability of precipitation with the front to low likely and
continued the mention of thunder ahead of the front. Cool and dry
high pressure builds over the area on Friday behind the front.
Temperatures through this period will general be above normal
with the warmest day on Wednesday as highs push into the middle
Aviation /19z Saturday through Thursday/...
surface high pressure is ridging down the middle Atlantic
coast...bringing NE winds and an influx of drier low level air into
the region in the near term. Meanwhile...middle and high level
cloudiness will stream east across the region. Isentropic lift is
expected to commence by early evening...providing light rain
potential and accompanying restrictions as low levels gradually
moisten. Light rain falling into cool dry air will lead to
evaporational cooling that could bring surface temperatures down to near
freezing north of Columbia. At this time...it appears freezing
rain potential will be north of our terminals. Generally followed
guidance trend of bringing restrictions down to MVFR tonight...but
IFR ceilings could be possible late tonight. Not much improvement
anticipated after sunrise Sunday with continued light
precipitation and IFR ceilings/MVFR visibilities persisting until the end of
the taf period.
Extended aviation outlook...IFR ceiling/visibility restrictions and a chance
of precipitation expected Sunday into Sunday night. Restrictions and
a chance of precipitation possible at times late Monday through