Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
406 am EST Thursday Feb 11 2016
high pressure will move across the region today and tonight. A
fast-moving upper disturbance will bring a brief chance of
precipitation to parts of the area Friday. A stronger dome of
Canadian high pressure will settle in for the weekend...ushering
in another period of cold temperatures. This will be followed
by another weather system which will produce a better chance of
precipitation early next week.
Near term /through tonight/...
as of 305 am...revised temperatures/winds do not produce wind chills quite
as cold as before this morning...but continue to warrant Wind Chill
Advisory as-is. There is no need to expand it beyond current extent.
A relatively tight upper height gradient persists over the County warning forecast area
today...with upper trough axis over the Atlantic coast. Northwest
flow into the Appalachians will continue...but will gradually weaken
in response to weakening gradient behind the departing trough. Band
of cloud cover over Kentucky/Tennessee is prognosticated to shift northeastward...and will
provide a continued source of moisture for light snow showers in
the upslope areas. The northern mountains are expected to see an uptick
in coverage as well. Probability of precipitation will taper off by midday. The downslope
flow...rising thicknesses...and partly to mostly sunny skies
will bring maximum temperatures up a couple of categories from Wednesday/S
values. That will still be about 10 degrees below climatology.
Heights rise into this evening as broad high pressure moves out of
the middle-Mississippi Valley...centering over the Tidewater region
by early Friday. However...quickly coming in the wake of the high is a
weak shortwave prognosticated to reach the Ohio Valley by daybreak. Backing
low to midlevel flow downstream of this wave results in slight
isentropic lift across our area in the wee hours of the morning. Moisture
is marginal...but is deepest over the northern half of the County warning forecast area...so I
will introduce a low pop there before 12z. Ptype expected to be all
snow...with warm advection not having occurred long enough to create
a warm nose in profiles over this area. Mins will remain several
degrees below normal. No wind chill issues are expected...with
lowest values almost entirely above zero even on ridges.
Short term /Friday through Sunday night/...
as of 220 am Thursday...a short wave diving into the East Coast
trough crosses the area Friday. A weak surface wave forming near the
Georgia/SC coast and moving north along the coast in response. The
guidance is in good agreement that there will be clouds forming
outside of the mountains...along with some flurries or sprinkles
over NC and the eastern upstate. Do not expect any accumulations
but cannot rule out some briefly heavier than flurry or sprinkle
precipitation. Expect another round of northwest flow snowfall across the
mountains with good low level moisture...cold advection and
strengthening northwest flow. Expect generally light accums in the usual
high elevation areas near the Tennessee border...but cannot rule out a
couple of inches by the time snow ends late Friday night or early
Expect very cold and dry conditions to develop Saturday and Saturday
night as a sprawling 1040+ Arctic high pressure builds into the
region. Highs Saturday and lows Saturday night will be 15-20 degrees
below normal. Advisory level wind chill values will be possible
across the mountains...along with the potential for a cold wave.
Long term /Monday through Wednesday/...
as of 405 am Thursday...guidance coming into better agreement
regarding the forecast of the storm system Monday and Tuesday.
But first...Sunday will be cold and dry as Arctic high pressure
settles in over the area. Highs will be near the normal lows for the
day with very cold wind chill values across the mountains in the
The guidance is trending toward a Miller a type system...but the
surface low is well inland with an I-20 to I-95 track. Moisture
spreads into the area late Sunday night and remains over the area
Monday and Monday night as the high moves east along the afore
mentioned track. With the very cold air in place at precipitation onset...
p-type should start out as snow. A warm nose develops as low level
warm advection takes place Monday as the low moves south of the
area. This will change the snow to rain south of I-85...and portions
of the SW NC mountains. That said...the surface temperatures could remain
near or below freezing north of I-85 and the warm nose could be
stronger and farther north. This would mean a transition to sleet
and freezing rain...changing mainly to rain south of I-85. Quantitative precipitation forecast could
be quite high creating the potential for significant accumulations
of a wintry mix before precipitation tapers off Tuesday as drier air
moves in behind the departing low pressure system. Will keep the severe weather potential statement
mention...but uncertainty remains and the forecast could change
significantly as the event approaches.
The rest of the medium range looks relatively benign. There will
likely be a period of northwest flow snow on the back side of the system
Tuesday and Tuesday night...tapering off Wednesday. Highs will warm
back to normal levels as seasonal high pressure builds in.
Aviation /09z Thursday through Monday/...
at kclt...VFR through the taf period. Upper jet over the region will
bring a few high clouds through today. Early on some midlevel clouds
will also be seen over the mountains...but these will dissipate this
morning. As low pressure moves off the East Coast and high pressure
replaces it from the northwest...initially westerly winds will back to SW
during the daytime...then veer around to NE tonight at all sites
except kavl. A lower VFR deck is expected to develop tonight as
warm advection develops ahead of a shortwave moving out of the
Outlook...a low pressure system centered near the mouth of the
Savannah River may spread restrictive ceilings over the Piedmont
on Friday. An Arctic air mass will build over the region this
weekend...resulting in upslope clouds along the west side of the
Appalachians. Temperatures well below normal are forecast for
Saturday and Sunday.
09-15z 15-21z 21-03z 03-06z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 100% high 100% high 100%
khky high 100% high 100% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% high 100% high 100%
The percentage reflects the number of guidance members agreeing
with the schedule taf issuance flight rule category. Complet hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
NC...Wind Chill Advisory until 10 am EST this morning for ncz033-