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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
303 PM EST Thursday Feb 11 2016

Synopsis...
a fast-moving upper level 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 Friday/...
at 230 PM Thursday...an upper trough will remain over the Easter USA
tonight and Friday. Channeled upper level vorticity rounding this
trough will approach the southern Appalachians late tongight...
crossing the western Carolinas on Friday. Meanwhile...at the
surface...the models are coming into alignment on developing a
surface wave over the Gulf states ahead of and to the south of the
channeled vorticity. Modest isentropic upglide to the NE of this
surface wave will support precipitation over our area...starting
before daybreak. Vertical profiles support mainly snow...with
perhaps some mixed precipitation in the upper Savannah River
valley...though very little ice accumulation is expected there.

By midday the surface low moves off the SC coast where it closes off
and deepens....while the bulk or precipitation moves east of our
area. Veering low level winds support upslope flow snow in the NC
mountains bordering Tennessee...with rain or freezing rain in the valleys
nearer the Blue Ridge. At this point the best bet for snow
accumulations appears to be in the NC mountains...where snow totals
may reach two inches on the highest peaks near the Tennessee border.

&&

Short term /Friday night through Sunday/...
as of 245 PM Thursday...a ridiculously cold weekend is in store for
the area for the short term with a strong upper trough in place
over the eastern Seaboard and cold Arctic high pressure building
in at the surface in the wake of the cold front crossing the area
Friday and Friday night. To start with however...we will continue
to see some lingering northwest flow snow showers in the northern
mountains through early Saturday...though do not really expect
much more in the way of additional accumulation...maybe another
half inch at most but probably not even that as moisture is pretty
anemic through the column. Other concern will be tight pressure
gradient as the surface high builds in...which will lead to strong
winds over the mountains. Do not quite meet Wind Advisory criteria
except at the highest elevations...but with colder temperatures
filtering in...definitely have widespread Wind Chill Advisory
criteria over the mountains. Since Friday night is still 3rd
period...will opt for now to leave the wind chill wording in the
severe weather potential statement but an advisory will likely be needed by tomorrow afternoon.

Deep layer...very strong cold air advection builds across the southeast Friday
night into Saturday...with at least weak cold air advection continuing through
Sunday morning. Resulting high temperatures on Saturday will barely
make it into the lower 40s for extreme southern zones...and remain
in the teens over the northern mountains. Sunday will be even
colder as the Arctic high pressure settles overhead...with highs
at best upper 30s extreme south and at or below freezing for a good
portion of the area. Sunday morning will see very cold temperatures
as well...and all this combined will lead to average temperatures
that meet cold wave criteria /average daily temperature of 25 or
less for Asheville...29 or less for Charlotte...and 30 or less for
gsp/. Will continue to highlight this in the severe weather potential statement but may have to
issue an Special Weather Statement sometime in the next 24-36 hours to cover the impacts
from this.

Clouds will be on the increase Sunday as the next system
begins diving down into the plains...which will be our next big
weather-maker as we transition into the extended.

&&

Long term /Sunday night through Thursday/...
as of 300 PM Thursday...the operational models have come into better
agreement with the next weather system expected to affect the
western Carolinas and northeast Georgia early next week. The GFS/ECMWF/
Canadian all have a similar depiction of the amplitude and timing of
the 500 mb trough expected to dig down over the plains on Sunday
night...with the trough axis crossing the MS river on Monday
afternoon. Thus...confidence is slowly increasing as the models
start to agree on an overall scenario of a higher amplitude trough...
even if timing remains off. The models generally show a more inland
track of a primary surface low across north Georgia Monday night and the
Carolina Piedmont on Tuesday morning. If that works out...it would
most likely mean strong warm advection across the Piedmont and
foothills Monday afternoon and night which would almost assuredly
force a changeover to rain across most of the Piedmont and even a
good bit of the mountains what remains to be seen is how much falls as
something other than rain before the transition occurs. Of
course...uncertainty remains high...so the Reader is urged to manage
his/her expectations accordingly.

Light precipitation should break out across the forecast area Sunday night and
Monday morning as moisture returns and isentropic upglide gradually
strengthens to the north of a developing warm front across the deep
south. Because we should begin the event with a cold and dry air
mass in place...anything that falls before about midday Monday
should be in the form of snow. However...as the low approaches from
the west...warm advection will increase from the south. The models
agree that a warm nose should develop on Monday afternoon that will
bring a changeover to sleet and then perhaps a brief period of
freezing rain across the area along and S of the I-85 corridor. We
lack a strong parent high to the northeast...which is a significant
limiting factor on the winter precipitation potential. Thus...it is hard to
imagine it will not be a mostly rain event across most of the region
Monday night...perhaps with some heavy rain that might cause minor
flooding issues. The NC foothills...Blue Ridge...and part of the northwest
Piedmont will be the exception...as usual...because cold air will be
trapped the longest...well into Monday night. As it stands right
now...the transition to freezing rain will occur early Monday
evening and then it will stay that way into early Tuesday morning.
This has the potential to produce ice accumulate of around one quarter
inch in the I-40 corridor and Blue Ridge before the changeover to
rain around daybreak Tuesday. Forcing is the strongest and moisture
the deepest Monday night. Have limited the precipitation probability to the likely
range for now...mostly over uncertainty in the precipitation type forecast. As
the low pulls away Tuesday...colder air will move back in from the
west...and precipitation will change back over to snow across the NC
mountains as the event winds down.

After 00z Wednesday...with the general exception of the
mountains...should see pretty quiet sensible weather conditions
for the end of the forecast period. In the wake of the early week
system...mean upper troughing will remain in place over the eastern
portion of the country...with another clipper system diving down the
flow and pushing into the southern Appalachians Tuesday night. The
12z European model (ecmwf) is much faster with this...really right on the heels of
the earlier system and exiting it out of the area by Wednesday
morning. The GFS holds onto some upslope snow in the northwest
flow aloft through Wednesday night. Have taken sort of a blend
but leaded toward the slightly snowier solution of the GFS for
the mountains as northwest flow snow is a reasonable expectation
with the strong upper trough in place. It should warm up enough
on Wednesday to change over to rain...but with below-freezing
temperatures again Wednesday night...anything else that falls would
be snow but very light and dry at this point...with dry air aloft
above about 750mb /5kft/ quickly develops as the brief deeper
moisture associated with the clipper moves east. Have included
generally trace accumulations of snow.

Behind this last clipper...upper ridging will build into the
center of the country. Operational models at odds with the
progressive nature of the longwave system...with the European model (ecmwf) quite
a bit stronger with the upper ridge...and resultant confluent flow
over the Great Lakes and New England allows a dry onset classical
cad event to develop...whereas the GFS pushes that upper ridge
right on through. Either way the end of the period looks dry...just
some uncertainty on temperatures so have taken a blend and show a
general warming trend as thicknesses increase with the increasing
upper ridging.

&&

Aviation /20z Thursday through Tuesday/...
at kclt...a low VFR ceiling will spread into the area late tonight...
falling to IFR by middle Friday morning...as low level moisture
increases. Winds are expected to veer from west-southwest to northwest this
afternoon...then to NE tonight. Snow showers are expected to reach
the area by dawn...persisting through midday...but at this point the
chances is quite low...and visibility restrictions will not be carried at
this time.

Elsewhere...high ceilings will arrive this evening...followed by low VFR
ceilings after midnight...as low level moisture increases. By middle
morning IFR ceilings are expected at SC sites. Foothill winds will veer
from SW to NE this evening...while kavl winds veer from northwest to southeast
overnight an back to northwest after dawn. Snow showers are expected to
reach NC sites before dawn...but chances are rather low...and visibility
restrictions will not be carried at this time. Snow cannot totally
be ruled out at SC sites...but is not in the forecast at this time.

Outlook...low VFR ot IFR ceilings are possible on Friday...as an
upper low moves up the Carolina coast. An Arctic air mass will build
over the region this weekend...with upslope clouds on the west side
of the Appalachians. A significant winter weather system is possible
early next week.

Confidence table...

20-02z 02-08z 08-14z 14-18z
kclt high 100% high 100% high 100% medium 75%
kgsp high 100% high 100% high 100% medium 68%
kavl high 100% high 100% high 100% high 81%
khky high 100% high 100% high 100% high 85%
kgmu high 100% high 100% high 100% medium 68%
kand high 100% high 100% high 100% medium 77%

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:

Www.Weather.Gov/gsp/aviation

&&

Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.

&&

$$
Synopsis...csh
near term...jat
short term...tdp
long term...PM/tdp
aviation...jat

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