Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 270544

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1244 AM EST Mon Feb 27 2017

Cool high pressure will then move off the Carolina coast tonight.
with warmer air returning during the first half of the upcoming
week. A warm front will lift north through the area Tuesday then a
cold front crosses from the northwest Wednesday night. Cool high
pressure brings temperatures a little below normal at the end of the


As of 1240 AM: Satellite imagery shows high cloud to our west, and
have delayed increasing cloud cover in the forecast suite. This also
necessitated a bit of a drop in the min temp forecast, with lows now
expected to settle a little bit below climo.

By Monday afternoon some lower cloud cover may begin to spread in
from the south, as a warm front associated with a developing Plains
low inches toward the CWFA. A few showers may develop in the
afternoon, mainly in the mountain upslope areas of our western
zones. Dewpoints should rebound enough to keep RH above the critical
25 percent threshold for fire wx, despite maxes returning above


As of 215 PM EST Sunday: The short term begins with west/southwest
flow continuing aloft with another in a series of embedded
shortwaves riding up the flow toward the Southern Appalachians,
while a surface high pressure off the Mid-Atlantic coast continues
to pump a warm and moist airmass into the Southeast. The shortwave
at the beginning of the period fizzles out pretty quickly as a
weakness over the South Atlantic Bight enhances, cutting off the
moisture feed from the ocean. Another shortwave lifts slightly to
our north on Tuesday afternoon, impacting mainly the mountains but
still continuing slight chance pops across southeastern zones. With
increasing thicknesses and low-level WAA, expect temperatures to
increase as well with a continued warming trend for Tuesday.

Longwave trough will push off the Rockies Tuesday night, with the
associated primary surface low lifting quickly into the Great Lakes
in the wee hours of the morning. This will drag a strong cold front
across the Ohio and Lower Mississippi Valleys during the day. Ahead
of the front, southwesterly LLJ will increase to 50-60kt, with
strong vort max and upper jet as well. Upslope/isentropic lift ahead
of the system will increase Wednesday afternoon, and with continued
low level WAA, instability will increase during the afternoon hours
as well. The GFS is advertising 400-500 J/kg sbCAPE with >60kt 0-6km
shear, and an area of >70kt shear pushing into the area by 21z
Wednesday. Shear increases further toward 00z and 06z Thursday, but
instability quickly decreases both with loss of daytime heating and
passage of the front. The operational GFS remains slightly faster
than the ECMWF but timing is fairly similar as confidence increases
in some sort of severe threat. STP increases to over 2 on both GFS
and ECMWF (though use ECMWF parameters like that with caution due to
lack of vertical resolution). SPC Day4-8 outlook has increased
severe probabilities to 15% for Day 4, which would at least be
translated to Marginal for the Day3, possibly even Slight. Right now
damaging winds look to be the main threat but hail and even
tornadoes not out of the question. Will continue to refine with
subsequent forecasts.

Front pushes through by the end of the period with deep-layer CAA
developing behind it. Much cooler temperatures combined with strong
upslope over the mountains, even with very anemic moisture, may lead
to some light snow showers toward daybreak across the higher
elevations, but moisture is less and less with each run so
confidence in wintry precip fairly low.


At 200 PM EST Sunday...On Thursday morning a low amplitude upper
trough will extend from the Great Lakes to the the Gulf States. The
trough progresses off the East Coast by Saturday, while low amplitude
upper ridging progresses across the MS River Valley. By Sunday the
ridge broadens to extend from the Rockies to the Appalachians, but
amplitude remains low. This pattern results in nearly zonal flow
across the southern tier of states for much of the period.

At the surface, on Thursday morning dry high pressure will be
spreading east across the Southern Appalachians in the wake of a
departing cold front. A modest cold front with limited moisture will
approach the NC mountains bordering TN on Thursday night, perhaps
supporting some light snow shower before dawn that may linger into
Friday morning. More dry high pressure will follow from Friday
afternoon into early Sunday, after which moisture from the Gulf of
Mexico will spread north and east, reaching the Southern
Appalachians late in the day. Any precipitation associated with the
gulf moisture would be liquid, and rather light. Temperatures will
cool from slightly above normal to slightly below normal, then warm
to above normal.


At KCLT and Elsewhere: VFR through the period, with gradually
increasing high and mid level clouds expected through the daylight
hours. Low level moisture will begin increasing by late Monday
evening, possible resulting in development of low VFR cigs by the
last couple of hours of the period, with any restrictions concerns
likely holding off until late Monday night. Otherwise, winds will be
light SE through much of the period, possibly becoming light NE by
late Monday evening.

Outlook: A warm front lifts overhead Monday night leading to
increased chances for precipitation/restrictions through Tue. Late
Wednesday a cold front approaches from the west and brings
additional chances of showers as well as some thunderstorms. Drier
conditions end the week following the fropa.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
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 scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:




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