Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 262334

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
634 PM EST Sun Feb 26 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 645 PM: A spectacular winter afternoon gives way to a quiet
evening across the region. No reason to make any changes to the fcst
at this point, other than to adjust temp/dewpt trends. Settled
weather will persist over the Carolinas and NE GA through Monday
morning, with a dome of high pressure shifting from the inland
Southeast to a position offshore.

Quasi-zonal flow over the eastern CONUS will carry a weak shortwave
up the Ohio Valley in the late night/morning hours. Abundant
midlevel moisture suggests a fairly thick high cloud deck will move
overhead. Furthermore, low-level warm advection begins to ramp up
overnight as the high sets up to our northeast. Min temps are thus
expected to be a little warmer than last night. 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 normal.


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. Essentially clear
this evening with light SW wind in most places. The very dry air
mass should preclude fog. Clouds will start to increase on Monday
morning ahead of a short wave moving up the OH Valley, but the
thickening clouds will mainly be a mid- and high levels. Low level
moisture and forcing will increase late Monday, but at this time it
looks like a low cloud ceiling will not reach the TAF sites before
the end of the period and light precip will remain to the SW.

Outlook: A warm front lifts overhead late Monday leading to
increased chances for precipitation/restrictions Mon night and
Tue. Late Wednesday a cold front approaches from the west and
brings additional chances thereof. Drier conditions end the week
following the fropa.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
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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