Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261940

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
240 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 1245 PM: 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. Dewpoints will
remain below 25 percent over much of the area through the afternoon,
albeit with light winds; this prompted the earlier issuance of a
Fire Danger Statement for northeast GA as well as a separate fire
weather discussion (below).

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. Dry high pressure crosses the area
this aftn/evening, moving off the mid-Atlantic coast by Monday
morning. Winds will taper off gradually into tonight. They will
back to SW at KCLT in the late afternoon (most likely 20-21z)
and flip to SE at KAVL during the evening. Elsewhere they will be
rather light/VRB overnight, before picking up SE in the morning. As
a shortwave moves up the Ohio Valley tonight and Monday, increasing
midlevel cloud cover should blanket the area.

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...

            19-01Z        01-07Z        07-13Z        13-18Z
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:


While surface winds will be rather light this afternoon, gusts
in the 15-20mph range may be experienced at times across the high
terrain. For the bulk of the area, winds won`t be a concern, though
low RH will. Most locations will see minimum RH of 15 to 20 percent,
but localized areas may see values as low as 10 percent. Given the
expectation of weaker surface winds, Fire Danger Statement criteria
are not met in NC/SC. However, the RH levels alone in northeast
GA have prompted a Fire Danger Statement valid until 600 PM.


GA...Fire Danger Statement until 6 PM EST this evening for GAZ010-


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