Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 251454
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
954 AM EST Sat Feb 25 2017

.SYNOPSIS...
A cold front will move off the Carolina coast late today as cool
high pressure builds into our region from the west. Temperatures
cool to near normal tonight through Sunday night, then warm up again
during the first half of the week. A warm front lifts north through
the area around midweek as a cold front approaches from the west
bringing showers and storms.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 945 AM: Low pressure now over southern Ontario continues to
drive a cold front across Appalachia. Winds are now NW and gusty
across our mountain ASOS/AWOS sites. Along the front, some towering
cu are evident from visible satellite as well as some light shower
activity. This is expected to strengthen a bit as it moves into
increasingly unstable air across western NC. For now per RAP prog
profiles, it looks like the Upstate will not see lapse rates good
enough to expect deep convection, though a shallow cu field should
form. There remains a tiny chance that one of the NC cells could
produce a damaging wind gust, particularly in the I-77 corridor,
where a few hundred J/kg of SBCAPE are expected to meet the front
around midday, as well as remarkable deep layer shear. The front
will exit the area by early aftn.

Beyond that a much drier/cooler airmass will advect into the
region as quasizonal flow builds aloft and sfc high pressure moves
in from the west.  Thus skies will clear out late in the day,
leading to optimal radiational cooling conditions and near normal
overnight lows.  Lastly, nwly veering winds will become quite
gusty behind the front this afternoon, which combined with the
possibility of little/no precip and low RH values, will support
enhanced fire danger conditions across SC and possibly GA as well.
Please refer to the Fire Weather section for details.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 305 AM Saturday, A low-amplitude/quasi-zonal upper air pattern
will persist through the short term period, with gradually building
heights anticipated across the East. The end of the weekend will be
marked by dry and seasonably cool conditions, with high clouds
expected to increase late Sunday into Sunday night, as a shearing
vorticity max moves rapidly from the southern Great Plains to the
Mid-Atlantic Sunday night through Monday. In response, moist
isentropic lift will develop across the western Carolinas and
northeast GA throughout Monday, with increasing clouds and
precipitation chances expected, peaking by Monday evening.

Some guidance sources are more bullish than others regarding the
overall extent of the precip Monday into Monday night. Some models
(e.g. the ECMWF) indicate a bit more in the way of surface wave
development along the Carolina coast, which tends to disrupt the low
flow across and shut off the upglide more quickly across our area.
The upshot of this would be significant QPF confined to our western
areas, with little to nothing across the eastern zones. With that in
mind, pops range from 60-70 across western areas, to 40-50 along
the I-77 corridor. Monday`s temps will be a bit tricky, depending
upon how quickly precip arrives. As sufficient low level dry air
should be in place to force establishment of in-situ cold air
damming where precip falls. Nevertheless, with current data
indicating that precip is likely to hold off until afternoon, will
advertise maxes near to slightly above climo across the west, and
about 5 degrees above normal across the NC Piedmont.

Pops taper off gradually Monday evening. However, isentropic lift is
expected to increase across the region once again by daybreak
Tuesday, as large scale height falls overspread much of the western
half of the Conus. Another round of precip is therefore possible by
the very end of the period. Temps Monday night will be well above
climo.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 155 AM EST Saturday: Low level SW flow at the 925mb level will
persist Tuesday and Wednesday ahead of the approaching cold front.
GFS 925mb wind speeds maximize on Wednesday with 30 to 45kts in the
vicinity of I-85 from GA to NC. Moisture will be abundant with GFS
Precipitable water around 1.4 along I-85 Wed afternoon. Instability
is generally restricted to along and south of I-85 Tuesday PM,
especially on the GFS where very low if any CAPE is north of the
corridor. On Wed PM, CAPE of 400 to 600 from NE GA to CLT area along
with the wind shear will give strong to severe storm concern. Of
course, timing of frontal passage coincident with max daytime
heating would make for the max circumstance with dynamics coming
together. The 500mb trough crosses the western states early Tuesday
with axis over the Plains States 12Z to 18Z Wed with low pressure
forming in the eastern trough inflection point and moving NE across
the Appalachians Wed evening. At least the models are in closer
agreement as compared to 24HRs ago. GFS still the fastest model in
taking the front across our area around midnight Wed while the EC
has it passing a few hours later.

After the front passes, there will be lingering moisture along the
TN border with NW Flow combined with shortwave energy crossing just
north of NC on Thursday and early Friday.  Thickness values will be
falling Wed night into Thursday and will be low enough for snow in
the NC Mtns by late Thursday morning. The second shortwave could
bring a brief NW Flow snow shower period around daybreak Friday for
the central and northern NC Mtns.

Temperatures are forecast to be 10 to 15 degrees above normal
Tuesday and Wednesday then fall to near or slightly below normal
behind the cold front for the second half of the week.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and Elsewhere:  VFR and possibly MVFR over the next
few hours along with a few SHRA invof cold front crossing the
region. Deeper convective development may occur late morning
further east along the I77 corridor region. Thus we do have a
TSRA in TEMPO at KCLT for a few hours.  Behind the front, TAFs go
dry with low clouds SCTing out to high cirrus, then SKC for the
remainder of the cycle. Swly winds will increase and veer nwly
behind the front with gusts reaching upwards of 20-30kts at times
today, before all winds weaken overnight.

Outlook: A dry continental airmass will maintain VFR thru
Sunday. Another wave approaches on Monday, once again increasing
chances for precipitation/restrictions which may last into Tuesday.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  96%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  86%     High 100%     High 100%     High 100%
KHKY       High  93%     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:

www.weather.gov/gsp/aviation

&&

.FIRE WEATHER...
Gusty W/NW winds and much drier air will overspread the area in
the wake of a cold front Today.  Minimum RH of 25 to 30 percent is
expected across much of the SC Upstate and Northeast GA, and may dip
below 25 percent in some areas.  Sustained winds will increase and
veer nwly behind a departing cold front into the 15-20mph range with
gusts nearing 30-35mph.  These critical conditions could overlap
for an hour or two this afternoon.  Thus a fire danger statement has
been issued for the all of northeast GA minus Rabun County, as well
as all of Upstate SC starting at noon today, running through 6PM.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Fire Danger Statement until 6 PM EST this evening for GAZ017-
     018-026-028-029.
NC...None.
SC...Fire Danger Statement until 6 PM EST this evening for
     SCZ001>014-019.

&&

$$
SYNOPSIS...DEO
NEAR TERM...CDG/Wimberley
SHORT TERM...JDL
LONG TERM...DEO
AVIATION...CDG/Wimberley
FIRE WEATHER...CDG/JDL



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