Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 190606

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
206 AM EDT Mon Mar 19 2018

A moist frontal system will approach the region tonight and will
slowly cross east through midweek. High pressure towards the end of
the week will allow for the return of dry conditions.


As of 200 AM EDT: Main update for 06Z TAF issuance along with minor
tweaks to temperatures and PoPs/Wx to coincide with latest trends,
as the rest of the near term forecast remains on tap.

Mild temperatures persist this morning (mid to upper 50s/around 60)
with opaque cirrus across the FA and mid level clouds beginning to
stream in as well. With plenty of moisture in place due to SW flow
and the aid of isentropic lift and upglide, weak returns continue to
push across the southwestern NC mountains as higher reflectivities
continue to blossom just south of the FA. Anticipate this activity
to gradually move into the extreme southern portions of
the FA over the next few hours.

Otherwise, a flat upper ridge is helping to push push sfc high
pressure off the Carolina coast this morning. Meanwhile, the Gulf
will continue to open up this evening with moisture return on the
back side of an 850mb ridge axis. Isentropic upglide and southerly
upslope flow will commence after sunset and with the increasing
moisture, light precip will begin to break out in the mid evening
near the Blue Ridge Escarpment and moving up from the south. As low
level forcing improves, the low clouds and light precip will expand
from there across most of the region by around daybreak.
Fortunately, with the warm advection, we should be well above
freezing, so precip should be only light rain and drizzle. The low
level forcing and warm advection at 850 mb persists across the
region thru the balance of the day resulting in a continued chance
of light rain, while the sfc high ridges back from the east, giving
us all the ingredients for what amounts to in-situ cold air damming,
or at least a strong cool pool east of the mtns. The lack of
instability will preclude thunderstorm activity across the region,
until perhaps very late in the day as some elevated CAPE works into
the fringes in northeast GA and southwest NC. High temps will have
some bust potential if the precip and clouds do not hold, but right
now high temps look like they will be on the order of 10-15 degrees
cooler than today.


As of 230 PM Sunday...A moist and active pattern expected over the
short range period. The guidance leaves much to  be desired as far
as run-to-run consistency and op model agreement. The 12z GFS is
quicker with an ulvl s/w to begin the period...which makes a big
difference wrt to the sfc reflection and sensible wx anticipated
early Tue. For now will count on a triple-point low to advance
toward the FA while a sfc wedge breaks down rather quickly thru

The NAM is much more sure abt the possibility of tstms across the
far srn zones remnant of upstream organized convec indicated by
convectively induced vort energy crossing thru 12z Wed.
However...the other op models have little deep layered forcing
during this time. Will split the difference a bit and include
thunder across the far sw/rn zones. There will be stg deep layered some of these storms could be quite strong and/or
loosely organized. A dry slow looks to work in Tue while an area of
cooler wedged air dives in from the northeast. The FA shud remain
mostly dry outside of -shra with -sn mixing in across the higher
terrain. The models once again have a hard time deciding on the
evolution and placement of the upper energy Tue night into Wed with
the GFS looking like an outlier by diving several rounds of stg vort
energy over the wrn zones thru Wed. This is not supported by the
other op models and a tempered soln will be used in this fcst.

Expect -snsh to continue across the NC mtns overnight and thru the
day Wed with good upstream moisture and added lift from a passing
upper low. For now...have amts across the ridges approaching or
reaching adv levels over a general 18-hr period. There is a chance
-snsh will break mtn containment across the I-40 corridor as the
ulvl low crosses east overnight and sfc temps will support low-end
accum. Expect the BL to warm quickly during the daytime Wed
however for much if any accums aft 14z or so. The NAM soundings look
interesting wrt to sf potential at KCLT btw 09z-16z Wed given enuf
sfc Tw cooling will take place. Yet once again...confidence is too
low given the warmer GFS soln...thus snow will not be included in
the grids at KCLT at this time. This could be a scenario to keep an
eye on tho given the overall uncertainty seen in the guidance
lately. Max temps will be arnd normal across the srn zones and
cooler than normal by a cat or so over the nrn zones Tue. Then with
the colder air moving in Wed...expect all areas to have below normal


As of 255 PM EDT Sunday: After some lingering NW flow snow showers
across the mountains Wednesday night, possibly adding another half
an inch of accums across the higher elevations, dry but cool high
pressure settles in across the area Thursday and Friday. Highs
around 10 degrees below normal Thursday rise around 5 degrees for
Friday. Lows Wednesday night and Thursday night remains nearly
steady 5 to 10 degrees below normal. Expect windy conditions across
the mountains and breezy elsewhere Wednesday night and Thursday.

A low develops east of the Rockies Friday with a warm front
extending east into the Tennessee Valley. As the low moves east,
isentropic lift activates along the warm front with increasing
precip chances. The GFS is faster than the ECMWF moving the front
and its associated precip east into the area. However, they both do
bring rain for Friday night into Sunday. Although temps show a
warming trend through the period, temps and thicknesses are cold
enough that the precip could begin as snow across the higher
elevations before changing to rain. For now, it appears that no
significant accums develop. There is also some disagreement on the
cold front that trails the low as it moves east of the area. The GFS
is faster with it but does bring another warm front into the area
late in the day. Therefore, keep a chance of precip in through the
end of the period.


At KCLT and Elsewhere: VFR will prevail over the next few hours, as
conditions are then expected to gradually deteriorate to MVFR with
lowering cigs and increasing chances for -SHRA through the early
morning hours due to increasing low level moisture and isentropic
lift. After daybreak, the continuation of increasing moisture and
moist upglide will aid in the further lowering of cigs ahead of
an approaching system, with IFR anticipated through the rest of
the afternoon. However, if the insitu wedge weakens any this
afternoon, a brief improvement to MVFR is possible, especially
at KCLT. Otherwise, expect VCSH/-SHRA throughout the day, with a
potent storm system bringing the potential for -TSRA at the SC
TAF sites, along with KCLT late this evening into the early
overnight hours. Lingering low cigs and precip are expected into
Tuesday, with a mix of MVFR/IFR.

Outlook: Colder air may wrap south into the region behind the system
into Tuesday night and early Wednesday, allowing for the potential
for mixed precipitation. Expect conditions to retreat to VFR on

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High  94%     High  83%     High  85%     Med   63%
KGSP       High  95%     High  91%     High  94%     High  96%
KAVL       High  90%     High  87%     High  90%     High 100%
KHKY       High  89%     High  96%     High  90%     High  92%
KGMU       High  91%     High  95%     High  92%     High  96%
KAND       High  84%     High  99%     High  99%     High  81%

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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