Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 141854

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
254 PM EDT Wed Mar 14 2018

Dry high pressure continues over our region Thursday into Friday.
A warming trend will commence Thursday through Friday...before a
cold front brings showers and cooler temperatures
to the region to start the weekend. High pressure is expected to
build in from the north Sunday into Monday. Low Pressure will
approach from the west by Tuesday bringing showers and perhaps a few


In response to depleting NW flow moisture and backing low level
flow, snow showers have tapered off to flurries, with skies quickly
clearing along the TN border this afternoon. NW winds will remain
gusty into the evening, but surface high pressure building into the
region from the Gulf Coast will allow winds to drop off somewhat
overnight in lower elevations, allowing for another cold night with
min temps in the neighborhood of 10 degrees below normal. The
exception to this will be across the high terrain, W/NW winds near
ridge top level forecast to accelerate to over 40 kts by daybreak
Thursday. This will be a warm advection, not-very-strong gradient/
low level jet scenario.  In other words, very gusty winds will
remain confined to exposed peaks and ridge tops until mixing deepens
Thu morning. We have decided to issue a Wind Advisory for areas
above 3500 ft from Buncombe County through the northern mtns.

Otherwise, there will be an abrupt end to the unseasonably cool
weather tomorrow, as heights build strongly upstream of quickly
departing upper trough, and downstream of high-amplitude/but
dampening ridge. Meanwhile, with surface high skirting by to our
south, a strong W/SW low level flow/deep mixing regime will develop
across the area. The result will be max temps about 20 degrees above
today`s readings in most locations tomorrow afternoon, or several
degrees above climo (for the first time in about 10 days for many
areas). Dewpoint recovery is also anticipated in the SW flow regime.
However, critical RH values will likely be realized, mainly along
and near the I-85 corridor. (See Fire Wx discussion for details).


As of 200 PM Wed: Confluent upper flow behind the departing trough
will permit high pressure to build south from Canada through the
Ohio Valley early Friday. A baroclinic zone will begin to develop
on the southern flank of this high. Low pressure in the lee of
the Rockies will activate the boundary as a warm front over the
Mississippi Valley, but the best way to describe the boundary as it
weakly pushes into our area early Friday is as a cold front. This
feature will be associated with increased low-level moisture. The
flow over the mountains will remain northwesterly and some
upslope-driven precip may develop there Friday morning. Most likely
this will not occur until temperatures have warmed several degrees
above freezing, so minimal wintry precip is expected. NAM/GFS
both depict a weak vort max drifting atop the boundary during the
afternoon, so we will permit PoPs to expand into the Piedmont. Max
temps are expected to be a few degrees above normal Friday.

Forecast confidence goes down Friday night into Saturday. The models
suggest that as an upper ridge progresses across the Southeast,
a weak sfc high sets up over the Mid-Atlantic region, while
the aforementioned boundary advects north as a warm front. PoPs
increase Friday night following the trend in moist isentropic
upglide, waning a bit Saturday as the better upglide sets up to
our north. Originally it had appeared likely in-situ CAD would
develop Saturday, but now it seems less certain with PoPs possibly
diminishing during the day, and most guidance indicating strong sfc
warming and moistening. It still looks reasonable to advertise cool,
below-normal temps in the NC NW Piedmont, but we will advertise a
gradient to above-normal temps in NE GA and the western Upstate,
i.e., a much more gradual transition than would be expected in a
strong wedge.


As of 230 PM EDT Wednesday...The 12Z models have come into better
agreement on the pattern for Sunday into next week. The upper levels
will feature a flat ridge across the Great Plains, shifting east to
the Southeast states by Monday. A rather complex-looking trough will
slowly drift east out of the Rockies to the Mid-MS Valley on
Tuesday, eventually crossing the eastern CONUS Wednesday thru
Thursday. At the sfc, a weak sfc low will cross the Central
Appalachians to the Mid-Atlantic, dragging a weak cold front thru
the CWFA. It will be more like a wind shift line than anything, as
temps will actually be rather warm behind it on Sunday. The GFS MOS
actually has upper 70s to around 80 across the Upstate and NE GA.
That may be a little too warm, but downslope flow with little change
in thicknesses should allow above normal temps. In the NW NC
piedmont, thicknesses do fall a bit behind the "front", so there
will be just around normal. As for PoPs, given the model agreement
on dry westerly flow across the area, I cut back PoPs Saturday night
thru Sunday. As the next upper trough approaches from the west,
another cyclone will form and push out across the Southern Plains
Sunday into Monday. Moist low-level southwesterly upglide flow will
ramp up across the region, and bring back clouds and PoPs from SW to
NE Sunday night thru Monday. There looks to be an in-situ wedge that
sets up Monday, keeping temps mainly in the 50s to mid 60s. The low
will cross the Ohio Valley Monday night then off to the Mid-Atlantic
on Tuesday. This will push another cold front thru the area. There
may be some INSTBY in the warm sector that could support some
thunderstorms. But the models are not in very good agreement on
this. There will certainly be plenty of shear, such that if we do
see some CAPE, organized storms may develop, but most likely near
the Gulf Coast. The low will quickly deepen as it turns into yet
another nor`easter Tuesday. So flow will turn out of the NW and
could be fairly gusty, especially in the high terrain. There may be
a NW flow snow event late Tuesday into Wednesday, but the new 12z
ECMWF does not have that. Temps will return to below normal behind
this system for Wednesday.


At KCLT and elsewhere: VFR expected through the period. Most sites
will experience gusty winds from the W/NW through the afternoon,
with winds diminishing to less than 10 kts by mid-evening, then
turning to the W/SW late tonight. SW winds increase again after
sunrise Thursday, gusting into the 20s by the end of the period.
(KAVL will see NW winds continuing through the period, but the
weakening/strengthening trend will hold.)

Outlook: VFR conditions are expected to persist through at least
Thursday. Chances for precipitation and restrictions will gradually
increase from late Friday through the weekend.

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:


Fire Danger Statement remains in effect for much of our northeast GA
counties through 7 pm. Otherwise, RH will remain in the 20 to 30%
range across much of the Piedmont/foothills into the early evening.
Winds will also be fairly gusty across much of the area before
diminishing this evening. On the heels of gusty W/SW winds, a rapid
warm-up is expected tomorrow, with temperatures expected to be
about 20 degrees higher than today`s readings. While a decent amount
of dewpoint recovery is also expected, RH is nevertheless expected
to range in the 20-25 percent range tomorrow afternoon, mainly along
and south of the I-85 corridor. Meanwhile, per NWS RAH`s
coordination with NC land management agencies, we will plan to issue
a Fire Danger Statement for our  southern tier of Piedmont/foothills
zones on Thu morning. While Red Flag criteria is expected to be
approached/met across much of Upstate SC Thu afternoon, land
management agencies in SC indicate fuel moisture remains a bit high
to support RFW issuance. Coordination for a potential FDS for SC (as
well as northeast GA) may occur tomorrow morning.


GA...Fire Danger Statement until 7 PM EDT this evening for GAZ017-


SHORT TERM...Wimberley
FIRE WEATHER...JDL is the U.S. government's official web portal to all federal, state and local government web resources and services.