Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220604

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
204 AM EDT Thu Mar 22 2018

Dry and unseasonably cool high pressure dominates our weather
through Friday. The next low pressure system arrives for the
weekend with light precipitation.  Canadian high pressure will
bring dry weather to start next week.


As of 200 AM EDT: This update is for the issuance of the 06Z
TAFs along with updates regarding the winter weather hazards.

The Winter Storm Warning and Winter Weather Advisory have been
cancelled and a Wind Advisory and Special Weather Statement
have been issued.

Isolated snow showers may linger along the TN border through
early this morning, with an additional snow accumulation of a
dusting possible, though would not entirely rule out an isolated
measurement of up to one inch across the Smokies. Elsewhere,
snow flurries are possible through the early morning hours
across areas previously under a winter weather hazard. Gusty
northwest winds that were previously mentioned in the winter
weather products are expected to continue through late morning
across the northern mountains along with areas above 3500 feet
of the northern Blue Ridge and central NC mountains through late
morning, thus warranting the Wind Advisory. While am expecting
the concern of black ice to become more widespread tonight
through into early Friday morning given warming temperatures and
melting of residual snow, only to refreeze with subfreezing
temperatures tonight, have issued a Special Weather Statement
for this morning to express the potential for isolated patches
of black ice across areas that were in the previous weather

Otherwise, quiet conditions prevail across the FA this morning with
temperatures subfreezing across the mountains, into the lower to mid
30s across the Upstate and NW Piedmont. As mentioned earlier,
diminishing radar returns are noted across the NC mtns as large
scale lift decreases on the back side of the exiting upper low.
There remains decent upstream moisture and nw/ly llvl winds are
continuing quite strong. A mtn wave has developed evident in a
standing Ci on GOES-16 and a gap wind could develop overnight
bringing gusty conds back over the Upstate through early


As of 220 pm Wednesday: Heights will be on the rise across the area
through at least the first half of the short term, as upper low/
trough axis pull away from the East Coast, and a high-amplitude,
albeit dampening ridge builds in from the west. The ridge will
continue to dampen toward the end of the period, as a mid-level
speed max rides the top of the ridge, shearing out as it moves into
the Ohio Valley and surrounding areas by the end of Saturday.

In terms of sensible weather, the period will begin dry and
unseasonably cool, with temps expected to average around 10 degrees
below climo Thu night and Fri. Precip chances will then increase
late Fri into Fri night, as warm front activates to the E/SE of
weakening cyclone (associated with aforementioned dampening short
wave). By Sat morning, pops range from a slight chance across the
Piedmont, to solid chances near the TN border. If precip does
develop during this time, forecast soundings suggest light snow, or
at least a rain/snow mix would be possible for all areas roughly
north of the French Broad Valley and mainly across the high
elevations south of there, with light accums possible across the
northern mtns. However, warm advection flow would likely allow for a
transition to rain during the day Saturday, at which time a
Miller-B scenario would likely be unfolding across the Southeast.

The highest pops for Saturday (likely) will be favored across the
western mountains with the approach of the dissipating inland
surface low, and across the I-40 corridor in the Piedmont/foothills,
where low level convergence and isentropic lift will develop along
and above an advancing back door cold front/developing surface
wedge. Uncertainty regarding the timing of this back door front
makes for a problematic temp forecast for Saturday, but for now,
maxes are expected to range from the 40s across the northern tier of
zones, to the lower/mid 60s across the upper Savannah River Valley/
Lakelands areas of the Upstate and northeast GA.


As of 235 PM Wednesday: Seeing a bit more clarity with regard to
the fcst early next week. The model guidance is fairly consistent
with the approach and passage of a Miller Type-B sfc low on Saturday
night and Sunday. The forcing and deep moisture generally support
the idea that precip will be likely overnight and during the morning
hours. The main concern is the shallow cold air the models show
diving southward to the east of the Blue Ridge as the secondary
low forms off the Carolina coast early Sunday. The models suggest
low level thickness supportive of mixed precip types (read: sleet
or freezing rain) but that would be way out of season east of the
mtns. Fortunately, guidance also suggests that temps will only
make it down to the upper 30s outside the mtns, so only rain will
be fcst. Not so at the really high elevations, where it seems like
winter does not want to give up, as profiles show the potential
for snow above about 5k feet. Precip should slowly diminish on
Sunday as the sfc low pulls away rapidly and the moisture dries
up, while a classic cold air damming wedge develops by the end of
the day. Temps are kind of tricky for Sunday and will depend on
how quickly the precip ends. Either way, they will be well below
normal. From that point onward, the guidance shows the cool and
dry air mass to be quite expansive as it is driven all the way
down to N Florida and westward into Alabama on Sunday night and
Monday. The trend in the models is for the dry air mass to win
out and both models have what amounts to a dry wedge for that
period. This far out, confidence is usually better on temps than on
precip chances, so this trend plays well into my fcst preference,
which is to eliminate any small chance of precip (and thus any
small chance of wintry precip east of the mtns) for Sunday night
and early Monday. The rest of the period remains dry and cool
thru Tuesday night as a chunk of the sfc high moves down off the
southeast coast by Wednesday morning. The wedge will get some weak
periodic reinforcement from weak warm advection and isentropic lift,
but it will stick around thru Tuesday not so much because of that,
but because there won`t be much to destroy it, and the edges will
be so far away that it won`t be able to mix out up into our region
until after Tuesday. The high center being off the southeast coast
on Wednesday should finally allow that to happen, so a big warm
rebound is planned for that day. Precip chances will begin to
work their way back in from the west over the mtns in the warm
advection pattern out ahead of the next system in the afternoon.


At CLT and elsewhere: Expect VFR to prevail through the valid TAF
period. FEW/SCT mid to high level clouds continue to linger across
the area this morning, with a drying trend expected to continue
today and through early Friday morning as sfc high pressure builds
in. This feature along with the exiting system to the northeast will
allow for a tightened pressure gradient to persist across the NC
mountains. Thus, have kept gusts at KAVL through today, with gusts
at KGSP/KGMU through this morning as well given the development of
gap winds. Gusty winds (with the exception of KAVL) will subside
through the late morning hours, with low end gusts returning into
the afternoon hours, persisting into the evening hours.

Outlook: Increasing precipitation chances and possible flight
restrictions are possible this weekend with another approaching
storm system. Otherwise expect VFR.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  99%     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:


NC...Wind Advisory until 11 AM EDT this morning for NCZ033-048>050-


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