Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 161141

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
641 AM EST Sat Dec 16 2017

Dry and cool high pressure will dominate our weather through Sunday
morning. Moisture and a gradual warm-up will return to the area
starting Sunday. A series of disturbances will pass across the area
next week, with a prolonged period of unsettled weather.


630 AM EST Update...Made some downward tweaks to hr/ly temps with
localized areas a few degrees below the fcst curve. Other than
that...the fcst is in good shape. Expect slowly rising temps thru
the next update.

Not a lot going on over the near term period. A developing ridge to
the west of the FA will instigate strong subs beginning this
afternoon while a 1026 mb sfc high centers across the Carolina
coastline. This will effectively shunt any chance for low cloud
development and precip chances over the area. Profiles show pwat
values remaining below 0.5 inches thru the period while the flow
becomes weak within the sfc-h7 layer. The weakened w/ly h85 flow will
limit the amount of d/s warming which will aide in keeping max temps a
little below normal. With the day beginning below freezing...the
llvl thermal trof will be slow to modify as sw/ly sfc flow remains
weakly advective. Even tho insol will be high...the lowest sun angle
week of the year will limit the heating potential as well. More
widespread upper clouds will move in from the west tonight which
will help keep lows a little warmer by a few degrees Sun morning.
Still...well below normal values by about 10-12 degrees.


As of 215 AM EST Saturday: Complicated split-flow pattern will be in
place over the country, with a cutoff midlevel low over NW
Mexico/Baja, a shortwave lifting into the Mid-MS Valley, and low-
amplitude ridging in place over the Appalachians. Moisture being
pulled across the Deep South from the weakening shortwave will lift
NE in the SW flow aloft as we start the period, but guidance
continues to delay onset of pops toward midday Sunday. By this time
the wave has almost completely filled with just a tiny ripple left
in the flow; the bulk of the moisture will lift north toward the
Great Lakes but with continued stream of moisture flux into the Deep
South. QPF pattern remains weak over the Southern Appalachians
Sunday in to Sunday night and with the lack of dynamic support have
trended pops slightly lower. Should see temps just a tad above climo
with low level WAA on the western side of an Atlantic surface high.

The surface WAA continues on Monday as the flow aloft flattens
(midlevel cutoff remains over the Southwest). Best pops Monday
remain to the south with the Gulf moisture flux continuing; the GFS
is quite a bit more robust than the ECMWF with the moisture, but
both agree on a continued warming trend. This southern stream wave
passes to the east by the end of the short term, but the Southwest
cutoff will be kicked into the Southern Plains (by a deepening low
pushing into the northern Rockies), to affect us as we push into the


As of 230 AM EST Saturday: GFS has trended much more toward the
ECMWF for the mid-week system, providing increased confidence in the
overall sensible weather solution. As mentioned above, the Southwest
cutoff will kick into the Southern Plains Tuesday, with upper level
diffluence resulting in widespread synoptic lift over the Lower MS
Valley and Deep South Tuesday night into Wednesday. Low-level WAA
will be maximized on Tuesday when highs across the Piedmont will be
into the mid 60s if not approaching 70. The southern stream moisture
will lift toward the Southern Appalachians Wednesday morning, with
pops increasing significantly across the area (whereas this time
yesterday we were advertising a dry forecast for Wednesday in line
with the GFS). ECMWF pulls the moisture farther north toward the TN
Valley whereas the GFS has suppressing surface high over the Midwest
that shunts the moisture slightly more to the south, but the trend
is at least all in the same direction. Slightly cooler across the
mountains for Wednesday but still a good 5 or so degrees above normal
for the Piedmont.

Following the passage of the southern stream wave Wednesday night, a
transient damming pattern sets up with another slight decrease in
temps for Thursday, though the weak low-level CAA will compete with
the increasing sunshine. Of significance on thursday is another high
amplitude, positively-tilted trough stretching from the Upper
Midwest to the Desert Southwest, with a very strong synoptic front
pushing across the center of the country. Some continued differences
in how the northern/southern stream moisture splits over the
mountains as we move into Friday, but either way should see another
increase in moisture at the end of the period. No significant changes
to temperatures as the front elongates and stalls in the southwest
flow aloft as the Desert Southwest cutoff remains in place, keeping
us in the warm sector for the time being.


At KCLT and Elsewhere: No flight restrictions thru the period at all
TAF sites. A broad area of high pressure will center over the region
and keep skies generally clear outside of some passing Ci. Soundings
show a very dry BL so no issues with VSBY or STCU during the morning
hours. With non/mtn sw/ly flow...some increase in sfc dewpoints will
be had...but not enough for Cu development. Increasing layered
clouds aft 00z yet remaining VFR. Winds will remain rather weak with
a loose p/grad and no sigfnt gust potential.

Outlook: Potential for short-lived restrictions on Sunday with rain
showers. Otherwise, expect VFR as a series of dry cold fronts move
through the area.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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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