Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211212

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
712 AM EST Tue Feb 21 2017

A frontal boundary will push across the area late Tuesday and
Wednesday, bringing a chance for some modest rainfall. This will be
followed by brief drying, before another frontal system brings
additional chances for rain and thunderstorms heading into next


630 AM EDT Update...No sigfnt changes need to the going fcst. Made
some mostly upward tweaks to temps and td/s due to good Ci deck.
Main precip shield with developing wrn GOM low is located across AL
attm...still a good half day away from reaching the wrn mtns. System
still looks to be all rain and a low qpf generator thru the
overnight period.

A strong ulvl ridge axis continues to track east of the FA today
while a closed off low pushes into the nrn GOM. This will leave the
area in a weakly difl Col this evening thru the overnight period. At
the sfc...a wedge of high pressure will retreat NE with an advancing
warm front reaching the mtns arnd midnight. High cloud cover will
persist and help keep a lid on max temps...however still expect
highs about 10 degrees above normal. Due to the weak upper level
forcing...precip will remain light and generally associated with
mech lift across the wrn zones and waa ascent to the east. It looks
to be a high pop / low qpf event. A very limited instability
potential is had with the nocturnal timing and mid levels remain too
warm for deep conv. Thus...will keep all precip as -shra with no
thunder mention. Mins overnight shud remain quite warm with arnd 50
non/mtns and m40s mtn valleys.


As of 215 AM EST Tuesday: The closed upper level low pressure system
over the Gulf of Mexico Wednesday morning will move southeast across
the southern tip of Florida through Thursday. North of this system,
southerly flow at 850 mb will continue through the day Wednesday to
keep clouds in place and provide some upslope enhancement along the
southern and eastern slopes of the mountains. Meanwhile, the surface
high center will migrate east of the NC Outer Banks but extend
westward over the forecast area. These features will combine to keep
plenty of clouds in the picture and cap maximum temperatures at the
lower end of guidance Wednesday afternoon. The deeper moisture will
persist across the northwest part of the forecast area Wednesday,
but with dwindling PoP through Wednesday night.

Some measure of low level upslope will likely persist Thursday
through Thursday night. In addition, as dewpoints continue to
recover through the day on Thursday, anticipate decent amounts of
SBCAPE mainly along and southeast of I-85 through the afternoon
hours. Triggering will be weak with the surface ridge over the area,
and limited forcing aloft, but isolated to scattered thunderstorms
will be possible. Temperatures should rebound some 6 to 8 degrees
over Wednesday maxes.


As of 230 AM EST Tuesday: By Friday morning, an upper ridge over the
eastern CONUS will amplify quickly as a surface cold front quickly
approaches the southern Appalachians. Warm, moist southeasterly flow
off an upper low centered over the FL peninsula will ensue ahead of
the front during the day on Friday, and heating will likely result
in a small amount of instability developing, especially across the
our southernmost zones. The best upper forcing associated with the
H5 shortwave will not arrive until late Friday, well after peak
heating. Any instability looks quite weak Friday, and generally too
much out of phase with the best dynamics for the front to look too
worrisome for our area Friday night. Models have been in good
agreement with the front clearing our entire area by 18Z
Saturday...which is a very good thing, considering both the latest
GFS and CMC spin up an axis of much better instability across the
eastern Piedmont zones Saturday afternoon. Overall, though, severe
potential in our area appears unimpressive both days at this time.

A dry surface high will waste no time in building into the southeast
Saturday afternoon and Sunday as the upper trough swings through the
eastern CONUS, bringing temperatures back down to around 10 degrees
above average. A more zonal regime aloft will set up with southerly
flow at the surface by early next week, and another system in the
low track will approach the area. There is still a large amount of
uncertainty as to the timing of any precip and available moisture by
the time the front arrives, so pops were kept to chance at the end
of the medium range.


At KCLT and Elsewhere: BKN/OVC Ci will persist across all TAF sites
through most of the period. increase in llvl moisture
will adv in from the Atl by mid morning / early afternoon and
generate VFR STCU in weak isen lift. Winds will remain rather light
as a sfc high remains wedged across the area and mixing remains
relatively low. Expect -shra to start moving in from the west
associated with a warm front late this evening and early morning. No
thunder potential as mid levels remain too warm with slowly
departing ridge and weak forcing aloft. Timing of VCSH will begin
arnd 02z west and 04z at KCLT. Higher precip chances and IFR conds
expected across all sites arnd 06z-07z.

Outlook: An area of low pressure will drift from the Southern Plains
to near FL, keeping a persistent moist southerly flow across the
area thru Wednesday. This will result in periods of restrictions
by way of stratus each day thru at least Thursday.

Confidence Table...

            12-18Z        18-24Z        00-06Z        06-12Z
KCLT       High 100%     High 100%     High  83%     High  85%
KGSP       High 100%     High 100%     High  85%     High  83%
KAVL       High 100%     High 100%     High  91%     High  85%
KHKY       High 100%     High 100%     High  94%     Med   79%
KGMU       High 100%     High 100%     High  85%     High  82%
KAND       High 100%     High  88%     Med   78%     Med   77%

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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