Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211756

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1256 PM EST Tue Feb 21 2017

A frontal boundary will push across the area tonight and Wednesday,
bringing a good chance for some modest rainfall. This will be
followed by brief drying, before another frontal system brings
additional chances for rain and thunderstorms late Friday or
Saturday. Overall, daytime temperatures will remain well above
normal through the weekend.


As of 1245 PM EST...The forecast is largely on track. Only updated
the latest winds and sky grids for the 18z TAFs. Otherwise, no

As of 945 AM EST...The main forecast challenge with this update will
be what to do with max temps this afternoon. Thicknesses support a
bump up of 2-3 degrees across the board, but there is a lot of
cirrus streaming in from the south. I expect that the cloud cover
will probably keep temps a couple degrees below what thicknesses
support, so will leave the temps as is. I also tweaked the PoPs,
delaying the ramp up in the west slightly, based on current trends
and the latest CAMs.

Otherwise, 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...the low levels will gradually moisten this evening thru
the overnight, as persistent southerly flow advects gulf moisture
into the area. I expect low VFR cigs to develop in the 22-24z time
frame, then cigs lowering to MVFR, then IFR overnight. Best chance
for showers will be in the 10-14z time frame, so will go with
prevailing SHRA. Precip rates should generally be light. A lingering
wedge may bring the winds around from SE to NE when the most
widespread precip moves thru, but then there`s high uncertainty on
whether they will turn back to SE around miday Wednesday. The
lingering wedge will keep low CIGS well into the day.

Elsewhere...As with CLT above, expect gradual deteriorating
conditions with MVFR cigs spreading across the area from late
afternoon thru the evening, then lowering to IFR at all sites
overnight. Showers should move in overnight, but will be generally
light. Still expect some VSBY restrictions in the precip with some
BR. Conditions will be slow to improve on Wednesday as a wedge
lingers across the area. This will bring winds around from SE to NE
across the Piedmont.

Outlook: Moist southerly to easterly low-level flow will persist
across the area until a cold front pushes thru on Saturday. This
will keep high chances of morning stratus and possibly fog each day
thru Saturday morning.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High  94%     Med   73%     High  81%
KGSP       High 100%     High  80%     Med   70%     Med   73%
KAVL       High 100%     High  87%     High  89%     High  91%
KHKY       High 100%     High  96%     Med   79%     High  86%
KGMU       High 100%     High  80%     Med   73%     Med   75%
KAND       High 100%     Med   67%     Med   60%     Med   79%

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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