Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261832
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
232 PM EDT THU MAY 26 2016

.SYNOPSIS...
Moist southerly flow will lead to warmer temperatures and mainly
afternoon chances of showers and thunderstorms through Friday. A
period of cooler and wetter weather may develop late in the weekend
as Atlantic low pressure moves toward the South Carolina coast.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 230 PM EDT Thursday: Lee troughing across the area and
continued southerly moist flow combined with a shortwave working its
way through the area aloft has allowed for convection to develop
along the Blue Ridge, with an area of showers behind it working its
way across the mountains (this showery activity has slowly moved
east from TN all morning). sbCAPE values have increased to between
500-1000 J/kg, very similar to what was progged yesterday for today.
CAMs have been over-forecasting convection across the Piedmont early
this afternoon but enough Cu bubbling up that there should be at
least isolated showers/thunderstorms. Guidance brings max sbCAPE in
by around 21z so expect increasing coverage between now and then,
with waning thereafter in a diurnal pattern. That said however, as
the upper weakness sort of stalls over the region, all the models
have an area of mid-level moisture drifting NW across the Southeast
as the surface high strengthens somewhat overnight. As this area of
moisture is lifted over the Southern Appalachians, pretty much all
the near-term models allow at least showery activity (if not
thunderstorms) to continue overnight, especially into GA. With that,
have continued slight chance PoPs especially across SW zones
overnight.

Surface high over the western Atlantic strengthens Friday as a cold
front approaches from the west. The front will be lifted over the
upper ridge and instability won`t be quite as high across the
Piedmont, so for now best PoPs remain over the mountains Friday
afternoon. Temperatures tomorrow should be pretty similar to those
today with not much change to thicknesses, with also very little
change to overnight lows tonight from those last night.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
At 230 PM Thursday, on Friday evening an upper ridge will be over
much of the east coast, while an upper trough will be upstream over
central and wester USA, and an upper low associated with a potential
tropical system will be northeast of the Bahamas. The models move
the coastal upper low to the SC coast by Saturday evening, while the
upper ridge weakens over the western Carolinas and northeast
Georgia. The upper low is shown to move very little over coast SC
through Sunday.

At the surface, moisture is expected to remain over the western
Carolinas and northeast Georgia on Friday evening, while areas to
the east remain dry ahead of the approaching coastal surface low.
the drier air appears to spread west over our area by Saturday
morning, persisting through the day. By Saturday evening the models
bring moisture associated with the surface low inland toward our the
southeastern portion of our area, spreading it toward the mountains
by Sunday morning, and then over the mountains during the day.
Instability will be waning Friday evening, and and modest at best
until Sunday afternoon, when instability increases over the
Piedmont. Precipitation will be rather reserved due to limited
vertical lift, and maximized mainly over the mountains.

Temperatures will initially run slightly above normal under the upper
ridge, then will exhibit a slightly reduced diurnal range as the
moisture arrives.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
As of 145 PM Thursday...Forecast confidence remains below avg for
the ext range. The op models continue to diverge wrt the track of
the eventual subtrop or trop low beginning Sun night. The GFS has
had varying ideas with this system and now brings the low onshore
north of Charleston. The track thereafter is odd looking with a jog
to the SW then up the SRV as it gets caught up in a broad ulvl trof.
The EC on the other hand has been consistent with keeping the low
track aligned along the Atl shoreline as a more acute s/w pulls it
NE of South Carolina through the period.

The GFS soln would be quite moist and more unstable than the EC
soln...as the BR area would see prolonged moist upslope flow likely
leading to hydro issues. Scattered afternoon and overnight general
thunder is probable in a deeply moist theta/e column with the
passage of any mlvl pockets of dpva. With the GEFS mslp spread
reaching high levels by Sun eve...the GFS op soln will be given less
weight than the EC. Thus...will continue with chance pops non/mtns
and low likely pops across the BR escarpment through the period. Max
temps could be tricky as well with varying direc/intensity flow and
airmass mixes possible. For now...will keep most the FA a little
below normal with the ne/rn zones a couple degrees below that. Mins
shud avg a few degrees above in high column rh and nocturnal
cloudiness.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Low VFR Cu increasing in coverage this
afternoon with a line of convection just east of the Blue Ridge.
Have included VCTS at most sites this afternoon, with VCSH at KCLT
where convection chances are lowest. Should see off-and-on SCT-BKN 4-
7kft with passing mid- to high-level clouds, but unless TSRA affects
a TAF site, no restrictions expected. Intermittent cloudiness should
continue overnight, with MVFR fog likely at KAVL/KHKY. Another round
of SHRA/TSRA expected tomorrow afternoon but for now have only
introduced PROB30 at KAVL. S to SSW winds through the period around
5kt, with LGT/VRB overnight.

Outlook...Mainly VFR conditions will prevail through the period, but
patchy morning fog chances continue at KAVL. Scattered afternoon
SHRA/TSRA coverage will return on Friday, with increasing chances
through the weekend and into early next week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
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  91%
KHKY       High 100%     High 100%     High  94%     High  94%
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 schedule TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...SBK
NEAR TERM...TDP
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...TDP



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