Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 261803

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

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.


As of 1100 AM Thursday: Area of showers associated with a mid-level
shortwave is beginning to move across the mountains at update time.
Have reduced pops for late morning elsewhere but increased across
the mountains accordingly. Updated CAM guidance seems to indicate
slightly more widespread convective development this afternoon so
trended PoPs up a little more quickly and expanded them farther east
into the Piedmont as well. Overall temperatures and dewpoints look
okay so only minor tweaks there to account for observed trends.

Otherwise, the moist southwesterly flow across the area will keep
copious low level moisture in place, leading to an increase in
cumulus development today. The continued low level moisture will
lead to an increase in instability with moderate sbCAPE values
likely across the mountains, and moderate MUCAPE values possible
across much of the CWFA. With the weak forcing and the potential
moderate instability, expect much better convective coverage to
develop today. The synoptic scale and convection allowing models
agree on good coverage developing across the mountains then breaking
containment and spreading into the foothills before dissipating
across the piedmont. Have followed these trends with highest PoP
across the mountains, low end scattered PoP into the NC Foothills
and I-85 corridor of the Upstate and NE GA, with isolated coverage
elsewhere. Wind shear is forecast to remain light, but can`t rule
out some strong storms across the mountains where instability and
forcing will be greatest. Convection should taper off through the
evening with lingering clouds overnight. Highs today and lows
tonight will be around 5 degrees above normal.


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.


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 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


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:




SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...TDP is the U.S. government's official web portal to all federal, state and local government web resources and services.