Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KGSP 171803

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
203 PM EDT Mon Jul 17 2017

A weak frontal boundary will approach the area today, increasing
the chances for widespread showers and thunderstorms. A strong
upper ridge will then gradually build into the region during the
mid-to-late week, bringing hot temperatures and reducing the coverage
of diurnal showers and thunderstorms.


Isolated -shra and tstms are developing across the mtns...generally
along the BR area. This activity has been pulsing up and down with
updraft strength remaining relatively low and within the SPS range.
Instability is pretty strong...arnd 2500 J/kg...yet no real triggers
are available so the main mechanism for development will be thermal
forcing. Expect better coverage as the afternoon progresses with
some activity developing over the non/mtns associated with existing
outflow bndrys. A few of these storms could reach severe levels with
damaging winds being the main threat.

A well agreed upon h5 s/w will cross the FA this evening and will
interact with elev instability keeping -shra/tstms active through
the overnight to some degree. Expect lingering debris clouds and
moisture leading to stcu development to persist arnd daybreak. The
best chance for denser fg development will be across the mtn
valleys....yet all areas could see patchy ground fg lifting by 14z
or so. Afternoon and evening convection will once again be probable
Tue as the upper trof continues to influence the pattern. Mid-level
LRs will be conducive for stg/svr storms as LFCs are easily reached
once again and sbCAPE reaches moderate levels. Max and min temps
thru the period will remain near normal levels.


As of 200 PM EDT Monday:  The short term fcst period kicks off
on Tuesday evening as a weak upper trof/disturbance slides east
across the Carolinas, while high pressure dominates at the surface.
Meanwhile to the west, a large H5 anticyclone will build, before
sliding east through the entire period.  With that, heights will
gradually rise through Wednesday and into Thursday atop northeast GA
and the western Carolinas leading to warming temperatures through
the profile.  Said warming will work to gradually tamp down
convective chances on Wednesday, and even further on Thursday.
With below climo pops fcst given decreased chances for diurnal
convection, the primary headline for the short term will be the
building heat.  Temperatures will warm each day with mid 90s
prevailing by Thursday across the piedmont, while upper 80s are
expected in the mtn valleys.  As such, given dewpoints in the upper
60s to lower 70s, am expecting heat indices to approach/exceed
100 degrees by Thursday.


As of 240 AM EDT Monday: the extended fcst picks up at 12z on
Thursday with very broad upper ridging covering most of the CONUS
and a lingering upper trof slowly moving off the Atlantic Coast.
Over the next couple of days the ridge will flatten as upper trofing
amplifies over Eastern Canada. By the end of the period early next
week, heights will start to lower again as the Canadian upper trof
digs farther southward. At the sfc, broad high pressure will be in
place over the southeast with the Bermuda High in place offshore.
The models keep some degree of weak lee trofing over the fcst area
for most of Thurs and Fri and then dissipate it as low-lvl sly flow
strengthens over the weekend. Other than that, no other significant
pattern changes are evident. As for the sensible fcst Thurs should
be the least active/driest day of the period, with the rest of the
period seeing a return to diurnally-driven climo PoPs each day.
Temps will be a good 4 to 6 degrees above climatology thru the
period with heat index values approaching advisory criteria over
the weekend.


At KCLT and elsewhere: A good Cu field is encompassing the area this
afternoon with some deeper destabilization indicated across the higher
terrain. Expect most of the thunder to remain across the mtns until
later this afternoon when cells begin firing across existing outflow
bndrys. Hard to pinpoint favored locales and hi-res models are back
and forth with timings and locales. Anyway...have maintained a TEMPO
TSRA at KCLT this afternoon with the other sites getting a VCTS. An
ulvl s/w will cross from the northwest overnight and help maintain
-shra and possibly a few tstms. With debris cloudiness and llvl
moisture lingering thru daybreak...periods of STCU may develop and
expand. For now...will keep the IFR CIGS limited to the mtn sites.
Some lowering of VSBY is also expected arnd daybreak with IFR VSBY
possible at KAVL and likely MVFR VSBY all other sites before
lifting/dissipating aft 14z or so.

Outlook: Scattered to afternoon and evening thunderstorms are
expected into Wednesday across the area, with better coverage over
the mountains. Morning fog development can be expected in the
mountain valleys and in areas that receive rainfall the previous
afternoon/evening. Drier air will likely limit convective coverage
for Thursday, with typical mid-summer conditions returning by Friday.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High  99%     Med   68%     Med   79%
KGSP       High 100%     High 100%     High  83%     High  91%
KAVL       High 100%     High  97%     High  91%     High  92%
KHKY       High 100%     High 100%     Med   78%     High  92%
KGMU       High 100%     High 100%     High  91%     High  90%
KAND       High 100%     High 100%     High  83%     High  87%

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:




AVIATION...SBK is the U.S. government's official web portal to all federal, state and local government web resources and services.