Severe Thunderstorm Warning 191, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
257 PM EDT Tue Aug 13 2019

.SYNOPSIS...
Hot and humid conditions will prevail through Wednesday as a weak
cold front drops south across our area.  Expect scattered to
numerous showers and storms until the front moves south of our area
on Thursday. Rainfall chances will decrease at the start of the
weekend but increase again to start next week as another front and
low pressure approaches.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 2:35 PM EDT Tuesday: convection has begun to fire up across
much of the fcst area over the past hour or so, in addition to a
robust line of convection that is currently crossing the Tenn/NC
Border and moving into our CWA. The latest CAM runs continue to
generate at least two rounds of convection over the CWFA thru late
tonight. It's still looking like the first round that comes thru
over the next 3 to 6 hrs will be the strongest. The heat is also
an ongoing concern, with heat indices already hitting 105 degrees
at several sites. As convection spreads, hopefully temps have peaked
and will begin to come down. SPC has included most of our CWA in
a Severe Thunderstorm Watch until 7pm, with damaging straight-line
winds still expected to be the main threat. There is a light curve
to the hodograph (S to SSW surface winds and NW winds aloft), so we
have a non-zero tornado chance. Large hail threat remains minimal.
Main convective threat should dwindle after 00z or so, with lingering
weaker convection and showers possible after that. As such, have
kept low-end pops thru the overnight hours with the front hanging
around and plenty of lingering moisture.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 250 pm Tuesday: Lower theta-e air filtering into the area in
the wake of weak frontal zone will provide a respite from active
convective weather and overly oppressive heat indices during the
short term. Pops for afternoon/evening convection are still
warranted, mainly across the mtns and southern and eastern areas,
but 20% chances are about the best that we can do. While max temps
will still be hot, generally lower 90s across much of the Piedmont
and foothills, dewpoints mixing out into the 60s each afternoon
should allow for heat index values to be primarily limited to the 90
to 95 range, with some spotty 95-100 values possible across southern
Piedmont areas.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 140 PM EDT Tuesday: Starting Friday evening with the 500mb
pattern showing a broad trough across North America with nearly
zonal west to east flow from northern California to the Virgina's.
As the surface front will be stalled out from Florida to along the
Carolina coast and weak high pressure controlling our weather, POPs
continue to be low on Saturday. It is still questionable concerning
any tropical low forming along the front and whether that influences
our weather going into next week.  The ECMWF forms a low near the
Big Bend area on Saturday then moves it over the Carolinas on
Monday. The GFS is vague but brings up tropical moisture from the
Gulf in the first half of next week. A strong shortwave crosses
Tennessee late in the weekend and becomes our weather maker for the
first half of next week. The EC closes off a low over Indiana late
Monday and it remains there through mid week. The GFS briefly closes
off a 500mb low on Tuesday over Alabama.  Seems a bit wet for the
first half of next week.  Temperatures will be slightly above normal
this weekend, then cool to a couple of degrees below normal toward
mid week under thick clouds.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: expect an active next 24 hrs across the fcst
area with multiple rounds of convection expected. A well-defined line
of robust thunderstorms is about to move across the Tenn/NC Border
and will likely begin impacting KAVL within the next hour or two.
I have TEMPOs for TSRA at all sites for this main line of convection
from roughly 18 to 24z today and another round of TEMPOs from roughly
00 to 04z for a secondary round of convection, although it might wind
up being mostly showers. Towards the end of the period tomorrow
afternoon, I included PROB30s for TSRA at KCLT and KAVL, with the
other sites likely needing them with the next taf issuance. Winds
will generally be SWLY thru the period except at KAVL where winds
will shift NWLY this afternoon, and remain predominately NWLY thru
the taf period. In addition, KAVL has the best chance of seeing
restrictions tomorrow morning. Thus, I included a few hours of IFR
cigs and MVFR visby beginning around 10z.

Outlook: showers and thunderstorms will continue thru Wednesday as
a cold front and associated moisture/forcing arrive from the northwest.
The boundary will stall southeast of the area mid to late week, with
lower end convective chances persisting. Early fog/stratus will be
possible each day across mountain valleys.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     Med   70%     High  85%     High  87%
KHKY       High 100%     High 100%     High  96%     High 100%
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 scheduled 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...Heat Advisory until 8 PM EDT this evening for GAZ026-028-029.
NC...None.
SC...Heat Advisory until 8 PM EDT this evening for SCZ010-011-019.

&&

SYNOPSIS...SGL
NEAR TERM...JPT
SHORT TERM...JDL
LONG TERM...SGL
AVIATION...JPT

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