Severe Thunderstorm Warning 162, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
525 PM EDT Sat Jun 27 2020

.SYNOPSIS...
An upper level disturbance will lead to an increase in showers and
thunderstorms on Sunday afternoon and evening. Unsettled weather
will continue throughout next week as a back door front moves south
into the region and stalls. Daily afternoon and evening showers and
thunderstorms will arise in the warm and humid airmass across the
area.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 515 PM EDT...Monitoring an MCS that is bowing out across
northern GA, making a beeline for our GA Piedmont counties. The
storms really forming a cold pool and may produce some severe gusts.
Otherwise, the rest of the forecast area is struggling to destablize
under plenty of thick mid-high clouds. Bumped up Pops ahead of this
line of storms, while lowering PoPs in the mountains, where there's
a lack of instability. Otherwise, added mention of haze thru Sunday
morning , as most sites are seeing some reduction in vsby with the
Saharan dust.

The atmos will remain unsettled thru the period as an energized
quasi-zonal flow persists, before a more defined upper s/w trof
crosses the region Sun afternoon and evening. Not expecting much in
the way of deep convec this afternoon as the mlvls remain fairly
warm, while mlvl cloud cover prevents good sfc-based destabilization
over most areas. The w/ly flow within the BL will also aide in
preventing deep cells outside the mtns, where a couple topo enhanced
tstms could become fairly strong. Southwesterly flow on the edge of
the Bermuda High will continue efficient GOM moist flux overnight,
which keep cloud cover high and hold min temps up a couple cats abv
normal.

Things get more interesting and tricky Sun, when the models bring an
energetic h5 s/w from the northwest to the FA by mid afternoon. This
will combine with a destabilizing atmos as all models indicate
increasing sbCAPE on the order of at least 1500 J/kg. The models
also show a developing llvl jet to arnd 30 kts during the afternoon
across the nrn zones. So...the ingredients will be there for a
possible organized lines of convection capable of producing severe
level winds as they form across the NC mtns then propagates east
thru the NC piedmont during the afternoon and early evening. There
is still moderate uncertainty as to exactly where the potential lines
may form as the NAM is further south into the NC zones than the GFS,
which keeps the better forcing and subsequent convec line mostly
north and east of the FA. This will be a situation to keep an eye
on. Max temps will be warmer than today in better insol with
readings right arnd normal.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 200 pm EDT Saturday: A mid level trof will pass just off to
the northeast on Sunday night as upper level ridging builds over the
Ohio and Tennessee valleys and a closed mid level low rotates across
New England. Weak short waves in this northwest flow pattern will
lead to an active convective regime Monday and Tuesday with the peak
in activity focused in the afternoon and evening hours. Showers and
thunderstorms may be somewhat enhanced by the approach of a weak
backdoor cold front.

Temperatures look to be a little above climo reaching into the lower
90s in the Piedmont and the middle 80s in the mountain valleys.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 200 pm EDT Saturday: Height falls mid week will permit above
climo PoPs to continue, with mainly a diurnal convective pattern
expected through late week as a dissipating boundary persists in the
vicinity, profiles remain moist and instability continues to
rebound. Temperatures through the middle and end of next week will
be around climo.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Generally VFR conds thru the period at all
TAF sites. There could be some lowering of VSBY with isol showers
across the area, but confidence at any TAF site is too low for
inclusion. Also, periods of MVFR VSBY due to HZ is possible across
the non/mtn sites, but for now kept at 6SM HZ as uncertainty is high
due to changes in cloud coverage. A better chance of -shra and
possible tstms at KCLT late in the period as an upper s/w trof
crosses the area.

Outlook: Scattered to numerous showers and thunderstorms are
expected each afternoon across the region thru the middle of next
week. There will also be potential low clouds and fog around
daybreak each morning, especially in the mtn valleys. Otherwise,
expect VFR conditions.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  98%     High 100%
KHKY       High 100%     High 100%     High 100%     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 are available at
the following link:

www.weather.gov/gsp/aviation

&&

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

&&

SYNOPSIS...SW
NEAR TERM...ARK/SBK
SHORT TERM...SW
LONG TERM...SW
AVIATION...SBK