417
FXUS62 KGSP 170023
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
823 PM EDT Tue Jul 16 2024

.SYNOPSIS...
Hot high pressure lingers above the region through Wednesday. A
pattern change begins to evolve by Thursday, as a cold front will
approach from the northwest then become stationary across our region
for several days. This will keep shower and thunderstorm chances
elevated through early next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 823 pm...still plenty of ongoing convection across the
region, working along outflow boundaries east of the mountains in an
environment that has residual 1000-1500 J/kg of sfc-based CAPE but
was also showing signs of stabilizing. This should continue through
sunset before finally diminishing. Can`t rule out a few more pulse
severe storms east of the mtns where dCAPE is sufficient, mainly
east of the I-85 corridor. We will also be minding the rainfall
amounts, looking for spots where storms repeat.

Overnight, the atmosphere becomes rather quiet after 02Z with
perhaps a few lingering showers over the ern zones thru 06Z. The
sfc layer remains a little mixed and with debris clouds hanging
around, dont expect much of a fog threat.

A wavy pre-frontal trof will push into the forecast area Wed
afternoon and likely produce more widespread storm activity across
the mtns and foothills. In fact, increasing shear may allow for some
storm organization and cold pool lines across the nrn foothills and
Northwest Piedmont. Highs Wed will reach a cat abv normal with td/s
mixing out into the u60s to l70s. Heat index values dont look to
reach adv criteria, but will come close across the I-77 corridor and
will be reassessed on the midnight shift for any possible product.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 200 PM EDT Tuesday: Height falls and an encroaching frontal
boundary from the northwest will be imminent as a digging upper
trough swings across the eastern half of the CONUS. Diurnal
instability and PWAT values on the order of ~2.00" will set the
stage for widespread convection across the area through much
of the forecast period, with an emphasis on coverage during
the afternoon and evening, but expect for lingering convection
during the nighttime period as well. Expect the primary threat
to be excessive rainfall as convective rainfall rates combined
with the potential for training cells along the boundary as model
guidance indicate that the boundary should sag far enough south to
hang out in the CFWA by late Wednesday into Thursday and becomes
quasi-stationary from that point on. Storm coverage for Thursday
could be in question, mainly across the mountain zones and I-40
corridor points north as the front may end up into the far southern
tier of the CFWA and allow for the continental high to filter in
drier air and thus, limit convective coverage. On the other side,
this would allow for convective coverage to become widespread across
the Piedmont zones, especially in CLT Metro, Upstate, and northeast
Georgia through Thursday, before the front sinks south of the CFWA
Thursday night. Heat indices will rise into the 90s for one more
day on Thursday, but definitely not as sweltering and should bring a
nice relief from the heat. Extensive cloud cover and elevated PoPs
will keep temperatures at bay as afternoon highs for Thursday will
be near-normal, while values drop to ~5 degrees below normal on
Friday. The frontal boundary seems like it`s going to wobble back
and forth across the CFWA and open up the door for another round
of convection Friday. Although the rain won`t be drought busting,
it will provide some relief even thought conditions will remain
very warm and muggy.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 230 PM EDT Tuesday: The upper trough from the short term
is shown being absorbed by the subtropical jet as the deep layer
flow will steadily come out of the southwest. As a result, high
PWAT values will remain in place as the quasi-stationary front
stays activated as guidance try to spin up an upper low over
the south-central CONUS. In this case, the pattern is likely
to be convectively active through the period, with a diurnal
emphasis. This will prolong an excessive rainfall threat through the
forecast period, but could become heightened in localized areas,
especially in locations that are prone to flooding. Otherwise,
temperatures will be at or slightly below normal through much
of the medium range as extensive cloud cover and elevated PoPs
continue through early next week.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Still dealing with some ongoing convection
this evening. What affected KCLT has moved off to the east and
has left behind a trailing stratiform rain area that will affect
the terminal for an hour or two. Can`t rule out a rogue lightning
strike, but this does not warrant an AWW or TSRA mention given the
low chance. Wind will toggle from light NW to variable. At KAVL,
an ongoing storm will move east in short order. Meanwhile, a loosely
organized band of showers and thunderstorms will move off the Blue
Ridge this evening and this could impact the Upstate terminals and
KHKY. Will include short TEMPOs for some. The convection should
weaken with sunset, leaving only cloud debris and a light variable
wind overnight. Wednesday looks like another active day in the model
data, with deep convection developing during midday and possibly
affecting all the terminals in the afternoon. Will employ PROB30s
for now, or until confidence in timing improves. Wind should be
light SW.

Outlook: Morning fog/low stratus possible each morning, especially
across the mountain valleys and for areas that received heavy
rainfall the day prior.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...PM/SBK
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...PM