350
FXUS62 KGSP 161609
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1209 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 TONIGHT/...
Noon Update...Seeing some early showers and a couple weak
thunderstorms pushing into the the wrn NC mtns. Not expecting
much development of this activity before 18z when the increasing
lift interacts with a more unstable atmos mostly across the
mtns. The Heat Advisory has been continued thru 00z.

Otherwise, hot temperatures and high pressure continues in the near
term. Flow aloft remains weak Tuesday with a continuation of
moisture advection from the SW sfc winds. Not expecting too many
clouds overnight, outside of some low-level stratus over areas that
received rainfall yesterday. Instability increases throughout the
day with ample heating at the surface. Guidance from modeled
soundings show a more modest inverted-V in the BL and around 1000-
2000 J/kg of sbCAPE. CAMs once again are having trouble depicting
afternoon convection, but scattered showers and thunderstorms are
possible, with the highest chances over the mountains (60%-74%).
Though the risk for severe weather is low, cannot rule an isolated
severe storm or two. Aside from storm chances, heat is the bigger
story for Tuesday. There is less dry air aloft to mix down during
the daytime, which suggests hot temps and hotter heat index values
likely. There is a catch though. if showers can get going, this
could reduce heat index values in a few of the areas and provide
some relief. But, considering the impacts, a Heat Advisory will be
in effect from noon through 8 PM for Cabarrus, Mecklenburg, and
Union (NC) counties. By Tuesday night, PoPs ramp down quickly and
humidity remains high, keeping overnight temps in the mid 70s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 245 am Tuesday: Heights will steadily fall across the eastern
half of the country during the short term, with a long wave trough
expected to be centered from the western Gulf of Mexico through the
northeast Conus by the end of the period. The leading edge of an
associated baroclinic zone is expected to sag across the TN Valley
during the day Wednesday. Hot and muggy conditions are again
expected across our area in advance of this front...although heating
and instability may be somewhat tempered by increasing clouds. This
makes one more day of Heat Advisory conditions possible...but hardly
a slam dunk in the Charlotte metro area. Moderate instability and
continued elevated precipitable water values of around 2" should
allow for good coverage of diurnal convection...while widespread,
pre-frontal convection may roll into western areas by the end of the
day. Likely PoPs are therefore advertised across the Piedmont/
foothills, with around 80% chances expected across the mountains.
Instability should be sufficient to support a handful of pulse
severe storms, while the primary threat may prove to be locally
excessive rainfall in light of the high moisture content. With the
front likely making a push into the CWA overnight Wed/early Thu, Wed
night should remain convectively active to some extent, with
continued potential for locally excessive rainfall.

The frontal zone is expected to sag southeast across the CWA on
Thursday, although how fast this occurs is the subject of some
controversy...making for a somewhat problematic convective forecast,
as some short term guidance sources indicate sufficiently low
theta-E air will advect into the mountains/perhaps the northern
zones to preclude much in the way of a threat. There`s a good enough
signal to advertise a 70 PoP across much of the area, but this will
likely need some refinement in the near future. The expectation of
more extensive cloud cover Thu may further constrain the severe
storm potential. However, virtually boundary-parallel storm motions/
increased potential for cell training, and continued very high
moisture content may increase the excessive rainfall threat. The
consensus in guidance is strong enough to anticipate the front
sagging south of the area Thu night...resulting in diminishing
chances for convection.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 310 am Tuesday: A portion of the upper trough (mentioned
above) is expected to separate from the main branch of the
subtropical jet...possibly evolving into a closed low over the lower
Miss Valley and vicinity early in the period. This will allow the
old frontal boundary to persist in or near our CWA through much of
the period, while deep SW flow will support continued high
precipitable water values. The upshot for our forecast area will be
cooler (near-to-a-little below normal temperatures) and convectively
quite active weather, with at least likely PoPs in the forecast each
day. While there will certainly be a diurnal trend to convective
activity, the pattern will be such that the overnight/early morning
hours could remain at least somewhat active. The main hazard concern
will be locally excessive rainfall, especially as hydrologic
conditions steadily deteriorate...at least on a localized basis.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR conditions prevail for most sites through
the end of the TAF period. A swath of mid level stratus should
dissipate after sunrise and lead to SCT or even SKC. Another
afternoon chance for showers and TSRA at all terminals, therefore a
PROB30 during the afternoon and into early evening hours. Moderate
confidence for the KAVL site so went ahead and gave a TEMPO for TSRA
from 17z-21z. As for winds, speeds should remain relatively light
and prevail SW. During the afternoon, winds could become VRB should
any TSRA develop with a brief period of gusty winds near these
storms. Any showers or TSRA looks to be out of the area after 00z
with sites continuing VFR conditions. There is a possibility for
vsby restrictions for BR at mountain sites, but confidence is low at
this time.

Outlook: An uptick in showers and thunderstorms Wednesday onward as
a cold front approaches and stalls near the region. 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...Heat Advisory until 8 PM EDT this evening for NCZ071-072-082.
SC...None.

&&

$$

SYNOPSIS...JDL
NEAR TERM...CP/SBK
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...CP