548
FXUS62 KGSP 072335
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
735 PM EDT Sun Jul 7 2024

.SYNOPSIS...
A weak surface front will increase the chance for thunderstorm
activity across the area this afternoon and evening. An active
pattern of afternoon and evening showers and storms is expected to
continue for the first half of this week. More typical mid-July
weather is expected toward the end of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 530 PM Sunday: For the evening update, widespread showers and
thunderstorms are currently moving off the mountains toward the SE.
Increased PoPs (50%-70%) through the NC Piedmont, off the foothills
as ongoing convection is continuing to develop. A few severe
thunderstorm warnings were issued for Greenville, Spartanburg, and
Polk Counties and quite a number of SPS`s. Conditions remain
favorable for the next few hours to support heavy rainfall and
strong gusty winds where these storms develop.

Otherwise, the synoptic pattern remains relatively unchanged with
broad longwave troughing draped across much of the country from the
Northern Rockies to the Ohio Valley. Stout upper ridging remains
centered over California along with another upper ridge over the
Atlantic, the western flank of which nudges into the southeast
states. An upper low associated with a tropical upper tropospheric
trough also continues to spin off the Carolina coast, but will be of
no impact through the near term period. At the surface, very moist
southerly onshore flow continues with a previously stalled frontal
boundary having lifted back north into the foothills north of the I-
40 corridor. The boundary is rather diffuse, however, and nebulous
in surface observations with location being determined by a subtle
moisture gradient and weak low-level surface convergence.

Ample moisture and warming into the upper 80s to low 90s has
resulted in moderate instability this afternoon with convection
blossoming across the mountains and along the boundary across the I-
40 corridor. With time, convection over the mountains is expected to
become loosely organized along composite cold pools with several
linear structures moving out of the mountains and into the Upstate
and foothills and eventually portions of the Piedmont. 2500-3000
J/kg of surface-based CAPE has been realized on area ACARS
soundings, which will be sufficient for several stronger updrafts
and the development of a mature cold pool. Instability profiles are
very tall and skinny, however, with poor lapse rates and limited
DCAPE. A modified 12z Peachtree City, GA sounding supported a
microburst composite value of 3, which combined with aforementioned
parameter space would be supportive of a few isolated severe
thunderstorms with locally damaging winds. The main threat will be
across the southern mountains, northeast Georgia and the Upstate with
this area being placed in a marginal risk for severe storms from the
Storm Prediction Center.

Convection will push out of the area this evening with at least a
few isolated to scattered showers lingering into the late evening
hours. Thereafter, a widespread deck of low stratus clouds is
expected to build in given a rather moist boundary layer with areas
of fog also possible. Heading into tomorrow, extensive morning
clouds will likely delay daytime heating and the atmosphere will
also remain worked over from today`s storms. Thus, the CAMs are not
overly enthused with the coverage of storms, especially outside of
the mountains. Several storms appear likely over the southern
mountains/escarpment with only isolated to scattered showers and
storms elsewhere. Temperatures will be in the upper 80s to low 90s
tomorrow, but could end up a degree or so cooler if morning clouds
take longer to lift and scatter.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 155 pm Sunday: A deep/weak SW flow will remain over the
southern Appalachians and vicinity through the short term...between
an anomalous trough across the central Conus...and a subtropical
ridge nosing into the Southeast from the western Atlantic. Resultant
quiescent, but very moist atmosphere will continue to support
higher-than-normal coverage of diurnal convection...PoPs mainly
60-70% across the mtns and 50-60% across the Piedmont...through the
period. Diurnal instability is forecast to be adequate for isolated
pulse severe storms...perhaps more than adequate on Wed, when a
consensus of short term guidance indicates sbCAPE will peak at
around 3000 J/kg. One change that is expected is that storm motions
should become a bit swifter, especially on Wed afternoon. This will
be a consequence of the acceleration of the mid-level flow as the
upper trough draws a bit closer...as the circulation associated with
the remnants of T.C. Beryl is expected to become absorbed into the
westerlies...and progresses the central Conus trough to the east.
Nevertheless, the very moist conditions, locally poor antecedent
conditions, and the potential for SW=>NE training cells will result
in a continued low-end threat for excessive rainfall. Temps are
forecast to be a couple of degrees above normal through the period.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 210 pm Sunday: The global models continue to trend
(unfortunately) toward a drier extended period, as upper trough is
expected to progress into the eastern states...albeit weakening and
lifting north of our area over the subtropical ridge. It`s looking
increasingly likely that the proximity of the trough will allow the
deeper/subtropical moisture to shunt east of the CWA during the
latter half of this week, resulting in dwindling chances for
convection. Daily instability and moisture should still be adequate
for diurnal showers and storms, but with coverage more typical for
the time of year. Daily PoPs therefore trend closer to climatology
for much of the period, with standard mid-July threats of a pulse
severe storm or three and locally excessive rainfall. Temps are
forecast at near-to-slightly-above normal through much of the
period.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Ongoing TSRA will start to taper off are all
terminals through midnight, with lingering VCSH afterwards. All
terminals had rain this evening and this will pose a higher
confidence in VSBY/CIG restrictions during the overnight hours.
Patchy BR is expected at all sites east of the mountains with FG
possible at KAVL, with a TEMPO for 1sm VSBY from 09z-13z. Most other
sites also have a TEMPO for a VSBY of 4sm and IFR CIGS during this
time. Conditions should improve after daybreak, but will be slow
given the deep amount of moisture in the area. Once VCSH/TSRA taper
off, winds will become VRB or calm through the overnight hours,
enhancing FG/BR potential. Winds should prevail more southerly once
speeds start to pick up outside the mountain zones. There is a
chance for another round of convection Monday evening, but coverage
is not expected to be as widespread. PROB30 for this at all sites
except KHKY, where confidence is the lowest.

Outlook: An active summertime pattern continues for most of the
upcoming week, leading to showers/thunderstorms and possible
restrictions each afternoon/evening. Fog or low stratus may develop
each morning, especially over areas that received rain the previous
day.

&&

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

&&

$$

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