070
FXUS62 KGSP 081358
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
958 AM EDT Wed May 8 2024

.SYNOPSIS...
A summerlike weather pattern lingers through mid-week leading to
mainly diurnal showers and thunderstorms and above normal
temperatures. Showers and thunderstorm activity will become more
numerous ahead of a strong cold front tonight into Thursday, with
severe storms possible. The cold front pushes east early Friday
morning but another system approaching out of the south may bring
shower and thunderstorm chances back again on Friday. Drier
conditions and below normal temperatures return just in time for the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 931 AM EDT Wednesday: A very busy forecast remains on tap for
the region with multiple rounds of severe thunderstorms expected
this afternoon through tonight. Will focus on the first round of
convection through this afternoon with this forecast update. A line
of elongated convection is ongoing across northern Tennessee along a
boundary draped from southern Illinois. The leading edge of this
activity will push into the mountains later this morning/early
afternoon. With time, a loosely organized line of storms is expected
to push across the mountains and into the foothills and Piedmont
through the afternoon hours. The environment ahead of these storms
will be favorable for severe weather with moderate instability,
steep lapse rates and modest deep-layer wind shear. Thus, a threat
for damaging winds and large hail can be expected.

Upper ridging will remain over the Southeast this morning before
pushing east this afternoon. A vort lobe embedded within the upper
flow will track overhead western NC this afternoon and early
evening, leading to another round of shower and thunderstorm
development. The 06Z CAMs are coming into better agreement regarding
convection through the near term, and are even trending towards an
increase in coverage. The 00Z CAMs were keeping activity mostly
confined to NC but the 06Z CAMs are now depicting activity across
the majority of the forecast area. Thus, increased PoPs this update
across the entire CWA through the period. SW`ly flow will lead to
the continued influx of Gulf moisture across the region today,
allowing dewpoints to climb back into the mid 60s and lower 70s east
of the mtns. Plentiful low-level moisture combined with 30-40 kts of
deep shear and SBCAPE values from 2,000-3,000 J/kg during peak
heating, will allow any storms that develop to become strong to
severe. The main hazards with any severe storms that develop will be
large hail and damaging wind gusts. A few brief tornadoes cannot
ruled out, but the limiting factor will be 0-1 km shear which
forecast soundings generally show <20 kts. So, the tornado threat
looks low today, but is certainly not zero. With all of this in
mind, The Day 1 SPC Severe Wx Outlook expansion of the Slight Risk
(across most of the forecast area) and addition of and Enhanced Risk
(across the western NC mtns, mainly along the southern and central
NC/TN border) seems reasonable. High temperatures this afternoon are
expected to be the warmest of the week, climbing into the mid to
upper 80s in the mtn valleys and east of the mtns. Areas near the
Charlotte Metro may even see highs reach the lower 90s! However,
developing convection may limit highs this afternoon. Nonetheless, it
will be another humid day with temps expected to remain around 9-12
degrees above climo.

Meanwhile, a strong cold front will continue to creep eastward
through this evening before pushing into the TN Valley overnight.
So, another round of overnight convection looks to be order now that
the 06Z CAMs are in better agreement, showing widespread convection
overnight. Went ahead and increased overnight PoPs to account for
this upward trend in coverage. The strong to severe storm threat
will linger overnight, with damaging winds and large hail still
expected to be the main hazards, but an isolated tornado or two
still cannot be ruled out. With multiple rounds of convection
expected today into tonight, the excessive rainfall/flooding threat
will also be a concern and will gradually ramp up through the near
term. The WPC Excessive Rainfall Outlook has the western zones in a
Slight Risk for excessive rainfall, with a Marginal Risk across the
eastern zones today into tonight. Lows tonight should remain around
13-15 degrees below climo.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 255 am EDT Wednesday: Pre-frontal, organized strong-to-severe
convection is likely to be ongoing in or very close to the forecast
area at the start of the period, with damaging downburst winds and
possibly brief, isolated tornadoes being of concern. How the
environment evolves beyond the morning is subject to a great deal of
uncertainty at this point. With surface front expected to be
west-through-north of the area through the day, low level moisture
will be more than adequate for diurnal destabilization. However, the
magnitude of insolation/heating depends upon how quickly morning
convection is able to clear the area, how quickly clouds are able to
thin (if at all), and how quickly any lingering cold-pool air mass
is the air mass is able to modify. Convection-allowing model
guidance is virtually unanimous in suggesting that the atmosphere
will be unable to recover sufficiently to support afternoon
redevelopment of convection. If a few storms are able to initiate in
the afternoon, deep layer shear of around 50 kts will support
organized convective structures, with any severe storm threat
dependent upon how much instability is realized.

The frontal zone is expected to sag slowly southeast across the
region Thu night and Friday...and won`t pick up much speed until a
short wave trough digs from the southern Appalachians to the
Carolina coast during the day Friday. As such, the front may not be
able to completely clear our area before diurnal destabilization
occurs. A consensus of short term guidance suggests scattered
convection will develop along/south of the I-85 corridor Fri
afternoon. Once again, there is considerable uncertainty as to how
much instability will be available Fri afternoon, but deep layer
shear is expected to be very strong, so at least a marginal severe
storm threat could evolve. The front is expected to finally push
southeast of the area Fri evening, allowing cooler and much drier
air to filter into the area. In fact, min temps Sat morning are
expected to end up a category or so below normal.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 315 am EDT Wednesday: A broad upper trough is expected to
progress across the East through the weekend, with dry air/pleasant
surface dewpoints supporting wide diurnal temp ranges...max temps
averaging around normal and min temps a category or so below climo.
By early in the work week, a split flow regime is expected to be in
place across the eastern Conus, with a short wave ridge developing
across the Southeast...downstream of a southern Great Plains upper
low. Global models are at odds regarding the evolution of this
feature, namely its interaction with the northern stream, and
eventual impacts on sensible weather across the Southeast. For now,
there`s enough of a signal to include chance PoPs across much of the
CWA by Mon night/Tue. Temperatures are forecast to be very close to
normal through the period.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Scattered showers and isolated thunderstorms
are noted across the western NC mtns this morning. Showers will
linger through at least mid-morning, impacting mainly KHKY and KAVL.
Although embedded thunder has developed in some of this activity,
confidence remains low on whether thunder will track directly over
KAVL or KHKY. Patchy fog may develop across the NC mountains and
Foothills this morning in association with the SHRA. VFR conditions
continue this morning and will linger through much of the TAF
period, outside of convection this afternoon and evening and again
overnight. Have TEMPOS across the terminals for TSRA this afternoon
and early evening; the exception being KAND where VCTS was
introduced. Confidence on whether activity will push far south
enough to reach KAND today remains low. SCT to BKN Afternoon cumulus
will develop this afternoon thanks to daytime heating. Winds will
generally remain SW through the period, although KAVL`s winds look
to be variable at times. Low-end gusts are possible this afternoon,
mainly for the SC Upstate terminals. However, low-end gusts cannot
be entirely ruled out at KCLT and KAVL. 06Z high-res guidance is
coming into better agreement regarding shower and thunderstorm
chances overnight, showing widespread convection possible. Thus,
introduced PROB30s for TSRA across the terminals towards the end of
the 12Z TAF period.

Outlook: A cold front will approach out of the west on Thursday
before tracking over the terminals Thursday evening into early
Friday morning. This will lead to continued convection, as well as
restrictions. A system lifting out of the south my increase shower
and thunderstorm chances again on Friday, but confidence on this
remains low. Drier conditions can be expected this weekend.

&&

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

&&

$$

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