172
FXUS62 KGSP 040722
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
322 AM EDT Sat May 4 2024

.SYNOPSIS...
A front will stall over the region through the weekend resulting in
periodic showers and thunderstorms. The best chance for widespread
showers and thunderstorms can be expected today into tonight, with
only scattered activity expected on Sunday. A general summertime
pattern sets up early next week, which will keep scattered
thunderstorm chances around each afternoon. Highs will trend well
above normal by Tuesday, remaining well above normal through at
least Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 am EDT Saturday: Isolated/scattered convection is ongoing
within general low level confluence zone/coincident deep moisture
plume within broad area of modest height falls. Convective coverage
is expected to increase steadily through the morning as a short wave
trough steadily approaches our area from the Deep South. Eventually,
categorical coverage of convection is expected from around late
morning through the afternoon. Precipitable water values will remain
very high...generally in the 90th-99th percentile of the daily
climatology for our area. A weak backdoor cold front is expected to
nudge into the CWA from the northeast later this morning, with the
leading edge likely settling in the vicinity of the NC/SC border by
this afternoon. This will provide an additional source of lift for
convective initiation, and could be the focus for locally heavy/
perhaps isolated excessive rainfall this afternoon. Deep S/SW flow
will also pose the potential for training cells within persistent
confluent zone. Heavy rain has been very spotty since Fri afternoon,
so dry antecedent conditions remain the norm across the forecast
area, but higher coverage of showers and storms combined with the
above factors will result in a ramping up of the excessive rainfall
threat today. Extensive cloud cover (max temps actually a little
cooler than climo) and poor mid-level lapse rates will result in
rather weak buoyancy through today, while shear parameters will
remain weak, so the conditional probability of severe storms remains
close to zero.

As the short wave trough finally drifts over the forecast area
tonight, the zone of low level confluence and moisture plume will
begin to shunt east of the area. However, this trend will be rather
slowly evolving, so convective chances will remain elevated through
at least the evening, before slowly winding down overnight. The
threat for locally excessive rainfall threat will persist through at
least the evening. Min temps will again be well above normal.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 230 AM EDT Saturday: A stationary front will be draped from
the Ohio Valley to the Southern Plains Sunday into Monday, remaining
well west and north of the western Carolinas. This will allow for
SW`ly flow at 850 mb keeping an influx of rich gulf moisture in
place across the region. Convective chances look to be much lower on
Sunday compared to Saturday thanks to a weak upper trough gradually
pushing east of the western Carolinas throughout the day. However,
isolated to scattered showers and thunderstorms are still expected
to develop throughout Sunday per the 00Z CAMs. Thus, have likely
PoPs in place across the northern zones, with chance PoPs across the
southern zones. Storm movement will continue to be slow on Sunday
with only about 10-15 kts of shear in place so locally heavy
rainfall will be possible, especially for areas that received rain
on Saturday. The majority of guidance shows SBCAPE values ranging
from ~800-1500 J/kg during peak heating Sunday afternoon. Model
soundings from both the NAM and GFS show an inverted-V and mid-level
dry air in place Sunday afternoon. Thus, an isolated severe storm or
two cannot be entirely ruled out, with the main potential impact
being damaging wind gusts. Shower and thunderstorm chances will show
a slight uptick on Monday as upper shortwaves track overhead the
western Carolinas. Went with categorical PoPs across the western
third of the forecast area on Monday, with likely PoPs elsewhere.
The strong to severe storm potential and locally heavy rainfall
threat return again on Monday thanks to continued weak shear and 800-
1500 J/kg of SBCAPE in place. Highs should end up a few degrees
above climo through the period, with lows around 10-13 degrees above
climo.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 200 AM EDT Saturday: Weak upper ridging builds into the
Carolinas on Tuesday while an upper shortwave tracks overhead the
forecast area. This will act to keep shower and thunderstorm chances
around across most of the forecast area. Have the highest PoPs
(likely) confined to the NC/TN border, with chance PoPs elsewhere
(the exception being the far southern tier of the CWA where there
are no mentionable PoPs). With shear values expected to range from
25-35 kts and SBCAPE values around 1500 J/kg on Tuesday afternoon,
isolated strong to severe storms seem plausible. Tuesday night into
Wednesday weak upper ridging will continue building across
Carolinas. This should generally lead to lower convective chances
compared to Tuesday. Thus, capped PoPs to chance across the western
two-thirds of the forecast area. However, since cloud cover is
currently expected to be lower on Wednesday, global models depict
SBCAPE ranging from 1500-2500 J/kg during peak heating, with shear
still generally ranging from 25-35 kts. Thus, diurnal strong to
severe storms will be possible again on Wednesday. At the sfc, a
cold front will slowly progress eastward out of the central US but
will remain well west of the Carolinas. This will lead to W/SW`ly
850 mb flow in place Tuesday into Wednesday, allowing temps will
climb into the mid to upper 80s east of the mts and across the mtn
valleys each afternoon. A few locations along I-77 in the southern
NC Piedmont may even see highs reach 90 degrees on Wednesday. Thus,
highs should end up around 6-12 degrees above climo. Lows Tuesday
night and Wednesday night should end up around 12-15 degrees above
climo thanks to some lingering cloud cover and SW`ly sfc winds.

The aforementioned cold front will continue trekking eastward
Thursday into Friday leading to better shower and thunderstorm
chances for the western Carolinas as well as the potential for
locally heavy rainfall (especially for areas that received rainfall
earlier in the week). Convection will be in place well ahead of the
front Thursday into Friday so have chance PoPs painted across the
entire area. The only exception is the NC mtns where likely PoPs are
in place for Thursday. The actual FROPA itself should track across
the western Carolinas Friday afternoon into early Friday evening.
The front will allow shear values to increase slightly, ranging from
35-45 kts. Guidance shows SBCAPE values ranging from ~1500-2000 J/kg
on Thursday afternoon so the potential for strong to severe storms
will return once again. Depending on how fast activity pushes south
and east on Friday, the potential for strong to severe storms may
return again Friday afternoon (mainly along and east of I-85). Temps
will climb back into the mid to upper 80s Thursday afternoon across
the mtn valleys and east of the mtns. A few locations along I-77 in
the southern NC Piedmont may once again see highs reach 90 degrees.
Slightly cooler temps can be expected on Friday behind the cold
front, with highs only climbing into the lower to mid 80s east of
the mtns. Lows Thursday night will remain ~12-14 degrees above
climo, becoming ~5 degrees above climo Friday night behind the cold
front.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Very messy aviation forecast this period, as
unusually high moisture levels for the time of year combined with
weak lift and instability will yield periods of convection and cig/
visby restrictions through much of the period. Isolated convection,
including some TSRA is ongoing across the area early this morning,
warranting VCTS at KAND/KGMU. The convective potential as well as
the likelihood of lowering cigs is expected to steadily increase
toward sunrise, warranting tempos for SHRA and IFR/MVFR conditions.
Can`t rule out a TSRA during this time frame, but believe the
potential should be higher later in the morning into the afternoon.
Cigs are forecast to settle to IFR by late morning, with conditions
expected to be slow to improve into the afternoon. The potential for
TSRA warrants a Prob30 for such at all sites from late morning
through much of the afternoon. This is accompanied by categorical
SHRA and MVFR visby. The convective potential is expected to
steadily decrease toward the latter few hours of the period.
However, at least VCSH is warranted Sat evening into the early part
of Sunday. Any modest improvement in cigs/visby during the afternoon
will be reversed by late evening.

Outlook: Enhanced moisture will combine with a weak/stalled front
through early next week, resulting in a period of active/mainly
diurnal convective weather each day. There will also be the
potential for restrictions associated with widespread fog and/or
low clouds each morning.

&&

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

&&

$$

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