114
FXUS62 KGSP 040604
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
204 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 TODAY/...
As of 150 am EDT Saturday: An upper ridge axis persists near the SE
Coast. Isolated-to-scattered convection persists this morning
upstream of the ridge, generally ahead of an approaching shortwave
trough. Little change in the pattern or vertical profiles will occur
overnight, such that a few hundred joules of MUCAPE will linger in
southerly flow regime. Thus scattered showers and a few t-storms are
expected to continue, mainly across western areas over the next 1-3
hours. However, signals in convection-allowing guidance remain
relatively strong that the main focus for scattered/perhaps numerous
convective coverage will shift to the eastern third or so of the CWA
toward sunrise. The main threats from any storms/deeper showers are
expected to be locally heavy rainfall and occl c-g lightning.
Outflow from earlier storms left behind a nearly saturated PBL in
some spots, and some locally dense fog can`t be ruled out in such
areas this morning. Min temps will be well above normal.

Convective coverage should increase throughout the daylight hours as
forcing from the approaching trough increases. Instability and shear
will remain on the weak side, while forecast profiles show an even
more saturated atmosphere...with PWATs in the 90th-99th percentile
for this date. This suggests even less chance of strong to severe
storms, with an uptick in the heavy rain potential. That said, the
overall flood risk remains low given the dry antecedent conditions.
Highs will be near normal due to clouds and precipitation.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
As of 240 PM EDT Friday: The rest of the weekend looks active right
into the first part of next week. A baggy upper trof overhead
on Saturday night slowly lifts northeast with a short wave
passage, and this bit of lingering forcing will be able to keep
shower/thunderstorm activity on a slow wane into the early morning
hours. Guidance suggests that it will never die off entirely,
so the fcst retains some fairly high precip probs. That sets the
stage for Sunday. Models show less forcing, but an uptick in the
available buoyancy in the afternoon. That should make for a more
thermodynamically-driven day, with better than climo coverage
of showers and storms. Forecast soundings off the NAM show some
pulse-severe wind damage potential with mid-level dry air and
a shallow inverted-V, so it would not come as a surprise if it
was a busier day than Saturday. A stronger short wave lifting
northeast over the TN/OH Valley regions on Monday will continue to
support diurnally-enhanced convection, so we continue with above
climo precip probs. Temps look to be on the order of five degrees
above normal.

&&

.LONG TERM /MONDAY NIGHT 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 /06Z 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/RWH/Wimberley
SHORT TERM...PM
LONG TERM...AR
AVIATION...JDL