078
FXUS62 KGSP 170621
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
221 AM EDT Fri May 17 2024

.SYNOPSIS...
A warm front and weak low pressure system will bring frequent
chances for showers and thunderstorms today through the
weekend. Somewhat drier conditions return early next week resulting
in only isolated afternoon and evening showers and storms Monday
and Tuesday.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1230 AM Fri: Broad area of upper divergence will shift east
out of the lower Mississippi Valley this morning, associated with
jet streak and shortwave south of the Great Lakes. Meanwhile,
a convective complex and associated MCV will move along the Gulf
Coast.  Abundant cirrus are creeping in our direction and should
follow the upper ridge axis. Not great confidence as to how well
these cirrus will inhibit radiation, particularly as they may
arrive too late to completely preclude fog development at least
near the major mountain valley and Piedmont rivers.

Vort maxes from the Gulf Coast convection look to advect northeast
to our vicinity later this morning, along with cooler air at 700
mb. Prog soundings show MUCAPE ticking upward to match, and CAMs
variously develop a wave of showers or storms from around midday
and early afternoon, although not in particularly good agreement
as to where this occurs. Light and increasingly moist low level
southerly flow will develop and could produce some light precip
near the SW NC mountains or Escarpment as well. Thus PoPs look to
increase a bit faster than we had previously advertised. Meanwhile,
warm front will shift northward thru the Deep South, associated
with developing sfc low to our southwest. As this front nears,
PoPs generally increase further through the afternoon, with likely
to categorical chances for the whole area this evening. The clouds
and showers will keep temps a few degrees below normal in the west,
but perhaps a degree or two above normal in the east there these
are less of a factor.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
As of 1245 PM EDT Thursday: Short Term Key Messages

1) Widespread Showers and thunderstorms are expected off and on
throughout the weekend.

2) Areas of heavy rainfall may lead to isolated flooding issues
this weekend.

3) Isolated strong to severe storms are possible through the weekend
but confidence remains low at this time.

Showers and thunderstorms will be ongoing across the western
Carolinas and northeast Georgia Friday evening into Friday night as
a low pressure system approaches out of the west. There may be a
lull in activity the first half of Saturday before another round of
showers and thunderstorms returns Saturday afternoon into Saturday
night as the low pressure system tracks into the forecast area. Have
likely to categorical PoPs (70% to 80%) in place during this
timeframe as global models and high-res models agree that there will
be multiple rounds of convection. All global models continue to
agree that the low will stall over the area on Sunday, thus
monotoned likely PoPs (60 to 70%) across the forecast area. With
PWATs expected to climb near or above 90th percentile, locally heavy
rainfall will be a concern, especially with wet antecedent
conditions already in place. The WPC Day 3 Excessive Rainfall
Outlook has a Marginal risk across the Carolinas as isolated flash
flooding will be possible, especially for areas that saw heavy
rainfall the day prior. The flooding threat will steadily increase
throughout the weekend as rainfall totals pile up. Currently 0.50-
1.50 inches of rain is expected to fall Friday night through Sunday,
with the highest amounts expected to fall across the western and
southern zones. Isolated strong to severe storms continue to look
possible thoughout the weekend but confidence on this is low as
thick cloud cover may limit destabilization. GEFS plumes show less
than 1,000 J/kg of SBCAPE through the weekend, with ~35-45 kts of
deep shear on Saturday and only ~15-20 kts of deep shear on Sunday.
Thus, Saturday still looks to have the better severe potential, and
this matches up with the Day 3 SPC Severe Weather Outlook which has
a Marginal risk in place east of the mountains. The main potential
hazards with any severe storms that develop are damaging wind gusts
and large hail. High temperatures have trended down slightly for the
weekend and are now expected to be a few to several degrees below
climo. Low temperatures will remain several degrees above climo
thanks to both cloud cover and precip.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 100 PM EDT Thursday: The low pressure system will linger over
the eastern Carolinas through Monday before gradually pushing
offshore Monday evening into Monday night. Thus, maintained chance
PoPs (15% to 30%) across much of the forecast area Sunday night into
Monday. Upper ridging and sfc high pressure will build into the
southeast Monday night into Tuesday night, leading to drier
conditions, while the low pressure system lingers just off the
Southeast Coast. A cold front will approach out of the west on
Wednesday before tracking across the forecast area Wednesday night
into early Thursday morning. This will allow shower and thunderstorm
chances to return towards the end of the forecast period. High
temperatures will remain a few to several degrees below climo on
Monday, becoming near climo to a few degrees above climo on Tuesday.
Highs are then expected to become a few to several degrees above
climo Wednesday into Thursday. Low temperatures will generally
remain a few to several degrees above climo through the period, with
the exception Monday night as lows east of the mtns will be near or
just below climo.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Relatively low confidence TAFs with multiple
sources of weak forcing and differing signals among guidance
members. Cirrus will increase early this morning but deck does not
look likely to fill in quickly enough to keep radiation fog at bay
in the river valleys. TEMPO MVFR vsby and SCT002 for KAVL, but the
other sites chance of fog small enough to omit. Lapse rates will
improve after daybreak with arrival of weak shortwave preceding
sfc/upper low in the southern Plains. This is expected to spawn
scattered SHRA/TSRA in the late morning to early afternoon which
has prompted TEMPO impacts earlier in the day than usual. Such
convective development is likely to result in spotty low VFR cigs,
aside from the higher cloud decks thickening. This activity may
weaken or become more isolated before more widespread precip and
perhaps embedded TSRA arrive with warm front tonight. Warm front
appears likely to produce MVFR and then IFR cigs tonight, with
areas of fog developing after precip. Generally southerly winds
this period.

Outlook: Periods of convection, which could be widespread at
times, are expected through the weekend. Late night/early morning
restrictions in low stratus and/or fog will also be possible. Drier
weather is expected to return early in the next work week.

&&

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

&&

$$

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