317
FXUS62 KGSP 180801
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
401 AM EDT Sat May 18 2024

.SYNOPSIS...
A weak low pressure system will track east across North Carlina
today, bringing another rounds of showers and thunderstorms to the
area. The low exits off the Carolina Coast on Sunday, with weak
high presure building in from the north. Somewhat drier conditions
return early next week resulting in only isolated afternoon and
evening showers and storms. A cold front will bring better shower
and thunderstorm chances back into the forecast late in the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
As of 320 AM Sat: Ill-defined pattern in place over the region
featuring very weak sfc high or cold pool, with synoptic warm front
seemingly near I-20. Southwesterly low-level flow continues between
flat ridge centered off the SE coast, and upper low now near the
Mississippi Delta region. Another weak shortwave is moving up
the Ohio River well to our north. A few sfc obs from NE GA and
the Upstate are reporting light rain and this is plausible due
to isentropic lift north of the front, but from a shallow enough
layer it is difficult to discern on radar. Although there is
some MUCAPE on short term analyses, prog soundings depict a deep
inversion. 925-850mb flow has veered to SW via the orientation of
the ridge but also following the shortwave to our north. PoPs have
been trimmed back mainly to the Upstate and I-85 corridor mainly
as a nod to the light stratiform precip; this may not expand much
farther north with the flow veering. That said, 850-700mb lapse
rates are shown to increase with the warm front after daybreak
and sfc dewpoints should also rise a bit; thinning higher cloud
decks should allow diurnal warming and perhaps even a few breaks
in the stratocu nearer the sfc. These developments suggest the
inversion will mix out and/or be overcome by sfc parcels by
late morning, so PoPs ramp up from the south, from then into
early afternoon. The mountain ridges also will destabilize via
the warming and the westerly flow may kick off a few showers
there as soon as late morning. Height falls will occur later
in the afternoon as shortwave arrives from the west. CAMs are
in rather good agreement on more vigorous convection developing
over the Escarpment around 20-21z, possibly an indicator of the
shortwave being key for initiation. 700-500mb lapse rates will
already be fairly good but should be maintained by the wave,
and altogether 1000-1500 J/kg SBCAPE is likely to be in play at
that time. Near-sfc winds will be light, and midlevel flow is
seasonably modest. Hodographs are not especially long and are
unidirectional. Sfc-midlevel delta-theta-e values are not too
remarkable either. Altogether, not seeing much to indicate all that
much of a severe risk. SPC Day 1 features Marginal Risk mainly for
wind threat; if the unidirectional flow and/or the convergence zone
near the trough axis promotes any upscale growth, a few instances
of tree damage could occur. Storms appear to be very efficient
rainfall producers and given consensus in initiation time/area,
PMM QPF is quite healthy with areas of 1-2" storm totals likely.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
As of 230 AM EDT Saturday: The positively tilted upper trough axis
will reach the Carolina Coasts by late Sunday, ushering in strong
height rises atop the forecast area. The associated sfc low pres
system be off the coast by 12z Sunday, with wrap-around moisture on
the north side of the circulation from the Mid-Atlantic SW into the
western Carolinas. Fcst soundings across the NC Piedmont and eastern
Upstate show potential for a stratus deck to gradually scatter out
thru the day, with a decent inversion atop the cloud layer. However
over the mountains and across the Upper Savannah Valley, sbCAPE
may still be realized with little to no CIN. This looks almost like
wedge setup, albeit not from CAD. So have trimmed PoPs back within
the wedge-like air mass, with solid chc PoPs in the mountains, but
only slight chc across most of the I-77 corridor. Any tstms that
do develop will have fairly weak shear and a somewhat suppressive
synoptic environment, so severe threat will be low. With steering
flow roughly parallel to the Blue Ridge out of the NE, training
convection could lead to isolated heavy rainfall. Highs will be
below normal, especially across the I-77 corridor.

Dry air continues to filter in from the N/NE Sunday night thru
Monday, but there may be some redevelopment/expansion of stratocu
overnight, before dissipating during the day Monday. Subsidence
from an upper ridge should cap most deep convection, except for the
higher terrain. There, enough CAPE and mountain-top convergence
could lead to scattered showers an perhaps a few garden-variety
tstms. Temps return to near normal under partly to mostly sunny
skies.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 AM EDT Saturday: A warming trend with generally dry
wx is expected thru Wednesday, as an upper ridge builds over
the Southeast. Guidance continues to back off PoPs, and it
looks like even the high terrain may be largely capped from deep
convection. Will keep some slight chc PoPs in the NC mountains for
now, both Tue and Wed aftns. With instability remaining weak and
a lack of upper support, severe threat should remain low. Highs
will be a category or two above normal, while lows will be 2-3
categories above normal.

A cold front will approach the forecast area from the NW Thursday,
as shortwave energy rides over the eastern CONUS ridge. Thanks
to the influence of the ridge, the front will struggle to reach
the area, and guidance seems to be trending drier for the latter
half of next week. There still should be some uptick in PoPs,
as shortwave energy ejects out of the Rockies and works to break
down the eastern ridge, but the National Blend of Models may be
overdone, given the model trends. Temps will continue to be above
normal with modest humidity.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Abundant low-level moisture beneath inversion
early this morning, but murky forcing regime, makes for tricky
TAFs. Weak warm front south of the terminal area. Some -DZ will
occur prior and accelerate decline to IFR which otherwise is likely
by 09-10z. Approach of shortwave from the west will activate warm
front in mid to late morning and focus light -SHRA development. The
front will also allow parcels to overcome the inversion aloft,
leading to lifting and perhaps partially scattering cigs by late
morning. With already favorable upper level lapse rates this also
will support development of TSRA during the afternoon, handled with
PROB30s. Southerly flow will continue today. Tonight, shortwave
will drift over the area while occluded front advances over the
Eastern Seaboard and weak sfc high builds in from the north. This
will induce a shift to northerly winds across the Piedmont in a
wedgelike scenario, with cigs again deterioriating from north to
south overnight. Elevated convection may be able to re-fire along
the backdoor front and persist in some fashion into Sunday.

Outlook: SHRA/TSRA remain possible Sunday and perhaps even Sunday
night until stronger high pressure settles over the region
Monday. Late night/early morning restrictions in low stratus
and/or fog will remain possible Sunday night; isolated mountaintop
convection still appears possible Monday.

&&

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

&&

$$

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