938
FXUS62 KGSP 150728
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
328 AM EDT Wed May 15 2024

.SYNOPSIS...
Low pressure brings showers and scattered thunderstorms to our
region today. Brief high pressure brings a mainly dry day on
Thursday. Showers and scattered thunderstorms return Friday and
continue into the weekend. Isolated diurnal convection expected
early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 238 AM EDT Wednesday: A ragtag band of showers leftover from
upstream convective activity over TN is still making tracks across
the NC mountains tonight.  It seems to have largely outrun forcing
associated with a deep upper low which extends from southeastern
IL into the Ohio Valley.  Widespread fog has broken out and will
gradually thicken in the coming hours.  For now, no dense fog
products will be issued, but at least an SPS seems more likely
than not before daybreak.

Over the course of tonight and today, the upper low will open
into a trough as it translates east across the upper Ohio Valley,
its base pivoting across the western Carolinas this afternoon.
As it does so, a lobe of 500mb vorticity will drift over the CWA.
Lapse rates will steepen a little in response to the upper pattern,
roughly coincident with the peak in diurnal instability.  The latest
round of HREF guidance supports a 90% chance of at least 1500
J/kg sbCAPE over much of the forecast area, but also indicates a
diminishing trend in deep layer shear, from 30kts or more early
in the afternoon to well below 30kts by mid- to late afternoon as
the base of the trough shifts east and the upper height gradient
loosens.  All in all, the CAMs depict greater coverage of convection
today compared to Tuesday, with initiation over the mountains and
cells shifting east with the trough.  Severe weather cannot be
ruled out with this setup.  The CAMs hint at a semi-organized line
developing over the NC Piedmont, which would support a wind threat
despite limited DCAPE, and forecast lapse rates are steep enough to
support a secondary risk of large hail as well, primarily over the
I-77 corridor.  An additional threat of localized heavy rainfall is
in order, especially given how primed many areas across the eastern
Piedmont are after Tuesday`s rainfall.  Storm motion generally
looks fast enough to preclude a more widespread risk of flooding.
Highs today will climb into upper 70s outside the mountains.

By late evening and into the overnight, a trailing cold front
will arrive, scouring out moisture and instability.  Skies will
gradually clear (notwithstanding some lingering NW flow showers and
associated cloud cover across the mountains) and winds will turn NW.
Models don`t depict particularly robust postfrontal CAA, and so
it`s not expected to become particularly breezy.  Temperatures will
drop into the low 60s or even upper 50s in some locations.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 255 AM EDT Wednesday: A short wave ridge moves in on Thursday
along with a drier air mass. Still, there may be just enough
lingering moisture for some diurnal showers along over the northern
NC mountains and the I-40 corridor. Dry conditions expected
elsewhere. Highs Thursday and lows Thursday night will be a few
degrees above normal. Shower and thunderstorm chances ramp back up
Friday and Friday night as an upper low and its associated surface
low move toward the area. There is some disagreement on the speed
and strength of this system, but there is good agreement on the
sensible weather. PoP increases into the likely to categorical
range. Instability and shear are relatively weak Friday but shear
does increase during the evening. Therefore, severe storms are
possible but uncertain. Isolated heavy rainfall is more likely given
the high PW values and strong forcing. Highs Friday will be near
normal with lows 5 to 10 degrees above normal Friday night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 315 AM EDT Wednesday: Shower and thunderstorm chances remain
high Saturday as the upper and surface systems move into the area.
Instability may be higher due to better lapse rates, but there is
still uncertainty on severe chances. High PW values and strong
forcing continue, so isolated heavy rainfall remains possible. The
GFS and Canadian show a slower movement with this system, and keep
scattered convection over the area Sunday. The ECMWF has been faster
but is showing a slowing trend. Will keep scattered diurnal
convection in place. Isolated to scattered diurnal convection
possible Monday and Tuesday with lingering low level moisture and
weak forcing. Highs near to slightly below normal Saturday rise to
above normal by the end of the period. Lows bounce around normal
through the period.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Dreary conditions again tonight as an upper
low pushes out of IL and into the Ohio Valley.  Periodic light rain
will be possible over the coming hours, but coverage is already
low and should continue to get more sparse as time wears on.
Ceilings are expected to lower to IFR or LIFR leading up to
daybreak; already, some sporadic reports of <1SM vis have come from
some TAF sites as well as surrounding METARs.  Expect visibility to
crash before daybreak as well.  Conditions should improve faster
today than they did on Tuesday, becoming VFR sometime around
late morning/early afternoon.  More widespread convection is
then expected as a lobe of upper energy arrives in the afternoon,
coinciding with peak afternoon instability.  All TAFs now include
PROB30s for TSRA and/or VCTS to handle this.  Winds will generally
be out of the S (SE at KAVL, SW everywhere elses) all day after
a period of light and variable winds overnight.  Once convection
lets up Wednesday night, winds will turn around to WNW in the final
hours of the TAF period as a drying cold front slides into the area.

Outlook: Drying will continue Thursday, before convection and
associated flight restrictions return ahead of a cold front over
the weekend.

&&

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

&&

$$

SYNOPSIS...RWH
NEAR TERM...MPR
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...MPR