808
FXUS62 KGSP 201057
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
657 AM EDT Sat Jul 20 2024

.SYNOPSIS...
A nearly stationary front will meander across our region through
next week providing a focus for above-normal chances of mainly
afternoon and evening showers and thunderstorms. Temperatures will
be near normal or just a bit cooler than normal.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 315 AM: Low clouds and patchy fog, along with scattered
showers will continue this morning.

The forecast area remains between a trough over the central CONUS
and the Atlantic sub-tropical ridge. This keeps southwesterly flow
aloft over the area through the period. A weak short wave moves
through the flow and across the area today. The right entrance
region of the upper jet is over the area as well. This will keep
weak synoptic forcing in place through the day. This weakens tonight
as the short wave moves out of the are and the jet weakens. At the
surface, a stationary boundary remain in place near or over the area
but the low pressure center along the front moves to our east this
morning. Copious deep moisture also remains in place over the area.
Instability is weak, but shear does increase, especially across the
Piedmont, as the short wave moves through. With these features,
expect scattered to numerous showers across the area through the
day, with scattered thunderstorms, especially this afternoon and
evening. Despite the weak instability, the increased shear could
lead to a few severe storms, especially across the Piedmont, with
damaging winds the main threat. The isolated heavy rainfall and
localized flooding threat also continues. Highs will again be around
5 degrees below normal.

Convection tapers off this evening as the forcing diminishes, but
isolated showers will linger across the mountains overnight. Low
clouds and patchy fog will again develop overnight. Lows will be
near to slightly above normal.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 221 AM Saturday: The synoptic pattern will remain relatively
unchanged Sunday into Monday with a tall upper ridge extending from
the Great Basin through the Rockies and into Alberta/British
Columbia. A large subtropical ridge is also progged to remain
centered over the Atlantic. Between these two ridges, broad upper
troughing will extend from the Great Plains to the Ohio Valley with
convergent southwest flow entrenched across the southeast states. A
plume of deep moisture with above average PWATs reaching from the
Gulf of Mexico across the Appalachians will help to foster numerous
to widespread showers and thunderstorms each afternoon and evening
along with below average temperatures. Forecast soundings depict
very moist profiles with high freezing levels and near moist
adiabatic lapse rates. Tall skinny CAPE profiles and only modest
instability will likely preclude a threat for severe thunderstorms,
although locally gusty winds cannot be ruled out with any water
loaded downdrafts. The primary focus, however, will be for locally
heavy rainfall. Any slow moving/training storms or clusters focused
along cold pools could result in a quick couple inches of rain that
could result in minor flooding of low lying/poor drainage areas.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 236 AM Saturday: The synoptic pattern is forecast to remain
stagnant through much of next week as upper ridging meanders over
the Great Basin and the Atlantic ridge remains locked in place. This
will continue to keep troughing centered just to our west with
periodic shortwaves diving across the Great Plains and Midwest. Deep-
layer southwest flow will thus persist through much of the period
with above normal chances for showers and thunderstorms persisting
each afternoon and evening. Temperatures will also remain below
average with the majority of the area likely to stay below the 90
degree mark, which would be an impressive feat for late July. As
with any summertime convection, a few stronger storms cannot be
ruled out with wet microbursts. However, poor thermodynamic profiles
within a very moist airmass will generally preclude a greater severe
threat.

Locally heavy rainfall may eventually become an issue, especially
after several days of convection. The main period of note that would
be worth keeping an eye on would be mid to late week. The 00z suite
of global model guidance is in fairly good agreement on a sharp
shortwave trough swinging across the Great Lakes on Wednesday and
across the Ohio Valley Thursday into Friday. This will in turn
strengthen the height gradient between the trough and upper ridge
over the Atlantic and thus increase flow through the column. IVT
values ramp up in turn with a plume of deep moisture advecting
across the area with PWATs surging to 1.75-2.25" and dewpoints in
the low to mid 70s. While the best synoptic forcing will remain
displaced north of the area, any mesoscale features that could focus
convection could be sufficient to realize a greater threat for flash
flooding. A pattern change may finally be on the horizon by next
weekend as a potent trough moving into the Pacific Northwest helps
to suppress and breakdown the Great Basin ridge. Troughing over the
Ohio Valley also lifts northeast and allows subtropical ridging to
gradually build back in across the southeast states. If realized,
this would allow for a return to more typical summer conditions with
isolated to scattered pulse convection and warmer temperatures more
common to late July.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Conditions vary from VFR to LIFR across the
area early this morning along with scattered showers. Expect MVFR
cigs through the morning with TEMPO IFR until 14Z. Only minor vsby
restrictions in the scattered showers. Shower coverage increases
through the morning with scattered storms by afternoon when cigs
finally rise to low VFR. Convection should taper off during the
evening with only a small chance of lingering SHRA overnight. Expect
cigs to drop back to MVFR then IFR overnight, with vsby restrictions
possible. Light wind early this morning becomes S to SW through the
morning into the afternoon. Light wind overnight.

Outlook: Expect scattered to numerous showers and thunderstorms each
afternoon/evening through the  middle of next week. Morning fog/low
stratus will be possible each day, especially in the mountain
valleys and across areas that received heavy rainfall the day prior.

&&

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

&&

$$

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