-- Discussion containing changed information from previous version are highlighted. --
145
FXUS62 KGSP 221725
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
125 PM EDT Wed May 22 2024

.SYNOPSIS...
Temperatures will remain several degrees above normal each day
through Tuesday of next week as humid subtropical air remains
over the Southeast. Chances for showers and thunderstorms increase
Thursday and will remain higher than normal for this time of year
into next week as well.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1201 PM EDT Wednesday: No major changes as the clock strikes
noon.  PoPs and dewpoints were revamped later in the period to match
the newest hi-res guidance, but the overall trend remains the same.
Cirrus and an expansive cumulus field are advancing across the
area already in a trend that will continue through the evening.

Otherwise...warm mid-level temps owing to a persistent upper ridge
will result in basically a dry day today. Most of the latest CAMs
are dry thru 00z today, except for the HRRR, which develops a few
cells in the Northern NC Mountains. Even if some deep convection
pops, it will likely be just showers, as diurnal activity the
last couple of days had little to no lightning. Otherwise, it
should be a warm day, with highs likely a degree or two warmer
than yesterday`s readings, around 5 degrees above normal.

Tonight, shortwave energy will cross the Mid-South and work to
start flattening the upper ridge across the Southeast. This should
result in more mid and high clouds streaming in overnight. Guidance
shows some convection developing across the TN Valley that will
drift toward the NC mountains. However, the activity is not
expected to arrive before 12z Thu, and should be weakening as
it approaches. Lows will be 7-10 degrees above normal under the
increasing clouds and an uptick in dewpts within a weak return
flow pattern.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 130 AM Wed: Baroclinic zone will be present across the Ozarks
and up the Ohio River Valley on Thursday. This feature will trail the
occluding low in northern Ontario and its western end will be
reactivated by the incipient low in the northern Plains. Jet streak
associated with the northern low and upper trough will promote
development of a weak shortwave over the front. This looks to ride
over our CWA over the course of the day Thursday, suppressing the
upper ridge and allowing decent deep layer lapse rates. The wave may
effectively pull the sfc front across the Appalachians, with a weak
sfc reflection developing over the Mid-Atlantic coast by Friday
morning.

Convective activity may start near the TN border late Thu morning, as
most guidance depicts early day activity in TN via the wave. The
remainder of the area will continue to destabilize diurnally. Shear
will be a bit better than usual for late May.  Furthermore, airmass
modification will bring dewpoints a few degrees warmer. Together these
suggest diurnal showers/storms will be above climo and so we will
advertise chance to likely PoPs for most of the area. Soundings
generally feature dry air around 700 mb and seasonable CAPE values, so
a localized damaging wind threat may develop. Enough shear is present
to think cells will also be semi-organized and capable of at least
marginally severe hail.  Activity may propagate into the Piedmont
following the shortwave or as a result of westerly storm motion.

The Plains low will approach the western Great Lakes on Friday.
Another, better defined shortwave will take a similar track out of the
Mid-South, helping to induce height falls along with the eastward
moving northern system. Once again the shortwave is timed to reach our
area near peak heating, but still perhaps late enough to keep storms
going into Friday evening across the Piedmont. Slightly better lapse
rates suggest higher instability; shear will be similar. Higher PWATs
and more CAPE in the hail growth temperature zone suggest severe
threat may shift more in favor of hail than wind. Although convection
is likely to diminish diurnally and/or as the shortwave moves east of
the area, some models indicate that convection along the cold front of
the aforementioned low will reach the mountains late Friday night if
not Saturday morning, so some PoPs linger all night in our west.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 230 AM Wed: Unsettled weather should continue through the
weekend and early next week; not much change from last night`s
forecast in that regard. It still appears a broad trough will
gradually shift across the CONUS, amplifying as shortwaves move east
of the Rockies and induce cyclogenesis. These features then look to
phase into a deep Eastern trough by early Wednesday. Through the
weekend, the pattern remains fairly ill-defined over our part of the
country, and confidence is thus relatively low. The frequency of
forcing mechanisms, along with expectation we will remain several
degrees above normal for temps each day, suggests PoPs will remain
above climo each day of the medium range.

The shortwave which will be over our CWA on Friday will drift off the
VA/NC coast Saturday morning and appears to spin up a weak sfc low to
our east. Meanwhile, low amplitude upper ridging will remain inland
over our area.  This would suggest suppressed convection for the CWA,
although GFS and GDPS output suggests the ridgetop convergence may
overcome any subsidence, and then there is the matter of the front
which may impinge on the Appalachians Saturday morning as noted in the
short term discussion. For now, at least we can say Saturday probably
will feature the least shower/tstm coverage.

The upper pattern remains progressive and the ridge axis is likely to
be to our east by Sunday afternoon. Concurrently, developing Plains
cyclone will activate a warm front across the lower OH Valley and
reestablish southwest flow over our area, as we come under the
periphery of the surrounding upper trough. The track and evolution of
this system will have implications for our weather Sunday through
Tuesday. There does appear decent model agreement Sunday on sufficient
CAPE and shear to expect a severe risk from any storms that do fire,
mainly of hail/wind. Monday and particularly Tuesday are a bit more in
question as models vary in how fast the upper low evolves and in how
soon the cold front reaches our area.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
At KCLT and elsewhere: Another quiet TAF period for most terminals.
An extensive cu field has begun to develop across most of the
terminal forecast area, and should increase in coverage in the
coming hours.  However, it should largely remain capped due to
robust upper ridging; the hi-res guidance depicts virtually no
convective activity this afternoon, even across the mountains, as
conditions will simply be too unfavorable for deep moist convection.
Any showers that do manage to develop will be weak and short lived,
and confined to the NC mountains.  At KAVL, confidence was too
low for any mention.  Tonight, cirrus will thicken across the
area ahead of an advancing wave.  Isolated shower activity may
make it into the mountains after midnight, but will largely
fizzle out upon arrival.  The increased cloud cover, though,
should somewhat hamper fog/low stratus in the mountain valleys,
such that KAVL is forecast to remain VFR through the overnight.
For KAVL, the first ripples of SHRA/TSRA will arrive during the
final few hours of the TAF period, late Thursday morning, and have
been handled with a PROB30.  Similarly, for KCLT, whose TAF period
extends into Thursday evening, a PROB30 was added for the arrival
of TS in the I-77 corridor at that time.

Outlook: Numerous showers and thunderstorms, along with associated
flight restrictions, will continue Thursday night and Friday as a
cold front crosses the region. A more active pattern may persist
through early next week.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...DEO/Wimberley
NEAR TERM...ARK/MPR
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...MPR