127
FXUS62 KGSP 221400
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1000 AM 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/...
As of 946 AM EDT Wednesday: No major changes this morning.
Quiet across the area with upper ridging extending from the Gulf
Coast up into the Carolinas.  Still appears that this is keeping
lapse rates subdued and surface conditions dry and clear.

Otherwise, a plume of upper-level moisture will cross the area
today, as it rides over a ridge axis that remains aligned along
the East Coast. While the associated cirrus should thin out at
times today, it may be just enough to take the edge off peak
daytime heating. This combined with warm mid-level temps from the
persistent ridging may 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.

&&

.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 /14Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: A little bit of fog and stratus has formed
near KAVL, but should clear out within the first hour of the 12z
TAF. Otherwise, VFR conditions are expected thru the period. With
high pressure holding on today, guidance shows only isolated
showers developing along some of the mountain ridges. Coverage
is expected to be too sparse to mention at KAVL. The Piedmont is
expected to be dry with just fair wx cu forming in the aftn. Winds
will be light, picking up to 5-10 kt this aftn out of the S/SW,
then becoming light again this evening.

Outlook: More numerous showers and thunderstorms, along with
associated flight restrictions, will return with a cold front late
Thursday into Friday. A more active pattern may persist through
early next week.

&&

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

&&

$$

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