-- Discussion containing changed information from previous version are highlighted. --
792
FXUS62 KGSP 211724
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
124 PM EDT Tue May 21 2024

.SYNOPSIS...
Warm high pressure will persist across the region through the
middle of the week with a few showers and storms possible each
afternoon over the mountains. Rain chances increase Thursday and
remain in the forecast each day through Tuesday.  Several weak waves
of low pressure will move from the lower Mississippi Valley to the
Carolinas.  Temperatures will remain above normal.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1139 AM EDT Tuesday: Forecast is on track. Cu field developing
across the NC Piedmont beneath a faint subsidence inversion, with
the upper ridge axis now located just east of I-77.  Blended some
HRRRTL into the going forecast, but otherwise kept things the same.

Otherwise...strong heating across the mountains will likely overcome
mid-level warm temps to produce scattered showers and possibly a
couple of isolated garden-variety thunderstorms this afternoon.
Steering flow will be weak, so convection will have potential to
dump locally heavy rainfall. But the isolated coverage should limit
the flood potential. Otherwise, light winds will continue across the
area thanks to associated sfc high centered over the area. Highs are
expected to be about a category warmer than yesterday, 4-5 degrees
above normal.

Like last night, convective outflow will be capped by mid-level
temps and likely spread east of the mountains in the evening and
take a while to thin out. But whatever convective activity that does
develop should wane fairly quickly after sunset. Mid-level flow is
expected to tick up slightly out of the NW overnight, which may help
clear out the clouds. So a slightly higher potential for mountain
valley fog is expected. Lows will be a few degrees above normal.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
As of 130 AM Tue: Upper ridge will persist over the Southeast
coast Wednesday. Cold front will push slowly past the Ohio River,
having limited dynamic support with parent low occluding north of
Lake Superior. The front looks to remain west of the Appalachians
thru Wed night. Max temps will trend warmer, both at the sfc and
at around 700 mb. Any uptick in low level instability looks to be
stifled despite good lapse rates developing above 700 mb; we also
lack much of a trigger, so deep convection looks questionable even
over the mountains.

Vort lobe encircling the Canadian low will rotate past the
Great Lakes Wednesday night, and RR quad of associated jet
streak will promote development of a weak, possibly convectively
enhanced shortwave. This may result in some convection in East
TN and remnants thereof could reach the mountains in the very
early morning. The shortwave itself is likely to push across the
Appalachians near peak heating Thursday, flattening the ridge a bit.
700mb temps cool slightly and although this may not totally erode
the inversion it makes convection more likely than Wednesday. Storm
motion will be a bit faster and steering flow westerly, so small
PoPs are warranted in the upper Piedmont in addition to the high
chance to likely values over the mountains. The better flow will
also translate to a bit better deep layer shear, perhaps above 30
kt. However the column may be too moist for the level of severe
threat than we would typically see with convection this time
of year, or for strong cold pool generation, thus not especially
concerned for severe. Locally heavy rain may be of greater concern.
Although increased cloud cover may knock temps back a little in the
higher terrain, the Piedmont will trend a little warmer Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
As of 200 AM Tue: An unsettled medium range period is in store,
initially as a result of an expansive but low-amplitude trough
centered over the southwest CONUS, through which multiple shortwaves
will pass Friday and the weekend. By early next week some of the
waves will phase, amplifying the pattern and leaving a deep trough
over the East. Temps are expected to remain above normal with strong
height anomalies over the western Atlantic and persistent west to
southwest low-level flow. PoPs will run above climo each day and the
frequency of the passing shortwaves makes it difficult to say at
this forecast range that any appreciable dry period will occur.

Friday still looks to bear severe wx risk, with the shortwave
tracking from the lower MS Valley toward the Mid-Atlantic coast.
This will not only offer a convective trigger but also enhance deep
shear and likely better low level moisture advection resulting in
more CAPE in the late afternoon.

Cyclogenesis looks to occur in the Miss and lower Ohio valleys
Sunday night or early Monday, effectively activating a warm front
over our area and resulting in a sharp increase in PWATs and perhaps
posing the greatest threat of heavy rainfall for the period, with
soils possibly being primed in some areas by repeated rainfall over
the previous few afternoons.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
At KCLT and elsewhere: VFR through the period for non-mountain
terminals, as upper ridging suppresses widespread convective
activity.  CAMs depict some isolated convection across the mountains
today, which like yesterday will be mainly showers.  Can`t rule
out some TS, but it`s looking isolated enough to forego mention
in even the KAVL TAF.  This was left a PROB30 as confidence still
isn`t great on initiation, which is lagging behind most of the
CAMs at this time (c. 1715z).  Tonight, some MVFR fog/ceilings are
expected in the major mountain valleys, with impacts only for KAVL.
More of the same tomorrow, with VFR conditions after daybreak and
isolated ridgetop convection in the afternoon..

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 into
the weekend.
-- End Changed Discussion --

&&

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

&&

$$

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