-- Discussion containing changed information from previous version are highlighted. --
339
FXUS62 KGSP 210731
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
331 AM EDT Tue May 21 2024

.SYNOPSIS...
-- Changed Discussion --
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, as multiple weak
waves of low pressure move out of the south central states and
pass through our area. Temperatures will remain above normal.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 300 AM EDT Tuesday: Similar conditions to yesterday
look on tap for today, as a positively tilted upper ridge axis
remains atop the forecast area. The ridge will work to keep the
atmosphere fairly suppressed. However, 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. 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, a fair wx cu field
can be expected across the Piedmont with light winds 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.
-- End Changed Discussion --

&&

.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 MONDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: High-based stratocu continues to expand
across the NC mountains and south into the Foothills and much of the
Upstate. Guidance seems to be too quick to dissipate the clouds,
and so will keep more clouds in the TAFs thru daybreak. This
results in much less fog potential than previously thought. Have
opted to remove fog mention with the 06z TAFs, as a result. AT
KCLT, despite clear skies, fog is not expected there, as air mass
looks too dry. Otherwise, today looks similar to yesterday. Another
round of VFR cumulus should develop by midday and persist thru the
afternoon and evening. Isolated to widely scattered convection is
expected across the mountains again today. With decent confidence
of SHRA never KAVL, will add a PROB30 for mid to late aftn. The
rest of the TAF sites are expected to be dry. Wind will be light
thru the period, favoring a S/SE direction, and not expected to
be above 5 kt this aftn.

Outlook: High pressure remains over the terminals through Wednesday
but isolated mountaintop convection is expected in the aftn.
More numerous showers and thunderstorms, along with restrictions,
may return with a cold front late Thursday into Friday. A more
active pattern may persist into the weekend.

&&

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

&&

$$

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