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817
FXUS62 KGSP 191911
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
311 PM EDT Mon May 19 2025

.SYNOPSIS...
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A stationary front remains over our region through Tuesday then
drifts north as a warm front before a cold front approaches from the
west by Wednesday. This keeps chances of showers and storms across
our region until the cold front crosses.  Cooler and drier
conditions return in the wake of the front by Thursday and into the
first half of the holiday weekend.
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&&

.NEAR TERM /THROUGH TUESDAY/...
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Key Messages:

1) Isolated/scattered showers and thunderstorms this and Tue
afternoon.

2) A couple of severe thunderstorms possible across ~the SW 1/3 of
the CWA this afternoon.

2) Temps remain above normal.

As of 145 pm EDT Monday: NW mid-level flow will continue through
tonight...downstream of a steadily weakening ridge that is forecast
to move over the southern Appalachians by the end of the period.
Extensive high clouds associated with a series of decaying
convective complexes continues over the area this afternoon, but
with some thinning occurring from the southwest. A rather
diffuse/quasi-stationary surface boundary remains draped across the
area...separating lower70s/upper 60s dewpoints across the SW portion
of our area from lower-60s dewpoints across the north. The
combination of improving insolation and elevated dewpoints has
resulted in an axis of 1500-2000 J/kg of sbCAPE from the upper
Savannah River Valley into far southwest NC. A thunderstorm across
extreme SE Tennessee is expected to ride along this instability
gradient into our GA zones and western portions of the Upstate over
the next 1-3 hours. Additional scattered convection is also likely
to develop in these areas as the air mass destabilizes a bit more
and interacts with the boundary, terrain features, and cold pools
from ongoing convection. Convective potential will be limited be
drier air across the northeast quadrant of the CWA, but token 20%
chances are carried there compared to 30-50% across the remainder of
the area. Deep layer shear will remain adequate for isolated
organized convective structures and attendant damaging downburst and
large hail threats across the southwest part of the area.

Convection will diminish this evening, with only token slight chance
PoPs advertised here and there through the overnight. Min temps will
remain 5-10 degrees above climo.

The boundary will remain over the forecast area early Tuesday, but
is forecast to begin lifting north as a warm front by afternoon in
response to large scale height falls to our northwest. Forecast
soundings depict moderate levels of sbCAPE...especially with
moisture pooling in the vicinity of the boundary...but also feature
some degree of CIN to overcome. As a result, CAMs are somewhat
reluctant to initiate convection...at least until evening.
Nevertheless, the surface boundary and terrain effects should
provide enough lift to allow for isolated/widely scattered
convection by late afternoon, and general 20-30 PoPs are advertised
across much of the CWA. Shear parameters are forecast to be a bit
weaker through the daylight hours, but one or two severe storms will
again be possible.
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&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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As of 310 PM EDT Monday...

Key Messages:

1) Strong to severe storms are possible Tuesday evening into
Tuesday night

2) Drier conditions gradually return on Wednesday with gusty
winds developing

3) Temperatures cool off starting Thursday

The main concern, possibly for the entire forecast period, revolves
around the severe weather threat arriving from the west Tuesday
after dark. Details are still somewhat sketchy more than 24 hours
into the future, but there`s a decent chance that some sort of
organized convection will reach the mtns in the late evening,
perhaps in the form of a linear MCS posing the possibility of wind
damage at least over the mountains. As per usual, the MCS would be
running out of fuel as it comes across the Great Valley of TN after
sunset, with the sfc-based CAPE dropping from about 1500 J/kg to
about 500 J/kg once it moves into the mountains. However, shear
will be sufficient to keep this activity potentially severe into
the mtns, with effective bulk shear on the order of 45 to 50 kt and
enough low level shear to keep the tornado threat mentionable. Note
this will be enough shear and buoyancy to warrant the Slight
Risk extending over the mtns and the expectation right now is for
warnable storms into the mountains late Tuesday evening/night. For
the most part, the line of storms would break up coming over the
mtns as the time of day will be unfavorable. Only one or two of the
CAMs have much in the way of anything east of the mtns. The short
wave driving this forth will move across the fcst area by daybreak,
thereafter only a token small chance of showers will remain on the
TN border thru the day, while areas east of the mtns remain dry
for the most part. Temps will remain above normal with the actual
cold front, associated with an upper low traversing the Midwest/OH
Valley, not crossing the region until late in the day or overnight
Wednesday night. By that time, a cyclonic flow aloft around the
upper low to our north will overtake the region, with weak sfc
high pressure building in thru Thursday. This air mass should be
drier than what we`ve had lately, and temps drop back to normal.
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&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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As of 130 PM EDT Monday...

Key Messages:

1) A drier air mass with below normal temperatures lingers into
Memorial Day Weekend

2) Winds remain gusty through Friday evening

3) Shower and thunderstorm chances return on Sunday

An atmospheric blocking pattern to our northeast will keep the
cyclonic flow aloft in place through the end of the week as another
upper low rotates down around the Great Lakes region on Friday to
the Mid-Atlantic coast on Saturday. For the most part, a cool and
drier NW flow will ensue for the first few days, perhaps with some
light rainshower potential on the TN border Thursday night and
Friday as a weak reinforcing sfc trof moves through, but chances
are barely worth mentioning. Temps will be on the order of five to
seven degrees below normal into the weekend before a warming trend
begins as a flat upper ridge starts building in from the west on
Sunday behind the departing upper low. Forecast uncertainty grows
considerably at that point, as we are once again exposed to an MCS
track Sunday into Monday with energy topping the flat upper ridge
axis to our west both days. Details are highly sketchy at this
stage, of course, so don`t give up on Memorial Day weather just yet,
but there is decent support from a consensus of the model solutions
for at least scattered storms. The forecast will feature a 30-40
prob for showers and thunderstorms with near normal temps on Monday.
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&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR conditions across all terminals for the
entire TAF period. Winds start out calm and should lightly pick up
early this morning. Winds should pick up out of the WSW/SW by early
afternoon. There is a slight chance for TSRA at most terminals this
afternoon, but confidence remains low. Will keep a PROB30 as the
chances have not increased enough to warrant anything higher. Timing
if storms get going is between 18z-23z, with the earlier time for
KAVL. Afterwards, winds turn more westerly and KHKY/KCLT turn more
NE at the end of the period, but remain light. SCT cirrus and some
mid-level cu today but all cigs remain VFR.

Outlook: Showers and thunderstorms activity possible each afternoon
through Thursday. Early morning fog/low stratus possible in the
mountain valleys and locations, especially where rain falls the
previous afternoon/evening.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...JDL
SHORT TERM...PM
LONG TERM...PM
AVIATION...JDL