537
FXUS62 KGSP 061048
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
648 AM EDT Mon May 6 2024

.SYNOPSIS...
The weather pattern will have a summerlike look to it through
Wednesday, keeping scattered thunderstorm chances around each
afternoon. A strong cold front will approach out of the west on
Thursday before tracking across the western Carolinas on Friday,
leading to better coverage of thunderstorms towards the end of the
workweek. Highs will remain above normal through most of the
workweek but will climb well above normal Tuesday into Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 am EDT Monday: Latest water vapor imagery and surface
analysis indicates occluding/stacked cyclone centered near St Louis,
with remnant warm conveyor belt/deep moist plume extending from the
central Gulf Coast through the TN Valley and southern Appalachians.
As this plume continues to advect over our CWA through the morning,
coverage of showers will continue to increase from the SW,
especially impacting the southern half of our area, where 40-60 PoPs
are featured through the morning. Meanwhile, areas just to our west
will become dry-slotted during the late morning and afternoon,
allowing a combination of strong insolation and a plume of
relatively steep mid-level lapse rates to result in strong
destabilization...just as height falls are overspreading the region.
Convection will fire in this regime...with some terrain induced
initiation also likely across the southern Appalachians...by early
afternoon, and is expected to overspread northeast Georgia and the
western Carolinas through the afternoon into the evening. Likely
PoPs appear warranted across much of the CWA during this time frame.

Convection could arrive in western areas with a bit of robustness
this afternoon. However, the environment is expected to be less
hospitable to convection over our area owing to morning
clouds/precip and relatively modest instability. While shear
parameters are improved over recent days...deep layer shear of 25-30
kts (as opposed to < 20 kts the past couple of days)...this won`t be
enough to allow for anything more than a very isolated severe storm
threat...with the upper Savannah River Valley being the most likely
area to see a stray downburst and/or large hail event. As flow turns
NW aloft this evening, convection-allowing guidance suggests
additional waves of scattered showers and storms could drop into
western NC from east TN through at least the evening hours, so PoPs
remain elevated in the 40-60% range near the TN/NC border during
that time, while steadily diminishing elsewhere. Max temps will be
slightly above normal, while tonight`s lows will again be around 10
degrees above climo.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 230 AM EDT Monday: Weak upper ridging will build across the
Southeast on Tuesday before flattening out on Wednesday. This along
with W/SW`ly 850 mb flow will lead to well above normal temps
through the short term, with the mid to upper 80s expected east of
the mountains and the mid 80s across the mountain valleys. Highs
should end up ~8-12 above climo, with lows ~13-15 degrees above
climo. Diurnal convection can be expected each afternoon and evening
so have chance to likely PoPs in place each day. 0-6 km bulk shear
should range from 25-35 kts each day, with SBCAPE values from 1500-
2000 J/kg on Tuesday afternoon and 2000-2500 J/kg on Wednesday
afternoon. NAM and NAMnest model forecast soundings show DCAPE
values from ~900-1200 J/kg each afternoon as well. Thus, strong to
severe storms will be possible each day, especially on Wednesday
thanks to higher SBCAPE values. The SPC Day 2 Severe Weather Outlook
(Tuesday) shows a Marginal Risk for isolated severe storms across
western North Carolina which makes sense considering CAMs are mainly
producing convection across the NC zones on Tuesday. The SPC Day 3
Severe Weather Outlook (Wednesday) shows a Slight Risk for scattered
severe storms across most of the mountain zones with a Marginal Risk
for isolated severe storms across the rest of the forecast area.
This looks plausible as coverage of convection should be higher on
Wednesday. Damaging wind gusts will be the primary hazard with any
severe storms that develop. Some concern will still exist for
locally heavy rainfall through the short term, especially for areas
that received heavy rain in the days prior.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 300 AM EDT Monday: An upper trough will approach out of the
west on Thursday before swinging across the Carolinas on Friday. At
the sfc, a strong cold front will track east over the TN Valley on
Thursday before pushing across northeast Georgia and the western
Carolinas Thursday night into Friday morning. Convection is expected
to develop well ahead of the main FROPA on Thursday so have likely
to categorical PoPs in place. The global models have sped up the
timing of the cold front compared to the last few runs, with some
solutions depicting much more stable air and drier conditions for
Friday. The exception is the 00Z GFS which has convection lingering
through Friday afternoon. Thus, lowered PoPs to chance on Friday but
PoPs may need to be lowered further in future updates if this faster
trend holds. Thursday continues to look like one of the more active
day of the week in regards to the severe weather potential. The
approaching cold front will allow 0-6 km bulk shear values to climb
to 35-45 kts, with up to 2,000 J/kg of SBCAPE in place Thursday
afternoon. Forecast soundings from the GFS depict ~1,000 J/kg of
DCAPE as well on Thursday afternoon, so damaging winds will be the
main concern with severe storms. The locally heavy rainfall threat
will return once again on Thursday thanks to 90th percentile (or
greater) PWATs expected ahead of the FROPA. However, faster storm
motion help offset this potential somewhat. The only kink in the
severe potential at this time is that widespread cloud cover is
expected to be in place on Thursday, which may limit destabilization
a bit. However, with a 40 kt 850 mb jet tracking over the western
Carolinas on Thursday (per the GFS), upper support should make up
for the lack of insolation. Temps will remain above climo Thursday
into Thursday night, but will be slightly cooler compared to
Wednesday/Wednesday night thanks to convection and cloud cover.

Global models show dry high pressure building into the region out of
the west behind the departing front Friday night into Saturday. The
00Z ECMWF and Canadian show another system impacting the forecast
area on Sunday, but the 00Z GFS does not have this system impacting
the area until after the forecast period. Thus, confidence on PoPs
will be low towards the end of the forecast period. Cooler temps are
expected to return this weekend, trending a few degrees below climo
for both highs and lows.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Showers are moving across the Terminal
Forecast Area this morning, while IFR cigs have developed at KCLT
and KAVL. All TAFs feature a tempo for -SHRA and either MVFR or IFR
cigs until late morning. Visby restrictions in the 2-4SM range are
possible as well. Flt conditions should improve through the late
morning, with VFR conditions expected by early afternoon. Most sites
will likely see a lull in convective activity of a few hours this
afternoon. Convection is then expected to initiate west of our
area...and across the mountains during mid/late afternoon and move
across our area during the late afternoon and especially the
evening. Due to the late timing, afternoon tempos for TSRA are
limited to KAVL, with Prob30s advertised at all other sites from
22/23Z through the evening hours. Additional round(s) of convection
could move into the area from the northwest into the evening and
early part of the overnight hours. This activity will primarily
impact KAVL if it materializes. Visby and/or cig restrictions return
to the area toward daybreak Tue, with MVFR conditions advertised at
most sites for now.

Outlook: Enhanced moisture will combine with a weak/stalled
front through the middle of the week, resulting in a period of
active/mainly diurnal convective weather each day. There will also
be the potential for restrictions associated with widespread fog
and/or low clouds each morning. A cold front moves in for later
in the work week with continued chances of diurnal convection.

&&

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

&&

$$

SYNOPSIS...AR
NEAR TERM...JDL
SHORT TERM...AR
LONG TERM...AR
AVIATION...JDL