762
FXUS62 KGSP 140004
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
804 PM EDT Mon May 13 2024

.SYNOPSIS...
Low pressure brings rain and some thunder to our region on Tuesday
and Wednesday. Brief high pressure brings one dry day on Thursday.
Rain and some thunder returns on Friday and remains through the
weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 630 PM: Forecast is in good shape. Tweaks PoPs based on latest
radar trends. Expect scattered light showers or sprinkles across the
area thru the evening with slowly falling temps and cloudy skies.

Otherwise...sfc high pressure now situated off the NC/VA coast. From
satellite imagery, moisture plume present over the region, into
sfc/upper cyclone now centered near Kansas City. Associated
isentropic upglide is developing over the sfc high. Deep dry
layer had been present at the surface but is beginning to be
overcome by very light precip developing in the upglide, with a
few obs sites in NE GA and the western Upstate having reported
light precip. Warming seems to have been halted or substantially
slowed by the evaporating precip, lending more confidence to the
previous expectation that in-situ CAD eventually would develop via
the present setup. All this said, the CAD does not look especially
strong, and development of more appreciable precip still looks to
take some time. CAMs have trended to show more shallow convection
developing in mainly the I-77 corridor late this aftn and early
evening, but the best case for widespread precip development will be
when the sfc warm front lifts north tonight and rides over the sfc
high. As such we still delay likely PoPs in the SW CWA until after
sunset, spreading NE thru the evening and reaching the NE CWA after
midnight. Temps still may warm a few degrees this aftn in the NC
Piedmont but in most areas temps will be somewhat steady thru early
evening and then slowly decline overnight. The Piedmont at large
will see lows in the lower 60s tonight with mountains/foothills
seeing mid to upper 50s. WPC QPF has trended down and hydro issues
are unlikely. Elevated convection and perhaps some rumbles of
thunder become possible late tonight across GA and the Upstate,
with inversion strengthening via WAA and viable MUCAPE forming at
that level. Can`t rule out highly isolated thunder elsewhere.

WAA/upglide over the wedging airmass will continue through Tue
morning, although weakening as LLJ diminishes and/or with true warm
front lifting north. Cloud layer looks to remain fairly thick;
we won`t have any real eroding mechanism until weak CAA develops
very late in the day, although diffluent flow in the mid to upper
levels could have some effect. The usually wedge-aware NAM had
kept SBCAPE at bay over most of the area on earlier runs, but
now shows some developing after 18z. Based on the limited QPF
response of synoptic models and disagreement among CAMs, felt
best plan was to allow PoPs to taper somewhat in the morning and
advertise mostly only likely PoPs in the afternoon. Very strong
flow will be present above 700mb and deep layer shear of 40+ kt
is likely. Furthermore, the approach of the upper low will induce
low-level backing which will enhance SRH. SPC inclusion of most
of our area in a Marginal Risk looks reasonable, with severe hail
possible along with secondary threats of wind and perhaps even a
tornado, the latter more likely if the wedge boundary does actually
lift into the CWA in late afternoon or early evening.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 150 PM EDT Monday: The first half of the short term will be
convectively quite active, as stacked/occluded cyclone is forecast
to track from the western Ohio Valley at the start of the period to
the Delmarva Wed evening. In advance of attendant upper trough/
frontal boundary, at least scattered convection is expected to be
ongoing at the start of the period, with coverage likely steadily
decreasing through the night as already-meager instability becomes
even more meager. Considering this weak buoyancy, the threat for
severe storms appears very low, but a small threat of locally
excessive rainfall could materialize in light of precipitable water
values increasing to around the 90th percentile of climo.

Lift associated with upper low passing north of the forecast area
should be maximized during the daylight hours Wed, when a consensus
of short term guidance suggests sbCAPE will maximize in the 1500-
2000 J/kg range during the afternoon. This should support numerous/
perhaps widespread convective coverage, favoring PoPs in the 70-80%
range across much of the area by mid-afternoon. The uptick in
instability should support an increased threat of isolated severe
storms, although that threat should be marginal in light of modest
shear and buoyancy parameters. Drier air advecting into the area in
the wake of a frontal boundary should remove much of the instability
fairly quickly Wed evening, while significantly limiting diurnal
destabilization on Thursday. As such, only the "token-est" of small
PoPs are advertised across the mountains and northern zones Thu
afternoon. Max temps will begin the period around normal, but return
to above-climo levels on Thu under increased insolation. Min temps
will be several degrees above normal through the period.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 215 PM EDT Monday: A relatively dry(er) air mass with weak
destabilization potential will modify early in the extended, while
the pattern will become more supportive of vertical motion as a
short wave ridge passes east of our area by early Friday. An area of
height falls and associated frontal boundary will begin penetrating
into the Southeast on Friday, while at least moderate
destabilization looks likely across our area Fri afternoon. Solid
coverage of diurnal convection is expected, with PoPs ranging in the
50-70% range across much of the area. The forecast for the weekend
depends largely upon the evolution of aforementioned height falls/
possible upper low across the Southeast...and the latest global
models are quite at odds regarding the details. Due to the inherent
uncertainty, the forecast trends toward more of a scattered diurnal
convective cycle Sat-Mon, but at least one period of more widespread
activity...along with an enhancement to the severe convective and
excessive rainfall threat...is possible across our area at some
point over the weekend. Temperatures are forecast to be a few
degrees above normal through the period.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: The chance of SHRA otherwise should slowly
increase from W to E later this evening, with increasingly precip to
lower cigs to MVFR and then IFR. KAND/KGSP/KGMU are expected to see
wedge-like ESE to NE winds given earlier development of cold pool,
but other sites should stay S/SE. Heaviest precip expected in the
early morning in the 06-12z time frame and isolated TS cannot be
ruled out. A lull in showers expected after daybreak, which combined
with light wind, could result in lowering vsby, but dense fog not
expected. Slight improvement in cigs/vsby possible Tuesday aftn but
widespread improvement appears unlikely Tue night. Guidance really
showing pronounced lull in convection thru the aftn, as clouds and
weak wedge limits instability. Given the trends, only mention TS
at KAVL, where terrain convection and also upstream activity to
the west may approach the terminal. The latest CAMs have some of
that activity from TN pushing across the forecast area after 00z
Wed. Confidence too low to mention at KCLT in the 00z TAF.

Outlook: Convection may cross the area overnight Tuesday,
but guidance is still not in good agreement on timing or
coverage. Restrictions should ease Wed morning but scattered TSRA
could redevelop in the aftn and cause brief return to IFR. Some
nocturnal restrictions likely again Wed night anyway. Brief drying
expected Thursday. Convection and associated restrictions return
ahead of a cold front on Friday.

&&

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

&&

$$

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