478
FXUS62 KGSP 131406
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1006 AM EDT Mon May 13 2024

.SYNOPSIS...
Moisture will increase today with rain returning by afternoon and
evening.  Rain and thunder are likely on Tuesday and Wednesday,
followed by a brief stint of drying on Thursday.  Active weather
will return for the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 945 AM: Change is on the way as an upper ridge axis moves
east of the area today. Short waves rotate around an upper low,
that drops into the mid MS valley, and across the area late today
and tonight.  This brings an increase in deep moisture later
today into tonight as deep southerly flow develops ahead of a
slowly advancing warm front and low pressure system. High-based
light precip has occurred over much of N GA so far this morning,
but the dry sfc airmass in place over our area has so far led
this precip to weaken or dissipate completely as it has advected
toward our CWA. Nonetheless, seeing how trace precip has given way
to measurable amounts at a few sites, saw fit to increase PoPs
slightly through the remainder of the day, particularly in our
southwest zones over the next 3-4 hrs. Also touched up temps a bit,
with the quicker onset of precip and already abundant cloud cover,
with highs being lowered a couple of degrees in many spots. Temps
still will feature an unusual gradient with the precip development:
almost normal over the I-40 and I-77 corridors where precip arrives
later, but below normal along and west of the I-26 corridor where
precip arrives earlier.

Low level moisture and insentropic lift, along with increasing
synoptic forcing from the short waves and upper divergence from
a coupled jet streak, move in during the afternoon. Clouds will
thicken and lower more quickly by that time as showers pick up and
saturate the low levels. The best coverage will be west of the I-26
corridor by the end of the day with light QPF. If any CAD develops,
it will be weak and late in the day despite the clouds given the
slow advancement of the showers. Winds will begin adjusting to
the SE where precip develops, but will be southerly through the
bulk of the day.

Precip coverage increases during the evening into the overnight as
moisture and forcing remain over the area. Isolated TSRA will be
possible overnight as weak MUCAPE develops with only a weak CAD at
best and better lapse rates. Moderate QPF is expected generally
from along the I-85 corridor to the Blue Ridge. Isolated heavy
rainfall will be possible as well. Lows will be around 5 degrees
above normal.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 243 AM EDT Monday: Deep trough will close off into an upper
low over the Ozarks on Tuesday, and ripples of DPVA will round
the base of this low into the Carolinas throughout the day.
A preexisting weak in situ wedge will be in place east of the
mountains early Tuesday, but as low-level WAA intensifies it
will erode, and the wedge front will gradually retreat northward.
This will likely expose at least the southern third of the forecast
area to some surface-based instability, to the tune of ~500 J/kg.
Meanwhile, a 500mb speed max will lift out of the lower Mississippi
Valley into GA and SC, allowing deep layer shear to surge to
45kts or more.  Thus, confidence on some severe risk on Tuesday
is increasing.  In theory, lapse rates appear too meager for a
widespread large hail risk; rather, wind looks to be the primary
threat with any severe storms that develop.  SPC`s Marginal Risk
for Severe Weather on Tuesday looks reasonable.  Highs will climb
into the low to mid 70s...limited by widespread clouds and rain.

Tuesday night will feature a lull in rainfall as diurnal instability
wanes and the most potent lobe of DPVA translates east of the
forecast area.  Lows will fall into the low 60s.  On Wednesday,
instability will be more widespread and enhanced, with most
operational models now depicting a plume of >1200 J/kg over the
eastern zones and the LREF ensemble mean landing right around
1000 J/kg for areas east of I-26.  So, coverage of convection
should be widespread ahead of an advancing surface cold front,
which will pass through during the afternoon hours.  Sans stronger
winds aloft, deep layer shear is only forecast to reach 25-30kts by
the bulk of guidance sources, so severe risk should be more muted.
Highs will climb into the upper 70s on Wednesday.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 253 AM EDT Monday: Rainfall chances will drop off sharply
by Thursday morning as the axis of an expansive upper ridge
translsates across the Eastern Seaboard.  Ensemble soundings
depict the development of a weak subsidence inversion at around
700mb, which should be enough to inhibit any convective response
on Thursday.  Afternoon highs will surge into the 80s.

The next disturbance will arrive in the form of a southern stream
shortwave trough, which will carry deep moisture and ripples of DPVA
forcing out of the Gulf Coast area and into the Carolinas.  Lapse
rates look slow to steepen on Friday, but enough instability will
develop by afternoon that most guidance is indicative of scattered
diurnally-driven convection.  By Saturday, the operational models
depict a robust frontal zone entering the Ohio Valley and spurring
a round of well-forced afternoon convection across the Carolinas.
Around 2/3 of the broader ensemble envelope feature a complete
frontal passage followed by the arrival of continental high pressure
for Sunday afternoon and beyond.  The remaining ensemble members
feature a slower frontal passage and lingering rainfall chances
on Sunday.  In general, the pattern looks dynamic enough going into
next week that confidence in any particular solution is pretty low.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Cirrus will continue to steadily thicken
with altocu moving in during the morning and low VFR stratocu cigs
by afternoon. Light NE wind this morning becomes SE by late morning
then S for the afternoon. S at KAVL all day. Low level moisture and
isentropic lift move in later in the day with cigs falling to MVFR
late in the afternoon or early in the evening. Cigs fall to IFR late
evening or early overnight. Precip chances will increase through the
afternoon into the evening as well. Expect vsby to become MVFR as
precip becomes more steady. Weak elevated instability is possible
during the evening and overnight but chance of TSRA too low for the
TAF at this time. Wind turns S to SE during the evening into the
overnight.

Outlook: Scattered thunderstorms develop Tue and Wed afternoons
bringing a chance for periodic restrictions. Some nocturnal
restrictions remain possible Tue and Wed nights. 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...MPR
NEAR TERM...RWH/Wimberley
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...RWH