651
FXUS62 KGSP 181805
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
205 PM EDT Sat May 18 2024

.SYNOPSIS...
A weak low pressure system will track east across North Carlina
through tonight, bringing another round of showers and thunderstorms
to the area this evening and tonight. The low will exit off the
Carolina Coast on Sunday, with high pressure building in from the
north. Somewhat drier conditions return early next week resulting in
only isolated afternoon and evening showers and storms. A cold front
will bring better shower and thunderstorm chances back into the
forecast late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1012 AM Saturday: All is quiet for the most part for the time
being. Still not entirely clear how the afternoon will play out,
with a Marginal Risk for severe thunderstorms retained by the SPC
on the Day 1 Convective Outlook update. The latest vis satellite
imagery suggests a plausible scenario would be for convection to
begin along/near the Blue Ridge Escarpment later this afternoon,
because those locations have already seen partial clearing and
have started to destabilize. The 12Z HRRR seems to have that
idea in mind. Fortunately, none of the CAM solutions imply much
organization to the threat, so the most likely outcome looks
like mostly garden-variety thunderstorms, with a few having some
potential to become severe with wind damage and marginal hail. Temp
trends might be a mess through early afternoon as various locations
break out to sunshine quicker than other places.

Otherwise...height falls will occur later in the afternoon as
shortwave arrives from the west. CAMs are in rather good agreement
on more vigorous convection developing over the Escarpment around
19Z-21Z, expanding in coverage through early evening and propagating
SE. 700-500mb lapse rates will already be fairly good but should
be maintained by the wave, and altogether 1000-1500 J/kg SBCAPE is
likely to be in play at that time. Near-sfc winds will be light, and
midlevel flow is initially modest but weakens under the shortwave,
so the aftn convection could be fairly pulsey. Models vary as
to how dry the midlevels remain, and that is likely key to the
level of severe risk. Sfc-midlevel delta-theta-e values look lower
than we usually see with severe pulse storms. SPC Marginal Risk
is certainly sufficient for this low-end threat. Storms appear
to be very efficient rainfall producers and given consensus in
initiation time/area, PMM QPF is quite healthy with areas of 1-2"
storm totals likely. Some storms could produce tree damage simply
from weak organization along cold pools if they develop, and trees
may topple more easily with many areas having saturated soils.

Pattern remains murky for tonight. A tilted ridge develops to
our north in the wake of the shortwave, and a weak sfc high
will build down the Eastern Seaboard. This looks to bring a
wedgelike backdoor front into the area, likely encountering
enough sfc moisture to create a low stratus deck and possibly
also initiate elevated convection, with lapse rates still good
above the associated inversion. PoPs thus diminish from north to
south across the Piedmont overnight, although see fit to keep a
slight chance all night there; chance values for the GA/SC zones
and Escarpment. Lows will be several degrees cooler than this
morning despite continuing clouds.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
As of 130 PM EDT Saturday: Mid level ridging and weak surface high
pressure will be in place across the region during the short range
period. This will lead to a general drying of the atmosphere and
lack of rainfall both Monday and Tuesday. The exception to this will
be over the favored high elevations where a shower or two will be
possible each afternoon during peak heating.

With the ridging and more sunshine in place, afternoon highs will
climb from the upper 70s in the mountain valleys and lower 80s in
the Piedmont on Monday to the lower to middle 80s respectively on
Tuesday. In other words, near climo on Monday and slightly above
climo on Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 140 PM EDT Saturday: Mid level ridging will remain in place
across the region for the middle of next week, but a weak trof
should weaken the ridge by the end of the week. High temperatures in
the Piedmont are expected to warm into the middle to upper 80s
through this period with lower to middle 80s expected in the mountain
valleys, all a few degrees above climo.

A more active convective pattern is expected toward the end of the
week with the breakdown of the ridge.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Main problem in the very near term is
the slowly lifting MVFR-level cloud base across the area east of
the mtns, both above and below 020. This should continue to lift
and scatter out thru the middle part of the afternoon, so most
places get to VFR finally by late afternoon. Wind should be light
SW. Meanwhile, extensive cirrus blowing off from the convection
to the south has spread over the region, acting to discourage
the convective development over the western Carolinas. For that
reason, away from KHKY, the TEMPO for TSRA has been pushed back a
few hours, and more or less follows the depiction seen in the HRRR
model. Think it likely that most places will still eventually have
to contend with restrictions from showers and thunderstorms. Some
lingering into the late evening can be expected. After the coverage
goes down, the guidance hints strongly at the development of an
IFR stratus deck, so all terminals get an IFR restriction, and
some possible LIFR as well. At the moment, the ceiling looks like
more of a problem than the vis. Wind will be variable. On Sunday,
most of the restrictions thru the morning will be mostly over the
mountains and foothills.

Outlook: SHRA/TSRA remain possible Sunday afternoon and perhaps
even Sunday night until stronger high pressure settles over the
region Monday. Late night/early morning restrictions in low stratus
and/or fog will remain possible Sunday night; isolated mountaintop
convection still appears possible Monday.

&&

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

&&

$$

SYNOPSIS...SCW
NEAR TERM...PM/Wimberley
SHORT TERM...SCW
LONG TERM...SCW
AVIATION...PM