560
FXUS62 KGSP 031428
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1028 AM EDT Fri May 3 2024

.SYNOPSIS...
Dry and warm high pressure moves off the Carolina coast as a
front approaches from the west then stalls over our region for the
weekend. This front will result in periodic thunderstorms and
showers starting today and lingering through the weekend. A general
summertime pattern sets up early next week, which will likely
support scattered thunderstorm development each afternoon.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1025 AM EDT Friday: Height falls will impact the East through
the near term, with associated slow-moving/zonally-oriented frontal
zone expected to sag toward our forecast area later today into
tonight. Deep layer lift...albeit relatively weak...will approach
the CWA late today into tonight, while SW flow will result in
increasing levels of moisture, with forecast soundings indicating
precipitable waters will be in the ~90th percentile category for the
day. Therefore, conditions will become increasingly favorable for
convective development as the day progresses. Scattered showers are
moving into the mountains west of the French Broad and the Upper
Savannah River valley, but are dissipating as they try to move east
of there. Have kept PoP limited to these locations this morning but
ramp PoP back up across the area through the afternoon.

Otherwise, high and mid level clouds will continue to increase
through the day...resulting in cooler conditions than on Thursday,
while mid-level lapse rates are forecast to be poor. As such,
surface-based instability will be quite tame at 1000-1500 J/kg of
CAPE this afternoon. Meanwhile, wind shear parameters will be very
unremarkable, with 0-6km bulk shear ~20 kts. So, the conditional
probability of severe storms is about as close to 0 as it gets.
There could be locally heavy rainfall with deeper cells and/or if an
area of training cells manages to materialize. However, dry
antecedent conditions should preclude a notable excessive rainfall
threat.

While a general decrease in coverage and intensity of convection is
expected this evening, high moisture content combined with continued
modest lift is expected to result in scattered convection (primarily
showers) persisting well into the overnight, with perhaps a locally
heavy rainfall event or two possible. Temps will be 5-10 degrees
above climo through the period.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 300 AM EDT Friday: Upper ridging will remain over the East
Coast on Saturday before gradually pushing east into the western
Atlantic Saturday night into Sunday. At the sfc the forecast area
will be caught in-between two sfc highs (one over New England/SE
Canada and one over the Northern Plains/Upper Midwest) as a cold
front slowly approaches out of the west. The front should remain
north and west of the forecast area Sunday into Sunday night. This
messy pattern will lead to 850 mb S/SW`ly flow allowing for an
influx of Gulf moisture across Southeast through the weekend,
leading to scattered to widespread showers and thunderstorms each
day. Went with likely to categorical PoPs Saturday through early
Sunday evening and chance PoPs Sunday night. With PWATs expected to
climb well above climo (~1.6 inches east of the mtns and ~1.3 inches
across the mtns) and weak shear (~10-15 kts) leading to slow storm
motion, heavy rainfall will accompany shower and thunderstorm
activity. However, the overall threat for flash flooding looks to
remain low due to dry antecedent conditions. Nuisance flooding
cannot be entirely ruled out, especially for areas that see heavy
rainfall repeatedly track over the same locations. SBCAPE looks to
range from ~700-1500 J/kg each afternoon per the HRRR, GFS, Canadian
and ECMWF. The NAM and NAMNest are much more bullish regarding
SBCAPE through the weekend but this looks overdone as widespread
cloud cover from the influx of Gulf moisture should limit
destabilization somewhat. Thus, the severe potential looks rather
low through the weekend thanks to the low wind shear and increased
cloud cover. The SPC Day 2 and 3 Severe Weather Outlooks have the
GSP forecast area in a general thunder risk which looks reasonable
at this time. However, a few strong storms cannot be entirely ruled
out, especially for any areas that see breaks in cloud cover. Highs
on Saturday will end up near climo to a few degrees below climo
thanks to SSE`ly sfc winds, convection and cloud cover. Highs on
Sunday will climb to around 3-5 degrees above climo thanks to sfc
winds turning more S/SSW. Lows through the short term will end up
around 10-13 degrees above climo thanks to clouds limiting
radiational cooling.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 330 AM EDT Friday: The workweek will kick off similar to the
weekend as the aforementioned cold front remains stalled over the
Lower Midwest/Ohio Valley region. This will allow for another round
of scattered to widespread showers and thunderstorms on Monday.
Despite SBCAPE looking slightly higher on Monday compared to the
weekend, widespread cloud cover and weak shear should linger,
allowing the severe weather threat to remain low. Highs on Monday
will be similar to Sunday`s, ending up around 3-5 degrees above
climo. Lows Monday night will remain around 10-12 degrees above
climo thanks to some lingering cloud cover. Drier conditions may
return for most of the forecast area, with the exception of the
NC/TN border, Tuesday through early Thursday as the stalled front
gradually lifts northward across the Ohio Valley/eastern Great Lakes
region. Convective chances increase again late Thursday into Friday
as an upper low approaches out of the northwest. Highs should climb
into the mid to upper 80s Tuesday through Friday, which is around 7-
12 degrees above climo. Lows should remain around 10-12 degrees
above climo through the long term.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: VFR conditions are expected to persist across
the Terminal Forecast Area through the day, with steadily increasing
high/mid clouds expected. An upper level disturbance and associated
moisture plume will approach the area throughout the day, allowing
for expansion of showers and thunderstorms, mainly during the
afternoon and evening. However, scattered showers are already
amassing just upstream of the area across north GA and east TN. Some
of these initial SHRA could brush past the upstate SC terminals and
KAVL later this morning, but the better chances should hold off
until this afternoon. Scattered coverage of convection is expected
this pm...at least across the western half of the area...warranting
Prob30s for -TSRA at most sites during the afternoon/early evening.
Current indications are that instability will decrease toward the
east, so thunder is omitted from the KCLT TAF for the time being.

While some diminishment of convective coverage is expected this
evening...showers will remain possible well into the overnight
hours/early Saturday. A consensus of high resolution guidance
suggests another period of scattered showers circa 12Z Sat, so most
TAFs receive another Prob30 (for SHRA) during that time frame.
Chances for restrictions in fog/stratus will also increase toward
sunrise Sat, and MVFR conditions are included at all sites. Winds
will generally be calm or light/variable early this morning,
becoming SW at 5-10 kts by afternoon.

Outlook: Enhanced moisture will combine with a weak/stalled front
through early next 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.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...JDL/RWH
SHORT TERM...AR
LONG TERM...AR
AVIATION...JDL