606
FXUS62 KGSP 180725
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
325 AM EDT Thu Jul 18 2024

.SYNOPSIS...
A pattern change begins to evolve today, as a cold front approaches
from the northwest, then becomes stationary across our region for
several days. This will keep shower and thunderstorm chances
elevated through at least early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 255 AM Thursday: A more typical summertime pattern arrives
today. It`s been a while since we have seen it cloudy like this,
with more consistent chances for rainfall. Taking a look at the
overall pattern across the CONUS, the more Extreme heat, at least
for this area, shifts to the western portion of the country. A
strong area of high pressure and ridge amplifies in the west,
translating to a strong trough downstream. Over the eastern portion
of the U.S., a trough dips southward and an area of low pressure
spins to the north of the CWA. What this means is a FROPA is headed
right for us and upticking convective activity this afternoon.
Guidance from the NAM and RAP show an increase in the amount of
sbCAPE, clocking in around 1500-2500 J/kg at peak heating time.
There will also be decent DCAPE nearing 1000 J/kg, leading the way
for strong downdrafts and microbursts. General flow from sfc-6km is
weak and almost unidirectional from the WSW/W, meaning the
enviroment doesn`t support the development of Twisters. Main hazards
today may feel like hand shaking Zeus with damaging wind gusts,
torrential downpours and cloud-to-ground lightning. Confidence is
higher for widespread convection with PoPs going green and red (60%-
89%), especially over the mountains and NC Piedmont. Rainfall totals
look like we are going in for 0.5-0.75 inch, with locally higher
amounts possible since storm motion is about 220 degrees, straight
out of the SW and slow. For all of this, SPC has put most of the CWA
in a Marginal risk. After the convection dies off later this
evening, the front continues to march across the area, changing the
wind direction N/NW, but still remains relatively light as the front
dissipates over the area. As for temperatures, heat relief is here
with today`s highs making a run for the low 90s. Humidity remains
high and sticks around well into the remainder of the forecast, but
we will continue to feel it and chase the forecast guidance.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 245 am Thursday: An upper trough will be centered from the
lower-to-mid-Mississippi Valley through the short term, while a
weakening, quasi-stationary surface boundary will persist near our
forecast area through the period. This boundary will likely be
draped over...or just south of our southern areas at the start of
the period, with less unstable/lower theta-E air expected to be in
place across northern portions of the CWA. Therefore, convection Fri
afternoon/evening should have a preference for the southern half of
the area...as well as the high terrain of southwest NC. Numerous
convective coverage is expected in these areas, supporting at least
likely PoPs. Deep S-to-SW flow will support very moist conditions in
these areas, so locally excessive rainfall will be the primary
threat, especially in locations with training convection. A couple
of pulse severe storms can`t be ruled out, but extensive cloud
cover/cooler conditions will limit destabilization.

Convective chances may become enhanced across the area Fri night,
when higher resolution short term models all depict a short wave
trough lifting steadily across the area from the southwest, As a
result, PoPs are 60-70% across the entire CWA through much of Fri
night, with continued...perhaps even a slight uptick in the
potential for locally excessive rainfall.

Very little change in the overall regime is expected for Sat/Sat
night, as conditions will remain very moist, modestly unstable
during the afternoon/evening, while the lingering weak baroclinic
zone beneath mid-level vort maxes rippling through the SW flow aloft
will provide sufficient lift to support at least likely PoPs through
the end of the short term. While coverage and intensity of
convection will correlate with the diurnal heating cycle, the
pattern will support some degree of convective activity lingering
well into Sat night. Locally excessive rainfall will remain the
greatest concern.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 310 am Thursday: Very active weather will linger into the
extended period, as deep SW flow between a slowly retrograding
trough over the lower half of the Miss Valley, and a building
subtropical ridge over the western Atlantic will provide plenty of
rich/deep moisture to our area, while a weak surface boundary and
terrain effects will provide the primary sources of lift to initiate
convection. While convection will remain primarily diurnal in
nature, nighttime periods are likely to remain at least somewhat
active given the pattern Sunday/Monday. This may begin to change
toward the middle of next week, as the ridge tries to assert itself
over the Southeast. Nevertheless, while convection may become more
typically diurnal in nature Tue/Wed, increasing instability will
continue to produce above-climo coverage of showers and storms.
After several days of high convective coverage/locally deteriorating
hydrologic conditions, a gradual uptick in the threat of locally
excessive rainfall is expected through the period. Temps are
generally expected to be slightly below normal.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VFR conditions for most sites to start and a
bumpy outlook for Thursday afternoon. A few lingering showers make
an exit this evening, leaving behind scattered low-level stratus in
areas that received rainfall earlier. First, areas in the mountains
and near KAVL show BR/FG seeping in. Confidence is moderate that
some sort of MVFR or even IFR vsby/cig could encroach on KAVL during
the overnight hours. A TEMPO for this from 09z-12z should suffice.
After daybreak, any lingering BR/FG should trickle out of the area
and all terminals remain at VFR through the rest of the TAF period,
with temporary restrictions during the afternoon hours. A cool front
approaches the area from the NW during the day and into the end of
the period. Second, this provides a moderate to high chance for
widespread TSRA at most terminals. TEMPOs for TSRA run from 19z-00z,
adjusted for specific sites with the mountain terminals having
earlier starts. KAND does not look as favorable for TSRA, so a
PROB30 for now, but will be re-evaluated next issuance. Lastly, the
front brings a wind shift from SW to N/NW. At KCLT, a NW wind is
likely to occur around 20z and shift NE by the end of the TAF
period. Wind speeds remain 5-10kts, with higher gusts possible
around any sites with thunderstorms.

Outlook: Scattered to numerous showers and thunderstorms each aftn/
evening thru the weekend. Morning fog/low stratus possible each day,
especially in the mtn valleys and over areas that received rainfall
from the previous day.

&&

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

&&

$$

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