491
FXUS62 KGSP 181028
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
628 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 555 AM Thursday: Radar is clear of any precip and satellite
shows a swath of fog/low level stratus in valleys of the mountains.
This has been persistent over the past few hours and should
dissipate after sunrise. A few minor adjustments to the forecast to
account of current obs, but no major changes at this time.

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 /12Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VFR conditions at most sites to start. Areas
of patchy fog should dissipate after 12z, making way for prevailing
VFR everywhere. A cold front approaches the area from the NW during
the day and into the end of the period. 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. Latest guidance still keeps KAND in
a lower confidence for convection, so a PROB30 for now. 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. Conditions start to quickly deteriorate after
00z as the front sits stationary over the area. Expect cigs/vsby
restrictions of IFR at most sites from widespread patchy BR and low-
level stratus, with KCLT likely to drop into the MVFR range. By the
end of the TAF period, KCLT winds are expected to become easterly
and toggle toward the S/SE afterwards.

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