597
FXUS62 KGSP 170734
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
334 AM EDT Wed Jul 17 2024

.SYNOPSIS...
Hot high pressure will weaken over the region today. A pattern
change begins to evolve by Thursday, 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 245 AM Wednesday: On the downward trend for heat and a patter
change emerges. Hot temperatures and high pressure stick around a
tad longer in the near term, with weak flow aloft. A steady stream
of moisture advection from the SW sfc winds persist and prime the
area for a more active pattern later in the week. Outside of some
low-level stratus over areas that received rainfall yesterday, not
expecting too much in the way of overnight cloud cover. By Wednesday
morning, daytime heating increases instability throughout the day.
Guidance from modeled soundings show around 1500 J/kg of sbCAPE with
steep sfc based lapse rates. CAMs hint at another round of scattered
showers and thunderstorms possible, with the highest chances over
the mountains (70%-85%) and elsewhere (45%-70%). Storm chances could
also contribute to heat relief as well. Wednesday highs are still on
track for the mid 90s and heat index values hover around 100. A few
showers linger into Wednesday night as well. Overnight temps will
remain elevated in the low to mid 70s and be muggy.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 250 am Wednesday: A full-latitude upper trough will extend
from east Texas through the Great Lakes at the start of the period.
The leading edge of an associated baroclinic zone will sag into the
CWA on Thursday and provide a focus for increased coverage of
showers and thunderstorms during the afternoon and evening.
Instability should be sufficient to support a small threat for
isolated pulse severe storms. However, the main threat should be
locally excessive rainfall, as precipitable water values will meet
or exceed 2", while boundary-parallel flow will support the
potential for training cells.

The boundary could push south of the area Thursday evening. However,
a split flow regime will evolve during the latter half of the short
term, as the northern portion of the upper trough passes north of
our region, and a southern piece  becomes separated from the main
branch of the subtropical jet and persists across east TX/the lower
Miss Valley into the extended period. The pattern will result in the
surface boundary becoming quasi-stationary in or near the forecast
area, while deep SW flow will support continued high moisture levels
across at least the southern half of our area. Scattered to
numerous, mainly diurnal convection is again expected on Friday,
warranting 50-70 PoPs across much of the CWA. Increased cloud
cover...along with advection of lower theta-E air into northern
portions of the area, will result in a significant cooling trend...
with max temps forecast to be almost 5 degrees below climo. Cooler
conditions/limited instability will temper the pulse severe storm
risk, but there may be an uptick in the excessive rainfall threat,
with the potential for training cells continuing in the vicinity of
the boundary. While convection will have a diurnal tendency, the
pattern will be such that some degree of activity...and attendant
excessive rainfall threat...will continue into Fri night.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 325 am Wednesday: Only gradual changes in the upper pattern
are expected during the medium range...as a trough over the lower
Miss Valley slowly retrogrades, while an intensifying subtropical
ridge builds into the Southeast from the western Atlantic. For at
least the first half of the period, a weak baroclinic zone will
persist over the Southeast, while deep SW flow will support a
continued supply of Gulf of Mexico moisture. As a result, the
weekend will remain very active convectively...primarily diurnal in
nature, but with some activity lingering well beyond the afternoon
maximum. Convective activity could begin to taper down early next
week as the ridge attempts to assert influence. However, a consensus
of guidance suggests above-climo PoPs for diurnal convection are in
order through Day 7. Slightly-below normal temps are forecast
through the period.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Prevailing VFR conditions for the TAF period.
Given the previous rainfall, mountain terminals could see BR or FG
overnight. Currently, KAVL is already gone down in cigs. A TEMPO for
LIFR will be in effect until 10z, with improvement after that. Calm
and quiet weather for the morning hours until the afternoon. Another
round of possible convection is slated during peak heating once
again. Confidence is moderate for showers and TSRA, so a PROB30 at
all terminals. Will likely change to TEMPOs at the next issuance.
Winds should prevail SW outside KAVL, which will toggle N/S, but all
sites will have light winds.

Outlook: Morning fog/low stratus possible each morning, especially
across the mountain valleys and for areas that received heavy
rainfall the day prior.

&&

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

&&

$$

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