191
FXUS62 KGSP 251349
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
949 AM EDT Tue Jun 25 2024

.SYNOPSIS...
Dry and less humid conditions continue today before the heat and
humidity returns Wednesday ahead of an approaching cold front. This
front will bring showers and thunderstorm chances back to the area
late Wednesday into Thursday. Hot and humid conditions will persist
into the weekend with a chance of showers and thunderstorms each
afternoon. Another cold front approaches the area late this weekend
keeping unsettled weather around.

&&

.NEAR TERM /THROUGH TONIGHT/...
1000 AM Update...Low clouds are lingering across the nrn NC
foothills and expect these to dissipate over the next couple hours
as LCLs rise into drier air. Updated the sky grids to reflect this
change, otherwise made little adj/s to the going fcst.

Otherwise, sfc high pressure will continue to build in from the
north and will remain over the western Carolinas and northeast
Georgia through tonight leading to continued dry weather. Although
humidity will remain low again today, with minimum RH values
dropping down to 30%-35% across much of the area this afternoon, hot
temperatures will return once again. Highs will climb into the low
90s in the mountain valleys and the low to mid 90s east of the
mountains. Lows tonight will be warmer (and ~5-8 degrees above
climo) thanks to 850 mb winds turning S/SW`ly. This will also allow
humidity to increase again tonight east of the mountains.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 130 AM Tue: Shortwave crossing the Great Lakes Tue night will
promote height falls Wed afternoon and evening over our region;
sfc front should reach the Ohio River before sunset. With midlevel
ridge to the west, we will mix up into dry air again for part of the
day, although 850-700mb flow will become southerly in advance of the
trough during the afternoon. Thus, despite diurnal instability model
QPF response is low during the day, and PoPs appear warranted only
over the mountains. Convection will develop ahead of the front in
KY/TN but with the front itself not reaching the mountains until
overnight, the convection is expected to ash out before it gets
to our border. Under exceptionally high thicknesses, temps Wed
may be the hottest of the year so far, with upper 90s across the
Piedmont and low 90s for the mountain valleys. As noted however
dewpoints will mix out enough that heat index should peak "only"
around 100 in the lower Piedmont.

Models differ as to how quickly the front settles through our area,
and it becomes rather diffuse as it is. It looks mainly to serve
as a source of weak convergence and promote moisture pooling,
thus a focus for diurnal convection. Confidence remains best for
mountain and northwest NC Piedmont PoPs during the day Thursday,
50 to 60% in those areas. The front should reach the southern half
of the CWA by the end of the day and our southern zones still get
at least 40% PoP. Shear will remain seasonably weak but lapse rates
not strong enough through a deep layer to produce especially high
CAPE, although a damaging microburst or two can`t be ruled out.
Dewpoints don`t look to mix out as much but temps will be slightly
cooler and heat index again peaks around 100 at worst.  Thursday
night into Friday morning, the major models depict a weak low
partially or completely shearing off from the base of the trough
near the Gulf Coast, and that will have the effect of stalling the
front and perhaps reactivating it.  Accordingly some PoP will linger
in the Piedmont Thursday night after diurnal convection diminishes.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 305 AM Tue: Sfc high on the cool side of the front will
migrate across the Northeast Friday into early Saturday. The
influence of this high will keep temps relatively mild Friday but
still actually a degree or two above normal. Low-level flow will
turn easterly and then southeasterly; remnant of the front or
weak low mentioned in the late short-term period should exit to
the east as heights rise. The onshore flow will bring dewpoints
a bit higher and suggests diurnal PoPs around climo, with some
chances lingering overnight into early Saturday. This general
evolution continues through Saturday, with temps and dewpoints
ticking upward via airmass modification. PoPs also rise slightly.

The real feature of interest for the period will be another
trough passing the Midwest and carrying another front south and
east. Global models/ensembles really agree fairly well on this
occurrence, just varying in the timing thereof. The GFS is fastest,
followed by the GDPS and then ECMWF, sometime between midday Sunday
and late Monday morning. GFS is also the most bullish with precip
coverage. Peak temperatures and PoPs are depicted Sunday, with
slightly cooler and lower values Monday, but still above climo in
both regards. Although dewpoint mixing will not be as effective
within this pattern, a slight afternoon dip is likely. Values may
edge above 100 each afternoon in the Piedmont, but Sunday would
be the day of most concern with most areas outside the mountains
rising to 100-104, with a few isolated spots perhaps exceeding 105.

Any thunderstorms in the period, even near the fropa, likely will
remain of the pulse or loosely clustered variety. PWAT values
upwards of 150% of normal can be expected and a localized heavy
rain threat is a reasonable bet, although dry soils may initially
mitigate flood concerns.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Key Messages:

1) Dry and VFR through Wednesday Morning

2) Shower and Thunderstorm Chances Return Ahead of a Cold Front
Wednesday Afternoon and Evening

3) Shower and Thunderstorm Chances Linger Wednesday Night into
Thursday as the Cold Front Tracks Over the Western Carolinas

At KCLT and elsewhere: VFR and dry through the 12Z TAF period thanks
to sfc high pressure over the terminals. Wind speeds will range from
5-9 kts east of the mountains through at least mid-morning before
gradually decreasing. Brief low-end wind gusts cannot be entirely
ruled out east of the mountains through 13Z as the pressure gradient
tightens but confidence remains too low to mention gusts for now.
Wind direction will remain N/NE`ly east of the mountains through mid-
morning. Winds may briefly turn more E`ly at KCLT later this
morning. Winds become light and VRB this afternoon into tonight
across the terminals. A few cumulus should develop this afternoon
before dissipating around sunset. Cirrus will gradually increase
from the west overnight but should generally remain FEW. Some low-
end VFR cloud cover may develop east of I-85 this evening into
daybreak Wednesday and may reach I-85 shortly after sunrise. Only
have this mentioned at KCLT for now as the TAF goes out 30 hours.
Winds at KCLT look to turn SE`ly this evening before becoming S`ly
tonight into Wednesday morning. SHRA/TSRA should hold off until
after the 12Z TAF period.

Outlook: Widely scattered SHRA/TSRA returns Wednesday afternoon and
evening as a cold front approaches out of the west. The cold front
will track over the terminals Wednesday night into Thursday before
stalling south of the area on Friday, keeping SHRA/TSRA chances
around.

&&

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

&&

$$

SYNOPSIS...AR
NEAR TERM...AR/SBK
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...AR