117
FXUS62 KGSP 161431
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1031 AM EDT Mon Jun 16 2025

.SYNOPSIS...
Hot and humid with daily showers and thunderstorms expected through
most of the workweek. A cold front pushes across the area early
Friday, bringing drier and slightly less humid conditions behind it
heading into the weekend. The humidity, as well as shower and
thunderstorm chances, return Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1025 AM EDT Monday...

Key Messages:

1) Another Hot and Muggy Day, Especially East of the Mountains

2) Better Coverage of Diurnal Showers and Thunderstorms Today

3) Severe Threat Remains Low but Isolated Flash Flooding Remains
Possible with any Storms that Develop, Mainly North of I-40

Dry conditions across the forecast area this morning with the
exception of a few isolated showers grazing the NC/TN border. Low
clouds and patchy fog that developed this morning have lifted for
most locations leading to plenty of sunshine this morning. Only made
some minor tweaks to cloud cover, precip chances, and thunder
chances through the near term based on the latest satellite/radar
trends and 12Z CAM guidance. Otherwise, the forecast remains on
track.

Today we slip right back into the same pattern we had late last
week with a weak mid/upper trof over the mid-MS Valley region and
the Atlantic Subtropical Ridge nosing west over the Southeast. The
result will be a continued WSW flow of moisture from the Gulf
that will raise our precipitable water back up to around 2 inches
or so east of the mtns this afternoon, raising the potential for
heavy rain over areas that have persistent convection. Fortunately,
the CAMs don`t seem to develop anything more than scattered storms
at any particular time, though with movement steadily to the east
and northeast, the net coverage for the afternoon will be into the
likely range across mainly the NC zones. The concern would be the
flash flood potential, mainly north of I-40. Note that Caldwell and
Alexander counties had some heavy rain 48 hours ago, but were fairly
rain-free yesterday, so that becomes less of a factor. Also note
the 3-hr PMM on the 00Z HREF shows an area of 2-2.5 inches along
the Wilkes/Caldwell/Alexander border, which is roughly equal to
the three hour flash flood guidance. If there would be a problem
area, that would be it, the way things look right now. However,
the QPF and convective coverage don`t support a Flash Flood Watch at
this time, and the latest 12Z guidance agrees with this assessment.
As for severe thunderstorms, moist profiles and poor lapse rates are
less supportive than the past few days, which turned out largely
quiet. Temps will be slightly above climo with high humidity. The
model guidance looks strongly diurnal, so the coverage of storms
should drop steadily after sunset, leaving us fairly quiet once
again after midnight. Low temps will remain mild.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 248 AM EDT Monday...

Key Messages:

1) Heat and humidity continue to build through the period, with
heat index values approaching the upper 90s, and even hitting 100
south of I-85.

2) Afternoon showers and thunderstorms are expected, with higher
coverage expected on Tuesday than on Wednesday.

3) Severe risk looks limited, while the threat of heavy rain and
isolated flash flooding continues.

Subtropical ridging will remain in place through the middle of
the week, and the resultant increase in low-level thicknesses
will drive afternoon temperatures into the lower 90s on Tuesday,
and lower to mid 90s on Wednesday.  Southwesterly surface flow,
meanwhile, will continue to pump Gulf moisture into the region,
resulting in diurnal showers and thunderstorms through the period.
Tuesday night, operational guidance depicts a weak open wave lifting
northeast out of the Mississippi Delta region...best visible on the
850mb charts...and translating into the Mid-Atlantic by Wednesday.
The result is a moderately more stable environment on Wednesday,
when moisture will be less pronounced behind the wave and lapse
rates comparatively less impressive (not that they`ll be all that
impressive Tuesday, either).  Indeed, forecast sbCAPE runs as high
as 2000 J/kg on Tuesday, maybe higher...but struggles to reach
even 1000 J/kg on Wednesday.  All that to say, convection appears
likely both days...but coverage might be lower on Wednesday given
less forcing and an overall less conducive environment.

Although an isolated severe storm can`t be ruled out - especially
Wednesday, when enough mid-level dry air will be in place that *if*
a cell can overcome the lack of good instability, it will have a
decent amount of dCAPE to work with - the bigger concern remains
hydro issues.  Both afternoons will feature fairly weak steering
flow, and on Tuesday in particular, forecast PWs continue to range
anywhere from the 90th to 99th percentile of NAEFS climatology.
By Wednesday, these numbers will start to come down as profiles
dry out...so any flash flood risk will depend more on antecedent
conditions, i.e. whatever winds up happening through Tuesday.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 319 AM EDT Monday...

Key Messages:

1) A cold front arrives Thursday evening, producing showers and
thunderstorms.

2) Drier conditions and a relief from the heat is expected on
Friday, but only temporarily.

A robust z500 trough will cross the Ohio Valley early Thursday,
quickly pushing east of the area and into the western Atlantic
by Friday morning.  At the surface, this will drive a cold
front across our area...and the strengthening trend observed in
long-range ensembles over the last 36 hours or so continues, with
the front now consistently depicted making a complete passage over
the GSP forecast area and ushering in some drier air on Friday.
Its timing remains a little in question, but the LREF consensus
puts it arriving between 00z and 06z Friday...when there`s still
some marginal instability present and enough shear for some loose
organization.  But...initiation remains in question...since the
better forcing still looks like it`ll be shunted to our north...over
central Virginia and the Mid-Atlantic.  Temperatures, meanwhile,
will make it into the mid 90s on Thursday...with widespread upper
90s and some lower 100s heat index values expected.

A brief spurt of drying is expected behind the boundary.  Dewpoints
should drop a bit and allow brief relief from the heat.  Moisture
will slowly build back in on Saturday and Sunday...but overall,
the weekend looks like the first dry, quiet stretch we`ll have
had in a while. That said...the Bermuda high won`t be dislodged
by this front...and moisture will begin steadily creeping back
into the area. Dangerous heat index values may be in store again
by the end of the weekend.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: We begin with patches of LIFR to IFR
stratus lurking around some of the terminals, most notably KCLT,
KHKY, and in the valley around KAVL. The stratus around KCLT will
require a one-hour TEMPO to start with, but it should mix out and
lift quickly. Not necessarily so at KAVL, but by 14Z it should be
breaking up. After that, most terminals are expected to stay VFR
until we start to develop a new low cloud deck with some heating
during the middle part of the morning, which could result in another
temporary broken ceiling, but this was not included for lack of
confidence. Beyond that, it looks to be a fairly typical summer day
across the fcst area. Low clouds scatter out by late morning, then
thunderstorms develop in the afternoon and linger into the early
evening, followed by cloud debris into the late night. Confidence
is high enough to go with a TEMPO over the mountains and foothills,
but will handle this for now with PROB30s at the other terminals.

Outlook: Showers and thunderstorms are expected each day thru
early next week. Late night/early morning fog and low stratus
restrictions will be possible each day.

&&

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

&&

$$

SYNOPSIS...AR/MPR
NEAR TERM...AR/PM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...PM