Pisgah Forest, North Carolina Weather Forecast Discussion

529
FXUS62 KGSP 161742
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
142 PM EDT Tue Sep 16 2025
.SYNOPSIS...
Low pressure on the North Carolina coast weakens as it drifts
northeast to be along the Virginia coast Wednesday and then the low
dissipates on Thursday.  Warm and dry high pressure returns for the
rest of the week with Friday being the warmest day.  Expecting low
chances of shower and thunderstorms by early next week as moisture
slowly increases.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 138 PM EDT Tuesday...
Key Messages:
1) Showers will develop across the NC mountains today, and may
spill out into the Upstate this evening.
2) Quieter conditions are expected on Wednesday.
3) Temperatures will be around normal for most of the area on
Tuesday and Wednesday.
The regime remains under the control of an upper low churning over
the Carolins and lower Mid-Atlantic.  At the surface, a coastal
low is analyzed northeast of Cape Hatteras, driving generally N
flow over the area...and supporting a broad surface ridge east
of the Appalachians.  Showers never quite died off this morning
west of I-26, and at this point mesoanalysis depicts a growing
lobe of 500+ J/kg sbCAPE, mainly over the Smokies and Balsams but
expanding...so activity may ramp up again soon.
Still expect a shortwave (or, really, a series of weak ripples) to
rotate across the area from the north this afternoon.  Areas west
of I-26 can expect 500-1000 J/kg sbCAPE to develop over the next
few hours; with the shortwave crossing the area at peak heating,
showers and at least some thunderstorms appear likely.  The bulk of
this activity should remain confined to the mountains, but there`s
an increasingly consistent signal in the 12z HREF for some cells
breaking containment and spilling over into the western Upstate and
Savannah River Valley as the afternoon wears on.  Neither shear
nor dCAPE parameters look impressive...so expect little severe
risk, and any heavy rain to be isolated and short-lived...to
the point that significant impacts aren`t expected.  Otherwise,
high temperatures are still expected to top out in the lower 80s
across the Upstate, though some locations may remain cooler owing
to the unexpected longevity of this morning`s showers there.
Forecast highs were raised along the I-77 corridor, where it`s
currently clear and where CAMs indicate minimal chance of any
rainfall today, compared to previous forecasts.
Tonight, as the surface low slips north into the Chesapeake region,
winds will become increasingly NW, the shortwave will exit the area,
and convection should come to an end.  Lingering moisture will keep
the clouds around, but another round of mountain valley fog should
occur nonetheless.  Lows will drop into the upper 50s.  Tomorrow,
coverage of rainfall looks much lower than today; the lack of any
good synoptic support as the low moves north will make initiation
more difficult, except for ridgetop showers in the mountains.
Highs tomorrow should be similar to today`s.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 100 pm EDT Tuesday:
Key Messages:
1) Warming Trend Continues as Drier Conditions Return
2) Highs ~3-5 degrees above normal.
3) Precip chances less than 20% through the period.
Upper low over the Mid-Atlantic will kick out and become absorbed
in the polar jet, as large scale height falls overspread eastern
Canada and the northeast Conus early in the period. The axis of a
baggy trough will be left behind from the Mid-Atlantic into the
Southeast which will linger over the region while continuing to
weaken. This pattern will tend to shunt any noteworthy moisture
east and southeast of our forecast area, and indeed, forecast
soundings are relatively dry (PWATS < 1.25") and stable through the
period. Thus, despite the fact that short term guidance generally
agrees in dropping a vort max across the area on Thursday, profiles
are forecast to be unsupportive of deep convection, and PoPs of <
20% are carried through the period. Progged thickness values will
support the continuation of a warming trend, and max temps are
expected to be around 3-5 degrees above climo. A relatively dry
air mass and good radiational cooling conditions each night are
expected to result in min temps near-to-slightly-below climo.
&&
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
As of 120 pm EDT Tuesday:
Key Messages:
1) Slightly cooler early next week.
2) Small chances for mainly mountain showers or a storm most
afternoons, but otherwise remaining dry.
Weak upper trough centered over the region at the start of the
period will continue to weaken over the weekend, becoming displaced
by weak ridging early in the new week. Meanwhile 1030-ish mb surface
high pressure building into the northeast Conus will result in an
inverted surface ridge developing down the Eastern Seaboard Saturday
through Sunday, with effective weak backdoor cold front forecast to
push into our CWA late Saturday/early Sunday. This will act to shave
a few degrees off of temperatures for Sunday/Monday, bringing them
more in line with seasonal normals...if not slightly cooler than
normal. Otherwise, the air mass is expected to remain relatively dry
and stable through the period, and PoPs are limited to (at most) 20%
chances for diurnal showers or a storm across the mountains each
afternoon. Temperatures are forecast to rebound to above-normal
conditions by Tuesday, when global models are in good agreement in
depicting significant weakening of the inverted ridge...as surface
high pressure progresses rather quickly off the New England coast.
&&
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Showers are ongoing across the NC Foothills
and northern SC Upstate circa 1730z, and should see a marginal
increase in coverage over the next couple hours...especially across
the NC mountains.  This evening, there is a chance that convection
will escape the mountains and slide south across the SC Upstate, but
confidence is limited.  Whatever showers develop will dissipate by
late evening, giving way to dry and mostly-VFR conditions overnight.
 As usual, the exception is the mountain valleys, where there`s a
strong signal in both the operational and statistical guidance for
reduced visibility and low ceilings; for now, fog looks somewhat
favored over low stratus...so went with MVFR fog mention at KAVL and
only hinted at IFR-level non-cig clouds.  Convection chances appear
more isolated on Wednesday, and entirely confined to the mountains.
N/NW wind expected through most of the period...possibly becoming
WSW across the Upstate near the end of the period Wednesday
afternoon.
Outlook: Dry conditions expected through Saturday. Some mountain
valley fog will remain possible each morning wherever clouds do not
inhibit nocturnal radiation.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...JDL
NEAR TERM...MPR
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...MPR

NWS GSP Office Area Forecast Discussion