Harris, North Carolina Weather Forecast Discussion

006
FXUS62 KGSP 221027
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
627 AM EDT Mon Sep 22 2025
.SYNOPSIS...
Scattered showers and thunderstorms are possible, mainly in the
mountains and foothills, today through Wednesday. Temperatures
will remain at or slightly above normal for this time of year. Rain
and storms are likely across much of the areas Thursday and Friday.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 130 AM EDT Monday: The area of surface high pressure off to
the northeast gets pinched and slides out to sea during the period.
Meanwhile, a very weak trough moves eastward toward the CWA before
flattening Monday night. By the late afternoon and evening, guidance
enhances a shortwave across the area with some weak DPVA sweeping
over the mountains. CAMs show a few isolated showers popping up
above the terrain during the late afternoon hours. Given the lack of
instability (less than 200 J/kg of sbCAPE), not anticipating much in
the way of convective activity. However, with daytime heating, there
could be just enough for an isolated thunderstorm. For this, will
cap PoP to slight chance (15-35%) for the far western NC mountains.
Outside of the few showers that may occur, nothing of significance
is expected during the near term. Daytime temps peak in the mid 80s
outside the mountains and overnight lows start to edge upward as
winds turn southerly.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 1215 AM Mon: Weakly forced regime effectively dominated by the
Bermuda High persists Tuesday. That said, some progression finally is
seen with the MS/OH Valley frontal zone: a weak shortwave moves
across the NE CONUS, pulling the front closer to the Appalachians but
still not seemingly bringing it into the CWA, and inducing weak
height falls although not necessarily better lapse rates. Midlevel
flow turns westerly and picks up a bit, promoting some moisture
advection into our area. Temps trend warmer thru airmass
modification. Together these changes should give ridgetop initiation
a better chance of leading to deep convection over our mountains, but
also offers more possibility of activity propagating in from points
west. PoPs increase to a solid chance over the mountains, and
mentionable values expand farther into the NC foothills given better
westerly steering flow.
Tue night into Wednesday, the deep 500mb wave or low over the western
Great Lakes already looks to be in phase with a similar feature
exiting the central Rockies. On Wednesday global models depict these
merging into a sizable closed low invof Illinois, with the GFS and
ECMWF having trended fairly close but the Canadian GDPS farther
north. GFS, ECMWF and NAM all depict a sfc cyclone taking shape as
well. Regardless the stalled front appears to activate as a warm
front north of our region, and heights flatten out if not rise
slightly aloft. Temps accordingly trend warmer another day. Vertical
profiles don`t look appreciably different compared to Tuesday w.r.t.
in-situ convective development. The best upper divergence and DPVA
still are favored over KY/TN/OH/WV during the day, but that suggests
still more potential for activity to fire west of the mountains and
some chance for such dynamics to enhance mountain initiation during
peak heating.  PoPs increase a few more percent and expand slightly
farther outside the mountains in the afternoon and early evening. The
system to our west and accompanying dynamic lift inch eastward Wed
night, but also a modest 850mb LLJ may promote elevated convection,
so PoPs increase slightly overnight and expand to all zones by early
Thu morning.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 100 AM Mon: Major models depict the cutoff low rejoining the
westerlies by Thu night as sfc low tracks NE across the Great Lakes.
The 21/12z ECMWF and GDPS now show a deep but open 500mb trough by
Friday, with the result being a cleaner fropa and a relatively fast
return to dry high pressure over a broad swath of the southeastern
CONUS.  The GFS instead shears the low apart back into shortwaves,
with the southern wave forming into a new cutoff low over the lower
MS Valley on Friday, in position to maintain unsettled warm-sector
weather for our CWA thru the weekend. These differences lead to a
rapid drop in forecast confidence beyond Thursday night.
Regardless, on Thursday moisture flux and upper divergence should
increase prior to the front, such that the peak rainfall
chances/coverage are expected then into Thu night. PWATs rise to more
than 150% of normal on the global models, and although the degree of
instability varies among models and ensemble members, heavy rain
potential from any convection should be appreciably higher than on
the previous days. 0-3km/0-6km both increase Thursday as well and
organization and severe weather (mainly damaging wind) cannot be
ruled out. The GDPS is the most progressive with the trough,
suggesting low precip chances Friday; the ECMWF still produces precip
over the area Friday, though PWATs decline with drying aloft,
suggesting lesser heavy rain potential. The GFS as noted before would
keep us active. Likely PoPs still are warranted for much of the CWA
on Friday given the 21/12z ECMWF solution. Post-frontal or NW-flow
showers could also result Fri or Fri night. Small PoPs Saturday are a
nod to the earlier solutions (still part of the NBM) reflecting a
more GFS-like solution. With less support for precip Sunday, PoPs
peak still lower that day.
Temps should trend cooler Thursday, most notably in the mountains,
and back to near normal in all areas Friday. The drier EC/GDPS
solutions would suggest sunnier conditions and some warming over the
weekend whereas the GFS would be near or below normal.
It is worth pointing out the last two runs of the GFS bring a
tropical system (arguably "the H storm") near the Outer Banks circa
Sunday, and the EC/GDPS have a system farther out in the Atlantic at
that time. The latter solutions favor development of a weak upper low
near the SE coast which could lead the storm to recurve, but such a
development could lead to precip redeveloping in the region by early
next week anyway.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: VFR conditions prevail at the majority of
terminals through the period. Persistent FG at KAVL this morning.
Will go ahead and prevail VLIFR through 14z. Also KHKY retains MVFR
restrictions for BR at 5SM, so will also prevail this through 13z.
Conditions at both KAVL and KHKY should quickly clear up after
sunrise and return to VFR. Winds start out calm at almost all sites
except KCLT and quickly pick up out of the S/SE. There could be a
few isolated SHRA/TSRA in the mountains, including KAVL during the
afternoon hours. A PROB30 should suffice from 18-23z. For tonight,
another round of BR/FG, this time will start the KAVL TEMPO earlier
given the pattern for the last few nights.
Outlook: Mountain shower and thunderstorm chances through midweek.
Fog and stratus possible each morning in the mountain valleys.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...Wimberley
NEAR TERM...CP
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...CP

NWS GSP Office Area Forecast Discussion