Royston, Georgia Weather Forecast Discussion

859
FXUS62 KGSP 150608
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
208 AM EDT Mon Sep 15 2025
.SYNOPSIS...
High pressure over the region today weakens as a low pressure system
moves north along the North Carolina coast Tuesday and along the
Virginia coast Wednesday. High pressure returns and remains in place
through the weekend.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 200 AM EDT Monday...
Key Messages:
1) Patchy Mountain Valley Fog and Low Stratus Possible Each Morning
but Confidence is Lower than the Last Few Mornings
2) Spotty Showers Should Develop this Afternoon into Tonight, Mainly
in Western North Carolina and Across the Mountains
3) Breezy Winds Develop this Afternoon and Early Evening Along I-77
4) Slightly Cooler Today, Especially in the North Carolina Foothills
and Piedmont, Thanks to Lingering Cloud Cover
A closed upper low meanders over the Carolinas through the near
term. Meanwhile, sfc high pressure gradually weakens as a coastal
low slowly lifts NNW towards the North Carolina Outer Banks. This
should allow rain chances to return this afternoon into tonight,
mainly across the mountains and in western North Carolina.
Dry conditions will continue area-wide through the morning hours.
Mountain valley fog and low stratus may develop through daybreak but
increasing cirrus should act to limit radiational cooling somewhat.
Thus, not expecting fog/stratus to be as dense or as widespread as
the last few mornings. Morning lows will end up a few degrees above
normal thanks to lingering cloud cover.
The CAMs remain at odds regarding the exact coverage of convection
this afternoon and evening. The 00Z HRRR depicts better better
coverage of showers compared to the 00Z NAMNest. However, both CAMs
show the potential for some shower activity to break containment of
the mountains this evening into tonight, sinking southward into the
South Carolina Upstate and northeast Georgia. Thus, it appears that
confidence on spotty showers will be highest across the mountains
and lower across northeast Georgia and the South Carolina Upstate
this afternoon and evening. The 00Z CAMs also depict some spotty
showers pushing into the North Carolina Piedmont overnight into
daybreak Monday as the coastal low lifts NNW. 00Z CAMs do seem to
agree that coverage with this activity should be mainly isolated,
scattered at best. Opted to remove any thunder mention the NBM had
through the near term as instability does not look all that
impressive, especially with scattered to broken cloud cover
remaining overhead. Cloud cover will allow for slightly cooler highs
this afternoon for most locations but especially across the North
Carolina Foothills and Piedmont. Highs across these locations will
only reach into the lower 80s. Breezy winds (15-20 mph) will develop
this afternoon and early evening along/near I-77 in association with
the coastal low lifting NNW. Gusts should diminish around 00Z.
Lows tonight will remain a few degrees above normal thanks to
lingering cloud cover. Patchy mountain valley fog and low stratus
could develop overnight into daybreak Monday but confidence is low.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 105 AM EDT Monday: Guidance in good agreement regarding the
Carolina coastal low during this period. Unfortunately, the result
is little in the way of some much needed rainfall for the area. The
low, while moving onshore across NC, remains much closer to the
coast than some earlier model runs were suggesting. This keeps the
deeper moisture and better forcing to our east. There will be enough
moisture and forcing on the developing easterly flow for scattered
showers Tuesday over the NC Piedmont and northern foothills, quickly
dropping off to no precip for most of the Upstate and NE GA. There
will be a chance of diurnal thunderstorms across the mountains,
including the Upstate and NE GA mountains, where some weak
instability can develop. Overall the QPF will be light, but some
brief, heavy rainfall is possible in any storms. The low north into
Virginia on Wednesday taking the deeper moisture and forcing with
it. This brings an end to precip chances for all but the NC
mountains where some lingering moisture and weak instability could
lead to isolated diurnal convection. The clouds and scattered
showers Tuesday will keep highs around 10 degrees below normal for
the NC Piedmont and northern foothills. Highs around 5 degrees below
normal expected elsewhere. Highs rise to within a few degrees below
normal Wednesday. Lows a few degrees below normal.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 145 AM EDT Monday: 00Z operational guidance is trending drier
for the medium rage. A short wave ridge slowly builds into the area
through Saturday. The ridge axis moves to the east on Sunday as
trough moves into the MS River valley. At the surface, weak high
pressure over the area Thursday and Friday is reinforced by high
pressure moving out of Canada into New England Saturday and Sunday.
There is a weak back door cold front associated with the reinforcing
high, however it remains dry and/or dissipates as it moves into the
area. The ridge of high pressure becomes squeezed by the end of the
period from the cold front associated with the trough to the west
and low pressure forming off shore along a baroclinic boundary but
remains strong enough to keep moisture and precip at bay. This 00Z
ECMWF has come in drier than the 12Z run trending toward the GFS and
Canadian. It does keep some precip over the area, especially the
mountains. Given the uncertainty have followed the guidance blend
which is weighted toward the older guidance with chance PoP over the
mountains and slight chance elsewhere Saturday and Sunday.
Obviously, confidence is low in this solution given the trends in
the guidance. Highs rise back to a few degrees above normal by
Friday then a few degrees below normal by Sunday. Lows near to
slightly above normal through the period.
&&
.AVIATION /06Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: VFR again through the 06Z TAF period outside
of mountain valley fog and low stratus this morning. SCT to BKN
cirrus hang around through the TAF period. Thus, restrictions across
the mountain valleys this morning are not expected to be as bad as
the last few mornings. Maintained a TEMPO at KAVL for IFR
restrictions closer to daybreak. Per usual, mountain valley fog and
low stratus will lift shortly after daybreak. Winds at KAVL will
generally remain calm through daybreak, although winds may pick up
out of the NNW briefly around sunrise. Winds east of the mountains
will also generally be calm through daybreak, but could go light
N/NNE at times. Winds at KAVL will gradually turn SE/ESE later this
morning before going calm to light and VRB again this evening into
tonight. Winds east of the mountains will turn more NE after
daybreak before toggling back N/NNE tonight. Wind speeds will range
from ~4-8 kts today. However, slightly stronger winds will develop
this afternoon/early evening at KCLT. KCLT will see wind speeds from
7-10 kts and gusts from 15-18 kts, with gusts diminishing ~00Z.
Spotty showers may develop this afternoon, lingering into tonight.
Confidence on whether showers will track directly over any of the
terminals remains low so maintained dry TAFs for now. SCT cumulus
may develop this afternoon/early evening, especially where any
showers develop.
Outlook: Mountain valley fog and low stratus remain possible each
morning but could be limited somewhat by lingering cloud cover
through mid-week. Rain chances will stick around through mid-week
with periodic MVFR restrictions possible at times. Drier conditions
should return by Friday.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...RWH
NEAR TERM...AR
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...AR

NWS GSP Office Area Forecast Discussion