Text Products for AFD Issued by GSP

Area Forecast Discussion
Issued by NWS Greer, SC
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FXUS62 KGSP 211711
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
111 PM EDT Sun Apr 21 2024

.SYNOPSIS...
Much cooler temperatures and widespread rain will continue the rest
of today before drier conditions return tonight into Monday as high
pressure builds into the region. Warmer weather returns on Tuesday
with dry conditions persisting over the area. Warm temperatures will
linger through the workweek despite a weak cold front tracking
across the western Carolinas on Wednesday. This front may lead to
rain showers along the Tennessee border Tuesday night into
Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
1000 AM Update...The fcst and high PoP trends are working out pretty
good this morning. A moist sfc bndry continues to slowly shift east
and expect periods of light rainfall over most areas to continue
into the afternoon. The far srn zones will likely experience rounds
of moderate rain with a couple embedded tstms possible as waves a h5
vort energy traverse the mid levels. Temps will rise little over the
next several hours due to deep layered clouds and precip with highs
holding in the 50s.

Otherwise, the main band of isentropic lift starts to translate to
the east, as does the upper divergence because the jet axis also
shifts eastward. The damage to the forecast will have already been
done by early afternoon, however, locking in a strange sort of in-
situ cold air damming wedge. Naturally, temps will be cool...quite a
bit cooler than recent days and not getting out of the 50s during
daylight hours. The high temps for the calendar day have probably
already occurred in most places. For tonight, this wedge is an
unusual set-up, what with the high pressure center over the central
High Plains and little reflection over the Mid-Atlantic region. This
odd arrangement comes to what seems to be an early end, as the cool
pool east of the mtns looks like it will drain away in the early
morning hours on Monday. Temps may cool off enough by daybreak
Monday and sky will start to clear off as high pressure builds in
over the mtns, to support some frost development in the mtn valleys.
As it stands, though, the wind forecast is too much to support frost
formation. Low temps should be 5-10 degrees below normal.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 110 PM EDT Sunday: Dry sfc high pressure will linger over the
Southeast Monday night into Tuesday leading to continued dry weather
and mostly clear skies. Great radiational cooling conditions as well
as light winds may allow for some patchy frost development Monday
night into daybreak Tuesday across portions of the NC Foothills and
northern NC Piedmont. However, lows Monday night look borderline at
best (despite being several degrees below climo) for frost
development in these areas so confidence is low. Lows Monday night
will dip into the mid 30s across the mountains, with the upper 30s
to lower 40s expected elsewhere. Despite the colder temps across the
mountains, frost formation is not expected in the central/southern
NC mountains (where the growing season is active) as forecast
dewpoint depressions are too large at this time. Temps on Tuesday
will be noticeably warmer thanks to great insolation and S/SW winds.
Highs will climb into the lower 70s across east of the mountains and
across the mountain valleys. Despite the warmer temps, highs will
still end up a few degrees below climo.

A cold front will approach out of the NW Tuesday night allowing
cloud cover to increase across the northern half of the forecast
area. Increased cloud cover along with S/SW`ly flow remaining in
place ahead of the front, will lead to much warmer lows Tuesday
night. Thus, frost development is not expected to be as much of a
concern. Lows should end up a few degrees above climo, ranging from
the mid 40s to lower 50s across the forecast area. The cold front
will track across the forecast area on Wednesday, allowing winds
across the mountains to turn NW`ly. Winds east of the mountains will
turn W`ly. This downsloping flow will allow temps to be a few
(across the mountains) to several (east of the mountains) degrees
warmer compared to Tuesday. Thus, highs will remain a few degrees
above climo Wednesday afternoon. Rain showers may develop along the
NC/TN border on Wednesday thanks to the cold front, so have slight
chance PoPs for these locations.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 330 AM EDT Sunday: Model guidance sag the aforementioned
frontal boundary through the rest of the CFWA during the day
Wednesday. The latest runs are showing some fanfare of showers
and thunderstorms developing along the boundary in the Piedmont
zones during peak heating. Decided to hold off on mentionable
PoPs for Wednesday afternoon since this is the first run(s)
showing this possibility. Afternoon highs will run slightly above
normal Wednesday with continued southwesterly WAA ahead of the
front as the surface centers itself between the Southeast Coast
and Bermuda. As of now, model guidance makes a clean fropa by
Wednesday night and a canadian surface high moves in behind the
front over the Great Lakes region by Thursday, while the front
becomes quasi-stationary south of the I-20 corridor. This will
set up a very pleasant day Thursday in this scenario with highs
at or slightly below normal. Surface high will remain in control
of the sensible weather through early Friday as it shifts across
the northeastern CONUS and settles offshore the Mid-Atlantic
Coast by Friday. Low amplitude upper ridging will move over the
eastern-third of the CONUS by late into the upcoming workweek, while
a digging upper trough induces surface cyclogenesis over the High
Plains. This is likely our next weather maker as the aforementioned
stalled boundary generates warm frontal activation and lifts north
of the CFWA, placing the area into a warm sector regime. Whether or
not showers and storms will form along the warm front is still in
question this far out, but the parent low is forecasted to move into
the Great Lakes region. Model guidance this far out noses a stronger
upper ridge into the area, which keeps the trailing frontal boundary
from reaching this far south and east through the forecast period.
Temperatures should remain near-normal or slightly above through the
end of medium range.

&&

.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: A mixed bag of rain and MVFR/IFR flight cats
across the area this afternoon. Expect a band of heavier precip
currently across the Upstate to help maintain IFR conds and bring
IFR CIGs to KCLT by 20z. General improving conds to MVFR and VFR
later this afternoon as drier air filters in from the north. Winds
remain aligned n/ly to ne/ly outside the mtns with periodic low-end
gusts possible as an insitu wedge pattern persists. Winds at KAVL
remain aligned nw/ly thru the period.

Outlook: Dry, VFR conditions continue Monday thru mid-week as high
pressure builds over the region from the west.

&&

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

&&

$$

SYNOPSIS...CAC
NEAR TERM...PM/SBK
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...SBK
National Weather Service Regional Headquarters
