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000
FXUS62 KGSP 211353
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
953 AM EDT Sun Apr 21 2024

.SYNOPSIS...
Much cooler temperatures and widespread light rain is expected
through this afternoon with drier weather returning by Monday.
Warmer weather returns by Tuesday and continues through the workweek.

&&

.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 200 AM EDT Sunday: Shortwave trough will be in the midst
of shifting across the CFWA, while surface high propagates
eastward from the Lower/Mid MS Valley on Monday. In this case,
cool north-northwesterly low-level flow and colder air aloft will
keep temperatures ~10 degrees below normal for afternoon highs,
with mostly sunny skies. The aforementioned surface high will set
up shop over the CFWA by Monday night and set the stage for good
radiational cooling conditions across the region. With light winds,
tight dewpoint depressions, and temperatures remaining 6-10 degrees
below normal, expect areas of frost to develop, mainly in the
southern/central NC mountains and locations along and north of I-40
(active growing zones). A Frost Advisory may be needed for these
zones Monday night, especially if trends continue to run cooler per
model guidance. Airmass will begin to modify Tuesday as the surface
high slips offshore the Southeast Coast and weak south-southwesterly
WAA filters into the area. Factor in rising heights and afternoon
highs will return to near-normal values for most locations. Stout
shortwave trough with an attendant frontal boundary will begin to
encroach from the northwest. The front is forecasted to be near the
TN/NC border by daybreak Wednesday. The parent low and better
forcing will reside well to the north and east of the CFWA, while
the front moves into a moisture starved environment. As a result,
only able to muster up slight chance PoPs along the immediate TN
border. Otherwise, overnight lows Monday will rebound and return to
near-normals values.

&&

.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 /14Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Starting out VFR, east of the mountains, but
this will quickly go downhill as the rain brings a low cloud ceiling
down to the MVFR level through mid-morning. Guidance suggests a
further downward progression into the late morning. The latest
guidance is quite pessimistic with its IFR stratus deck lingering
through much of the day. I`m not yet convinced of the IFR and have
kept most places prevailing MVFR for the time being, with a TEMPO
for IFR in the early afternoon. Wind should remain NE through the
daytime. The rain will get carried off to the east in the late
afternoon and early evening, and when that happens, expect the
vis/ceiling to recover gradually. Most places end the period VFR.

Outlook: Dry, VFR conditions continue Monday 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...PM