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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 220741
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
341 AM EDT Sun May 22 2022

.SYNOPSIS...
-- Changed Discussion --
A cold front will approach the region from the west today but
won`t finally move across the region until maybe late Monday or
early Tuesday. In the mean time, the weather should remain warm
and humid because of a weakening Bermuda High. Once the front
finally sinks to the south, cooler temperatures are expected for
the middle part of the week due to high pressure ridging down
from the northeast. A stronger cold front will move in from the
west on Thursday and is expected to cross the region on Friday,
hopefully providing some much needed widespread rainfall.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM EDT Sunday: With a longwave ridge axis now well to
the east of the Carolinas, strengthening moisture flux has allowed
profiles to remain moist in the wake of Saturday`s convection, and
widespread cloud cover is observed in satellite imagery across the
western Carolinas.  Guidance suggests that a weak shortwave will
traverse this ridge from around dawn through the early afternoon,
dredging up some weak DPVA mainly over the southeastern tier
of the CWA, and perhaps resulting in increased cloud cover and
even some sprinkles here early Sunday.  Otherwise, heights gently
fall from Sunday afternoon onward, as a deep trough out over the
Midwest begins to encroach on the forecast area.  850 and 700mb
charts indicate a frontal passage late in the day on Sunday, which
should be enough to trigger some convection across the region in
the afternoon and evening.

CAMs look tame through mid-afternoon, with sparse coverage
of light showers and perhaps a bit of thunder across the area.
Destabilization is expected ahead of the front, but with less gusto
than on Saturday; absent much synoptic support, midlevel lapse rates
look more anemic.  So, HREF and SREF are in pretty good agreement
on sbCAPE of only 1000-1200 J/kg.  Furthermore, lax 850mb flow means
poor low-level shear, and even the most aggressive CAMs only produce
in the neighborhood of 15kts of deep-layer shear.  Consequently,
early-afternoon convection looks to be poorly organized and not
especially interesting.  By early evening, however, the arrival
of the cold front will help to focus activity along a narrow band
where moisture pools ahead of the boundary.  This looks to trigger
a line of convection that will sweep across the western Carolinas,
and although it`s unlikely to grow upscale into an MCS due to the
weakly-sheared environment, activity just along the front will be
prone to gusty winds and brief heavy rain.

The ARW and NAMnest are in remarkably good agreement that the
frontal convergence zone will be near or east of the I-85 corridor
by 06z Monday, and fully south and east of the forecast area
by daybreak.  Profiles look to dry out at least a bit, but winds
quickly rebound and become southerly again, limiting the amount
of drying likely at least through Monday morning.  Cloud cover
expected throughout the near term should reduce diurnal temperature
variation, with lows near or above climo and highs only a category
or two above climo.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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As of 314 am Sunday: The forecast for the early part of the week is
tricky as we undergo a complicated and messy transition to a cold
air damming wedge. A short wave riding up and over the eastern
upper ridge will keep the cold front in close proximity through
Monday...probably draped across the mtns and then along the VA/NC
border...warranting a relatively high precip probability as we
have that focus for convective development. The guidance moves a
large sfc high over the flattened East Coast upper ridge Monday
night, sliding it across Ontario to Quebec and into a prime spot
to support the development of a cold air damming wedge that should
set up early Tuesday morning as the old front slides southward
with the cool part of the diurnal cycle. Assuming that happens on
that timeline, Tuesday would remain cloudy and cool, perhaps 5-10
degrees below normal in spots, with light precip in the morning
and convection developing on the boundary across the srn part of
the fcst area. At this time, the amount of rain looks beneficial,
and the relatively stable boundary layer across most of the region
would preclude severe storms for the most part.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 243 am Sunday: The latter half of the week appears tonight as
more of a slow moving target. The new guidance rebuilds the upper
ridge off the East Coast more quickly Tuesday night in response
to the deepening upper low over the Plains. The net effect will
be that our parent sfc high will remain more anchored closer to
the New England Coast for longer, which means we will still be
dealing with the cold air damming wedge on Wednesday morning, or at
least what looks like a stubborn remnant cool pool. The guidance
has trended toward a more northwestern track of the Plains upper
low and also trended toward lifting it out earlier, which means
a renewal of isentropic lift perhaps by Wednesday afternoon. All
this makes temps really tricky, which could easily end up 5-10
degrees warmer or cooler than fcst. Strong southerly warm advection
should overwhelm the remnant wedge by Thursday morning. Thereafter,
paints an optimistic picture with plenty of response to the influx
of deep moisture and forcing, so high precip probs are still in
order. The guidance has sped up the progression of the front,
suggesting that the main threat for severe storms and heavy rain
might be Thursday/Thursday night, but confidence in either remains
to low to mention. The front should be to our east by the end
of Friday. In its wake, expect an upstream ridge to support high
pressure through the weekend. Will keep the weekend dry for the
time being. Temps will be close to normal for Thursday through
Saturday, with a warmup likely by Sunday.
-- End Changed Discussion --

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Remnant convection has ended across the
western Carolinas, with prevailing VFR conditions expected at
the TAF sites for the next few hours, gradually degrading to at
least MVFR ceilings with some periods of IFR, especially later
in the night.  Have presently timed the introduction of MVFR
ceilings at 08-09z, but low confidence on this timing given lots
of disagreement between guidance sources.  Not anticipating any
visibility issues except in isolated locations in the mountain
valleys.  Conditions will generally return to VFR after daybreak, as
a mixed layer grows and cloud bases rise accordingly.  Convection is
once again a distinct possibility, with VCSH/VCTS warranted across
the region early in the afternoon, then prevailing -SHRA with
PROB30s for -TSRA in the evening as a cold front pushes across
the NC Piedmont.  Timing and intensity of this rain/thunder is
still somewhat in question, but generally looks to be better in
coverage but lower in intensity compared to Saturday`s convection.

Outlook: Diurnal convective chances continue thru much of next
week, with associated restrictions possible with any showers or
thunderstorms. Nocturnal fog/stratus will be possible as well,
especially where rain has recently fallen.

&&

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

&&

$$
SYNOPSIS...PM
NEAR TERM...MPR
SHORT TERM...PM
LONG TERM...PM
AVIATION...MPR