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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 181032
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
632 AM EDT Thu Apr 18 2024

.SYNOPSIS...
Showers and thunderstorms are possible Friday as a weak cold
front crosses the area, but unseasonably warm weather continues
through Saturday.  Below-normal temperatures and widespread light
rain is expected Sunday with cool and unsettled weather persisting
through Monday.  Drier and warmer weather will return to the area
Tuesday through Thursday next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 615 AM Thursday: Lots of deep layered dry air atop the
region today along with a building s/wv upper ridge will support
near record high temperatures, averaging 12-14 deg F above the
mid-April normals. Expect the mean flow to back to a more
westerly direction as mid-CONUS s/wv energy approaches,
spreading in considerable mid/upper clouds back in this evening.
We expect to be monitoring the progress of eastward moving
tstms as convection allowing models propagate activity, albeit
in a weakened state, into the mountains after midnight.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
As of 330 AM Thursday: A weak cold front will be approaching from
the west at the beginning of the period Friday morning underneath
weak shortwave energy rapidly propagating within zonal flow aloft.
The latest CAM guidance suggests that showers and possibly a few
weak thunderstorms will be ongoing, with an area of activity
likely associated with the upper-level energy departing the
southeastern zones early Friday morning as decaying convection
enters the mountain zones from the north and west along the front.
With little to no instability, the Friday morning activity will
quickly dissipate across the area.  However, some reactivation along
the front is expected Friday afternoon if we can evacuate enough
of the cloud debris from the morning convection and sufficiently
destabilize.  Initial development is expected across the mountains
where the best chance of showers and thunderstorms is expected,
but the instability there is expected to be weakest.  For now,
forecast soundings support SBCAPE of 750-1250 J/kg across the
Piedmont, with the highest values further south and west over the
western Upstate and Savannah River Valley as high temperatures
once again reach the mid-80s.  Steep low- to mid-level lapse
rates and 0-6km bulk shear values of 30-40 kts are sufficient
enough to support strong to severe thunderstorms Friday afternoon,
especially east of the mountains.  The profiles are supportive of
strong downdrafts and hail with deep-layer mixing, ample dry air
aloft, and sufficient instability within the hail growth zone.
At this time, however, a lack of large-scale forcing within the
zonal flow aloft suggests that coverage will be limited and that
any storms that develop will be isolated to widely scattered in
nature. Given the expected coverage and storm-motion, rainfall is
not expected to be appreciable overall.

The front clears out of the area Friday night, but the modified
airmass behind the front will not result in a significant cool down
for Saturday.  Isolated showers and perhaps a general thunderstorm
are possible across the Upstate Saturday afternoon with ample
low-level moisture in place, but the profiles are not supportive
of strong convection given poor lapse rates.  With mostly cloudy
skies expected for much of the day on Saturday, high temperatures
will top out in the lower to mid-70s or slightly above normal in
the mountain valleys and near 80 across the Piedmont, which is
still 4-6 degrees above normal.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 330 AM Thursday: The weather pattern remains unsettled
to begin the extended period as a low-amplitude southern stream
shortwave trough ejects out of the southern Rockies and rapidly
propagates across the southern tier during the day on Sunday.
Surface high pressure behind this shortwave will reinforce a
northerly flow across our area as isentropic lift ahead of the
shortwave induces widespread light showers across the region.
With dewpoints in the 40s, these showers will support dynamic
cooling of the low-levels and the development of in-situ CAD.
Therefore, temperatures will struggle to rise much from morning lows
as rainfall develops during the daytime hours.  The result will be
a dramatic change in the sensible weather with high temperatures
about 12-14 degrees below normal, struggling to reach the upper
50s in the mountain valleys and the lower 60s across the Piedmont.

CAD will persist into Monday while a stronger northern stream
shortwave trough crosses over the area Monday afternoon, resulting
in another chance of light showers across the region.  For now
guidance is suggesting temperatures will moderate a bit without a
source region of cool air, resulting in highs a few degrees warmer
than they were on Sunday but still 8-10 degrees below normal.
However, with lower thicknesses due to the shortwave trough,
mostly cloudy skies, and light precipitation, it would not be a
surprise to see these highs drift a degree or two lower in future
forecast packages.  This sets us up for a chilly Monday night
and Tuesday morning.  Frost is not out of the question for higher
mountain elevations where low temperatures are expected to reach
the mid- to upper 30s.

With the shortwave energy rapidly propagating offshore by
Tuesday, we will dry out and warm up as we head into the middle
of the work week.  High temperatures will return to near normal
Tuesday afternoon under mostly sunny skies. Temps will max out 3-5
degrees above normal on Wednesday as we tap into a bit of southerly
return flow on the west side of Atlantic high pressure ahead of an
approaching cold front from the north and west. The proximity of
the weak cold front across the Ohio Valley Wednesday afternoon and
evening reintroduces slight chance PoPs across the mountain zones,
but overall the area will remain relatively quiet and dry.
-- End Changed Discussion --

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
At KCLT and elsewhere: Cloudiness across the FA today will be
limited to MVFR lvl stratocu along the Tennessee border this
morning.  These clouds will thin as the morning wears on leading to
just a few cumulus in the mountains this afternoon.  Overall, winds
will be on the light side and tending from the west.  Clouds will be
on the increase as higher level cigs develop later tonight.  Western
portions of the FA stand the best chance for seeing a shower or
thunderstorm overnight.

Outlook: Unsettled conditions are expected Friday and into the
weekend, with periodic precip/possible TS and restrictions. Drier
conditions return for Monday/Tuesday.
-- End Changed Discussion --

&&

.CLIMATE...

RECORDS FOR 04-18

  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      90 1896     44 1921     60 1927     28 1905
                                        1891
   KCLT      93 1896     45 1983     66 1896     32 2001
   KGSP      89 2002     51 1983     66 1927     28 1905
                1967

 &&

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

&&

$$

SYNOPSIS...JMP
NEAR TERM...CSH
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...CSH
CLIMATE...GSP