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221
FXUS62 KGSP 201438
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1038 AM EDT Thu Jun 20 2024

.SYNOPSIS...
Strong high pressure will keep the area dry through Friday and cause
a heat wave to build across the region through early next week.
More typical shower and thunderstorm activity will gradually return
to the area Saturday through Monday as a weak cold front approaches
from the west.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1030 AM Thursday: Very broad upper ridging will remain
centered to our north and help keep the atmosphere suppressed
thru the near-term period. The center of the ridge is expected
to retrograde westward today/tonight while modestly flattening
as broad upper trofing over Canada expands southward. At the
sfc, sprawling high pressure will continue to dominate much of
the Atlantic basin and keep relatively dry, ELY low-level flow
over our area today. A weak sfc wave is expected to become more
organized just north of the Bahamas today, but it remains
unclear whether this feature will develop into a sfc low
pressure system before it moves over Florida early Friday.
Regardless, it is not expected to have a significant impact on
our sensible wx, with the deeper moisture associated with the
system remaining to our SE thru the end of the period. Much like
the past few days, any diurnal instability should be limited-
to-non- existent today. Thus, a dry fcst persists thru the
period. Highs today should be a degree or 2 warmer than
yesterday (Wednesday) and slightly above climatology for the 3rd
week in June.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 330 AM EDT Thursday: The upper-level pattern will be evolving
through the short-term period as the impressive 597dm ridge
centered over the Mid-Atlantic and Ohio Valley at the beginning of
the period begins to respond to a weak easterly wave approaching
the northern Florida and Georgia coastlines.  The inverted trough
associated with the wave will cause a weakness along the Atlantic
coastline in the expansive anticyclone which will persist through
the end of the period Sunday morning.  Guidance is in fairly good
agreement that weak low pressure along the wave will move across
Georgia and northern Florida later Saturday into early Sunday,
well south of the area.  Therefore, the main story through the
period will be the building heat across the forecast area resulting
from the subsidence overhead.  Friday`s high temperatures will
start us off about 2-4 degrees above normal and that will be the
"coolest" highs through the remainder of the forecast.  Fortunately,
dewpoints will remain below 65 as weak easterly flow persists so
the humidity will not be oppressive to end the work week.

The easterly low-level flow will begin to veer southeasterly Friday
night into Saturday as Atlantic high pressure shifts south towards
Bermuda.  This will cause a gradual increase in moisture advection
beginning on Saturday from the subtropical airmass associated
with the easterly wave as deep-layer ridging settles overhead.
Expect the sinking airmass to cause high temperatures to peak a few
degrees warmer than Friday, reaching 90 across the mainstem mountain
valleys and 93-95 east of the Escarpment or about 5-7 degrees
above normal area wide.  The current guidance is unfortunately a
bit more aggressive with dewpoints on Saturday afternoon across
the southeastern-most zones in response to the moisture from the
easterly wave.  With dewpoints in the upper 60s to near 70 now
possible in the lower Catawba and upper Savannah River valleys, heat
indices may approach 100 in isolated locations Saturday afternoon.

The favorable low-level flow and modest moisture advection is
introducing slight-chance to chance diurnal PoPs back into the
National Blend guidance for the mountains on Saturday afternoon.
However, the NAM and GFS profiles suggest the subsidence-induced
inversion around 650mb is going to be quite difficult to overcome.
The official forecast therefore tempers expectations just a bit
for now.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 330 AM EDT Thursday: The extended period begins with continued
westward retrogression of the upper-level anticyclone in response to
height falls across the Ohio Valley and Mid-Atlantic in response to
a shortwave trough.  An attendant weak cold front will be entering
the Ohio Valley on Sunday while remnants of the easterly wave stall
over Georgia.  Therefore, the forecast area can expect increasing
diurnal PoPs as the lower heights aloft work to chip away at the
inversion capping convective activity.  Unfortunately, overall QPF
is meager at best and will do nothing to combat the increasingly
dry conditions.  The heat ridge will persist in the lower half of
the atmosphere as a southwesterly flow pattern develops; therefore,
our high temperatures for Sunday actually look to be another degree
or two higher than Saturday while the increasing moisture across
the area results in dewpoints in the upper 60s to lower 70s from
the mountain valleys to the Piedmont.  With highs solidly in the
mid-90s east of the Escarpment, expect pockets of low-100 heat
indices across the favored lower Catawba River and upper Savannah
River valleys, including the Charlotte metro.

The weak cold front will be approaching our area Sunday night into
Monday morning, therefore it looks like Monday may offer our best
coverage of showers and thunderstorms.  With the proximity of
the front, PoPs will persist Sunday night through Monday night,
peaking with the heating of the day Monday afternoon.  However,
with the weak front and a subtropical ridge axis stretched across
the Gulf Coast, we lack sufficient forcing or Gulf moisture flux
to advertise anything more than a tenth of an inch of total QPF.

The guidance has been trending towards a cleaner frontal passage
for Monday night into Tuesday, and PoPs have therefore trended down
for Tuesday as it is looking to be a fairly dry day across the area.
Guidance is suggesting yet another front may be approaching the area
later Wednesday so diurnal PoPs return to the forecast Wednesday
afternoon.  Regardless, there is no synoptic scale pattern change
to erode the lower-level heat dome in place across the southern US
through the end of the forecast period.  Expect highs to reach the
mid-90s each day through Wednesday.  At this time, Tuesday looks
to be the most tolerable of the period, with the frontal passage
shaving a degree or two off the highs and ushering in dewpoints
in the lower 60s.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Expect VFR conditions to continue thru
the 12z taf period across our area. It`s looking like we won`t
see much if any fog development this morning. Otherwise, we can
expect little change in the synoptic pattern for today with dry
high pressure in control. The lyr of sct to bkn cirrus currently
over our area will gradually sct thru the morning with another
round of sct VFR clouds expected this aftn and evening. Winds
will remain light to calm at most sites thru the morning and
then pick up from the ENE outside of the mtns for the afternoon/
evening. At KAVL, winds will pick up from the SE this afternoon
and remain SELY thru the evening.

Outlook: An expansive upper ridge will keep things mostly dry
with VFR conditions through Friday. Mtn valley fog and/or low
stratus will be possible each morning. Isolated diurnal convec-
tion will be possible over the mtns on Saturday, with a return
to more sct convection across the region Sunday and Monday.

&&

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

&&

$$

SYNOPSIS...JMP
NEAR TERM...JDL/JPT
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...JPT