569
FXUS62 KGSP 161830
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
230 PM EDT Sun Jun 16 2024

.SYNOPSIS...
Strong high pressure will gradually build over the region through
much of the week keeping temperatures above normal. Showers and
thunderstorms will be possible this afternoon and again tomorrow
afternoon, but drier conditions are expected to return Tuesday.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 200 pm Sunday: Per the latest SPC Mesoanalysis, the atmosphere
has destabilized to the tune of 2000-3000 J/kg of sbCAPE across the
western ~third of the forecast area this afternoon. Scattered deep
convection has fired across the ridge tops of the Smokies, Balsams,
and adjacent mountain ranges this afternoon, with a few strong cells
noted...primarily just west of the CWA. With an anticyclone centered
virtually overhead, steering current are very weak at < 10 kts, so
any cell that develops will have the potential for dropping a quick
1-2" before raining itself out...and can`t rule out an isolated
excessive rainfall threat with storms that become anchored on
terrain features and exhibit a little more longevity. With
instability being quite robust, occasional strong storms will
continue, while one or two pulse severe storms are probably a good
bet...with favorable downdraft CAPE supporting a microburst threat.
(Very high freezing levels of around 15kft should preclude even a
marginal large hail threat.)

The potential for at least isolated convection should eventually
spread east of the mtns, particularly the foothills where a weak SE
upslope flow, a weak surface boundary (reflected by wind shift zone
near the NC/SC border), and perhaps an outflow boundary or two
emanating from mountain convection will provide the main sources for
parcel lift. Having said that, instability decreases across the
eastern third of the area, esp across the NC northern foothills and
northwest Piedmont, where low clouds have stubbornly held through
the day. PoPs will therefore feature a decreasing trend from
west-to-east. Convective chances will linger into the evening hours
across much of the area, steadily tapering down from late evening
through the overnight. Min temps will be several degrees above
climo.

Upper anticyclone will begin wobbling northeast away from the area
on Monday, but will nevertheless remain the dominant synoptic scale
feature impacting the sensible weather across the Southeast and
Mid-Atlantic. Meanwhile, surface ridge extending from strong high
over the northwest Atlantic will build more strongly into our CWA,
which will act to begin advecting lower theta-E air into the eastern
zones throughout the day. Deep layer/mean cloud bearing flow is also
forecast to become increasingly weak...less than 5 kts by Mon
afternoon. The lower instability and weak steering flow suggests
mountain diurnal convection is more likely to stay confined there on
Monday, and PoPs range from 50/60% across the mountains...to barely
slight chance across the Piedmont. Instability will again be
sufficient to support a brief pulse severe storm or two, but locally
heavy/perhaps excessive rainfall may become more of a threat owing
to the expectation of even slow cell motion. Max temps are forecast
to be 0-2 degrees above climo.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 130 PM EDT Sunday: A large upper ridge will be centered over
the Carolinas and VA as we move into the short term, and will slowly
elongate as it drifts north, expanding across New England and down
the Eastern Seaboard through the period. Strong surface high
pressure centered over the northern Atlantic will be ridging toward
the Carolinas bringing east to southeasterly upslope flow off the
Atlantic. The placement of this surface high so far to the north
will somewhat balance out the subsidence and increasing thicknesses
from the upper ridge (not for long), keeping temperatures through
the near term pretty close to seasonal normals. No convection
expected under the expanding ridge but typical scattered afternoon
Cu, especially Tuesday afternoon in the mountains closer to the
moisture fetch off the Gulf along the western periphery of the high.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 145 PM EDT Sunday: The strong upper ridge will remain firmly
in place over the Mid-Atlantic as we move into the extended, while
the Atlantic surface high begins to slowly shift southward, bringing
the surface flow a little more southeasterly. The dry forecast will
continue on Thursday as temperatures begin a slow climb. Meanwhile,
and this is already noted on the latest NHC outlook, guidance is
wanting to develop some sort of tropical wave near the Bahamas at
this point in the easterly flow around the southern edge of the
surface high (the wave may develop before that of course, this is
where the outlook has highlighted). So as we move toward the end of
the work week, while temperatures continue to climb with the
oppressive ridge overhead, we will have to be monitoring the
progression of this system. 00z guidance was bringing it farther
north than 12z guidance has it (new GFS keeps it well to our south)
but imagine it will continue to waffle some over the next couple of
days. We could use the rain, and considering the heat associated
with the upper ridge as it drifts back south toward the weekend,
with highs Saturday approaching the mid 90s in some areas, relief
from the moisture/clouds/rain would be welcome. Even without the
tropical influence, likely to see a return to more of a diurnal
convective pattern with slightly cooler temperatures at 500mb, but
suffice it to say that confidence in sensible weather impacts for
the weekend are particularly low.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Deep convection is bubbling across the
mountains this afternoon, and coverage should gradually expand
through late afternoon...esp across the mtns and foothills. For the
time being, coverage is expected to be limited enough such that a
tempo for TSRA is confined to KAVL between 19-23Z. VCSH or VCTS
suffices for now at the other sites...except for KAND where activity
is expected to be more isolated. Convective chances will continue
through much of the evening. The low levels will remain quite moist
into the overnight/early morning hours, creating good potential for
low cloud development, along with perhaps some mountain valley fog.
IFR conditions appear most likely at KHKY, while MVFR is generally
forecast at the other sites. Morning restrictions are expected to be
short-lived, with VFR likely by late morning. Another round of
(mostly) mountain convection is expected Monday afternoon, but
primarily after the end of the period. Winds will generally favor
light SE through much of the period.

Outlook: An amplifying upper ridge is likely to result in mostly
dry/VFR conditions Tuesday thru Thursday, although early morning
fog/stratus could develop each day, mainly in the mountain valleys.
Diurnal convection could return to the area on Friday.

&&

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

&&

$$

SYNOPSIS...TDP
NEAR TERM...JDL
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...JDL