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353
FXUS62 KGSP 040721
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
321 AM EDT Thu Jul 4 2024

.SYNOPSIS...
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The heatup will continue today as hot and humid conditions return
from now into the weekend.  Afternoon showers and thunderstorms will
return, mainly for the mountains, before a cold front arrives Friday
evening and into Saturday, allowing more widespread thunder chances.
A typical seasonal pattern will set in starting Monday.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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As of 315 AM EDT Thursday: Should remain quiet through daybreak,
with only some high clouds dropping down from the north over the
top of a few patches of lingering high-based stratocu. Temps were
running a bit over the fcst, but no changes are suggested.

Over the next 24 hours, upper ridging over the Carolinas and
Mid-Atlantic will be gradually flattened by nrn stream short waves
tracking from the upper OH Valley to the nrn Mid-Atlantic coast. As
the center of the old upper anticyclone gets suppressed farther
south, the flow will come around to more southwesterly across
the region today. This should allow for temps to climb up another
category higher compared to yesterday even as sfc high pressure
relinquishes control. The modification of the air mass through
increased low level RH should also provide for more buoyancy this
afternoon, and while fcst soundings are not very impressive, they
are at least uncapped. Differential heating over the mtns should
be able to trigger a few showers and storms this afternoon and the
CAMs generally move whatever develops eastward across the foothills
and Piedmont, favoring NC and the nrn Upstate and remaining more dry
across the Lakelands and lower Piedmont. There looks like a hint of
some organization along a low level boundary dropping southeastward
over the western Piedmont late this afternoon, so that might be
interesting for awhile. The convection should wane in the middle
part of the evening, so most of the region should be without precip
shortly after sunset. Temps will be warm overnight tonight. A small
precip chance will be ramped up on the TN border toward daybreak
Friday in the event that some convective remnant reaches the mtns.
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&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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As of 224 AM EDT Thursday: Subtropical ridging will get shunted
off to the east of the forecast area on Friday as a deep trough
churning over the Upper Midwest works its way into the upper Ohio
Valley and Ontario.  Deep layer SW flow will allow the atmospheric
column to saturate as Atlantic moisture streams into the area.
Sfc instability on the order of 1500-2000 J/kg will develop Friday
afternoon based on the new 00z HREF cycle, so any parcels which
manage to get a "push" should have no trouble developing into
showers and thunderstorms during the afternoon and evening hours.
Sans much shear or any dry air aloft, the severe risk looks
minimal...but with ensemble PW estimates ranging from 1.8-2.3"
for much of the forecast area, some brief heavy downpours will
certainly be in the works.  Right now, it still looks like the
best opportunity for triggering will be over the mountains, so
that`s where we expect the bulk of coverage.  Temperatures on
Friday will also be of some interest - given highs are expected
to climb into the upper 90s for most of the non-mountain zones,
with soggy dewpoints to boot, we can expect heat index values to
surge to 105 degrees for many locations...and a Heat Advisory may
eventually be necessary.

A lobe of vort energy will rotate across the Ozarks Friday evening,
entering the Tennessee Valley by early Saturday and driving
a vigorous surface into eastern Tennessee before daybreak.
In the resultant prefrontal trough, instability values will
surge to 2000-2500 J/kg, more than enough for numerous showers
and thunderstorms to develop.  A decent amount of activity should
escape the mountains as the front crosses the region.  In fact,
there`s a group of ensemble members, composed mainly of GEFS and
ENS members and representing about 1/3 of the 12z LREF cycle,
which depict the front arriving so quickly that the westernmost
zones of the CWA may actually see a FROPA before afternoon
instability can get going.  Regardless, those zones which do see
afternoon destabilization - likely a majority of the forecast -
can expect numerous showers and thunderstorms, with severe risk
once again low-end, but localized heavy rain a bit of a concern.
Meanwhile, the faster propagation of the cold front continues to
have ramifications for the afternoon heat...with highs as much
as a category cooler than Friday`s for the western 2/3 of the
forecast area.  The eastern zones, especially those south and east
of I-85 where the front will almost certaintly not have penetrated,
can still expect balmy heat index values above 100 on Saturday.
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&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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As of 243 AM EDT Thursday: As its upper support lifts north over
the axis of the stagnant ridge over the Atlantic coast, a surface
cold front will stall somewhere over the forecast area Sunday,
where it`ll gradually weaken to the point of being unresolvable
by the start of the new workweek.  At that point, we`ll fall into
a typical July pattern, with S/SE flow driven by the Bermuda high
and ample moisture being pumped into the region off the Atlantic.
Seasonal highs in the lower 90s can be expected each afternoon,
with diurnally-driven showers and thunderstorms each afternoon.
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&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VFR should prevail at all terminals through
the period. Only high thin clouds through daybreak for the most
part, but a few high-based stratocu will also linger. Wind will
be light/variable or calm until after sunrise, at which time the
direction should be SW as we begin to feel the approach of the next
system. Convection should not be as suppressed as the last few days,
and a further increase in moisture should fuel some development
of showers and storms mainly over the mtns/foothills. We start out
with a PROB30 at KAVL/KHKY and will evaluate the overnight guidance
to see if we can warrant a TEMPO instead. At this point, the rest
of the terminals are most likely to remain dry, with only a few
high stratocu. Around sunset, the wind will go light SW or variable.

Outlook: Typical mid-summer humidity and diurnal convection will
continue into early next week, leading to scattered TSRA and
possible restrictions each afternoon/early evening. Fog and/or
low stratus may develop each morning, especially for areas that
received rain the previous day.

&&

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

&&

$$

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