993
FXUS62 KGSP 041326
AFDGSP

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 930 AM EDT Thursday: Other than a few minor tweaks to the
temps, no major changes for the morning update. Forecast continues
to be in good shape.

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 higher temps and slight
increase in humidity will push some apparent temps into the lower
100s, still enough below Heat Advisory criteria that one was not
issued, but this will have to be monitored. 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. Think the risk of severe storms is low. 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.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: VFR should prevail at all terminals through
the period. Only high thin clouds through mid-morning 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. Opted for a
TEMPO at KAVL based on better agreement for coverage in the recent
HRRR runs, but left a PROB30 at KHKY. 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...CP/PM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...PM