726
FXUS62 KGSP 041724
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
124 PM EDT Thu Jul 4 2024

.SYNOPSIS...
Hottest day of the week expected on Friday. A cold front moves in
from the north on Friday night, increasing shower and thunderstorm
chances into the weekend. A typical seasonal pattern of afternoon
showers and storms set in starting Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1130 AM EDT Thursday: Dewpoints are starting to mix out a tad
more than aniticpated. Adjusted temps and heat index forecast to
account for the change. Still expecting hot heat index values east
of the mountains, but well below any criteria for a heat advisory.
Slight adjustments to PoPs as confidence is still low for showers
and thunderstorms this afternoon.

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 /18Z THURSDAY THROUGH TUESDAY/...
At KCLT and elsewhere: VFR conditions are expected to prevail across
all terminals during the TAF period. SCT cirrus and stratocu this
afternoon with a few showers or thunderstorms possible at KCLT and
KAVL. Confidence is low for severe storms and exactly where these
storms could develop. Will keep a TEMPO at KAVL and KCLT this
afternoon for TSRA. Winds will remain SW and light this evening and
at some sites, become calm overnight. There could be some VSBY
issues with developing stratus in the mountain terminals if rain
falls this afternoon, though confidence is low. Friday, expect
similar conditions with more widespread thunderstorm activity
ramping up during the afternoon time frame once again. Winds should
remain S/SW through the end of the TAF period.

Outlook: 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...CP
NEAR TERM...CP/PM
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...CP