686
FXUS62 KGSP 301424
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1024 AM EDT Sun Jun 30 2024

.SYNOPSIS...
Hot and humid conditions will arrive today, as well as showers
and thunderstorms, ahead of a robust cold front.  Drier and cooler
conditions will set in behind the front Monday and Tuesday, before
the summer heat returns Wednesday and beyond.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Sunday...The biggest changes needed for this update
were to the sky and PoPs to line up with latest satellite and radar
trends. Skies have really cleared out this morning, and combined
with a light downslope NWLY flow are allowing temps to warm a
little faster than expected. Also, convection is not firing across
the mountains quite yet, so have delayed the ramp up of PoPs with
latest hourly NBM grids. So I have bumped up highs a deg or two to
reflect the better heating. As for dewpts, the downslope and more
intense heating should allow for some mixing. In these situations,
blending in the 10th percentile NBM dewpts usually verifies
well. And that did lower dewpts some. So with all that being said,
the higher temps and lower dewpts net about the same heat indices,
and the Heat Advisory still looks good. No major changes in thinking
as regards the severe weather threat. Still expecting a few severe
storms with damaging winds being the main threat.

Otherwise...The next 24 hours should be a little more active
across the region as the nearly zonal flow we`ve been under
for the past several days finally buckles as a short wave digs
down over the Appalachians today and helps to amplify a broad
mid-level trof along the East Coast. The upper wave will help to
drive a cold front from the OH Valley southeastward toward the
region today. Before it arrives, we have the matter of the Heat
Advisory to contend with. And then there is the possibility of
better convective coverage this afternoon, as forcing should be
sufficient to bring the best chances that we`ve had in the past few
weeks for some needed rainfall across the western Carolinas. The
CAMs are in general agreement that a lee trof will be the focus of
storm development east of the mtns early this afternoon. This could
also be aided by an outflow boundary from the ongoing convection
to the WNW. The extra cloud cover and storm coverage could limit
the high temps and keep us from reaching Heat Advisory criteria
in some places. The trend in the guidance was slightly down on the
Heat Index. Suffice to say, no indication the Advisory needs to be
expanded. However, we won`t shrink it either at this point, even
though confidence in reaching criteria is trending downward. The
front should bring another round of showers and storms into the
mtns this evening, and then east of the mtns overnight. Weak shear
could help to organize this activity. As to the severity, the lapse
rates remain relatively weak and we lack mid-level dry air. A
Marginal Risk on the Day 1 from SPC looks okay just on general
principles with a boundary moving across the area, but it might
be a stretch to get more than a few strong storms. For tonight,
the front will move to the east after midnight and help to keep a
chance over the eastern zones through daybreak Monday. Low temps
will continue to run above normal.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 215 AM EDT Sunday: The short term is shaping up to be a dry
few days as ill-defined surface high pressure migrates out of the
Great Lakes and across the Upper Mid-Atlantic.  The resulting
subsidence aloft will hold any prospects of convection at bay,
while ushering in cooler temperatures and drier dewpoints after
the oppressive weekend heat.  A CAD-like regime will set up on
Tuesday, further cooling and drying the forecast area.  On Monday,
afternoon temps will only reach the mid- to upper-80s with RHs in
the upper 40s; on Tuesday, they`ll stay in the lower 80s with RHs in
the lower 40s.  It`s worth noting that forecast soundings from both
the GFS and the NAM depict a steep dropoff in dewpoints around 750mb
each afternoon...which hints at the possibility of a dewpoint crash.
For now, accounted for this by giving added weight to the raw model
output for the dewpoint forecast...as this tends to perform better
in these scenarios.  An afternoon breeze is likely on Monday as what
remains of constrained postfrontal flow aloft mixes to the surface;
by Tuesday even fleeting wind gusts will be difficult to come by.
By all accounts, both days should be beautiful!

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 224 AM EDT Sunday: An increasingly summer-like pattern will
set in for the medium range.  Deep upper ridging will set up over
the southern Great Plains and into the Southeast, while Atlantic
high pressure allows a southerly moisture flux to develop with
a weak Gulf fetch.  In the latest round of operational guidance,
the more potent moisture transport is depicted remaining displaced
to our west.  So forecast profiles remain basically dry through
Wednesday, and only begin to exhibit modest moistening on Thursday.
With minimal synoptic forcing and a questionable amount of available
moisture, it therefore seems like any diurnally forced showers and
thunder will be focused over the mountains, and limited in coverage,
through Thursday afternoon.

By Friday, better moisture should be working into the forecast
area...with even the driest members of the latest LREF cycle at
least as moist as the consensus on Thursday in the 850-700mb layer.
So, somewhat better coverage of mountain showers and thunderstorms
is expected, and convection is more likely to break containment
and start developing over the Piedmont and Upstate by the end of
the week.  At this point, temperatures will also be on the rebound
beneath the ever-intensifying heat dome.  On Friday and Saturday,
temperatures may surge into the upper 90s, paired with downright
soupy dewpoints.  So, heat index may once again become an issue
toward the end of the 7-day period.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: The bulk of the day will be VFR with a
light S to SW wind, altho ceiling/vis could be lower and wind
variable near any thunderstorms. The CAMs remain in decent
agreement with the timing for the best chances of storms, and
that is generally mid-afternoon through mid-evening. This will
be handled with TEMPO to hold the restrictions. Thereafter, will
employ a PROB30 to cover the lingering convective precip. The
cold front is expected to push southeast late this evening or
early Monday. There is some indication that a restriction might
form around daybreak Monday.

Outlook: The cold front will push thru and stall just south of
the area, resulting in quieter weather for Monday thru mid-week.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 8 PM EDT this evening for GAZ018-026-028-
     029.
NC...Heat Advisory until 8 PM EDT this evening for NCZ070>072-082.
SC...Heat Advisory until 8 PM EDT this evening for SCZ008>014-019-
     104>109.

&&

$$

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