-- Discussion containing changed information from previous version are highlighted. --
914
FXUS62 KGSP 071346
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
946 AM EDT Tue May 7 2024

.SYNOPSIS...
A summerlike weather pattern lingers through mid-week with mainly
diurnal showers and thunderstorms expected. Temperatures will trend
well above normal through Thursday. Showers and thunderstorms will
become more numerous ahead of a strong cold front on Thursday.
Activity may linger through early Friday as the cold front pushes
east of the western Carolinas. Drier conditions and below normal
temperatures return for the weekend as high pressure builds in from
the west.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 944 AM EDT Tuesday: An area of low stratus and dense fog
developed across the Upstate this morning, but improvements have
since been noted. The dense fog advisory will likely be canceled
early as conditions continue to improve. Isolated to scattered
storms will be possible again this afternoon mainly along the I-40
corridor.

Otherwise, a weak upper shortwave trough will finally push east of
the forecast area by mid-morning. Drier conditions are now in place
across most of the forecast area, but some a line of showers
continues across the northern NC zones. Patchy fog and low stratus
have developed across portions of the area thanks to widespread
convection last night. Fog and low stratus should lift shortly after
daybreak. Lows this morning will end up around 10 degrees above
climo thanks to lingering low clouds.

upper ridging will build across the Southeast today leading to much
warmer temperatures as well as lower coverage of diurnal convection.
Temperatures this afternoon will climb into the lower 80s in the mtn
valleys and the mid to upper 80s east of the mtns. This will yield
highs around 8-10 degrees above climo. CAMs agree that isolated
storms will develop mid to late afternoon across the NC mtns and
Foothills before pushing east into the NC Piedmont late this
afternoon into early this evening. With the rest of the forecast
area expected to remain dry, went with chance PoPs across western NC
for today. The SPC Day 1 Severe Wx Outlook shows a Marginal Risk for
isolated severe storms across western NC today. This make sense as
25-35 kts of deep shear and up to 2,500 J/kg of SBCAPE will be in
place this afternoon, allowing for severe storm development. Large
hail and damaging wind gusts will be the main hazards with any
severe storms that develop. Any lingering convection this evening
should quickly wane around sunset with the loss of daytime heating.

Another round of overnight convection may develop as a cold front
slowly approaches out of the west. However, with CAMs not in
agreement on shower and thunderstorm activity, confidence will
remain very low regarding tonight`s PoPs. Lows tonight should end up
around 13-15 degrees above climo, especially if cloud cover and
convection manage to develop.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 305 am EDT Tuesday: Convection may be ongoing at the start of
the short term...and in fact the highest PoPs for Wed will be in the
morning. An elevated mixed layer is forecast to advect into the area
from the southwest  during the afternoon/evening. This will act to
impressively steepen mid-level lapse rates...to the tune of 7.5 C/
km. However, it will also act to cap the atmosphere, as forecast
soundings depict a strengthening inversion between 5 and 7 kft. As a
result, most model guidance...in particular the convection-allowing
models...have very little in the way of a convective response across
our area Wed PM. Having said that, the afternoon air mass will
actually become quite volatile due to the cooling aloft and strong
insolation/hot boundary layer (max temps of around 90 across much of
the Piedmont), with sbCAPE of around 3000 J/kg expected during
mid/late afternoon. If a couple of cells are able to initiate in
this environment...perhaps before capping becomes too strong during
mid-afternoon...they are likely to become strong-to-severe, with
deep layer shear of ~35 kts suggesting good potential for
supercellular structures.

If anything, forecast soundings indicate stronger capping Wed night
into early Thu. However, convection originating from the very
unstable and strongly sheared pre-frontal environment to our west
could certainly make a run toward our western areas at any point
during this time frame. Convective chances then ramp up across our
area during the daylight hours Thursday as frontal zone pushes in
from the west...most likely during peak heating. The forecast is
somewhat muddled due to the potential for early day convection
cooling/stabilizing the atmosphere...at the very least, more in the
way of cloud cover is expected on Thu that will act to somewhat
inhibit heating/destabilization. However, while the cap is forecast
to be eliminated by the daylight hours Thu, a remnant elevated mixed
layer regime is still expected to result in rather steep mid-level
lapse rates, so it won`t take a great deal of heating to yield at
least moderate levels of sbCAPE during the afternoon. Shear
parameters will only continue to improve, with 0-6km bulk shear of
40-45 kts expected. Westerly/quasi-boundary-normal shear vectors
once again suggest the potential for supercell structures and
perhaps smaller linear segments...with low level shear parameters
being adequate for perhaps a couple of tornadoes in addition to
large hail and damaging downbursts. Convection is expected to come
to quick end Thu evening as a drier air mass advects into the area
in the wake of the front.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 330 am EDT Tuesday: The 00Z GFS is an outlier in its depiction
of a potent short wave trough digging into the TN Valley and
southern Appalachians on Friday (other guidance is considerably
farther north). As a result of this, the GFS solution would have a
surface wave develop across the baroclinic zone across the Deep
South, with additional rounds of convection making a run for our
forecast area during the day Fri. Again, this is an outlier, but
there`s enough a signal in deterministic and ensemble guidance to
include chance PoPs during the day. The remainder of the extended
should be cooler and much drier as a long wave trough becomes
established across the East. Surface dewpoints in the 40s...possibly
in the 30s across the mountains will result in wide diurnal
temperature ranges...with below normal min temps and near-to-
slightly-above normal highs through the period.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Most of the convection has pushed east of
the forecast area, although an area of showers has developed once
again across the far northern tier of the forecast area. This will
mainly impact KHKY over the next 1-2 hours. IFR to MVFR cigs are
noted across most of the terminals this morning as of 1030Z. Patchy
fog has also developed across portions of the terminals this
morning. Both vsbys and cigs should lift shortly after daybreak. VFR
conditions are expected through the rest of the 12Z TAF period
outside of isolated thunderstorms tracking across western NC this
afternoon into early this evening. Went with PROB30s at all of the
NC TAF sites to account for TSRA. Afternoon cumulus will develop
thanks to daytime heating and low-end wind gusts will be possible at
KAVL and the SC Upstate terminals this afternoon. Wind direction
should generally be SW east of the mtns and W/WSW across the mtns
through the TAF period. Rain chances may return overnight,
especially for KAVL, but confidence on this remains very low.

Outlook: Diurnal convection returns again on Wednesday. There is
potential for restrictions associated with widespread fog and/or low
stratus each morning for any terminals that receive rainfall the
day/night prior. A cold front will approach out of the west on
Thursday before tracking over the terminals Thursday night into
Friday morning. This will lead to better convective chances,
as well as restrictions, towards the end of the workweek.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
GA...Dense Fog Advisory until 11 AM EDT this morning for GAZ010-017-
     018-026-028.
NC...Dense Fog Advisory until 11 AM EDT this morning for NCZ059-062-
     063.
SC...Dense Fog Advisory until 11 AM EDT this morning for SCZ010-
     101>107.
-- End Changed Discussion --

&&

$$

SYNOPSIS...AR
NEAR TERM...AR/TW
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...AR