503
FXUS62 KGSP 051431
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1031 AM EDT Sun May 5 2024

.SYNOPSIS...
A general summertime pattern sets up today through Wednesday,
keeping scattered thunderstorm chances around each afternoon. A
strong cold front will approach out of the west on Thursday before
tracking across the western Carolinas on Friday, leading to better
coverage of thunderstorms towards the end of the workweek. Highs
will remain above normal through the workweek but will climb well
above normal Tuesday through Thursday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1025 AM EDT Sunday: The latest water vapor imagery indicates a
slow-moving short wave trough has cleared the CWA this morning with
only a few light showers east of I-77. Additional precip should hold
off until afternoon convection begins.

12Z RAOBs show a moderately unstable air mass at KFFC with a low
wetbulb zero level. Instability hadn`t reached KGSO with a relatively
moist profile. Still expect drying aloft and periods of
sunshine/good insolation for the afternoon which will result in max
temps returning to above-normal levels while also allowing for some
destabilization even over the eastern forecast area. Continued poor
mid-level lapse rates will limit the degree of instability, but
sbCAPE of around 1500 J/kg is likely across much of the area by mid-
afternoon. Differential heating should result in scattered
convection developing along ridgetops...esp near the Blue Ridge
escarpment by mid-afternoon, which will then drift southeast on
outflows and W/NW mean cloud-bearing winds into the foothills and
Piedmont during late afternoon/early evening. Afternoon PoPs will
range from likely along the escarpment to 20-40% across much of the
remainder of the area. Shear parameters will remain weak, while
modest instability will limit the depth of updraft cores, but can`t
completely rule out an isolated microburst, especially given the
potential for DCAPE values to approach 1000 J/kg.

Diurnal convection should wind down across the Piedmont this
evening. However, the next short wave trough/associated occluding
cyclone is forecast to eject from the southern Great Plains this
evening, with associated remnant warm conveyor belt/moisture plume
forecast to overspread the CWA from the west between 09-12Z Monday.
This will increase the potential for convection...primarily SHRA to
move into western areas by daybreak, warranting an increase to
chance PoPs. Min temps will again be almost 10 degrees above normal.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 230 AM EDT Sunday: Weak upper ridging will be in place over
the Southeast Monday before an upper shortwave trough tracks over
the Carolinas Monday evening into daybreak Tuesday. Embedded
shortwaves will track overhead the western Carolinas during this
timeframe keeping shower and thunderstorm chances around. Have
likely PoPs area-wide on Monday, with chance PoPs Monday night.
Shear will remain fairly weak, ~15-20 kts, so slow storm motions
will continue the first half of the short term. 850 mb flow will
remain SW`ly through the the period keeping the 90th percentile
PWATS around. This may lead to locally heavy rainfall, especially
for areas that received heavy rain over the weekend. Overcast skies
should limit daytime heating somewhat on Monday so the severe wx
potential should remain low. However, with SBCAPE from ~1000-1500
J/kg expected Monday afternoon, a few strong storms cannot be ruled
out. Highs on Monday will end up around 2-4 degrees above climo,
with lows Monday night expected to be ~10-13 degrees above climo
thanks to mostly cloudy skies.

Weak upper ridging builds back across the Southeast Tuesday into
Tuesday night, kicking off a warming trend. Temps Tuesday afternoon
should climb into the lower to mid 80s across the mtn valleys and
east of the mtns, which will be ~7-9 degrees above climo. Diurnal
convection is expected on Tuesday, with generally lower coverage
expected compared to Monday. Thus, have likely PoPs confined to the
western NC mtns with chance PoPs elsewhere. Shear values will
increase slightly on Tuesday, ranging from 25-35 kts, allowing for
an increase in storm motion. Higher shear along with guidance
depicting 1500-2000 J/kg of SBCAPE Tuesday afternoon may lead to
isolated severe storms during the afternoon and early evening hours.
The main potential impacts would be damaging wind gusts and locally
heavy rainfall. Have PoPs winding down Tuesday evening but
maintained chance PoPs across the western zones as global models
shows convection lingering into the overnight hours. Lows Tuesday
night should remain around 10-13 degrees above climo.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 300 AM EDT Sunday: Upper level ridging flattens out on
Wednesday while a cold front draped from the eastern Great Lakes to
the Southern Plains makes little eastward progress. This will lead
to another warm day and another round of diurnal convection.
However, the 00Z GFS and ECMWF show convective chances increasing
from the west Wednesday night. With the 00Z Canadian still showing
drier conditions Wednesday night, capped PoPs to chance Wednesday
into Wednesday night for most locations. The exception is areas
along the NC/TN border where low-end likely PoPs are in place.
Wednesday will also feature similar shear and SBCAPE values as
Tuesday, so isolated severe storms will remain possible once again.
Damaging winds still look like the main potential impact with any
severe storms that develop. Highs on Wednesday will climb into the
mid to upper 80s east of the mtns and across the mtns valleys which
would be ~9-12 degrees above climo. The CLT metro area may even see
highs flirt with 90! Lows Wednesday night will remain ~13-15 degrees
above climo thanks to increasing cloud cover well ahead of the
aforementioned cold front.

The cold front will push into the TN Valley on Thursday before
tracking across the western Carolinas and northeast Georgia late
Thursday into early Friday. With model runs being inconsistent with
the timing of the front, confidence remains low on when exactly the
front will track across the forecast area. Nevertheless, shower and
thunderstorm activity is expected well ahead of the main FROPA on
Thursday, with convection likely lingering across portions of the
forecast area on Friday. However, with models not in agreement on
the exact timing/coverage of convection, confidence on PoPs will
also be low towards the end of the workweek. Went with likely to low-
end categorical PoPs across the western half of the CWA on Thursday,
with chance PoPs across the eastern half of the CWA. Capped PoPs to
likely across the western zones on Friday and chance across the
eastern zones. Shear values should climb to 40-50 kts on Thursday
and 50-60 kts on Friday, with SBCAPE values up to 2500 J/kg on
Thursday and up to 1500 J/kg on Friday across portions of the
forecast area. This combined with the 00Z GFS showing an 850 mb jet
tracking overhead the Carolinas on both Thursday and Friday will
lead to the concern for severe weather both days. Thursday looks
like the main day to watch for now, but Friday could be another day
to watch depending on how fast the FROPA pushes east. Temps will
remain well above climo Thursday into Thursday night, with temps
becoming near climo to a few degrees above climo Friday into Friday
night behind the cold front. Below climo temps and drier conditions
return on Saturday, but NW flow convection may linger across the NC
mtns.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: SHRA have ended but IFR to LIFR cigs and
patchy vsby restrictions remain. Expect the vsby to improve before
noon, but cig restrictions could linger into early afternoon.
Scattered convection is expected to develop across the mountains
during early/mid afternoon and move E/SE. Prob30s for
afternoon/early evening TSRA are warranted at all sites, while a
tempo for TSRA appears prudent at KAVL beginning at 18Z. Convection
will diminish this evening, followed by lowering cigs again
overnight. Most sites should see at least VFR conditions by daybreak
Monday. Showers may redevelop from the west toward the end of the
forecast period, but this remains uncertain.

Outlook: Enhanced moisture will combine with a weak/stalled front
through the middle of next week, resulting in a period of
active/mainly diurnal convective weather each day. There will also
be the potential for restrictions associated with widespread fog
and/or low clouds each morning.

&&

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

&&

$$

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