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000
FXUS62 KGSP 201330
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
930 AM EDT Sat Apr 20 2024

.SYNOPSIS...
Unseasonably warm weather will continue today with showers this
morning across the western North Carolina mountains and isolated
showers and thunderstorms this afternoon for the North Carolina
Piedmont and South Carolina Upstate. Much cooler temperatures and
widespread light rain is expected overnight into Sunday with drier
weather returning by Monday. Warmer weather returns by Tuesday and
lingers through the workweek.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 925 AM EDT Saturday: Rain held together as it pushed across
the NC/TN border this morning so added chance PoPs along the western
NC mountains to account for this activity through the morning hours.
Light to moderate showers continue pushing farther east into western
NC but no lightning activity is present per the latest radar mosaic
loops. Also lowered cloud cover a bit east of the mountains per the
latest visible satellite loops.

Otherwise, the western Carolinas and northeast Georgia will remain
under a nearly-zonal flow through the near term that will have some
weak vorticity moving across the Southeast, but nothing significant.
The flat flow should allow for a weak cold front to lay down and
move south across the SC/GA part of the fcst area today and then
stall closer to the Gulf Coast tonight. Along this boundary, some
weak convergence will persist into the afternoon, enough so that a
few of the CAMs manage an isolated thunderstorm or two east of the
mtns. The RAP/GFS manage about 1000-1500 J/kg of sfc-based CAPE this
afternoon, but unlike yesterday, the effective shear is only about
25-35kt and from the west. So...not quite as favorable as
yesterday...when we saw the development of a few supercellular
storms east of the mtns...but still enough instability and shear to
support an mini-supercell-like storm or two...which the HRRR hints
about. Will include a small chance of storms and will also mention
the isolated severe storm chance in the HWO. Temps will not be as
warm as yesterday, but still on the order of five degrees above
normal. Any isolated convection will end with the loss of daytime
heating, and with that concluded, we will await the development of
isentropic upglide that should develop ahead of a broadly-defined
srn stream wave moving into the MS Delta region early Sunday. The
CAMs agree that light precip will develop/spread northeast into the
fcst area after midnight...to what extent remains a bit unclear.
Either way, we should be on our way to developing a cold air damming
wedge by daybreak Sunday. Overnight low temps will be about a
category above normal, but this should be one of those odd
situations when the calendar day high temp occurs right after
midnight, and the calendar day low happens late in the day.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 145 AM EDT Saturday: Baroclinic zone stretching from the Lower
MS Valley through the Southeast, while a stalled boundary sets up
shop over the Gulf Coast will help set the stage for increasing
PoPs on Sunday. A coastal wave will ride along the boundary and slip
east through S GA/Fl Panhandle during the daytime period Sunday. The
associated precip shield will overrun the entire CFWA, but lack of
instability should keep rain rates at bay, with light to moderate
QPF response. Factor in a strong surface high settling over the
Central High Plains, with a piece of the high breaking off over the
Mid-Atlantic, and an in-situ wedge will nose into the region with
north-northeasterly flow at the surface. Precip overriding this
stable dome will help to lock it in. As a result, temperatures
will run 15-20+ degrees cooler compared to Saturday. Most of
the rain should taper off by Sunday evening as the coastal low
shifts offshore, into the western Atlantic. High temperatures
for Sunday may occur early Sunday morning before the sun rises
as temperatures in the afternoon will struggle to get out of the
50s for most locations. In-situ wedge will lingering over the area
Sunday night into Monday before the surface high centers over the
area by Monday night. Overnight lows on Sunday will run on the cool
side as most locations are forecasted to run 5-10 degrees below
normal, but elevated winds at the surface ultimately shuts down any
frost potential across the active growing zones. Temperatures will
rebound slightly on Monday, but should remain ~10 degrees below
normal with continued north-northeasterly flow and colder air
aloft thanks to a quick moving shortwave trough that will swing
over the CFWA during the daytime period. Monday night will be the
coldest night as light winds and mostly clear skies lead to good
radiational cooling conditions. Tight dewpoint depressions and
temperatures should remain just warm enough to avoid any frost
development, but if trends lean slightly cooler between now and
then, the southern/central mountains of NC and the I-40 corridor
zones could end up with a Frost Advisory as overnight lows will
run 5-10 degrees below normal.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 300 AM EDT Saturday: An upper trough will swing into the
eastern CONUS late Tuesday into Wednesday with an attendant
boundary. Model guidance produce a moisture starved fropa with
only a light QPF response along the NC/TN border during the
day Wednesday. With the better forcing confined to the north
and east, not expecting much besides a wind shift across the
CFWA. Temperatures will rebound Tuesday and Wednesday ahead of
this feature as heights recover and the flow turns out of the
south-southwest with near-normal values Tuesday and slightly
above for Wednesday. Northwesterly flow aloft will remain in place
through the middle part of next week with surface high settling over
the northeastern CONUS. In this case, airmass modification will
take more time than normal to occur. Current trends indicate that
upper ridging will build back in by D6/D7 of the period with an
unsettled synoptic pattern beginning to traverse from the central
CONUS towards the eastern CONUS, but this activity is beyond the
current forecast period.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: The main concern this morning is the mess
of variable ceiling and visibility across the Charlotte metro area,
fortunately not so much right at KCLT. Vis ranges from VFR to VLIFR
around the area, but with sunrise happening, it would appear that
KCLT will be no worse than MVFR, but the edge of the low stratus
was only a few miles south of the terminal. Cannot rule out some
brief LIFR/IFR as a result. The mtns are the other place where low
level moisture could sneak in first thing, what with widespread MVFR
ceiling on the west side of the mtns. A TEMPO will be included at
KAVL to account for this.  Wind will be light and northerly. The
rest of the fcst for today looks relatively benign. Wind should
stay mostly N. A few of the models develop isolated storms again
in the afternoon, but the chance is too low to include in any of
the TAFs. Wind comes around to NE this evening and increases as
the next system approaches from the SW. Isentropic lift commences
after midnight, and will reach the terminals toward the end of
the period. For now, the arrival of the ceiling restrictions will
probably happen an hour or two after the arrival of the precip,
so this will be handled in a PROB30. Only KCLT has to deal with the
actual deterioration of the ceiling down thru MVFR after daybreak
on Sunday.

Outlook: Rain and possibly isolated thunderstorms are expected
to develop on Sunday as a weak low pressure center passes just
south of our area, likely resulting in restrictions for at least
the southern part of our fcst area. Drier conditions return on
Monday and linger into Tuesday.

&&

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

&&

$$

SYNOPSIS...AR/CAC
NEAR TERM...AR/PM
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...PM