493
FXUS62 KGSP 121434
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1034 AM EDT Wed Mar 12 2025

.SYNOPSIS...
Dry high pressure continues today with temperatures well above
normal. A couple isolated showers may return Thursday, mainly across
the southwest mountains and northeast Georgia. A powerful storm
system will impact the area Saturday into Sunday and will bring
widespread heavy rain and thunderstorms, some of which are expected
to be severe with damaging winds and tornadoes. Dry and seasonable
weather returns early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1018 AM EDT Wednesday: Lots of bright sun this morning
allowing for a quick warmup now that our morning inversion has
been mixed out. Temps are warming up a little bit quicker than
fcst. The bigger problem, as usual in these situations, will be
the dewpoint/RH. With so much dry air aloft, it looks reasonable
that the RH will drop down even lower than already indicated this
afternoon. After additional coordination this morning, it was
determined the Increased Fire Danger statement should be expanded
for the remainder of northeast GA.

Otherwise...Quasi-zonal flow aloft will continue today, while
a surface high remains in control as the center shifts from the
eastern Gulf and over the Florida Peninsula by this afternoon. The
sensible weather stays quiet, while airmass modification will
be very evident, especially this afternoon as max insolation and
warm thicknesses aid in temperatures reaching 12-18 degrees above
normal for highs. With very warm temperatures and deep mixing of
dry air above the surface, relative humidity values are expected to
plummet to 15-25% across much of the CFWA. A very slight uptick in
southwesterly winds and low-end gusts thanks to weak WAA filtering
into the region will help to elevate fire danger conditions. In this
case, an Increased Fire Danger Statement will be issued for all of
western North Carolina and northeast Georgia after coordination
with land managers and neighboring WFOs. Expect the worst of the
fire danger conditions to be exacerbated between 16Z today through
00Z Thursday.

A shortwave trough will travel from the Four Corners region through
the Southern Plains today and encroach the CFWA from the west by
daybreak Thursday. No impacts for the current forecast period, but
some instances of upper/mid-level clouds may begin to filter into
the western portions of the area by the very end of the forecast
period. The surface high over the Florida Peninsula during the
afternoon is expected to move offshore the Florida Coast later in
the afternoon and evening. The airmass will further modify as weak
WAA continues and thus, dewpoints gradually increase. As a result,
overnight lows will run 4-8 degrees above normal despite mostly
clear skies through much of the nighttime period.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 246 AM Thursday: A weak shortwave trough is forecast to be
located over the Lower Mississippi Valley by Thursday morning with
northern stream flow displaced into southern Canada. Farther
upstream, along the west coast, a potent trough will be taking shape
which will ultimately become our weather maker for the weekend. The
shortwave along the Gulf coast will continue to weaken as it slides
across the southeast states with forcing for ascent rapidly waning.
A loosely scattered cluster of showers and perhaps a couple of
thunderstorms will be ongoing from northern Mississippi into
Alabama. This activity will shift east/southeast towards the area by
Thursday afternoon/early evening, but will encounter an increasingly
hostile environment characterized by dry air and poor forcing. Thus,
a few isolated showers may make graze into the southwest mountains
and northwest Georgia, but this will be the exception and not the
rule as the forecast has trended drier. Despite increasing cloud
cover, forecast soundings continue depict a deeply mixed boundary
layer up to 800mb which will support afternoon highs in the low to
mid 70s, but a couple ticks below highs today.

The first day of a multi-day regional severe weather outbreak will
ramp up on Friday as the previously mentioned west coast trough digs
over the Desert Southwest and subsequently ejects across the Great
Plains. This will be a powerful storm system with a vigorous trough
and exceptionally deep surface low. The low will form in the lee of
the Rockies and then rapidly deepen with pressure dropping into the
~974mb range as it lifts into the Midwest. Incredible mass response
to the deepening cyclone will draw a very large and expansive warm
sector across much of the area from the Mississippi River and points
east. Across the Southern Appalachians, dewpoints will rise into the
low to mid 50s as southeast moisture return off the Atlantic
increases. A couple isolated to scattered warm advection showers
will be possible across portions of the Upstate and
Piedmont/foothills with the greatest rain chances painted along the
southern Blue Ridge escarpment where upslope flow will be maximized.
Some degree of uncertainty begins to be introduced into the forecast
Friday night as deep convection blossoms across the Mississippi
Valley and pushes east in a band of arcing convection from western
Ohio to central Tennessee. A conditional threat for a more discrete
storm mode will also exist across portions of Mississippi into
Alabama. This initial round of convection will encroach on east
Tennessee and could make a run at western portions of the forecast
area by daybreak Saturday morning. By this point, convection will
begin to outrun better upper level support and will be entering less
than ideal parameter space where a more robust warm sector has yet
to become established. Thus, will advertise a chance for showers and
a couple thunderstorms overnight late Friday night but will need to
evaluate CAM guidance once the event draws nearer to iron out
whether a low-end severe threat could materialize in the overnight
hours.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 307 AM Wednesday: A very busy period of weather will continue
into the weekend as the second and third days of a large scale
severe weather episode continue to unfold. By Saturday morning,
guidance is in remarkably good agreement that the lead vigorous
trough will have lifted into the Midwest/Great Lakes while an
intense Pacific jet dives through the Great Basin and into the base
of the larger scale trough. This will act to reload the trough and
carve out an impressive wave over the lower Mississippi Valley. At
this point, the pattern becomes highly amplified with a downstream
blocking ridge quickly strengthening from Maine into Atlantic Canada
where H5 heights will be in the 99th percentile for mid March. The
result will be a slowing of the wave and attendant surface cold
front which allows time for a moisture rich warm sector to become
established across the Deep South as early as Saturday morning. At
the same time, a plume of steep lapse rates associated with an
Elevated Mixed Layer (EML) will get advected east atop the warm
sector with classic loaded gun forecast soundings. These profiles
will eventually get advected across the southern Appalachians as
well with a rare remnant EML being depicted across the Upstate late
Saturday night into early Sunday morning. Exact convective evolution
remains uncertain, but model depicted QPF patterns would indicate
multiple rounds of vigorous deep convection extending from portions
of Mississippi across Alabama, Georgia and Tennessee through the day
Saturday and into the evening hours. As the event progresses, it`s
likely that convection will grow upscale into a robust QLCS within
a pre-frontal surface trough, especially as stronger forcing arrives.

The parameter space ahead of the QLCS across the forecast area will
be rather pronounced, especially in terms of shear profiles. A
screaming 50-70kt low-level jet will translate across the area and
help to elongate large cyclonically curved hodographs. Resulting
vertical wind shear within the 0-1km layer will be characterized by
40kts of bulk shear and 400-500 SRH. Deep-layer shear vectors are
favorably oriented just north of east which would support a well
balanced updraft/downdraft convergence zone within the QLCS. As to
be expected with an overnight/early morning early season QLCS,
thermodynamic profiles aren`t as robust as the shear with 100-300
J/kg of MLCAPE. Intense synoptic forcing should easily augment
marginal thermodynamics with well established deep convective
updrafts also helping to maintain the line of storms. This parameter
space would support embedded supercell structures within the line
and a discrete supercell ahead of the line cannot be completely
discounted either given favorable off boundary shear vectors. With
that being said, confidence remains moderate to high for a severe
weather episode primarily centered during the overnight Saturday to
early Sunday morning timeframe with a threat for damaging winds and
tornadoes. AI and machine-learning severe weather outlooks also
maintain healthy severe weather probabilities across the area.

Convection will shift east Sunday morning and is currently expected
to clear the area by early afternoon. A brief period of northwest
flow showers may grace the mountains, but will be short lived as dry
air quickly arrives in the wake of the frontal passage. Dry and
seasonable weather returns early next week.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: VFR conditions will prevail through the
forecast period at all terminals. Clear skies continue through the
daytime period today as winds pick up to 6-10 kts out of the south-
southwest, with low-end gusts being possible during peak heating.
Current thinking is that the gusts will likely occur over the
Upstate sites and KAVL, so placed a TEMPO or prevailing gust mention
at these sites. KAVL will switch to a southerly wind by the
afternoon and remain in this direction through the rest of the
period. Some mid/high clouds may start to encroach the region from
the west by daybreak Thursday. Otherwise, partly to mostly clear
skies are expected overnight tonight, while winds subside after
sunset.

Outlook: VFR generally continues through Friday, although a
front may bring brief showers and restrictions Thursday. A more
substantial front is expected to bring showers, a few thunderstorms
and associated restrictions Saturday into Sunday.

&&

.FIRE WEATHER...
RH values reach critical levels this afternoon with most locations
dropping to 15-25%. South to southwest winds will remain relatively
light through much of the afternoon, with some low-end gusts
possible. Given the minimum RH forecast and ripe fuels, a Fire
Danger Statement has been issued for western North Carolina
and northeast Georgia this afternoon following land manager and
neighboring WFOs coordination.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Increased Fire Danger until 8 PM EDT this evening for GAZ010-
     017-018-026-028-029.
NC...Increased Fire Danger until 8 PM EDT this evening for NCZ033-
     035>037-048>053-056>059-062>065-068>072-082-501>510.
SC...None.

&&

$$

SYNOPSIS...TW
NEAR TERM...CAC/PM
SHORT TERM...TW
LONG TERM...TW
AVIATION...CAC
FIRE WEATHER...