541
FXUS62 KGSP 111449
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1049 AM EDT Tue Mar 11 2025

.SYNOPSIS...
Dry high pressure continues today and tomorrow with temperatures
well above normal. A couple isolated to scattered showers may return
for some locations Wednesday night into Thursday, mainly across the
southwest mountains and northeast Georgia. A notably strong storm
system will impact the area Saturday into Sunday and will bring
widespread heavy rain and thunderstorms, some of which could be
severe.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1045 AM EDT Tuesday: Forecast more or less floating along this
morning, with clear sky now that the fog around the big lakes has
finally mixed out. Temp trends look ok. Will monitor the dewpoint
trend into the afternoon to see how far down the RH drops.

Otherwise...drying airmass settles over the CFWA as quasi-zonal
flow aloft and recovering heights filter in through the forecast
period. Max insolation and a weak downslope component closer to
the surface will support a nice rebound for afternoon highs as
values run 10-15 degrees above normal. Combination of very warm
afternoon temperatures and deep mixing of dry air above the surface
will result in widespread RH of 15-25%. This will likely enhance
fire danger conditions for the North Carolina mountains and I-40
corridor, where little to no rain fell on Monday. Wind gusts will be
low-end, so not expecting any fire weather products at this time.
Surface high over the Gulf will remain in control through tonight
as the center shifts toward the Florida Peninsula. Boundary layer
will struggle to fully decouple overnight despite good radiational
cooling conditions under mostly clear skies. In this case, overnight
lows should remain a category or so above normal.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 201 AM Tuesday: Heading into Wednesday, broad northern stream
flow will be draped along the Canadian border with a weak and
progressive southern stream shortwave trough ejecting out of
northern Mexico and into the Southern Plains. Across the Southern
Appalachians, the pattern will be much more nebulous with neutral
height tendencies within a belt of modest westerlies. The surface
pattern will remain dominated by dry high pressure. Very efficient
and deep mixing in the dry airmass (forecast soundings mixing up to
800mb) will foster very warm and well above average high
temperatures in the low to upper 70s Wednesday. Dewpoints will also
mix out with humidity values falling to near critical for elevated
fire danger. 10-20mph wind gusts may occasionally mix down to the
surface and a fire danger statement may eventually be warranted
pending coordination with land managers. By Thursday, the previously
mentioned shortwave trough over the Southern Plains is forecast to
swing into the Lower Mississippi River Valley and slide across the
Tennessee Valley and into the far southern Appalachians. Guidance is
in good agreement that the wave will weaken as it approaches the
area with attendant moisture encountering an increasingly hostile
dry airmass. As such, a couple isolated to widely scattered showers
may make a run at the southwest mountains and northeast Georgia but
coverage will be limited and eastern extent farther into the
mountains/western Upstate remains highly uncertain. Increasing cloud
cover, however, will keep highs on Thursday a couple ticks below
Wednesday but still a good bit above average.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 232 AM Tuesday: A very active weekend is in store as an
intense storm system brings wide ranging impacts to much of the
country. The stage will begin to be set as early as Thursday as a
vigorous trough dives out of the Pacific and into the Desert
Southwest and subsequently ejects into the Southern Plains on
Friday. A powerful storm system will rapidly intensify through the
day on Friday as the pattern becomes highly amplified as an intense
Pacific jet dives through the Great Basin towards the base of the
trough. Cyclogenesis in the lee of the Rockies Friday morning will
instigate a surface low that is progged to quickly lift into the
Midwest as it deepens substantially. Ensemble support is incredibly
strong with nearly all members depicting a very impressive ~975mb
low. Tremendous mass response to the deepening low will help blossom
robust wind fields with a large and expansive warm sector becoming
established across much of the Mississippi Valley and points east.
Low-level moisture return will also ramp up across the Southern
Appalachians on Friday with isolated to scattered orographically
enhanced warm advection showers possible across the mountains,
especially along the southern Blue Ridge escarpment. Temperatures
will also remain well above normal with highs in the upper 60s to
mid 70s.

This setup, featuring a powerful trough and surface low, has the
appearance of a multi-day regional severe weather outbreak with the
first day of severe weather on Friday centered across the middle
Mississippi Valley into portions of the Midwest and Ohio Valley.
Things become more interesting from the Deep South to the southeast
states Saturday into Sunday with the trough reloading as intense jet
energy dives out of the Desert Southwest and into the base of the
trough. The pattern will become even more amplified at this point as
an upstream ridge extending from Maine to Atlantic Canada
strengthens further. Ensemble mean 500mb heights at St. John`s,
Newfoundland of 564dam fall in the 99th percentile for mid March.
Resulting blocking will in turn act to slow eastward progression of
the trough allowing time for a robust warm sector to become
established from central Mississippi across much of Alabama by
Saturday afternoon. At the same time, an elevated mixed layer will
be advected east with classic loaded gun forecast soundings apparent
across this area as soon as Saturday morning. The arrival of strong
deep-layer forcing and a screaming 50-70kt low-level jet will
support the development of widespread vigorous upstream convection
by Saturday evening.

With time, convection will likely grow upscale into a well
established QLCS that will push east across east Tennessee and
Georgia within a pre-frontal surface trough. Exact timing remains
somewhat uncertain, especially if downstream blocking further slows
progression of the trough, but it appears likely that the QLCS will
be moving across the forecast area during the early morning hours on
Sunday. Forecast soundings within the near storm environment are
more than supportive for a continuation of a severe weather threat
despite the nocturnal instability minimum. Upwards of 100 J/kg of
MLCAPE combined with intense synoptic forcing should easily maintain
any QLCS across the area. Shear profiles are very impressive with
40kts of 0-1km shear and 400-500 0-1km SRH. This would even be
supportive of embedded supercell structures within the QLCS itself.
With that being said, confidence is increasing that a severe weather
threat will be realized with the main hazards being damaging winds
and line-embedded tornadoes. This is further supported by AI and
machine-learning severe weather outlooks, which paint healthy
probabilities across much of the area. A plume of rich moisture with
PWATs over 1.5" will accompany the deep convection with a couple
inches of rain in a short amount of time possible. This may also
result in at least minor/nuisance type flooding.

Depending on what the ultimate timing ends up being, convection will
push east of the area through the day on Sunday but cold advection
will lag considerably. Cooler air eventually arrives Sunday night
with dry air and quiet returning into early next week.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR conditions will prevail through the
forecast period as mostly clear skies are expected through tonight.
Vsby restrictions are lingering over the Upper Savannah River Valley
terminals as fog is forming over bodies of water and vicinity, which
is currently impacting KAND. Fog has lasted through much of the
night, but showing signs of improvement, so placed a TEMPO for vsby
restrictions through 13Z. Otherwise, winds are north-northwesterly
at most TAF sites and should remain this way through the morning
hours. Winds are expected to toggle to a southwesterly component by
this afternoon and going mostly light and variable overnight
tonight. KAVL will maintain a north-northwesterly wind through most
of the period, with some low-end gusts late in the morning through
the early afternoon hours. Model guidance depict a slight disruption
in the upvalley wind component at KAVL near the 00Z Wednesday time
frame, so shifted winds to a westerly component for a few hours to
try and capture the sudden change before the upvalley wind resumes.

Outlook: Dry high 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 Sat/Sat night.

&&

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

&&

$$

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