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000
FXUS62 KGSP 102308
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
708 PM EDT Wed Apr 10 2024

.SYNOPSIS...
Showers and scattered thunderstorms, some with potentially heavy
rainfall, can be expected ahead of a cold front approaching from the
west tonight and Thursday.  Very windy conditions develop Friday.
Dry and warm weather return for the weekend into early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
645 PM Update...Starting to see widely scattered showers develop
across the I-77 corridor as llvl Atl moist flux kicks in ahead of a
vigorous low currently located over the srn MS Valley. Not expecting
much rainfall with these showers, but they will likely linger into
the evening. The NC mtns will also see light precip during this
time. More widespread showers are still expected to move into NE GA
arnd midnight and become more widespread east thru the overnight
period.

As of 300 PM EDT Wednesday: Rain has lifted north this afternoon,
and is mainly confined to northern North Carolina. Widespread cloud
cover remains in place, with the thickest clouds noted across the
western two-thirds of the forecast area. A brief lull in rain is
expected this afternoon and early this evening. Highs this afternoon
should climb into the mid to low to mid 70s east of the mountains
thanks to 850 mb SW`ly flow. Highs across the mountain valleys
should climb into the upper 60s to lower 70s, with the mid 50s to
mid 60s across the higher elevations.

Cloud cover and rain chances ramp up again this evening into
Thursday as a low pressure system approaches out of the west. Have
high-end chance to likely PoPs across the western zones around
midnight tonight, with likely to categorical PoPs across the entire
forecast area by daybreak Thursday. Lows tonight will end up around
15-18 degrees above climo thanks to both cloud cover and rain
limiting radiational cooling. Southerly winds will gradually
increase this evening into tonight, becoming gusty, as the cold
front associated with the low pressure system approaches out of the
west. Gusty winds will linger throughout the day Thursday as the
front tracks across the western Carolinas and northeast Georgia.
Wind gusts should remain below Wind Advisory criteria across most
locations, although higher elevations along the NC/TN border and the
western North Carolina mountains may see gusts near advisory level.
Widespread rain will linger through the morning hours before
gradually tapering off from west to east Thursday afternoon.
Embedded thunderstorms may develop early Thursday morning into
Thursday afternoon thanks to both MUCAPE and SBCAPE ranging from 500-
1000 J/kg and 0-6 km bulk shear values ranging from 50-60 kts. SPC
has a Marginal Risk for severe storms on Thursday, and this seems
well placed as isolated strong to severe storms will be possible
Thursday morning into Thursday afternoon ahead of and along the cold
front. However, the overall threat continues to look low for now.
Scattered showers may redevelop behind the main line of convection
associated with the cold front thanks to wrap around moisture from
the low pressure system. With both the HRRR and NAMNest depicting
this, have chance to likely PoPs through the end of the near term.
Latest QPF guidance has come in lower than previous runs, showing 2-
3" along and near the Blue Ridge Escarpment and 0.5-1.0" elsewhere.
Locally higher amounts are possible, especially along the southern
Blue Ridge Escarpment, where rainfall totals near 4" are possible.
WPC has a Marginal Risk for Excessive Rainfall in place across the
western Carolinas and northeast Georgia for Thursday, so isolated
flooding cannot be ruled out (especially for locations along and
near the southern Blue Ridge Escarpment). Luckily, temps will remain
warm enough behind the front for all liquid precip. Highs on
Thursday should be similar to today`s but may be limited somewhat by
cloud cover and rain.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 230 PM Wednesday: The short-term period begins as a 500mb,
negatively tilted shortwave trough axis moves over the region
from the south and west.  Current CAM guidance suggests that the
primary axis of heavy rain and storms will have moved well east of
the I-77 corridor by the time the period starts, and it is true
that convective complexes tend to outrun the responsible storm
as well as the guidance forecasting it.  PoPs will therefore be
rapidly trending down Thursday night, with isolated to scattered
shower activity associated with the upper-level trough lingering
into the early overnight hours.  A few residual upslope showers
may develop along the TN state line in the stout westerly flow
through Friday morning, but the primary story will be the strong
pressure-gradient winds behind the trough through Friday.

At this juncture, the overall meteorological setup looks favorable
for widespread 30-40mph gusts during peak mixing Friday afternoon
as the attendant surface low deepens to near 980mb over Ontario and
strong 50-75kt mid-level winds interact with a very deep (5-6kft)
mixed layer across the forecast area.  Wind Advisory gust criteria
is >45mph and guidance continues to suggest that some areas may
reach this threshold, especially across the higher elevations of
the foothills and mountains, where the ground level is closer
to the stronger winds aloft and mixing will be most effective
at bringing a portion of those winds to the surface.  Wind gusts
exceeding 50mph are not out of the question at elevations greater
than 4500-5000 feet from mid-morning Friday into the early overnight
hours.  However, we are still four forecast periods out and blend
guidance typically overestimates the gust potential.  Therefore,
we will highlight this potential threat in the HWO for now and
reevaluate our confidence in Advisory criteria for the next package.

While winds will be strong behind the departed frontal system,
they will predominantly be westerly, not northwesterly, and
therefore the source region advecting into the area will be from
the central Plains, not Canada.  Therefore, we will cool down on
Friday, but modestly so, with downsloping likely to mitigate CAA
east of the mountains, where high temperatures will only be a few
degrees below normal.  Across the mountains the effects of lower
thicknesses underneath the longwave trough and CAA will be a bit
more pronounced.  Therefore, highs are expected to top out 7-9
degrees below normal.

An embedded shortwave trough will deepen the longwave trough
extending from the southern Appalachians north into Canada Friday
night and the longwave trough axis will quickly propagate east to
the Atlantic Coast by Saturday morning.  Thicknesses will increase
during the day on Saturday as low-amplitude ridging builds east
from the Plains and surface high pressure propagates underneath
the inflection point along the Gulf Coast.  Therefore, winds
will remain gusty as our area is still within a weakened pressure
gradient and mid-level winds remain strong in the NW flow aloft
behind the trough axis, but peak gusts will be lower than those
on Friday and well below Advisory criteria.  Nevertheless, RH
values may bottom out in the lower to mid-20s Saturday afternoon
and combined with the remnant gusty winds fire weather may be
a concern.  Temperatures will quickly rebound on Saturday, with
highs 3-5 degrees above normal area wide.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 230 PM Wednesday: The extended period looks to be mostly
quiet and warm across the forecast area as upper-level ridging
gradually amplifies into the middle of next week in response
to a strong closed low ejecting out of the southern Rockies.
This system will not directly impact our area through the period,
but its upstream effects will result in high temperatures reaching
the lower 80s in the mountain valleys and the mid-80s points east
Monday through Wednesday, which is 8-12 degrees above normal.
Low temperatures will be 12-15 degrees above normal each night,
and may not drop out of the 60s for much of the Piedmont Tuesday and
Wednesday nights as dewpoints slowly increase through the work week.
A backdoor cold front will struggle to reach our area Monday and
some of the guidance squeezes out a bit of moisture along the front,
so a slight chance of upslope showers cannot be ruled out across
the mountains and possibly the NW Piedmont Tuesday into Wednesday.
The proximity of the front will increase cloud cover, especially
overnight each day, limiting radiational cooling.  Otherwise, the
forecast looks dry.  Early in the period, RH values bottom out in
the upper 20s on Sunday and Monday with wind gusts of 15-20mph
possible each day.  Therefore, fire weather may be a concern.
However, with increasing moisture, afternoon RH values looks to
bottom out in the mid- to upper 30s Tuesday and Wednesday so fire
weather concerns will diminish as the work week progresses.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: An active TAF set in store with a vigorous
low pressure system tracking up the TN Valley pulling a cold front
across the Carolinas and NE GA. The first concern will be se/ly
gusty winds which develop ahead of the cold front arnd TAF issuance
or a couple hrs later. Winds will remain elevated with low-moderate
gusts as they begin to veer and become sw/ly by the early afternoon.
A strong llvl jet will traverses the area overnight and this will
lead to LLWS at 2 Kft due to speed changes on the order of 40-50 kts
beg after sunrise lasting thru noon or the early afternoon. Still
expect a chance of thunder as the main convg line passes east, which
will generally occur during a 3-4 hr window arnd sunrise thru late
morning. CIGs will also drop to IFR before midnight across most
terminals and stay down, before lifting or scattering to MVFR/VFR by
the early to mid afternoon.

Outlook: Gusty winds will linger Thursday night into Friday, with
the strongest winds expected on Friday. VFR conditions persist
Friday into the weekend as high pressure builds across the terminals.

&&

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

&&

$$

SYNOPSIS...DEO
NEAR TERM...AR/SBK
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...SBK