Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS62 KGSP 101826

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
226 PM EDT Sat Jun 10 2023

Dry high pressure will move offshore the remainder of the weekend,
allowing temperatures trend back toward typical June values.  A warm
front will lift across the area Sunday, bringing shower and
thunderstorm chances, followed by a cold front on Monday.  Brief
drying is expected on Tuesday, before more active weather arrives
the second half of next week.


As of 215 pm EDT: A longwave trough will carve out from the Great
Lakes to the mid-Mississippi River Valley tonight, with the trough
axis slowly approaching the Appalachians through the day on Sunday.
Meanwhile, the increasingly offshore low-level high pressure center
will permit flow to turn southwesterly and steadily increase
moisture over the region through the period. Expect mainly
increasing mid and high-level cloudiness for the nighttime hours,
but with lower clouds developing Sunday morning, and then rain
showers breaking out from the southwest as upper shortwaves eject
east of the developing trough and upper jetlet divergence improves.
Despite the clouds, instability should rebound through the day on
Sunday under the southwesterly flow, with 500 to 1000 J/kg of sbCAPE
expected. Forcing and moisture will be less in northeast sections
and precipitation may encounter a bit more dry air  that will
curtail PoPs somewhat. PoPs will thus range from categorical across
southwest sections to 30 to 40 percent east of the I-77 corridor for
Sunday. Expect a smaller diurnal range on temperatures than has
recently been observed for tonight through Sunday given the
increasing cloudiness.


As of 154 PM EDT Saturday: Sunday evening and night may feature
the arrival of a ragtag line of showers and thunder leftover
from earlier robust convection across the Tennessee Valley, with
guidance supportive of 500+ J/kg sbCAPE along the NC-TN border
and some 30kts of deep layer shear to keep the system moving.
SPC`s Marginal Risk for severe thunderstorms along the southern
Blue Ridge looks reasonable...but any severe threat should quickly
taper off as night wears on.  During the overnight hours, lingering
convection primarily over the SW NC mountains and SC Upstate may
begin to present a low-end heavy rain threat, as locally-enhanced
rainfall rates develop with any sustained updrafts in a plume of
1.5-1.7" PWs. That`s about all this stuff will have going for it,
though, since antecedent conditions are fairly dry, and raw QPF
numbers just aren`t all that impressive.

Thereafter, the fate of Monday`s weather hangs in the balance of
subtle timing uncertainties in the synoptic pattern. The guidance
can agree on the big picture: an upper low migrating southeast
off the Great Lakes, bringing a 500mb trough and associated speed
max across the upper Mississippi Valley on Monday and amplifying
mositure flux into the mid-levels. The exact timing of the surface
reflection, however, will be pivotal in Monday afternoon`s thunder
chances...with most members of the European ensemble and GEPS
depicting a slower FROPA, allowing for some 1000-1200 J/kg sbCAPE
to develop east of I-26 on Monday afternoon. Several of the 06z
GEFS members, however, as well as the new 12z GFS itself, predict
a much faster progression...limiting the ability of much good
instability to develop before profiles begin to dry out. Should
the slower solution play out, developing convection will once again
find itself in the presence of ~30kts of deep layer shear, kind of
borderline but enough to warrant another Marginal Risk from SPC,
this time for the southeastern third of the forecast area.

Monday night and beyond, models have come into much better agreement
on the complete passage of the front...resulting in drier conditions
across the area.  Monday night`s lows are now progged to be a
category or more below climo, and Tuesday should be a temperate,
if still somewhat cloudy day.


As of 216 PM EDT Saturday: By Tuesday night, the bulk of forcing
directly associated with the upper low over the Great Lakes will
have shifted east of the CWA, and the low will show signs of
nudging eastward.  But, moisture will be fast increasing following
its Tuesday lull as mid-level ridging or broad anticyclonic flow
develops over the US Southwest and Chihuahuan Desert, and cycles a
blast of southern stream moisture across the Deep South and into
the Carolinas. Fairly good agreement that this`ll interact with
some decent synoptic forcing to generate another round of rain on
Wednesday, although a smattering of GEFS and ECE members deviate
from this pattern.  Most guidance depicts some modest instability
developing over the Carolinas during this we can
expect at least some diurnal thunder.

In a refreshing change of pace from the past few days, the majority
of operational guidance agrees on a secondary trough sharpening
over the upper Midwest on Friday, resulting in, you guessed it,
another round of rainfall late in the week or next weekend.
Timing still isn`t clear, though, so it`s too early to begin
focusing on impacts.  Instead, we`ll simply note that temperatures
will be on the rise...reaching the upper 80s by the end of the week.


At KCLT and elsewhere: FEW to SCT cirrus early will give way to
increasing mid and high clouds overnight. Low-level moisture will
return to southwest sections through Sunday morning, and some MVFR
cigs will be possible late in the period at the Upstate sites and
KAVL - with PROB SHRA expected before 18Z. Despite the longer TAF
period at KCLT, restrictions and showers are less likely there given
the drier air in place near the I-77 corridor, but even KCLT will
see a PROB30 for showers late day. Expect steady south to southwest
surface winds generally 10 kt or less through the period, but with a
few gusts possible at times at KAVL. Thunderstorms may hold off
until just beyond the current terminal period, but cannot rule out
some late morning rumbles in the Upstate.

Outlook: A cold front will approach from the west Sunday night and
cross the region on Monday, with showers, thunderstorms, and
restrictions expected. Brief drying is possible on Tuesday, but
conditions could stay unsettled over the region through mid week if
the boundary stalls near the area or returns quickly north.




AVIATION...HG is the U.S. government's official web portal to all federal, state and local government web resources and services.