Simpsonville, South Carolina 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

122
FXUS62 KGSP 221146
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
646 AM EST Sun Dec 22 2024

.SYNOPSIS...
Cold air will continue to filter into the area over the next couple
of days high pressure remains in control of the area. However,
temperatures are expected to trend back toward normal for Christmas
with more moisture returning to the area as well. The latter half
of the week looks warmer than normal, but unsettled.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 6:15 AM EST Sunday: Other than some patches of stratocu that
have developed over the eastern Upstate during the past few hrs, we
remain mostly clear across the fcst area with temperatures in the
20s to upper teens. Numerous sites are reporting calm winds, yet
dewpts should remain low enough that fog/reduced visby won`t be a
concern this morning except possibly in the sheltered mtn valleys.
Lows still appear on track to bottom-out about 10 to 15 degrees
below normal.

Otherwise, heights will gradually rebound thru the period as broad
upper trofing lifts off the Atlantic Coast and nearly zonal upper
flow settles over the Southeast. At the sfc, broad Canadian high
pressure will persist over most of the eastern CONUS today and into
Monday. This will keep things dry with mostly clear skies today and
tonight. With the high remaining centered to our north, low-level
winds will remain light and favor a N to NE direction, veering to a
more ELY direction later today. Despite plenty of sunshine, the NLY
flow will help keep temps about 10 to 12 degrees below climatology
today.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 254 AM EST Sunday: The main concern for the early part of
the week is the possible development of light precip early Tuesday
morning over the Piedmont of the Carolinas. The model guidance,
particularly the operational GFS, continues to insist on developing
a weak wave on the old arctic front off the GA coast on Monday,
then spreading clouds and light precip northward ahead of the low,
perhaps clipping the southeastern part of the Charlotte metro
area some time between midnight and noon Tuesday. The problem
is...temps will be borderline 32F-ish in the pre-dawn hours
owing to the ongoing dry cold air damming wedge...raising the
possibility of a p-type issue if the precip develops far enough
into cold air. The models are not in especially good agreement
with the northwestern extend of the light precip, however, with
the op-GFS and NAMNest being the most favorable. Until we get a
better look with the mesoscale models...the morning run of the
HREF should go out far enough...prefer to minimize the precip
chances and slightly undercut the NBM. This makes some sense when
you consider that light precip will be fighting its way into the
initial dry air across NC. Temps are another matter. This looks like
a classic situation of an early low temp in the late evening hours
as temps drop quickly under a mostly clear sky, then the clouds
arrive after midnight along with some warm advection, raising the
temps steadily as the precip tries to develop. Bottom line is the
possibility for measurable precip to overlap with sub-freezing
temps looks minimal at this point, so the forecast is engineered
with that in mind. Stay tuned, though, because it won`t take much
of a change to introduce some light freezing rain chances around
metro Charlotte if either the temps trend colder or the models
suggest a farther NW extent of precip. Either way, it should be
short-lived, with temps warming steadily after sunrise and the
light precip moving off to the northeast by midday. Upper ridging
will build somewhat across the area on Tuesday and temps should
make it a few degrees above normal for highs. By Tuesday night,
though, a new parent high will be established over eastern Canada
and we will be right back into the dry cold air damming wedge.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 321 AM EST Sunday: Still not a lot of confidence in the
model guidance out in the medium range as we await more clarity
on where a blocking pattern might set up later in the week,
and how strong a cold air damming sfc ridge will be. The first
issue crops up mid-week as the GFS continues to show a dampening
short wave lifting over the TN/OH valley regions on Wednesday,
with moisture running much farther east over the wedge than the
other model solutions. The overall trend continues to be toward a
weaker and drier scenario so precip probs are kept fairly low for
Wednesday and Wednesday night. Fortunately, temps are warm enough
to only worry about some precip-type issues maybe at elevations
above 6k feet. With that system out of the way, a weak consensus
develops with mid/upper ridging over the East Coast supporting a
cold air damming parent high over New England for the rest of the
period. The next short wave to lift northeast out of the mid/upper
trof to our west would be over the weekend. The latest ECMWF and
Canadian develop this system quicker and farther east than the
GFS and would spread precip in from the west late in the week. In
spite of this wedge pattern, mid-levels remain warm and the air
mass appears too warm for anything other than rain. So, we are left
with a somewhat non-descript chance of precip and temps generally
above normal while we wait for more clarity in the model guidance.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Expect dry, VFR conditions to prevail
thru the 12z taf period as broad sfc high pressure builds in
from the north. We`ve seen some patches of VFR stratocu develop
over the eastern Upstate over the past few hrs, but it doesn`t
look like these clouds will impact any taf sites. Otherwise,
expect mostly clear skies and light NE winds with winds veering
to a more ELY direction during the afternoon/early evening and
remaining light. At KAVL, winds should remain NLY thru mid-
morning and then go light and vrb. They will eventually favor
a SLY to SELY direction by this evening with speeds of 5 kt or
less.

Outlook: Expect broad high pressure and mostly dry conditions
to persist thru early next week. Precip chances and associated
restrictions increase by mid-week.

&&

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

&&

$$

SYNOPSIS...PM
NEAR TERM...JPT
SHORT TERM...PM
LONG TERM...PM
AVIATION...JPT