NWS GSP discussion
Key message 2: A
low pressure system moves into the area tonight
and Sunday with a chance of rain or snow, mainly outside of the
North Carolina mountains. Guidance continues to trend toward
minimal impacts.
The aforementioned longwave
trough will sharpen through today
into tonight as a strong
shortwave extends across the Mid/Lower-MS
Valley tonight and a
baroclinic zone shifts offshore the Southeast
Coast on the leeside of the
trough, while the frontal boundary from
earlier in the day stalls along the coastline, helping to induce
weak surface
cyclogenesis via weak coastal low. Deeper
moisture
transport will accompany the system to go along with stronger
frontogenesis, allowing for an axis of precip to develop. At
the same time, colder air from a secondary boundary will move
in from the northwest overnight tonight in association with the
trough axis. The mountains will slow down the colder air moving
into the area as the precip develops,
likely leading to just a
cold rain at the onset of the precip around midnight or shortly
after in the Piedmont zones. However, evaporational cooling
should help temperatures to drop during the night and
likely
a window of opportunity for the cold air to get into the area
just in time for a transition over the snow, especially along
and northwest of I-85 through daybreak Sunday and even taking on
this transition a little further south and east of I-85 shortly
after daybreak. Ground temperatures will be above freezing and
QPF
will be relatively light, so only little to no snow accumulations
are expected. However, some of the CAMs, in particular the
NAM
indicates a narrow deformation band developing where the axis of
heaviest precip occurs. In this case, a surprise half inch to an
inch plus can`t be totally ruled out, but good luck pinpointing
where that
likely develops over the Piedmont areas across the
Upstate and North Carolina, with guidance struggling to find a good
consensus. Model guidance are taking on its usual northwest trend
as we get closer to the event and tried to apply that to the latest
forecast. Areas along I-85 and vicinity currently seem like the best
locations for a longer period of snow and thus, highest chance for
light snow accumulations Sunday morning. This is highly subject to
change despite being 24-36 hours from the event. With confidence
remaining low on the overall setup and snow accumulations below
Advisory criteria in the current forecast, decided to just keep a
HWO mention for the time being and will need to further investigate
the trends throughout today to determine whether or not an Advisory
is needed for portions of the
CWFA. Any snow accumulations will
likely melt by the afternoon anyways as afternoon highs reach into
the upper 30s to lower 40s across the Piedmont zones with clearing
skies late in the afternoon, while the Arctic air arrives across
the mountains with widespread 20s and lower 30s expected.
NWS Columbia
Area Forecast Discussion
National Weather Service Columbia SC
1249 AM EST Sat Jan 17 2026
.WHAT HAS CHANGED...
Higher resolution guidance highlights the potential for a brief
snow band to set up over portion of the area Sunday morning
into early afternoon. High end amounts continue to be below
winter weather advisory criteria, however and much of the area
likely will receive little to no snow accumulation.
KEY MESSAGES...
1) A rain/snow mix is possible Sunday, but the potential for
significant accumulation is low. Patchy black ice possible
early Monday morning.
DISCUSSION...
Key Message 1: A rain/snow mix is possible Sunday, but the potential
for significant accumulation is low. Patchy black ice possible
Sunday night.
The overall synoptic pattern for the system Saturday night into
Sunday remains the same with a deepening 500mb trough into the
Missippi Valley leading to cyclogenesis along the northern Gulf
coast. Surface low pressure will move along the coast of GA/SC in
what is a typically favorable setup for winter weather in our area.
The issue we will run into is high confidence in temperatures in the
40s Saturday night and while a colder air mass will begin to push in
and overrunning will lead to rain developing, allowing for
evaporative cooling, climatologically it is difficult to get any
kind of meaningful snow accumulation when the cold air is not
already in place. Rain will likely transition to a rain/snow
mix Sunday morning but light snow will struggle to accumulate
with temperatures likely near freezing and ground temperatures
likely above freezing.
HiRes models do still indicate the potential for mesoscale banding
associated with warm advection and a strengthening band of
frontogenesis leading to sufficient lift in the dendritic growth
zone. This would lead to some higher snow rates which would likely
be able to overcome marginal surface temps leading to some
accumulating snow at the surface. Higher end amounts continue to
remain around a half inch and much of the area would likely receive
less than this (or no accumulation at all). With high confidence
that total snowfall remains less than an inch, we will not be
issuing a Winter Weather Advisory with this package. There may be
some minor impacts for a brief period, likely late morning into
early afternoon, if and where this band sets up but overall,
widespread impactful winter weather is not expected over the
forecast area.
Precipitation expected to push east of the area late Sunday
afternoon with a colder air mass pushing into the forecast area as
high pressure settles over the Deep South. Blended guidance shows
about a quarter to a half inch of total liquid precipitation with
this system and as temperatures drop below freezing Sunday night,
there will be potential for black ice to develop on roads. This will
likely not be a widespread issue as a lingering pressure gradient
will lead to breezy winds into Sunday night which will help to dry
out roads, but patchy black ice is possible.