641
FXUS62 KCAE 101020
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
520 AM EST Fri Jan 10 2025

.SYNOPSIS...
A cold and dry air mass remains in place ahead of an impactful
winter storm which will move through the area today, yielding a
wintry mix of snow, sleet and freezing rain across Midlands and
CSRA. Winter Weather headlines remain in effect much of today,
before the system is forecast to exit the region on Saturday
morning. Dry and cold weather then follow and continue well into
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Message(s):

- A Winter Storm Warning is in effect from 7 am this morning until
7 am Saturday for our northern and northwestern counties.

- A Winter Weather Advisory is in effect from 7 am this morning
until 4 am Saturday for the remainder of the counties in the CWA.

- Confidence is high that an impactful Winter Storm will affect the
area today and tonight, with the greatest impacts expected across
the northern forecast area.

- Some uncertainty remains regarding surface temperatures
particularly during the day today, but confidence has slightly
increased that it will be a degree or two cooler than previously
expected.

============================================
SYNOPTIC OVERVIEW
============================================

Deep, positively tilted upper level trough now extends from
Wisconsin southwest across western TX. High pressure over the Ohio
Valley continues to weaken and lift northeast this morning while a
strengthening area of low pressure is moving onshore along the LA/MS
coastline. West and southwest flow aloft is boosting both mid and
upper level moisture, as indicated by increasing clouds over the
area in the past several hours. Very dry air remains in place at the
surface, with dew points currently in teens and low 20s.
Temperatures dropped quickly earlier in the night, and haven`t
really budged much despite the incoming cloud cover. Many locations
around the Midlands and CSRA have current temperatures in the mid
and upper 20s. Starting the day off so chilly with skies becoming
increasingly overcast will make the temperature forecast for the
rest of the day, including the p-type forecast, very tricky.

The surface low will track inland this morning with moisture
continuing to increase across the southeast. Broad area of precip
associated with a mid-level shortwave will advect eastward ahead of
the low, encroaching on our Western border in the hour or two after
sunrise. Since we will likely still have temperatures in the 20s to
around 30 as this occurs and dewpoints should still be quite dry,
this initial band of precip will mainly work to moisten our lower
levels, but any precip that does make it to the surface is expected
to be of the frozen variety. Since the depth of the warm layer aloft
won`t be at its strongest just yet, believe a brief period of snow
and/or sleet or even some brief freezing rain can be expected before
temperatures warm up a few degrees and a changeover to rain occurs
early this afternoon. However, it can`t be overstated that a slight
shift in temperatures to either side of the freezing mark may have
significant consequences for any precip that reaches the ground with
this first wave.

Additional forcing, warm advection and strong height falls/vorticity
advection, will overspread the forecast area this afternoon. The
elevated warm layer will increase quickly as a 30-40 knot LLJ
overspreads the area. As such, rain becomes the dominant p-type for
much of this afternoon, except along our SC/NC border counties where
temperatures are progged to remain cooler and precip should remain
of the frozen variety for a bit longer. The p-type gradient will
generally stretch from south to north, with some fairly efficient
precipitation rates, especially along and north of I-20.
Temperatures then fall again this evening with the loss of daylight
with the surface low tracking across southern GA. This should be the
best timeframe for widespread accumulations of freezing rain, again
with the counties in the Warning potentially accumulating in excess
of 0.25" of ice. Warm advection then extends down to the surface
once again late tonight, with temps along the I-20 corridor and
south likely to bump up above 32F sometime after 9p or 10p, with the
northern forecast area explicitly forecast to remain below freezing
now.

Precip is expected to generally decrease from west to east early
Saturday morning as the low pulls away off the NC coastline. Despite
some increase in temperatures around midnight, overnight lows should
still hover around the freezing mark (29-33 DECs F) for much of
the region.

============================================
IMPACTS & FORECAST UNCERTAINTIES
============================================

Impacts may begin late this morning with the initial wave of precip,
particularly if anything of the frozen variety is able to reach the
ground. While it still appears it will be too dry for impactful
accumulations early, a few models like the NAM/CAN remain adamant
that freezing rain may occur as far south as our southern counties.
As such, we did add the remainder of the forecast area into the
Winter Weather Advisory for at least a light glaze or a few
hundredths of an inch of ice accumulation.

The overall trend with the latest suite of model solutions (and MOS
guidance as well) continues to trend cooler and wetter. We have
boosted QPFs across the region to between 0.5" and 0.75" of storm
total accumulation, the potential for ice accumulation up to about
1/3 of an inch, and perhaps up to about 1/2" of sleet/snow. In
general the threat for these highest values is in the Winter Storm
Warning area, and amounts decrease from northwest to southeast
across the forecast area. Given the overcast skies and cold airmass
in place this morning, still expect it will be difficult to get
temperatures warmer than the mid 30s across most of the forecast
area, particularly if wet-bulbing occurs this morning with the first
batch of precip.

Overall, as is typical with mixed wintry precipitation events, these
accumulation values over the next 18 to 24 hours are likely to
create travel challenges in addition to accretion on trees/power
lines that may lead to isolated power outages. This is especially
true across the western Midlands and CSRA where the trees are still
weak from Hurricane Helene`s impacts back in September.

Our biggest challenge remains the changing state of the temperature
profiles as the storm passes through the region. While confidence is
fairly high that the northern portion of the forecast area will stay
near to or below freezing for the duration of the event, there is
less certainty for areas included in the Winter Weather Advisory
where forecast surface temperatures have more model spread and
profiles are isothermal with occasional wiggles one way or the other
between the snow growth zone and the surface. Wet-bulbing will also
likely have an effect, and the strength and time that it takes to
moisten up the surface layer will affect p-types across the region.

It should be noted that the surface sub-freezing airmass is likely
to be so shallow that freezing rain will be the predominant precip
type for much of the event, particularly this evening. Confidence is
high that our southern tier of counties is likely to remain above
freezing for much of the event as they`ll be too close to the
surface low to really support much in the way of freezing rain
outside of this morning which was the main reasoning for extending
the Advisory to the south.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Key Message(s):

- Cold weather continues.

With surface low pressure departing the area this weekend, moisture
will rapidly decrease as a much drier air mass settles over the
region with high probability of HREF PWATs below 0.6 inches by
Saturday morning and remaining low through the weekend.
Climatologically, we are entering the coldest part of the year and
with general troughing over the eastern US and high pressure
settling over the southeastern US, blended guidance supports
temperatures around 10 degrees below seasonal average. Highs will be
in the low to mid 40s with lows generally in the low to mid 20s,
although stronger radiational cooling Saturday night with light
winds in the boundary layer under surface high pressure which will
likely lead to colder locations dropping into the teens.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Key Message(s):

- Brief warm up followed by more cold weather.

GEFS and EC ensemble members support a dry forecast with a brief
increase in PWATs Monday leading to the potential for some increased
clouds but otherwise all members have PWATs below a half inch
through the extended period with a dry forecast expected. A
brief warmup expected Monday with temperatures closer to
average. Blended guidance continues to support below average
temperatures through the extended with GEFS mean and EC
ensemble mean indicating 850mb temperatures continuing below
average. As a result, expect generally cold and dry weather
through the extended.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
VFR conditions expected through the first half of the TAF period,
with mixed wintry precip and associated restrictions likely this
afternoon through tonight.

High clouds are beginning to move in from the west ahead of a winter
storm. Ceilings will remain VFR through the majority of the day,
with lowering expected as precip begins moving in and lower levels
slowly moisten up from the top down. MVFR CIGS and VSBYS should hold
off until after 10/18z, with the possibility of IFR ceilings not
expected until after 11/00z.

In addition to the clouds, mixed wintry precip will be moving into
the region after sunrise, impacting the AGS/DNL terminals by 15z-16z
and slightly later at CAE/CUB/OGB. It may also take an hour or two
longer for the lower levels to moisten before precip makes it to the
ground, so there is still some uncertainty. When it does begin, the
initial precip will be rather light, and do expect to have a mixture
of -Rn/-SM/-PL through 18z. A change over to all -Rn should
occur through the afternoon, although temperatures may hover
close to freezing. This will bear watching as a slight change in
surface temperatures would cause a shift in surface precip
type. With that said, the main period with potential for -FZRA
should occur close to and after 11/00z. Warm air advection then
likely turns precip back to all rain late tonight into Saturday
morning.

Winds light and variable overnight, then shifting easterly
through the day on Friday, generally less than 10 kts. A 30-40
kt low level jet may also lead to a period of LLWS this evening.
Considerations for this will be included in the 12z TAF issuance.

EXTENDED AVIATION OUTLOOK...Ceiling and visibility restrictions
likely late tonight into early Saturday morning as a winter storm
begins to move out of the region. Restrictions slowly lift on
Saturday with no additional aviation concerns through Tuesday.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...Winter Storm Warning from 7 AM this morning to 7 AM EST
     Saturday for SCZ016-018-020>022-025-026-115-116.
     Winter Weather Advisory from 7 AM this morning to 4 AM EST
     Saturday for SCZ027>031-035-037-038-041-135>137.
GA...Winter Storm Warning from 7 AM this morning to 7 AM EST
     Saturday for GAZ040.
     Winter Weather Advisory from 7 AM this morning to 4 AM EST
     Saturday for GAZ063>065-077.

&&

$$