091
FXUS62 KFFC 191148
AFDFFC

Area Forecast Discussion
National Weather Service Peachtree City GA
648 AM EST Sun Jan 19 2025



...New 12Z Aviation Discussion...

.SHORT TERM...
(Today through Monday)
Issued at 434 AM EST Sun Jan 19 2025

At a glance:

    - Chance for flurries this afternoon/evening for areas north and
      west of the Atlanta Metro

    - Hazardous and unseasonably cold airmass moves in across the
      Southeast beginning tonight

    - Monday morning: Extreme Cold Warning in effect for the Atlanta
      Metro and points north, Cold Weather Advisory in effect for
      the remainder of north and central Georgia

In the wake of the surface frontal pressure system that supported a
rather dreary Saturday, lingering showers are ongoing across the
southern half of the forecast area this morning. Expect the
aforementioned precipitation to continue to taper off through mid-
morning as a shot of much drier air rounding the base of our
presiding mid-level trough noses into the Southeast.

More notably, the eastern fringes of a strong Arctic surface high
(the airmass within which originated from far, far to our north
across Siberia) will spread toward the Eastern Seaboard over the
course of the next 24 hours. As it does so, the stage is set for a
hazardous cold snap to begin across the state. Highs today (in the
upper 30s to lower 60s) are likely to be set early in the day as
temperatures will begin tumbling downward as the cold air mixes in
from northwest to southeast. Wraparound moisture moving in across
portions of north Georgia this afternoon is thus likely to support
periods of snow flurries -- and perhaps light snow for locales at
the highest peaks. Flurries are by definition non-accumulating, so
not expecting any impacts there besides the requisite shock and awe
at winter weather in the South.

Breezy to gusty conditions post-front will continue overnight
tonight, which when combined with lows already forecast to plummet
into the single digits to lower 20s will support what will certainly
be the coldest morning of the season thus far. Wind chills as far
south as metro Atlanta will be close to zero or a just few degrees
below, and are likely to fall into the single digits to teens
elsewhere. The Extreme Cold Watch that was issued yesterday has
been upgraded to an Extreme Cold Warning due to high confidence in
the aforementioned dangerously cold wind chills (portions of
northwest and northeast Georgia at elevation may "feel like" as
much as 5 to 15 degrees below zero). For the remainder of north
and central Georgia, a Cold Weather Advisory has been issued. An
important caveat, which will be discussed further in the long term
section of the AFD, is that temperatures are likely to be below
freezing for a longer duration than is typically the case. Highs
on Monday are forecast to be in just the teens to lower 40s, and
areas along and north of I-20 may not breach 32F. Proper
precautions will need to be taken to prepare for an extended
period of frigid temperatures -- remember the 4 P`s of winter
preparedness (people, pets, pipes, plants) and be sure to leave
your faucets dripping and under sink cabinets open before heading
to bed tonight.

96

&&

.LONG TERM...
(Monday night through Saturday)
Issued at 434 AM EST Sun Jan 19 2025

Key Messages:

-Hazardous cold temperatures will persist Monday night into
Wednesday, with dozens of hours below freezing likely across
portions of north Georgia during this time.

-Confidence is increasing on chances for winter weather on Tuesday
into Wednesday. A Winter Storm Watch has been issued for central and
portions of north Georgia from 10 AM Tuesday until 7 AM Wednesday.

Forecast:
With a lot of moving parts to discuss in the extended period, this
discussion will be broken down into three subsections: the
abnormally cold airmass, the potential winter storm on
Tuesday/Wednesday, and the late week forecast.

1. Cold Conditions:
An Arctic airmass will be firmly in place across north and central
Georgia as the long term period begins on Monday night due to the
influence of a strong (1045+ mb) Arctic high pressure over Great
Plains. This high will continue eastward Tuesday into Wednesday,
though will remain to the west of Georgia, with little change to the
airmass expected over that time. Overnight into Tuesday morning,
temperatures are expected to decrease to lows in the teens roughly
along and north of the I-85 corridor and low 20s to the south, which
will be 10-15 degrees below climatological normals. Winds will
thankfully be lighter than on Monday morning, but wind chill values
will still be pretty brutal Tuesday morning, between 5-10 across
portions of far north Georgia and between 10-20 elsewhere in the
forecast area. Wind chills in higher elevations in far north Georgia
could furthermore drop to between 0-5 degrees.

High temperatures on Tuesday will be in the low to mid 30s in north
Georgia and in the upper 30s to low 40s in central Georgia, before
quickly falling below freezing across the area once again after
sunset. High temperatures on Wednesday are forecast to be in the low
to mid 30s across the majority of the area. Many locations in north
and central Georgia, particularly to the north of I-85, could
experience well over 48 consecutive hours of below freezing
temperatures starting within the short term period early Monday. 48
consecutive hours is important because this is typically when
problems begin with exposed pipes freezing and bursting. NOW is the
time to ensure your home is prepared for the prolonged period of
below freezing and abnormally cold conditions.

2. Winter Weather Potential:
On Tuesday morning, the axis of a longwave trough will advance
through the SW CONUS and through Texas and northern Mexico. As this
occurs, it will push a shortwave disturbance into the northwestern
Gulf of Mexico. GLobal scale model guidance is coming into better
agreement with the development of a surface low associated with
these features. This low pressure system will then advance eastward
through the Gulf over the course of the day on Tuesday and Tuesday
night. Moisture on the north side of this low and on the east side
of the longwave trough axis will meanwhile advance northward over
the Gulf Coast and into the Deep South, ultimately overrunning the
Arctic airmass already in place across the forecast area.

Model guidance is also trending towards a consensus that
precipitation will begin to nose its way into the southwest corner
of the forecast area by mid-afternoon on Tuesday, then spread east
and northward as the surface low continues its trek across the Gulf.
At this time, chance to low-end likely PoPs are being carried across
the area on Tuesday afternoon, followed by chance PoPs along the I-
85 corridor, and likely to categorical PoPs to the south and east
Tuesday night into early Wednesday morning.

The character of the initial airmass will influence the nature of
winter precipitation as moisture associated with the Gulf low
spreads over north and central Georgia. First, it should be noted
that this airmass will be much drier than what was observed on
January 10th, so this event will not play out exactly like the last
one. Dewpoints are forecast to be in the single digits to teens
areawide mid-morning/early afternoon Tuesday. Precipitation falling
into this dry airmass will cause a wet-bulbing effect, in which the
evaporation of the precipitation cools and moistens the airmass.
This would gradually decrease temperatures and increase dewpoints
through the atmospheric column and eventually at the surface. How
much wet-bulbing occurs will have a significant impact on which
locations receive the most snow and how much could ultimately occur.

Regarding P-Type:
A look at forecast thermal profiles backs up this possibility of
evaporative cooling temperatures below freezing through the
atmospheric column, especially in north Georgia. Thus, it appears
at this time that the dominant precipitation type will be snow for
the majority of this event. Sleet is shaping up be slightly more
likely than in previous forecasts, but is overall expected to be
confined to the far southern/southeastern portions of the forecast
area Tuesday night until just after midnight. The latest guidance
appears to be backing off of chances for freezing rain in all
except the far southeastern corner of the forecast area on early
Wednesday morning. Even then, ice accumulation is currently
forecast to be less than 0.10 inch

Regarding Snow Amounts:
Exact snow accumulation amounts remain uncertain at this time and
will vary greatly on the strength of the Gulf low and how far
north the mid-level moisture on the north side is able to advance.
The ECMWF and CMC ensembles continue to indicate significantly
wetter solutions than the notably drier GFS ensembles. The latest
forecast has seen a northwestward shift in the axis of highest
precipitation, but it should be noted that the highest snowfall
amounts remain south of the Atlanta metro area. Inner quartile NBM
guidance indicates snowfall totals of 1.5 to 2.5 inches in
central Georgia, with highest amounts in west-central Georgia
(including Columbus). Below are some probabilities at a few
locations for >1 and >2 inches of snow from the 01Z NBM run:

Probabilities of 1+ inch of snow
Columbus: 70%  Macon: 55%  Atlanta: 50%  Athens: 45%

Probabilities of 2+ inches of snow:
Columbus: 55%  Macon: 45%  Atlanta: 40%  Athens: 35%

However, it should be noted that the spread in ensemble members
remains quite large with respect to amounts. This is illustrated by
"reasonable lowest amount" (90% or 9/10 exceedence) probabilities
indicating no measurable snowfall and "reasonable highest amount"
(10% or 1/10 exceedence probabilities indicating as much as 6-8
inches of snow in some locations in central and west Georgia.
Given this large spread in ensemble members, deterministic
forecasts of snowfall will remain variable. Therefore, will
continue to recommend favoring probabilistic guidance over
deterministic.

A Winter Storm Watch has been issued this morning for portions of
central and north Georgia, which will be in effect from 10 AM
Tuesday until 7 AM Wednesday. This watch covers an area roughly
along and south of a line from Carroll county to Hall county, and
also includes the Atlanta metro area, Columbus, and Macon.
Considering the multiple hours near or below freezing in advance
of this system, it is likely that any wintry precipitation that
falls will stick to roads instantly. Thus, it will not take much
accumulation to create hazardous travel conditions.

3. Late This Week:
Late Wednesday into Thursday, the high pressure system will begin to
weaken and move off towards the central Atlantic coast. The airmass
will begin to gradually moderate over the Southeast through the end
of the week into the weekend. Temperatures on Wednesday and Thursday
are nonetheless forecast to rise above freezing for only a few hours
each afternoon, only to drop into the teens Wednesday night into
Thursday morning and low to mid 20s on Thursday into Friday. Snow
and ice that do occur will be likely to hang around given the
limited time for melting and a certainty of refreezing during the
overnight and morning hours. This is especially true in sheltered or
shady areas that do not see a lot of sunlight.

A low pressure system developing off the Carolina coast could
potentially spread freezing rain into portions of east-central
Georgia during the daytime Thursday into early Friday. Freezing rain
would most likely be mixed with rain in the daytime hours, and
chances remain 30 percent or less at this time. At this time, any
ice accumulations that occur appear to be limited to a light glaze.
However, much uncertainty remains with respect to this potential low
pressure system, and we will continue to monitor this scenario as it
comes closer into focus this week. While morning lows will remain in
the low 20s on Friday and Saturday morning, a warming trend will
become more apparent through the high temperatures, which are
forecast to warm into the low to mid 40s on Friday afternoon and
into the upper 40s and near 50(!) on Saturday afternoon.

King

&&

.AVIATION...
(12Z TAFS)
Issued at 637 AM EST Sun Jan 19 2025

BKN to OVC LIFR cigs to linger until 13-14Z, lifting to IFR and then
MVFR for the remainder of the aftn. Periods of LIFR vsbys in
FG/BR likely thru daybreak. Non-accumulating SN flurries are
possible for ATL after 19-20Z, associated with wraparound moisture
in wake of sfc low. Gusty NW winds exp thru the TAF period, at
8-15kts sustained with gusts to 25-28kts psbl.


//ATL Confidence...12Z Update...
Medium confidence cig/vsby progression and chances for flurries.
High confidence all other elements.

96

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          52  19  36  19 /  10   0   0   0
Atlanta         48  16  31  20 /  10   0   0   0
Blairsville     43   7  26  10 /  20   0   0   0
Cartersville    45  13  29  15 /  10   0   0   0
Columbus        54  21  37  22 /   0   0   0   0
Gainesville     48  16  33  19 /  10   0   0   0
Macon           58  21  39  22 /   0   0   0   0
Rome            43  14  30  15 /  10   0   0   0
Peachtree City  49  16  32  19 /  10   0   0   0
Vidalia         64  26  42  27 /  20   0   0   0

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Extreme Cold Warning from 1 AM to noon EST Monday for GAZ001>009-
011>016-019>023-030>034-041>045.

Dense Fog Advisory until 10 AM EST this morning for GAZ006>009-
013>016-020>025-027-030>039-041>062-066>076-078>086-089>097.

Winter Storm Watch from Tuesday morning through Wednesday
morning for GAZ022>025-027-031>039-042>062-066>076-078>086-
089>098-102>113.

Cold Weather Advisory from 1 AM to 11 AM EST Monday for GAZ024-
025-027-035>039-046>062-066>076-078>086-089>098-102>113.

&&

$$

SHORT TERM...96
LONG TERM....King
AVIATION...96