Area Forecast Discussion
Issued by NWS Atlanta, GA

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298
FXUS62 KFFC 180011 AAA
AFDFFC

Area Forecast Discussion...UPDATED
National Weather Service Peachtree City GA
711 PM EST Sun Dec 17 2017

.UPDATE...
Updated forecast to include more mention of fog and drizzle
tonight and Monday. Low clouds, fog and drizzle likely to persist
much of the day now and may affect temps as well.

SNELSON

&&

.PREV DISCUSSION... /Issued 221 PM EST Sun Dec 17 2017/

SHORT TERM /Tonight through Monday Night/...
Broad cyclonic flow over the western 2/3rds of the country has
allowed for the transport of deep Pacific moisture via the
subtropical jet over the Southeast US amidst a southwest mid level
flow regime. A weakening mid level shortwave trough currently over
the Midwest is helping provide additional lift in the mid
levels...while at the sfc strong WAA ahead of a subtle wave is
also contributing the deteriorating conditions this afternoon.

Rest of today and tonight: Rather widespread rain is ongoing across
much of north Georgia. This is expected to slowly move into portions
of central Georgia through the evening before dissipating to into
isolated light showers. Instability is minimal with this activity so
no thunder is expected through tonight. Given the rapid transport of
lower level moisture...fog is expected overnight. In
addition...HRRR/RAP/NAM12 sounding data also suggests the potential
for drizzle through much of the night into Monday morning.
Overall...expecting damp conditions over the next 12 hours. Temps
have been struggling across the north to even make 50 today...so
have adjusted high temps down across this area of the CWA and
adjusted future trends /mainly MET guidance/ to represent this.
Given ample cloud cover and fog potential...do not think temps will
fall that much overnight.

Monday is tricky. A warm front associated with the aforementioned
sfc wave will stall across the local area and become a stationary
boundary early Monday. The exact location of this boundary through
the day tomorrow will determine where the most moisture resides and
hence where highest rain chances will be confined. Right now think
it will be in the Columbus to Macon vicinity. Multiple weak
perturbations traversing through the mid level southwest flow will
provide additional ascent atop the stalled boundary to allow for the
development of rain through the day. Some MUCAPE is noted across
central Georgia so isolated thunderstorms could be embedded within
the broader rain shield. The stalled boundary will continue into the
long term...with a wet pattern to continue.

Kovacik

LONG TERM /Tuesday through Sunday/...
Unsettled weather still expected for much of the long term period of
the forecast. In addition, the potential for locally heavy rainfall
is increasing across portions of northern GA.

Stationary frontal boundary will set up across portions of north GA
by Tuesday night. This old front will serve to focus precip for
Tuesday night into early Thursday with the models coming into
agreement that this period will be wet. Several perturbations in the
mid level flow will interact with the stalled boundary, potentially
causing several rounds of precipitation. A stronger wave aloft along
with a surface low should move along the stalled front during the
day on Wednesday, with periods of locally heavier rainfall. For now,
amounts between one and three inches are possible, with some locally
higher amounts, especially across areas north of the Atlanta Metro.
Since the axis of heaviest rain will depend upon where the old
boundary will stall, am not confident on pinpointing on exactly
where it will set up. Currently, models are progging an area just
south of the TN/NC/GA line.

Another frontal boundary/low pressure system should impact the CWFA
for the late part of the week into the weekend.

Above normal temps expected through the period.

NListemaa

&&

.AVIATION...
00Z Update...
Conditions already at IFR to near IFR at most north Georgia
airports and expected to continue to worsen tonight and remain at
IFR or LIFR thru much of Monday. Some improvement expected after
23Z Monday. Bulk of rain should remain south of ATL metro airports
Monday but rain likely after 18Z at KCSG and KMCN. Sfc winds
will remain E to NE 2-5kts but will switch to W around 15-16Z
Monday.


//ATL Confidence...00Z Update...
Medium confidence on IFR/LIFR timing Monday
High confidence on all other elements

SNELSON

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          42  61  48  68 /  50  30  30  30
Atlanta         44  61  51  66 /  50  30  30  40
Blairsville     39  59  40  62 /  40  10  10  60
Cartersville    42  58  46  64 /  40  20  20  50
Columbus        54  66  56  71 /  50  60  40  20
Gainesville     42  60  48  64 /  40  20  20  50
Macon           53  64  53  71 /  50  50  40  10
Rome            39  57  45  63 /  40  10  10  60
Peachtree City  44  62  50  68 /  50  50  40  30
Vidalia         57  68  59  74 /  40  50  40   5

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...SNELSON
LONG TERM....20
AVIATION...SNELSON



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