Area Forecast Discussion
Issued by NWS Atlanta, GA

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FXUS62 KFFC 222318

Area Forecast Discussion
National Weather Service Peachtree City GA
618 PM EST Wed Nov 22 2017

Updated for the 00Z Aviation Discussion.


.PREV DISCUSSION... /Issued 224 PM EST Wed Nov 22 2017/

SHORT TERM /Tonight through Thursday Night/...
Broad area of high pressure over the central CONUS has pushed into
parts of north and central Georgia today. Northerly winds and lower
dewpts/humidity exist this afternoon with just some high clouds
streaming across the area from the southwest. Afternoon temps were
generally in the mid-upr 50s (northwest zones) to around 70F (far
south -- Cordele to Dublin to Swainsboro).

Main player the next 24-36 hours will center around a surface wave
of low pressure and associated upr lvl trough currently digging
across the northern Gulf of Mexico. This "wave" is expected to
become better organized as it drifts slowly northeast. Models are in
pretty good agreement with movement/track of this low with the
exception of the NAM which shows a more northerly track. The
divergent solns have more of an impact on forecast late Thursday
night into Friday (vs. tonight/tomorrow) with placement and
intensity of rainfall.

All this said, expect a gradual increase in moisture across the area
tonight into Thanksgiving, especially south of I-85/I-20. This will
mainly result in mostly cloudy skies, but a few light rain showers
and/or drizzle could develop by daybreak, generally along and south
of a Columbus to Macon to Sandersville line. A piece of the Low is
expected to track across north Florida Thursday night along with the
upr trough. This should gradually diminish the threat for any
rainfall across the southern counties by Friday morning.


LONG TERM /Friday through Wednesday/...
At the beginning of the long term forecast period around 12z
Friday...the mid and upper level synoptic regime will be slightly
less amplified than during the short term...albeit only temporarily.
Tight...more quasi-zonal westerlies will exist across the northern
Rockies into the Northern Plains as a shortwave ejects from the
Washington State Coast into eastern Montana. Downstream from
this...loose and broad cyclonic flow will be in place across the
eastern US...with a nuisance trough affecting the SE coast. At the
sfc...a wave induced by mid level vort maxes within the nuisance
trough will push northeast just offshore the Carolinas along a
pre-existing frontal boundary.

Friday forecast is a bit tricky as the 12z guidance has yet to get a
decent handle on the evolution of the eastern Gulf trough. Although
the southern stream flow is overall progressive pattern
would likely suggest keeping an open wave trough as the system
progresses northeast. This makes 12z NAM guidance a noticeable
outlier with a potent closed low moving across southern Ga. For
now...have discarded this solution and trended more towards
EC/GFS/CMC. This will keep slight chance POPs across far SE counties
until midday Friday. Will have to watch trends closely over the next
24 hrs tho given the degree of disagreement. A stronger/closed low
would push rain chances farther north into the CWA.

Once this system clears late Friday another cold front will push
through the CWA Saturday. This front will be dry and the only
sensible weather effects will be increased cloud cover during its
passage. Temps Sat should reach into the 60s most areas with a shot
of slightly cooler air for Sunday /mid 50s north to mid 60s central/.

Post-frontal high pressure at the sfc will dominate Sunday through
Monday and keep things dry and pleasant...though the mid and upper
levels will become highly amplified again as a strong cyclone pushes
into the Pacific Northwest and induces downstream ridging across the
middle US.

With the upper pattern becoming more meridional...sfc high pressure
will move offshore by Tuesday. This will help advect moisture from
the Atlantic as flow begins to take on a more southerly component in
the lower levels. Weak upper ridging should be enough to shunt any
precip activity on Tuesday. By late Tuesday operational EC and GFS
diverge significantly but will trend toward the GFS for now given
its better resemblance to GEFS and EPS ensemble data. This would
argue for another fropa by mid week...although elongated nature
of the front as the parent cyclone remains across Canada points
towards a potentially dry passage. Have kept slight chance POPs
across the north for now to compromise somewhat given this is 7
days out.



00Z Update...
Moisture begins spreading north tonight with cigs becoming MVFR
late tonight all areas. Low clouds will dissipate rapidly Thursday
morning across the ATL/AHN areas. Cigs across CSG/MCN will become
VFR by late morning Thursday. Winds will become light northeast
or calm this evening and remain east to northeast through

//ATL Confidence...00Z Update...
Medium on cigs late tonight.
High on remaining elements.



Athens          41  56  38  63 /   0   0   0   0
Atlanta         42  58  42  64 /   0   0   0   0
Blairsville     32  56  32  61 /   0   0   0   0
Cartersville    36  58  36  64 /   0   0   0   0
Columbus        46  62  44  66 /   5   5   0   5
Gainesville     40  56  38  61 /   0   0   0   0
Macon           47  58  42  65 /  10  10   5   5
Rome            34  58  34  63 /   0   0   0   0
Peachtree City  40  59  38  64 /   5   5   0   0
Vidalia         50  59  46  64 /  20  20  30  20




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