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Area Forecast Discussion (AFD)

Issued by Peachtree City, GA (FFC)

FXUS62 KFFC 181920

Area Forecast Discussion
National Weather Service Peachtree City GA
320 PM EDT Sun Mar 18 2018

.SHORT TERM /Tonight through Monday Night/...

Regional radar view shows considerable activity presently over SW
Alabama riding the energy provided by embedded shortwave in
largely westerly flow aloft. Expect the most robust of this
activity to ride along the best instability axis this evening
which is roughly from Columbus to Vidalia and points southward
currently. Some CAPE values just south of the area running close 
to 1500 J/KG so some strong to severe activity not out of the 
question and SPC slight risk for just a few counties looks on 

For the remainder of the overnight period, rain chances will
increase rapidly as istentropic processes combine with shortwaves
to produce widespread rain with embedded thunderstorms for
southern sections. Previous model runs had indicated the potential
for some isolated flooding across the southern tier. Latest runs
though indicate around an inch to an inch and a quarter which 
Central GA should be able to handle through the overnight period. 
As far as severe potential into the overnight, developing easterly
flow should inhibit expansion of instability axis and even 
elevated CAPE looks manageable through 12Z Monday so prospects 
look low at this time for any robust convection.

Very difficult call for Monday afternoon as some models indicate
low clouds and stable conditions will stay with the entire area
for the balance of the day. But there is a very sharp instability
gradient with in excess of 2000 J?KG just along and south of our
southern CWA border. Shear not the best but sufficient for some
rotating discreet cells should activity be able to develop across
the southern tier. 

Final wave which looks to be of the most concern will be Monday
evening into the first part of the overnight period. Even
instability associated with this feature is less in the models
than this time a few days ago. But with positive CAPE values, feel
activity that develops over Alabama will be able to maintain
itself over the local area and take advantage of very strong shear
values to produce strong to severe storms. Pretty much everything
on the table for this one including damaging winds, isolated
tornadoes and large hail. Some hi res guidance wants to weaken
this feature as it gets south of the metro but thinking this may
be premature given similar events in the past and will advertise
severe risk well into Central GA for this one.



LONG TERM /Tuesday through Sunday/...
Mainly only tweaks to the long term based on the latest guidance.
Thunderstorm chances will be over portions of central GA mainly
E and S of MCN on Tuesday and then just chances for showers
into Wednesday favoring N and E GA.


As a surface low moves across Tennessee Monday evening, widespread 
thunderstorms will be ongoing and rapidly progressing eastward 
Monday night ahead of the attendant cold front. The severe 
thunderstorm threat will have increased by this point with 
substantial surface instability and favorable shear in place. 
Supercellular convection with the threat for large hail, damaging 
winds, and tornadoes will be a concern during the evening hours. The 
highest severe threat will exist across portions of north and 
central Georgia outside of the influence of the wedge which, though 
retreating, will help limit instability across northeast Georgia. 
The overall severe threat will then quickly diminish from the 
northwest as the cold front sweeps southeastward through early 
Monday morning.

Additional showers will return on Tuesday as a followup upper wave 
and cold front push into the region. Northwest winds will pickup 
late Tuesday behind this secondary cold front, and significantly 
cooler temperatures will advect into the state. Before the light 
rain ends, some brief rain/snow mix may be observed across the high 
elevations of far north Georgia during the early morning hours 
Wednesday; however, accumulations or impacts would not be a concern.

Wednesday will bring clearing skies and below average temperatures 
with a sunny and cool Thursday also on tap. Temperatures will 
rebound by Friday with the next chance of rain likely holding off 
until Saturday morning at the earliest.



.AVIATION... 18Z UPDATE... Challenging forecast as we have three 
potential waves of precipitation moving across the terminals. 
Fortunately, it looks as though the third wave is now delayed 
enough to be just outside the ATL TAF cycle. Prior to this, we 
will be dealing with some developing cigs as well with BKN VFR 
arriving later this evening...transitioning to MVFR around 08Z and
quickly to IFR early Monday morning. Light rain will accompany 
this as well for all sites although will need to monitor for SHRA 
at CSG and MCN with TSRA not out of the question either this 
evening. Prob30 slated for ATL aft 18Z Mon although as 
mentioned...majority should be after 00Z.

Medium on TSRA chances and IFR duration Mon.
High on remaining elements.



Athens          54  65  54  70 /  80  60 100  40 
Atlanta         55  68  54  67 /  90  50 100  40 
Blairsville     49  61  47  62 /  70  60 100  50 
Cartersville    53  69  51  66 /  80  80 100  50 
Columbus        58  74  58  73 / 100  40  80  30 
Gainesville     52  62  52  67 /  70  60 100  50 
Macon           57  72  59  75 / 100  60  60  50 
Rome            53  69  51  64 /  80  80 100  50 
Peachtree City  55  71  54  69 /  90  40 100  40 
Vidalia         59  73  63  77 /  90  60  40  60