FXUS62 KFFC 191913

Area Forecast Discussion
National Weather Service Peachtree City GA
313 PM EDT Thu Jul 19 2018

.SHORT TERM /Tonight through Friday Night/...

Showers and thunderstorms have already developed across portions of
the region. Given the front is mainly draped across
central/southern GA, most of the activity is confined in that
region. However, with some mid level lift moving overhead,
lingering deep layer moisture and sufficient instability
>2000j/kg, we will see widely scattered thunderstorms through the
remainder of the afternoon/evening hours. Given such weak flow,
these heavier showers and thunderstorms will have little movement
to them causing some minor flooding. Also, gusty winds are
possible with some dry air within the atmospheric column. These
storms may linger with ample instability at the surface well after
sunset. As the activity diminishes late, debris clouds will
result in mostly cloudy skies through the overnight with moisture
becoming trapped by the early morning leading to stratus through
mid-morning Friday.

For tomorrow, believe there will be less precipitation activity
overall as strong high pressure noses into the area from the NE and
wake behind a low moving up the NC coast leading to some subsidence.
So while there is a little bit of upper level support, I do not
think there will be much thunderstorm activity, apart from some
development across the SE portion of our CWA during the afternoon.
However, in regards to Friday evening through the overnight, there
will be a front and associated shortwave approaching from the north.
This will provide enough lift with some instability already in place
at the surface to support a potentially strong thunderstorm complex
to impact north GA. The main questions are in regards to timing and
overall extent of this system. Since models are delaying the
arrival until after 06Z, instability may be waning. However, with
so much upper level support and elevated instability, it may not
matter. We will continue to monitor, but as it stands we feel this
system will diminish as it moves toward central GA early

Temperatures will be around climo.


.LONG TERM /Saturday through Thursday/...

Synoptically, the long term begins with a strong, cutoff, mid-level
low pressure system centered around the southern tip of Lake
Michigan. The associated negatively-tilted longwave trough will be
anchored through the Carolinas. As the trough axis moves overhead of
the Carolina coastline, baroclinic generation of a surface low
pressure system should occur off the Carolina coast near MHX. This
surface low will take advantage of a remnant frontal boundary,
situated through Central/Southern Georgia, that will have been the
focus for previous thunderstorm development in the area and push it
off to the southeast. This type of scenario would usually yield
pleasant weather conditions for north and central Georgia, but alas,
upper-level northwest flow combined with enhanced moisture, shear
and instability of the mid-level trough positioned to our north will
provide great conditions for the formation and maintenance of one or
two Mesoscale Convective Systems that are projected to move into the
forecast area early Saturday morning through late Saturday night.

Timing will be key as the the evolution of convection at the start
of the weekend, and frankly, low-res models tend to handle these
events poorly. Furthermore, an initial round of convection will
often corrupt model output for subsequent rounds of convection until
higher-resolution models can once again initialize with updated
atmospheric conditions. Therefore, it's difficult to pinpoint the
exact evolution of the storms through the weekend, but in general,
we're expecting likely thunderstorms which could be strong to
severe, with widespread strong wind gusts and heavy rainfall which
may cause concern in urban and previously saturated areas.

By Sunday, The upper-level cutoff low begins to move southward, with
the center of the low over the southeast CONUS by Monday afternoon.
A potential dry slot could limit precip chances for the morning and
afternoon before deep moist convergence takes hold of the region by
Monday into Tuesday. Even as the cut-off low deteriorates at the
beginning of next week, southwesterly flow and isentropic lift takes
over. With the belt of warm, moist air persistently pushing into the
area, next week will be filled with numerous showers and
thunderstorms every afternoon and evening from Monday onward.



18Z Update...
Mainly VFR criteria across all TAF sites with some MVFR cigs with
lingering stratus moving through the metro. Scattered convection
has already developed across west and central GA. Expect this
activity to continue, likely blossoming closer to the metro TAF
sites later this afternoon into the evening. Would not be
surprised to see this activity linger through the evening hours.
Partly to mostly cloudy skies overnight with low stratus
developing by early morning, around 1-2KFT. It will take some
time for skies to break and cigs to lift in the AM. Thunderstorm
activity seems a bit more limited tomorrow with a system dropping
into north GA Friday evening/overnight. Winds will mainly stay out
of the east.

//ATL Confidence...18Z Update...
Medium to High for all elements.



Athens 71 86 72 87 / 60 30 50 60
Atlanta 72 88 73 89 / 50 20 50 60
Blairsville 65 82 65 82 / 40 30 60 70
Cartersville 71 89 72 89 / 40 20 60 60
Columbus 75 92 75 92 / 60 30 40 60
Gainesville 70 86 71 86 / 50 20 60 60
Macon 73 88 73 91 / 60 40 30 60
Rome 71 90 71 90 / 40 30 60 60
Peachtree City 72 88 72 89 / 60 30 50 60
Vidalia 74 88 74 91 / 60 60 50 40




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