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Area forecast discussion
National Weather Service Peachtree City Georgia
300 PM EDT Thu may 25 2017



Short term /tonight through Friday night/...
an anonymously deep upper level low [at least for this time of year]
will continue to pivot toward the northeast through the short term.
Residual shower activity associated with this low has diminished
this morning across the area, thanks to sufficient subsidence. In
the same vein, we have also seen cloud coverage diminishing given
the drying within the column. Clear skies expected from this evening
through tomorrow as surface high pressure builds into the area from
the south. Gusty west winds will diminish this evening and increase
by mid-morning tomorrow, not as gusty.

26



Long term /Saturday through Thursday/...
only minor adjustments have been made to the extended forecast.
Models continue to advertise decent potential for mesoscale convective system to impact
the southeast on Saturday, and have kept pops high across north
Georgia through the day. Sunday into Monday still looks to have
the potential for robust storms as well. Otherwise, previous
forecast discussion is applicable and is included below.

31



/issued 509 am EDT Thu may 25 2017/

Extended period begins with shortwave ridging building in in the
wake of the anomalous upper low exiting. ECMWF centers a weaker
ridge over the northern Gulf while the GFS and sref slightly
stronger. All of the models put the Tennessee Valley and north Georgia in a
slightly diffluent flow atop the ridge centered over the north
central Gulf. Current consensus is to run low pops across the
north on Saturday...but a deeper look into the environment makes
one wonder if the atmosphere will behave. GFS, ECMWF, and NAM all
destabilizing the airmass across far north Georgia significantly on
Saturday. Lapse rates forecast to exceed 8.0 deg c/km and even
approach 8.5 depending on what model you look at. Combined with 0-
6km shear values 40 kts and sb cape values at or above 2000 j/kg and even
more in the GFS mean that if storms or an mesoscale convective system develops further
north in the favored portion of the ridge, Saturday eve could be
interesting. Definitely something to watch for potential mesoscale convective system
development across the central US on Friday can ride the ridge
southeast and re-ignite during the day Saturday. Hail and wind
would certainly be a threat, but just don't have a lot of
confidence on coverage. Day 3 Storm Prediction Center outlook has the slight risk
coming into far northwest Georgia which may have to expand a bit southward if
it looks like coverage could be higher further south.

Another significant vortex starts swinging south into the northern
Great Lakes Saturday into Sunday forcing the ridge southeast and
pushing a frontal boundary into Georgia during the day on Sunday. Models
in general agreement on the front working into north Georgia by late
Sunday into early Monday resulting in increase shower and
thunderstorm chances. Once again, cannot rule out severe chances
given 40-50kts of 0-6km bulk shear and 7.0-7.5 deg c/km mid level
lapse rates forecast for Sunday afternoon/evening across the
state...particularly north central. Will need to again see the
evolution of things on Saturday and the timing of the shortwave
that rotates through the broad trof digging over the Great Lakes
region.

Sfc boundary sags south and hangs up across the state on Monday also
presenting an unfortunate increase in storm chances on our Memorial
Day. Current parameters suggest there would be some severe chances
but too early to tell how it all plays out given the previous day
convection influence on the following day. Model consensus
running 50 to 60 pops on Monday attm and see now reason to
disagree.

Boundary sags south of the cwa on Tuesday and Wednesday giving the
region a shot of drier air and reprieve with a large trof taking
over the eastern half of the US. Would expect below normal temps a
good portion of next week.

30

&&

Aviation...
18z update...
VFR conditions observed across the region and we anticipate this
to continue through the taf period. A deep upper level low will
pivot northeast exiting the region with subsidence helping to dry
out the atmospheric column through the remainder of the
afternoon. This will result in broken cigs eroding to sky clear by around
sunset. Gusty west winds will diminish this evening. Pleasant
flying conditions through Friday. Clear skies and westerly wind
with the occasional gust possible.

//Atl confidence...18z update...
high confidence on all elements.

26

&&

Preliminary point temps/pops...
Athens 55 83 65 88 / 0 0 0 5
Atlanta 58 83 66 87 / 0 0 0 5
Blairsville 50 79 60 82 / 5 0 5 20
Cartersville 54 84 64 86 / 0 0 0 10
Columbus 57 86 64 89 / 0 0 0 5
Gainesville 56 81 65 85 / 0 0 0 10
Macon 55 85 63 90 / 0 0 0 0
Rome 53 85 64 86 / 0 0 5 20
Peachtree City 53 84 62 87 / 0 0 0 5
Vidalia 59 85 66 92 / 0 0 0 0

&&

Ffc watches/warnings/advisories...
none.
&&

$$

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