Special Weather Statement, NWS Atlanta, GA

Area Forecast Discussion
National Weather Service Peachtree City GA
738 PM EDT Sat Jul 15 2017

.UPDATE...
Area of convection has shifted into central GA with north GA
seeing only isolated showers. Do not see any redevelopment of
convection across north GA so have dropped the pops to slight
chance. The convection central Georgia will diminish through the
evening hours and have made a few adjustments to the pops for this
evening. Rest of the forecast looks on track.

&&

.PREV DISCUSSION... /Issued 324 PM EDT Sat Jul 15 2017/

SHORT TERM /Tonight through Sunday Night/...

The Bermuda High which was controlling much of our sensible weather
this past week is now being undercut by an approaching front. Aloft,
we can see the midlevel trough is pivoting south through the mid-
Atlantic region with a trailing cold front eventually working its
way through the Appalachians.  We expect that this front will push
through northern GA this afternoon/evening before becoming stall
across central GA.  This will mean better coverage of
shower/thunderstorms through the period. So lets break things down a
bit.

This afternoon/Overnight:  As the front moves through northern GA,
expect to see the best activity across our northern tier through mid-
afternoon. As the front continues south, this will be the axis for
the better precipitation activity. Given sufficient insulation and
instability, discrete/less organized storms are possible south of
the boundary. With MUCAPE values around 2000J/kg this afternoon,
marginal lapse rates and DCAPE around 500-1000J/kg, the main impacts
from these storms will be the strong gusty winds, frequent lightning
and hail. Also with weak steering flow, high PWAT values and
elevated warm cloud height, heavy rain leading to localized flooding
is also a potential.  It appears that the best time to see this
convection across metro ATL will be mid afternoon into the early
evening. The front will move south of the metro later this afternoon
allowing the boundary to interact with more unstable air across
central GA. Thus, expect there to be better coverage of
thunderstorms south of I-20 later this afternoon into the evening,
especially from a line from Columbus to Macon and eastward. Coverage
should diminish a bit tonight with loss of heating. However, given
we have a bit more upper level support, can not rule out isolated
shower/thunderstorms, especially along or just south of the metro.

Sunday: With the boundary stalled somewhere across central GA, this
will be the axis by which we see redevelopment of
showers/thunderstorms.  That will mean less coverage across the
north and more coverage across central GA. We will likely see the
potential for strong to a few severe thunderstorms on Sunday as
well.  While there may be sufficient cloud coverage across central
GA which may inhibit insulation and thus cut down on the instability
across the region, there is still plenty of upper level support with
a series of impulses riding the weak trough. This should be enough
to warrant pretty good coverage of precipitation. Also, with the
stalled front we may see training of storms which could lead to
localized flooding. Therefore, the main threat will be gusty winds,
frequent lighting and heavy precipitation.

Sunday Night: While some models show convection dwindling during the
late evening, there looks to be another trough axis that tries to
cross the region. This may help support convection through the
overnight. Hard to say at this point how much coverage we will see,
but there is the potential.

Temperatures will be around normal for this time of year.

26

LONG TERM /Monday through Saturday/...

No big changes for the long term except some minor tweaks to cloud
cover. Otherwise current forecast looks good. Models still
showing a front dropping into GA first part of the upcoming week.
Some drying indicated over the north half but not enough to take
pops out completely except for a couple of night time periods.
Previous discussion is included below.

41

LONG TERM /Sunday Night through Friday/...
The frontal system that moves into N GA in the short term will
have moved into central GA by the beginning of the extended. Even
with the frontal boundary in place we will still see a mainly
diurnal trend as daytime heating will continue to spark convective
development each afternoon and evening. The frontal boundary
continues moving south into FL into the middle of next week as it
also continues to weaken. With the front making little progress
southward...expecting a similar trend in the weather Sunday
through Tuesday. The front will likely "wash out" on Tuesday with
the mid level trough slowly becoming replaced by a large
ridge...so convective coverage may be somewhat less Wed through
Fri.

Expecting a large ridge to build into the area Wednesday with a
bit drier air mass across the region. This pattern would mean
hotter and drier weather for the end of the extended forecast but
given the time of year...isolated convection will still be
possible Wed- Fri. Temps will have no problem pushing into 90s
across the area.

01

&&

.AVIATION...
00Z Update...
Convection has diminished across ATL/AHN area but continues in the
CSG/MCN. This will also diminish through the evening hours. Patchy
fog will develop later tonight, mainly in areas that received
rain this evening. Convection will develop again late Sunday
morning and continue into the afternoon. Winds will be light
westerly and continue into Sunday.

//ATL Confidence...00Z Update...
High on all elements.

17

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          72  87  70  87 /  30  50  40  50
Atlanta         73  86  71  87 /  20  50  40  40
Blairsville     65  83  63  84 /  20  40  30  30
Cartersville    70  87  70  88 /  20  40  30  40
Columbus        75  88  73  88 /  60  60  40  50
Gainesville     71  85  70  86 /  20  50  30  40
Macon           73  89  72  89 /  60  60  40  50
Rome            70  88  70  89 /  20  30  30  30
Peachtree City  71  87  70  87 /  40  50  40  50
Vidalia         74  89  73  88 /  60  60  50  60

&&

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

SHORT TERM...17
LONG TERM....20
AVIATION...17

Hazardous Weather Outlook...Updated
National Weather Service Peachtree City GA
600 PM EDT Sat Jul 15 2017

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-161030-
Baldwin-Banks-Barrow-Bartow-Bibb-Bleckley-Butts-Carroll-Catoosa-
Chattahoochee-Chattooga-Cherokee-Clarke-Clayton-Cobb-Coweta-
Crawford-Crisp-Dade-Dawson-DeKalb-Dodge-Dooly-Douglas-Emanuel-
Fannin-Fayette-Floyd-Forsyth-Gilmer-Glascock-Gordon-Greene-
Gwinnett-Hall-Hancock-Haralson-Harris-Heard-Henry-Houston-Jackson-
Jasper-Jefferson-Johnson-Jones-Lamar-Laurens-Lumpkin-Macon-
Madison-Marion-Meriwether-Monroe-Montgomery-Morgan-Murray-
Muscogee-Newton-North Fulton-Oconee-Oglethorpe-Paulding-Peach-
Pickens-Pike-Polk-Pulaski-Putnam-Rockdale-Schley-South Fulton-
Spalding-Stewart-Sumter-Talbot-Taliaferro-Taylor-Telfair-Toombs-
Towns-Treutlen-Troup-Twiggs-Union-Upson-Walker-Walton-Warren-
Washington-Webster-Wheeler-White-Whitfield-Wilcox-Wilkes-
Wilkinson-
600 PM EDT Sat Jul 15 2017

This Hazardous Weather Outlook is for portions of North and Central
Georgia.

.DAY ONE...Tonight...

Scattered to numerous thunderstorms are expected across north and
central Georgia this evening, with isolated severe storms possible.
A frontal boundary through the area will bring increased moisture
and instability to the area. Some storms may be strong to severe
through the evening with the main hazards being strong gusty winds,
heavy rainfall, frequent lightning, and hail. Although a few
isolated thunderstorms may linger after midnight, no severe
thunderstorms are expected through the early morning hours.

.DAYS TWO THROUGH SEVEN...Sunday through Friday...

Isolated to scattered thunderstorms are possible each afternoon and
evening through Friday. Widespread thunderstorm development with
isolated severe storms is expected across the area Sunday and Monday
with the frontal system still affecting the area.

Heat Index values will approach 105 degrees over portions of central
Georgia, generally Wednesday through Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not requested but spotters are encouraged to
submit reports of severe weather through the web by going to
weather.gov/atlanta.

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