Special Weather Statement, NWS Atlanta, GA

Area Forecast Discussion
National Weather Service Peachtree City GA
1029 AM EDT Sat May 20 2017

.UPDATE...
No major changes to the forecast needed this morning. Have tweaked
the hourly temp/dew and sky grids.

Environment will become more favorable for convective development
late this afternoon into the evening hours. The upper ridge will
begin to push off to the east, allowing for the erosion of the cap
that has been in place for the last several days. Plenty of
available surface instability and moisture will be on the
increase. PWATS are expected to increase to well above normal
values by late this afternoon and evening. With BL winds 20kt or
less, slow moving/heavy rainers are anticipated. The most likely
area for strong/isold severe storms this afternoon/evening should
be in the far west, where a bit more mid level energy will be
present as a shortwave trough moves through the area.

&&

.PREV DISCUSSION... /Issued 756 AM EDT Sat May 20 2017/

PREV DISCUSSION... /Issued 418 AM EDT Sat May 20 2017/

SHORT TERM...
Primary forecast concerns are onset and location of convection this
afternoon and evolution tonight and Sunday. 00Z models and, in
particular, CAM guidance showing more complex evolution of precip
today thru Sunday with several rounds of warm advection forced
convection. First round likely late this afternoon over westcentral
GA spreading north and slowly west. Fcst instability quite high at
18Z with GFS SBCAPE 3000+ J/kg over westcentral GA and large area of
1500+. While sfc forcing and vertical wind shear will be weak, as is
typically the case this time of year, believe there could be
isolated severe storms late this afternoon and evening with heavy
rain potential.

Next round of convection likely early Sunday morning. Quite a bit of
difference in CAM guidance. 4km NAMnest much more active over north
GA at this time while local WRF suite guidance all pointing to
westcentral GA again spreading east. Rich moisture will be in place,
assuming Saturday convection does not become to widespread and
vigorous resulting in stabilization. Instability progged by large
scale models (likely more representative of untouched prestorm
environment) to remain high with SBCAPE 1500-2000 J/kg. Vertical
wind shear may be a bit stronger but still fairly weak. Tornadoes
highly unlikely in either round with this environment. Will need to
watch this day for another round of isolated severe storms with
heavy rain and possibly flooding. Total rainfall likely to exceed 3
inches in a few spots based on model and WPC guidance for this event
so may need extra emphasis on heavy rain and possible flooding as
opposed to wind/hail threats.

SNELSON

LONG TERM /Sunday Night through Friday/...

Long term period begins with frontal boundary continuing to move
through the area with embedded shortwave activity and plenty of
moisture to work with. Categorical pops warranted for the metro
through 06Z Monday and then transitioning to likely pops for
Central GA as front moves into the NW zones by 12Z. Models in
really good agreement with timing initially but GFS does bring
drier air in faster than the ECMWF.

Regardless...will not get that long of a reprieve at all as next
in a series of strong shortwaves moves out of the gulf coast and
toward the local area. Surface wave forms at the surface as a
result. Continued divergence at this point in the models as ECMWF
is much further north with main features including aforementioned
surface low. As a result...precip shield is also further north
than the GFS. Will use a blend for now which results in highest
pops over Central GA but this axis may need to be shifted
northward with subsequent forecasts if ECMWF is correct.

Just cant get any good agreement in the long term portion as both
models have an upper trough moving toward the area on Wed but GFS
is much stronger with a closed off low aloft and at the surface.
Diffluent pattern aloft should result in high precip coverage but
position of low and strength of upper trough will ultimately
dictate the severe threat for Wed so stay tuned.

Finally some tranquil conditions after Wed which the GFS maintains
through the remainder of the extended although the ECMWF does
bring back slight chance pops for next Sat.

Deese

AVIATION...
12Z Update...
IFR stratus deck may try to sneak into ATL 12-14Z, currently this
deck located about 20nm SE of ATL and moving north. Any stratus
should burn off after 15-16Z. TEMPO TS likely at most airports
after 21Z thru at least 01Z with lingering isolated SHRA possible
thru 04Z. IFR cigs possible after 10Z Sun again. And another
round of SHRA/TSRA possible after 12Z Sun, have added PROB30
13-18Z at ATL. Sfc winds will remain SSE thru 12Z.

//ATL Confidence...12Z Update...
Medium confidence on IFR cigs this morning and Sunday morning.
Medium confidence on TSRA timing and likelihood this afternoon.
High on all other elements.

SNELSON

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          89  68  79  66 /  30  60  80  80
Atlanta         86  70  79  67 /  50  60  80  80
Blairsville     84  64  74  61 /  40  80  80  70
Cartersville    87  69  78  65 /  60  80  90  70
Columbus        87  71  82  69 /  60  60  80  80
Gainesville     85  68  76  66 /  40  70  80  80
Macon           88  70  85  68 /  50  50  80  70
Rome            87  68  79  65 /  60  70  90  70
Peachtree City  86  68  79  66 /  60  60  80  80
Vidalia         89  71  88  69 /  50  40  80  60

&&

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

Hazardous Weather Outlook
National Weather Service Peachtree City GA
645 AM EDT Sat May 20 2017

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-210845-
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-
645 AM EDT Sat May 20 2017

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

.DAY ONE...Today and Tonight...

Showers and thunderstorms will be on the increase...especially by
late afternoon into the evening hours as numerous storms affect the
western tier. Isolated strong the severe storms will be possible
with this activity with large hail, damaging winds and heavy
rainfall the main threats.

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

The increase in storm chances will continue into Sunday with
widespread activity developing. Some strong to isolated severe
thunderstorms will be possible on Sunday with damaging winds,
hail, and heavy rainfall the primary threats. Rainfall through
Monday will average 2 to 3 inches across most of the area.
Additional opportunities for numerous showers and thunderstorms
can be expected into mid week.

.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.

Special Weather Statement
National Weather Service Peachtree City GA
1250 PM EDT SAT MAY 20 2017

GAZ071-072-081>083-094-201730-
Peach GA-Monroe GA-Bibb GA-Crawford GA-Jones GA-Twiggs GA-
1250 PM EDT SAT MAY 20 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN PEACH...SOUTHEASTERN
MONROE...BIBB...NORTHEASTERN CRAWFORD...JONES AND NORTHWESTERN TWIGGS
COUNTIES UNTIL 130 PM EDT...

At 1249 PM EDT...a strong thunderstorm was over Skipperton, or near
Macon...moving north at 25 mph.

  HAZARD...Up to 40 mph wind...frequent cloud to ground lightning
           and heavy rain.

  IMPACT...Expect minor damage to tree limbs and blowing around of
           light...unsecured objects. Heavy rain may cause temporary
           street flooding especially in poor drainage areas.

Some locations in the path of this storm include
Macon, Gray, Byron, Payne, Payne City, Postell, Lake Tobesofkee,
Bradley, Wayside, Griswoldville, Wesleyan, Skipperton, Arkwright,
James, Bolingbroke, Jack Brown Estates, Rutland, Dames Ferry, Clinton
and Huber.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People outdoors should seek shelter immediately. If you can hear
thunder...you are close enough to be struck by lightning. Motorists
should slow down and be prepared for possible loss of control due to
hydroplaning.

LAT...LON 3300 8399 3310 8345 3268 8350 3267 8364
      3269 8370 3267 8371 3266 8380
TIME...MOT...LOC 1649Z 170DEG 23KT 3276 8369

WIND...40MPH

Special Weather Statement
National Weather Service Peachtree City GA
120 PM EDT SAT MAY 20 2017

GAZ108>110-201800-
Telfair GA-Wilcox GA-Dodge GA-
120 PM EDT SAT MAY 20 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN TELFAIR...EASTERN
WILCOX AND SOUTHWESTERN DODGE COUNTIES UNTIL 200 PM EDT...

At 119 PM EDT...a strong thunderstorm was over Queensland, or 7 miles
north of Fitzgerald...moving north at 20 mph.

  HAZARD...Up to 40 mph wind...frequent cloud to ground lightning
           and heavy rain.

  IMPACT...Expect minor damage to tree limbs and blowing around of
           light...unsecured objects. Heavy rain may cause temporary
           street flooding especially in poor drainage areas.

Some locations in the path of this storm include
Abbeville, Milan, Rhine, Temperance, Browning, China Hill, Cedar
Creek, Antioch Church and Workmore.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People outdoors should seek shelter immediately. If you can hear
thunder...you are close enough to be struck by lightning. Motorists
should slow down and be prepared for possible loss of control due to
hydroplaning.

LAT...LON 3179 8304 3179 8305 3180 8308 3181 8309
      3181 8310 3182 8311 3181 8311 3181 8314
      3182 8314 3182 8315 3183 8315 3185 8318
      3184 8321 3185 8337 3209 8339 3201 8288
      3178 8302
TIME...MOT...LOC 1719Z 193DEG 16KT 3181 8323

WIND...40MPH