Flash Flood and Hail in Georgia, August 8 to 9, 2018

Area Forecast Discussion
National Weather Service Peachtree City GA
234 PM EDT Wed Aug 8 2018

.PREV DISCUSSION... /Issued 1127 AM EDT Wed Aug 8 2018/

UPDATE...

Forecast is on track. Expecting a busier afternoon for much of
north GA later this afternoon as outflow from previous convection
to the west approaches. The outflow boundary looks to arrive in NW
GA between 17-18Z. This may result in initiation of showers and
thunderstorms around that time, primarily across the northern
tier. Some of these storms could become strong to severe with
damaging wind gusts being the main impact. If enough shear is
present, we could see these showers and thunderstorms congeal into
a line/bow segment as it marches south and east later this
afternoon/evening. The trajectory of this convection looks to be
SE, but depends on the cold pools that develop.

Otherwise another hot and humid day across the region with
apparent temperatures, albeit unpleasant, just under heat
advisory criteria.

PREV DISCUSSION... /Issued 725 AM EDT Wed Aug 8 2018/

PREV DISCUSSION... /issued 403 AM EDT Wed Aug 8 2018/

Increased Thunderstorm Chances Today and Thursday...

SHORT TERM /Today through Thursday/...

Unlike previous nights, all is quiet on radar at this hour
although cannot totally rule out something popping up prior to
sunrise. Upstream however is a different story with continues
convective development entering the Tennessee Valley. This usually
leads to a good setup timing wise for enhanced thunderstorm
development as energy and outflows arrive after an afternoon of
rising temps and building instability.

Short term guidance seems to be picking up on this nicely with
most convective allowing models developing a line of storms either
just north of then area or directly over far North GA later this
afternoon. Most models then quickly translate this activity
quickly through the remainder of North GA including the Atlanta
metro by late this afternoon and more likely into the evening
hours. Have gone likely pops everywhere and pretty close to
categorical across the far north. There is indication in the
models of some weakening as the line approaches Central GA and we
have loss of heating but feel this is overdone and have kept pops
in the likely range.

Storms should be moving at a decent clip so other than some
isolated instances, flooding will not be the main threat today.
That distinction will belong to the winds which with higher DCAPE
values across the metro could lead to a cold pool driven line of
strong winds later this afternoon. As far as heat indices go
today, slightly reduced values below the 105 thresholds mean no
advisories for today.

A Boundary will stall across North GA for Thu with deep layer
moisture increasing as well. Precipitable water values will be in
excess of 2 inches across the northern half of the area. Am
worried a little about ongoing precip and clouds limiting the
chances for redevelopment in the afternoon with reduced
instability values. But with mid level temps still at or just
above average for this time of year, decided to go with higher
pops and in line with the guidance values of likely.

Deese

LONG TERM /Thursday Night through Tuesday/...
Pattern in long term period defined initially by positively-tilted
short wave over the mid-south with weak westerlies over GA all
within a broad trough over the eastern CONUS. Medium range models
this cycle showing the large scale trough deepening over the
eastern states which should bring some slightly cooler daytime temps
and above average rainfall. By early Sunday, most 00Z models
showing a cutoff low developing over the OH valley and an upper
trough extending south into GA, reinforcing the cool air aloft and
at the sfc, while high-amplitude upper ridge quickly builds north
over the central CONUS with another upper low trapped underneath
this ridge over western OK/TX. This high-over-low pattern is
well-known for being stagnant and can be difficult to forecast its
evolution. Some indication that deep moisture that is present thru
almost all of long term period, may shift south as OH valley upper
low tries to shift east a little on Mon/Tues, but with high
uncertainty, best to leave in chc for shra/tsra. Threat for deep
moisture and periods of heavy rain in this pattern, but appears
tropical feed and PW values not at the level they were a week ago
during the extreme heavy rain and flooding. Will continue to
monitor.

SNELSON

.AVIATION...
18Z Update...
VFR conditions to start the TAF period with CU building across
the region. Most shower and thunderstorm activity across north GA
will shift east and south eventually. The timeline for the best
chance of thunderstorms for the metro will be between 20-00Z with
AHN holding on a bit longer as the bulk of the precipitation
moves east this evening. MCN and CSG will have scattered
convection. BKN CU will diminish overnight with debris clouds
lingering. The CU deck will develop again by mid/late morning with
showers initiating by the early afternoon. West winds through the
period.

//ATL Confidence...18Z Update...
Low to Moderate on timing and location of the convection.
Moderate to High on all other elements.

26

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          92  72  90  71 /  70  50  60  30
Atlanta         90  73  89  72 /  60  60  70  30
Blairsville     84  66  81  65 /  70  30  60  30
Cartersville    90  71  87  70 /  70  40  70  30
Columbus        93  74  92  74 /  40  60  50  30
Gainesville     88  71  87  71 /  60  40  60  30
Macon           94  73  91  73 /  40  60  50  30
Rome            91  71  88  70 /  70  30  60  30
Peachtree City  92  72  89  71 /  60  60  60  30
Vidalia         93  75  92  75 /  30  30  40  20

&&

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

SHORT TERM...Deese
LONG TERM....SNELSON
AVIATION...26

Hazardous Weather Outlook
National Weather Service Peachtree City GA
1147 AM EDT Wed Aug 8 2018

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-091600-
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-
1147 AM EDT Wed Aug 8 2018

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

.DAY ONE...This Afternoon and Tonight...

Scattered to numerous thunderstorms are expected this afternoon
and evening. Thunderstorms should develop after noon, especially
over north Georgia and increase in coverage as they move south
during the afternoon and evening. Some storms could be strong to
severe with damaging winds, frequent lightning, large hail up to 1
inch in diameter and heavy rain.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday...

Scattered showers and thunderstorms are expected each day, mainly
during the afternoon and evening. Widespread severe weather is
not anticipated, however, some storms could produce strong winds,
frequent lightning and heavy rain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed through tonight.

Special Weather Statement
National Weather Service Peachtree City GA
1241 PM EDT WED AUG 8 2018

GAZ006-007-081715-
Gilmer GA-Fannin GA-
1241 PM EDT WED AUG 8 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN GILMER AND FANNIN
COUNTIES UNTIL 115 PM EDT...

At 1240 PM EDT...a strong thunderstorm was over Cherry Log, or near
Blue Ridge...moving east at 15 mph.

  HAZARD...Up to 40 mph wind...pea sized hail and frequent cloud to
           ground lightning.

  IMPACT...Expect minor damage to tree limbs and blowing around of
           light...unsecured objects.

Some locations in the path of this storm include
Blue Ridge, Morganton, Dial, Cherry Log and Loving.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People outdoors should seek shelter immediately. If you can hear
thunder...you are close enough to be struck by lightning.

LAT...LON 3478 8449 3487 8449 3492 8421 3475 8421
TIME...MOT...LOC 1640Z 269DEG 12KT 3482 8441

HAIL...0.25IN
WIND...40MPH

Special Weather Statement
National Weather Service Peachtree City GA
1257 PM EDT WED AUG 8 2018

GAZ009-081715-
Towns GA-
1257 PM EDT WED AUG 8 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN TOWNS COUNTY UNTIL
115 PM EDT...

At 1256 PM EDT...a strong thunderstorm was over Titus, or near
Hiawassee...moving east at 25 mph.

  HAZARD...Up to 40 mph wind...pea sized hail and frequent cloud to
           ground lightning.

  IMPACT...Expect minor damage to tree limbs and blowing around of
           light...unsecured objects.

Some locations in the path of this storm include
Tate City, Macedonia, Plum Orchard Gap Shelter, Titus and Mountain
Scene.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

People outdoors should seek shelter immediately. If you can hear
thunder...you are close enough to be struck by lightning.

LAT...LON 3495 8355 3494 8360 3492 8359 3491 8363
      3490 8363 3488 8366 3485 8366 3485 8373
      3495 8374 3499 8359 3499 8355
TIME...MOT...LOC 1656Z 257DEG 21KT 3491 8364

HAIL...0.25IN
WIND...40MPH

Special Weather Statement
National Weather Service Peachtree City GA
259 PM EDT WED AUG 8 2018

GAZ001>005-011-012-019-081930-
Chattooga GA-Whitfield GA-Catoosa GA-Walker GA-Gordon GA-Dade GA-
Murray GA-Floyd GA-
259 PM EDT WED AUG 8 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHERN CHATTOOGA...WHITFIELD...
CATOOSA...WALKER...NORTHWESTERN GORDON...DADE...MURRAY AND
NORTHEASTERN FLOYD COUNTIES UNTIL 330 PM EDT...

At 258 PM EDT...a line of strong thunderstorms was along a line
extending from Fairview to near Sulpher Springs...and moving
northeast at 35 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 these storms include
Dalton, Calhoun, Lafayette, Summerville, Chatsworth, Ringgold,
Trenton, Fort Oglethorpe, Chickamauga, Trion, Varnell, Lookout
Mountain, Eton, Tunnel Hill, Cohutta, Resaca, Menlo, Center Post,
Crandall and Subligna.

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 3499 8462 3495 8462 3449 8487 3447 8550
      3477 8556 3498 8544
TIME...MOT...LOC 1858Z 246DEG 40KT 3494 8531 3464 8553

WIND...40MPH