Special Weather Statement, NWS Atlanta, GA

Area Forecast Discussion
National Weather Service Peachtree City GA
755 PM EDT Thu May 4 2017

.PREV DISCUSSION... /Issued 321 PM EDT Thu May 4 2017/

SHORT TERM /Tonight through Friday Night/...
Water vapor loop this afternoon reveals the center of a strong
closed low across northeast AR with vort ribbon extending south
across MS and into LA. Its sfc reflection is characterized by an
area of low pressure centered across western KY with a cold front
draped to its south across AL. This closed low will migrate south
toward the southern Appalachians through the short term...allowing
for a rather anomalous May weather set-up.

Rest of Today: Cloud cover is largely winning the forecast battle
today. Area of thinning clouds earlier across AL has since filled in
and become a source of pre frontal shower development. Have watched
SPC mesoanalysis analyzed MU/SB CAPE values slowly rise but they
remain noticeably unimpressive. Do think some thunder will be
possible with these showers as well as the line of precip along the
actual front...but severe chances have slimmed significantly. Even
SPC has taken the CWA out of the marginal risk. Nonetheless...given
favorable shear/helicity values...if CAPE should rise...environment
is favorable for damaging thunderstorm wind gusts and tornadoes. So
remain aware that isolated severe weather is not entirely impossible
today. Large area of mainly stratiform rain from earlier in the day
continues to shift east...with rather robust activity perhaps
threatening far SE counties until about 4pm or so. Big story today
has been the wake low winds. These strong wind gusts have brought
down numerous trees. Have let the High Wind Warning expire at noon
but will keep Wind Advisory through 8pm. Not seeing as high of gusts
as earlier today.

Tonight & Friday: This frontal system will pull east of the CWA
tonight...where a much cooler airmass will filter in. Do not expect
low temps to be very cold tonight given ample cloud cover and
perhaps the development of some drizzle along with some light wrap-
around rain showers beginning to filter in from the north. Temps
will not rebound much on Friday and it will actually feel chilly
with winds expected to remain elevated. The interesting part about
tomorrow lies in the vertical profile of the atmosphere. Most of the
saturation from wrap-around shower activity will extend above the
freezing level...meaning below zero /500mb temps plummet to almost -
20C and 850mb to just over 0C to put things into perspective/ and
some Bufr soundings indicate some saturation wrt to ice in the -10C-
15C range. Therefore...would not be surprised to see some
graupel/ice pellets mix with the rain showers tomorrow. Think the
best chances will be across higher elevations of northeast
Georgia...tho could be seen as far south as ATL. All precip activity
will slowly dissipate Friday night with lows headed back to the 40s.

Kovacik

LONG TERM /Saturday through Thursday/...
Have made a significant change to Saturday and Saturday night.
Both GFS/NAM/ECMWF show a significant short wave dropping on the
backside of the H5 low and moving across north GA Saturday into
Saturday evening. Enough instability with this to increase pops
and add a slight chance of thunder to north GA. Have also
increased winds across the CWA as H8 winds progged in the 30 to
40kt range Saturday afternoon.. No other changes planned. Previous
long term discussion follows...

17

LONG TERM /Friday Night through Wednesday/...

A deep closed upper low sits over the TN Valley region at the
beginning of the period. The low gradually fills and pushes
eastward over the Appalachians through Saturday night. Wrap around
showers will affect much of north and central GA Friday night and
mainly north GA Saturday and Saturday night. Northwesterly flow
will dominate the state for the remainder of the period as a deep
trough settles off the Atlantic Coast and the upper ridge builds
west of the MS river. A short wave drops into the Appalachians
Tuesday into Wednesday...but have left us dry for now due to
uncertainty of amount of moisture. Cool temperatures will continue
into the weekend...but begin to recover by the first of the week.
Models in general agreement through the period.

41

&&

.AVIATION...
00Z Update...
Showers continuing across the area this evening as frontal
boundary moves across the state. The main boundary should be
through the ATL area by 03z but still expecting drizzle and VCSH
through Friday evening. Mainly MVFR ceilings expected through the
TAF period with some brief periods of IFR ceilings in and around
SHRA/DZ activity. VSBYS should be mainly VFR. Winds are out of the
SE right now but will turn to the SW as the front passes through.
Wind speeds will stay up through this TAF period with readings in
the 10-15kt range with gust to 20kt.

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

01

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          53  59  45  72 /  90  40  20  20
Atlanta         52  57  46  70 / 100  50  30   5
Blairsville     49  53  41  64 / 100  60  60  40
Cartersville    52  56  45  71 / 100  50  30  20
Columbus        52  61  48  74 / 100  30  10   0
Gainesville     52  56  45  69 / 100  50  30  30
Macon           53  62  46  74 /  90  20  10   0
Rome            51  56  44  72 /  70  60  40  20
Peachtree City  51  58  44  71 / 100  50  20   0
Vidalia         56  67  49  75 /  80  10   5   0

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 8 PM EDT this evening for the following
zones: Banks...Barrow...Bartow...Carroll...Catoosa...Chattooga...
Cherokee...Cobb...Dade...Dawson...DeKalb...Douglas...Fannin...
Floyd...Forsyth...Gilmer...Gordon...Gwinnett...Hall...Haralson...
Jackson...Lumpkin...Murray...North Fulton...Paulding...Pickens...
Polk...South Fulton...Towns...Union...Walker...White...Whitfield.

&&

SHORT TERM...01
LONG TERM....Deese
AVIATION...01

Hazardous Weather Outlook...Updated
National Weather Service Peachtree City GA
135 PM EDT Thu May 4 2017

GAZ001>009-011>016-019>025-027-030>039-041>062-066>076-078>086-
089>098-102>113-050830-
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-
135 PM EDT Thu May 4 2017

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

.DAY ONE...This afternoon and Tonight...

Gusty winds will continue across parts of north and central Georgia
in the wake of moderate to heavy rain earlier today. Winds gusting
25 to 35 mph at times, with locally higher gusts, can be expected
through this evening, especially north of a Carrollton to Atlanta to
Athens line.

Showers and a few thunderstorms are expected along and ahead of a
strong cold front. This front will move west-to-east across north
and central Georgia between 5pm and 11pm this evening. Enhanced wind
gusts along with locally heavy rain and some cloud to ground
lightning, will be the primary threats.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday...

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected through tonight.

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