Flood Watch 4, NWS Atlanta, GA

Baldwin County, GA, Banks County, GA, Barrow County, GA, Bibb County, GA, Bleckley County, GA, Butts County, GA, Clarke County, GA, Clayton County, GA, Crawford County, GA, Crisp County, GA, Dawson County, GA, DeKalb County, GA, Dodge County, GA, Dooly County, GA, Emanuel County, GA, Forsyth County, GA, Fulton County, GA, Glascock County, GA, Greene County, GA, Gwinnett County, GA, Hall County, GA, Hancock County, GA, Henry County, GA, Houston County, GA, Jackson County, GA, Jasper County, GA, Jefferson County, GA, Johnson County, GA, Jones County, GA, Laurens County, GA, Lumpkin County, GA, Macon County, GA, Madison County, GA, Marion County, GA, Monroe County, GA, Montgomery County, GA, Morgan County, GA, Newton County, GA, Oconee County, GA, Oglethorpe County, GA, Peach County, GA, Pulaski County, GA, Putnam County, GA, Rockdale County, GA, Schley County, GA, Stewart County, GA, Sumter County, GA, Taliaferro County, GA, Taylor County, GA, Telfair County, GA, Toombs County, GA, Treutlen County, GA, Twiggs County, GA, Walton County, GA, Warren County, GA, Washington County, GA, Webster County, GA, Wheeler County, GA, White County, GA, Wilcox County, GA, Wilkes County, GA, Wilkinson County, GA

Area Forecast Discussion
National Weather Service Peachtree City GA
152 PM EDT Tue Jun 20 2023

...New 18Z Aviation Discussion...

.SHORT TERM...
(Today through Wednesday)
Issued at 441 AM EDT Tue Jun 20 2023

Today: Patchy fog is noted in observations across portions of the
CWA at the time of this writing, and will be possible until 14z.
Current mid-level water vapor satellite imagery shows a dry slot
overspreading the portion of the CWA along and south of I-85 as a
cut-off low spins over north-central TN and south-central KY. This
dry slot will likely limit coverage of showers this morning
across much of the CWA. This afternoon, however, scattered to
numerous showers and thunderstorms will develop as instability
climbs amid the moist air mass and broad ascent from the upper
low. SPC has the entire CWA outlooked in a General Thunderstorm
risk as progged instability and shear parameters are not
suggestive of severe storms. That said, a strong storm or two will
be possible with gusty winds, frequent lightning, and heavy
rainfall (PWAT values are 1.6" to 1.8" while the daily mean per
sounding climatology is ~1.4"). WPC has a portion of northeast
Georgia outlooked in a Slight Risk (level 2 of 4) for flash
flooding. This area received between 1" and 3" of rain over the
last 48 hours and 1-hour flash flood guidance is only 1.5" to 2.0"
across portions of this area. So, any storms that produce
especially heavy rainfall and/or train over this area could cause
localized flash flooding. High temperatures will be in the mid-
70s to mid-80s.

Tonight and Tomorrow: Isolated to scattered showers and
thunderstorms will persist overnight with the greatest PoPs over
northeast GA. The cut-off low will continue to meander over the
Southeast tomorrow (Wednesday) amid the weak flow aloft, so yet
another day of numerous primarily-diurnal showers and
thunderstorms is expected. Like today, SPC has the entire CWA
outlooked in a General Thunderstorm risk as instability and shear
parameters are expected remain marginal. WPC has the portion of
the CWA along and south of I-85 outlooked in a Slight Risk for
flash flooding as storms continue to pose a heavy rainfall threat
and soils become increasingly saturated from previous days of
rainfall. In addition to heavy rainfall, any strong storms will be
capable of producing gusty winds and frequent lightning.
Overnight lows will be in the 60s and afternoon highs will be in
the lower 70s to lower 80s.

Martin

&&

.LONG TERM...
(Wednesday night through Monday)
Issued at 441 AM EDT Tue Jun 20 2023

Key Messages:

* A wet pattern will continue into the long term through Friday,
  after which new model guidance is beginning to forecast a slight
  break in the continual rains before a frontal system pushes into
  the area early next week.

* 2 to 4.5 inches of rainfall are forecast over the next 84 hours
  from 12Z Tues to 00Z Sat.

* With cloudy skies and continuous rains, temperatures will stay 6
  to 12 degrees below normal to start the forecast period, then
  gradually increase to near-normal conditions by the weekend.

* A Flood Watch is not being issued at this time, but with
  increasing forecast rainfall values on Wed/Thurs, one may be
  issued in the coming day or two.

Moist Pattern Continues:

A cutoff, upper-level low pressure system will continue the wet
pattern from the short term into the long term. With an upper-
level high pressure system expected to sit over the Great Lakes
region, this will complete the Rex Blocking pattern that is
responsible for the stagnant weather pattern. The high pressure
begins to slide to the east by late Thursday, and will allow the
cutoff low, which will overstay its welcome, to retreat northward
while pulling Gulf moisture northward with it on Friday.

As for environmental conditions, PWATs under the stagnant low
will likely stay just above 1.5 inches through the forecast
period, according to GEFS and EPS runs, and with pseudo-moist
adiabatic profiles in place, instability will be present but
limited to around 1000 J/kg each afternoon of SBCAPE values on
average. This means, numerous to widespread showers and
thunderstorms will be likely each day, but severe potential will
be very limited.

It won't be until Saturday when the cutoff low reverts back into
the general wavepattern as a shortwave trough and pushes eastward,
allowing a weak shortwave ridge to replace it through the
weekend, when we could see a brief reprieve from at least the
heavier rain pattern on Saturday and Sunday.

The emergence of the shortwave ridge through the weekend has been
the first major deviation from previous forecasts, the second is
the introduction of a shortwave trough and accompanied frontal
system early next week and Monday and Tuesday. This system could
introduce periods of heavy rainfall and storms to areas recovering
from the onslaught of rainfall this week, introducing potential
flooding concerns, but there is still plenty of time to evaluate
that threat in the coming days.

Thiem

&&

.AVIATION...
(18Z TAFS)
Issued at 152 PM EDT Tue Jun 20 2023

A SCT CU field with low VFR clouds will RA and possibly some TSRA
this afternoon between 19-00Z. Winds will be out of the SW at 5-
8kts; with gusts at 15-20kts possible in areas of TSRA.  As storms
die off after 00Z, MVFR with some IFR CIGS will linger through the
overnight hours.

//ATL Confidence...18Z Update...

Medium to high on all elements.

Vaughn

&&

.PRELIMINARY POINT TEMPS/POPS...
Athens          67  75  66  78 /  80  90  90  90
Atlanta         67  76  67  78 /  70  90  80  90
Blairsville     62  72  61  72 /  60  90  80  90
Cartersville    67  77  65  78 /  70  90  80  90
Columbus        68  79  68  83 /  70  90  80  90
Gainesville     66  74  65  77 /  80  90  80  90
Macon           68  79  67  82 /  90 100  90  90
Rome            68  79  67  79 /  50  90  70  80
Peachtree City  66  77  66  80 /  70  90  80  90
Vidalia         70  82  69  82 /  60  90  90  90

&&

.FFC WATCHES/WARNINGS/ADVISORIES...
None.
&&

SHORT TERM...Martin
LONG TERM....Thiem
AVIATION...Vaughn

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