Scientific Forecaster Discussion
fxus62 kffc 231939
Area forecast discussion
National Weather Service Peachtree City Georgia
339 PM EDT Tue may 23 2017
..Tornado Watch continues for portions of east central Georgia
until 6 PM and Flash Flood Watch for majority of area except far
north Georgia through Wednesday afternoon...
Short term /tonight through Wednesday night/...
Latest wave of showers/tstorms slowly exiting the County Warning Area and by this
evening this area of showers/tstorms will have pushed east out of
the region. With instability remaining over the County Warning Area tonight will
need to keep low end chance pops for showers/tstorms all areas. The
next wave of precip will be along and ahead of the cold front late
tonight and Wednesday. Models have waffled a bit on timing of this
front and precip but general consensus is that a line of
showers/tstorms will develop along and head of the front, moving
into northwest by between 10 and 12z, moving rapidly across the County Warning Area
and by mid afternoon Wednesday this round of showers/tstorms will be
east of the region. Convective available potential energy will be 1000+ at 12z ahead of the cold
front along with 60kts bulk shear. With the forced lifting of the
front, this should be enough for a few storms to become severe with
gusty winds and possibly a qlcs tornado as the line moves across the
County Warning Area.
The 500 mb low will be dropping into the Tennessee Valley Thursday
evening with very cold air aloft (-20 to -22c at 500 mb which is quite
cold for this time of year). This will continue to keep the
atmosphere destabilized as evident by the +100 convective available potential energy on all models
Wednesday night. Will need to increase pops across north Georgia
Wednesday night and with the very cold temps aloft, there is the
risk of small hail with any thunderstorm.
Forecast quantitative precipitation forecast through 00z Thursday should remain less than an inch,
however can't rule out an isolated 1 to 2 inch amount in some of the
heavier thunderstorms. With the previous 2 days of rainfall, flash
flooding remains a possibility with the next wave of precipitation
late tonight and Wednesday. Will therefore continue the Flash Flood
Watch through 18z Wednesday.
Long term /Thursday through Tuesday/...
Made minor cosmetic changes to fcst mainly to limit some precip
chances in the north for a quicker departure of the upper
low/moisture by Thursday evening. Also expanded Saturday slight
chance pops for north Georgia given the zonal flow/disturbance
influence. Otherwise rest looks on track with neighboring offices
and previous discussion follows...
Previous discussion... /issued 351 am EDT Tue may 23 2017/
Long term /Wednesday night through Monday/...
Much of the area will be on the backside of deep moisture plume and
associated cold front by Wednesday night with anomalously cold upper
level low approaching from the northwest. Breezy and much cooler
conditions will prevail into Thursday with clouds and scattered
showers across north Georgia. Lapse rates appear steep enough to
support a few embedded thunderstorms, again mainly north of I-20.
Small hail will be possible with any storms. By late Thursday into
Thursday night, drier air will work across the area and any
showers/storms will diminish.
Temperatures will gradually moderate closer to normal Friday into
the weekend as an upper level ridge over the Gulf of Mexico builds
slowly north. Battle between the gom ridge and a strong upper trough
digging across the northern plains/upper Midwest occurs over the
weekend creating an increasingly zonal flow across the area,
especially north Georgia. Moisture will begin to increase as this occurs
with chances for rain picking up late Saturday into Sunday. Medium
range models appear to deepen longwave trough across the eastern
Continental U.S. Thus resulting in an extended period of rain setting up once
again - Sunday into Monday - across the southeast region. However,
this is 5 to 6 days out and things will likely change.
current wave of showers/tsra moving across central/East Georgia will
end from the west this afternoon with scattered showers remaining
through the rest of this afternoon and evening elsewhere. A squall
line is expected to develop along a cold front and move into
western Georgia late tonight/early Wednesday and spread across the
forecast area through the morning hours, exiting to the east by
18z Wed. Mostly VFR with scattered MVFR/IFR cigs will hold through
this evening with widespread IFR/MVFR cigs by 06z Wed. Cigs will
remain IFR/MVFR through 18z Wed.
//Atl confidence...18z update...
high on winds.
Low to medium on remaining elements.
Preliminary point temps/pops...
Athens 63 75 57 73 / 30 80 40 20
Atlanta 65 73 56 71 / 50 90 30 20
Blairsville 60 69 52 66 / 50 90 60 40
Cartersville 64 74 55 72 / 60 90 50 30
Columbus 66 77 57 76 / 60 90 20 5
Gainesville 63 73 56 69 / 40 90 50 20
Macon 67 77 57 76 / 30 80 20 10
Rome 63 72 54 72 / 70 80 60 30
Peachtree City 65 75 56 72 / 50 90 20 10
Vidalia 69 79 61 77 / 70 80 30 10
Flash Flood Watch through Wednesday afternoon for the following
Tornado Watch until 6 PM EDT this evening for the following