Scientific Forecaster Discussion
fxus62 kffc 240002
Area forecast discussion
National Weather Service Peachtree City Georgia
802 PM EDT sun Jul 23 2017
Numerous showers and thunderstorms continue across the region,
especially toward Athens. Those traveling I-85 north and along
I-20 east of the Metro atl should heed caution as very strong
storms may cross these interstates over the next couple of hours.
Gusty winds, heavy rain and frequent lightning are the main
threats. We have had some reports of small hail with these
storms. Training of storms may also lead to localized flooding.
Anticipate this activity to continue to move southeast and
diminish through the evening with loss of daytime heating.
Previous discussion... /issued 734 PM EDT sun Jul 23 2017/
Previous discussion... /issued 308 PM EDT sun Jul 23 2017/
Short term /tonight through Monday night/...
recent analysis of afternoon water vapor imagery reveals a mid level
synoptic pattern over the Continental U.S. Characterized by a persistent ridge
over the western US...and an amplifying cyclonic flow regime over
the eastern US. The most notable feature east of The Rockies is a
southeastward moving shortwave trough over the western Great Lakes.
Meanwhile at the sfc...a weak sfc front extended roughly from the
Great Lakes S/SW through in,IL, MO, and Arkansas...with a weak trough
extending down the Piedmont of the Carolinas into Georgia.
Rest of today and tonight: forecast is complicated by numerous
outflow boundaries and convectively induced perturbations in the
mean flow. This morning's mesoscale convective system over Kentucky has diminished...although
its outflow boundary has helped several complexes develop over
eastern Tennessee and western NC. Think highest concentration of
convective coverage will be across north Georgia where any larger
scale outflow could be influenced by orographic processes and
perhaps the weak sfc trough. Nonetheless...with MLCAPE between
2000-3000j/kg across the entire County Warning Area...storms could pop up
anywhere. Downburst winds the main threat with low level lapse
rates over 7c/km and pws near 2 inches. The hrrr has been
consistent in showing redevelopment across Kentucky/Tennessee towards sunset
tonight /likely influenced by morning mesoscale convective system and the weak front/. It
is possible some of this convection could impact far north Georgia
after midnight...though confidence is low given time of day and
weak flow. Showing slight pops for now to reflect this
possibility...with a diminishing trend towards sunrise.
Much of the same story for Monday as sfc troughing continues and
Great Lakes shortwave moves into New England. Aforementioned weak
front will likely be closer to the state...but still far enough away
to not have a profound impact on convective initiation. Forecast
will be complicated again by outflow boundaries and convectively
induced perturbations in the mid levels. All things
considered...trend should still remain largely diurnally driven.
Temps will be hot...and it will be humid.
Long term /Tuesday through Sunday/...
no major changes to the long term from the previous forecast. A weak
trough of low pressure will remain over the County Warning Area early in the long
term. This will develop into a closed low over Georgia by Wednesday
and as the 500 mb ridge builds over the middle of the country, this will
push the low out of Georgia however there are discrepancies in the
models as to how much moisture will be pushed out as well. Due to
this will maintain pops across the County Warning Area for the latter half of the
week. The next short wave will move out of the upper plains and
toward the County Warning Area toward next weekend increasing the chances of precip
late in the week and next weekend. Temperatures will remain at or
near climate norms through the long term.
scattered to numerous showers and thunderstorms moving across the
northern taf sites this evening. This activity will work south
and likely dwindle with loss of heating. Some lingering
isolated thunderstorms across southern taf sites should decrease
to just vcsh the next couple hours. While activity in Tennessee is
becoming better organized this evening, feel these thunderstorms
will likely diminish as they cross far northern Georgia. VFR conditions
are expected (apart from any precipitation activity) through the
overnight as convective debris erodes. Fog/stratus formation
seems fairly limited given dewpoint depressions. However, for
those that received plentiful rain this afternoon/evening, you may
see patchy ditch fog by early morning. Cumulus decks will increase by
mid morning tomorrow to around 4kft. Another convective day in
store with development expected by 16-17z. West winds will
continue through the taf period.
//Atl confidence...00z update...
medium confidence on evening/overnight convection potential.
High confidence on all other elements.
Preliminary point temps/pops...
Athens 96 75 91 73 / 60 40 50 40
Atlanta 91 75 89 74 / 60 40 50 40
Blairsville 89 69 85 67 / 60 50 50 40
Cartersville 92 73 88 72 / 60 40 50 40
Columbus 95 75 92 75 / 50 40 50 40
Gainesville 91 74 88 73 / 60 40 50 40
Macon 93 75 92 74 / 50 40 50 40
Rome 92 72 89 73 / 60 40 50 40
Peachtree City 92 73 90 72 / 60 40 50 40
Vidalia 92 76 92 74 / 60 40 50 40