Scientific Forecaster Discussion
Area forecast discussion...updated for aviation
National Weather Service Peachtree City Georgia
138 am EDT Thursday Aug 21 2014
/issued at 1005 PM EDT Wednesday Aug 20 2014/
have left low probability of precipitation in until 06z...all storms have dissipated except
for a few along the Alabama border. Have also kept in mention of fog
after midnight. Some locations have already reached at or slightly
below overnight minimum temperature forecast due to widespread rain.
Have tried to adjust forecast to account for this.
short term /tonight through Thursday night/...
dealing with quite a bit of convection out there this afternoon.
Incredible cape values of 4000-4500j/kg and dcape over 1000j/kg over
much of the area. Weak disturbance aloft helping to organize some of
the convection as well. Will continue to see scattered to at times
numerous storms with isolated severe potential. Wind gusts would be
the main threat but some small hail cannot be ruled out. And of
course as with any summertime thunderstorm...very heavy rain and
Upper ridge remains in place to our west leaving US in northwest
flow aloft. Intermittent disturbances will continue to slide down
the northwest flow...but as the ridge builds the chance of rain will
decrease over the next couple of days as the peripheral convection
pushes east. However...if convection does manage to develop and get
past whatever cap there is from the ridge-induced subsidence...
thunderstorms could easily and quickly go severe with the amount of
low level heating and instability. Not much in the way of
organization but something to be aware of.
Speaking of low level heating...quite a few areas this afternoon are
flirting with 105 degrees. Some uncertainty in dewpoints as met is
cooler but more moist and mav is warmer but drier...so have
generally taken a blend but leaned toward the worst-case scenario
given that dewpoints this afternoon are a few degrees higher than
originally expected. With higher temperatures expected
tomorrow...will go ahead and issue a heat advisory for portions of
central Georgia for tomorrow afternoon. See extended for more
information...but will likely need one Friday and possibly again on
Long term /Friday through Wednesday/...
mainly only tweaks to the long term based on the latest guidance.
medium range models continue to show the forecast area dominated by
strong upper-level ridging through the majority of the extended
forecast period. GFS and European model (ecmwf) remain in good agreement through the
weekend but diverge somewhat going into early next week with the
European model (ecmwf) flatten the ridge over US while the GFS...although showing
some weakening... keeps the ridge over the region through Wednesday.
Still...these differences do not alter the general trend of hot and
mostly dry through the weekend with moderating temperatures and
increasing precipitation chances early next week...which is what we
have been carrying in the extended forecast for the past several
days now. With this in mind I do not plan on deviating too much from
previous trends in the forecast grids. Through the weekend the
GFS/European model (ecmwf) keep the center of the upper ridge west of the state with
the best subsidence remaining west of US as well. With this in mind
I will keep the slight chance probability of precipitation into the weekend with chance probability of precipitation
as we head into the first half of the new week.
earlier convection is dissipating and expect this trend to continue
with nearly a rain free area by 06z. Ample ground moisture around
from Wednesday late convection... which could result in patches of
LIFR/IFR/MVFR ceilings developing around 09-10z this morning. Will
continue to show sct008 by 09z this morning for all taf sites for
now...but would not be surprised to see LIFR to IFR ceilings threaten
some of the taf sites later this morning. Some IFR/MVFR visibility
also possible. Increased upper ridge influence should hold afternoon
convection down to isolated in coverage...so not enough confidence
to include in tafs at this time. Light northwest winds this morning will
increase to around 6-8kts later today.
//Atl confidence...06z update...
medium on early morning stratus. Medium to high on all other
Preliminary point temps/pops...
Athens 71 97 72 99 / 30 20 5 20
Atlanta 74 96 75 95 / 40 20 5 20
Blairsville 66 91 66 90 / 50 30 20 20
Cartersville 70 96 70 95 / 50 20 5 20
Columbus 74 98 75 97 / 20 20 10 10
Gainesville 72 95 73 94 / 40 20 10 20
Macon 72 98 72 98 / 20 20 10 20
Rome 70 96 70 96 / 50 20 5 10
Peachtree City 70 95 70 96 / 30 20 5 20
Vidalia 74 100 75 98 / 20 20 10 20
heat advisory from noon to 8 PM EDT Thursday for the following