Scientific Forecaster Discussion
fxus62 kffc 180542 aac
Area forecast discussion...update
National Weather Service Peachtree City Georgia
1240 am EST Mon Nov 18 2019
..06z aviation forecast discussion...
updated grids twice this evening, mainly for temps and dewpoints
which are trending quite a bit higher than forecast. Also finally
seeing some light showers developing over areas just east of atl
Metro over to eastcentral Georgia which matches hires model guidance
and current fcst pops well. Still appears precip will struggle to
measure but may expand pops just a tad before mid shift sits down.
Previous discussion... /issued 827 PM EST sun Nov 17 2019/
Previous discussion... /issued 238 PM EST sun Nov 17 2019/
Short term /tonight through Monday night/...
Satellite imagery shows the cutoff low-pressure system centered 250
mi southeast of Wilmington, NC. With the system in little hurry to
completely exit the region, backside NE winds have helped bring in
additional low-level cloud cover which has been slow to fade away
throughout the morning.
Satellite imagery also shows the next three waves that will influence
the forecast area over the next 48 hours...
The first is a weak mid-level ridge already positioned across the
southeastern Gulf states that will provide enough subsidence to
clear the skies this afternoon and help to push the cutoff low-
pressure off to the northeast where it's expected to eventually
rejoin the broader flow.
The second shortwave will be by far the strongest of the three.
Currently the axis of the trough is stretched from Minnesota/WI through the
Ozarks plateau down to the arklatex region, moving eastward. With
northerly flow and the weak ridging preceding it, the trough will
have little moisture to work with as pwats are expected to settle
around 0.4-0.8in tonight. Still, cloud cover should increase
overnight and very light, isolated showers may be able to form in
the eastern portions of the forecast area. With the axis moving
through the forecast area early tomorrow morning, skies should begin
clearing on the backside of the axis as Ava covers the region. A
cold front will also follow this shortwave, but will begin to lag
and lose its reinforcement as it approaches the forecast area Monday
evening, manifesting only as a slight wind shift.
The third shortwave is currently over the Pacific northwest, and its
low-amplitude will allow it to move pretty quickly around the high-
amplitude ridge over the western conus, however, it is expected to
deepening somewhat as it digs into the southeastern US, from cold air advection due
to the previously mention cold front. Again, with little deep
moisture in the region, only on increase in cloud cover is expected
going into tomorrow night.
Long term /Tuesday through Sunday/...
The long term looks generally consistent with the current
forecast. The next couple of short waves crossing the Ohio Valley
Monday and Tuesday still show limited moisture to produce rain for
our area. Only an increase in cloudiness remains reasonable. The
upper ridge builds in through the end of the week with moderating
temperatures. Southwesterly flow begins to pull deeper moisture
back across Georgia late Thursday into Friday. This should set US up
for a wet pattern through the end of the period. GFS and European model (ecmwf)
still diverge on handling a surface low developing on the front
Saturday and Sunday. The GFS is faster with taking the low
northeast. Have kept pops in across the entire area through the
weekend to compromise. The only adjustment was to tweak pops up a
bit for Friday through Sunday.
Mix of VFR and MVFR ceilings across the forecast area to start.
Should MVFR ceilings increasing in coverage through the overnight
hours with taf sites in the MVFR range by 08-10z. Lower-level clouds
sweep out from west to east between 12z and 18z. Winds light, 5kt or
less, and variable in direction should become southwest to west by
10z. Wind speeds increase to 5-9kt by 16-18z. Some light showers are
expected over eastern portions of the forecast area through 12z,
however little impacts on ceilings or visibilities are expected with
//Atl confidence...06z update...
Preliminary point temps/pops...
Athens 46 61 39 60 / 20 10 0 5
Atlanta 47 59 38 58 / 10 0 0 5
Blairsville 42 55 33 52 / 10 5 0 5
Cartersville 41 59 36 59 / 5 0 5 5
Columbus 47 63 40 63 / 5 0 0 0
Gainesville 46 59 38 57 / 20 5 0 5
Macon 48 65 40 62 / 10 5 0 5
Rome 39 59 35 59 / 0 0 5 5
Peachtree City 46 60 37 60 / 10 0 0 5
Vidalia 48 65 42 64 / 20 10 0 5