Scientific Forecaster Discussion
fxus62 kffc 200303
Area forecast discussion
National Weather Service Peachtree City Georgia
1103 PM EDT Tue Sep 19 2017
light showers and a few thunderstorms continue just across the far
west central County Warning Area boundary in Alabama this evening. Have gone ahead
and continued mention of slight chance thunder through 06z. The
weakening/diminishing trend is expected to continue as the precip
area moves into the state.
Otherwise, have made only minor changes to hourly trends, and the
forecast appears to be on track.
Previous discussion... /issued 732 PM EDT Tue Sep 19 2017/
/issued 315 PM EDT Tue Sep 19 2017/
short term /tonight through Wednesday night/...
convection to the west has been more plentiful in coverage than
earlier models might have projected but mesoanalysis indicates
plenty of reasons why. Mixed layer cape values over portions of
Alabama are in excess of 2000 j/kg and sfc based over 3000 j/kg.
With precipitable water over 1.50 inches, this along with the
robust energy has been more than enough to warrant the enhanced
coverage to our west.
The big question remains how much of this activity holds together
for the local area. Although no where near that much energy
resides currently over the western zones, rap does bring some 1500
cape values in late this afternoon. Have therefore continued with
the high end chance pops through this evening for northwest corner but
stopped short of likely based on hrrr models quick dissipation.
Shortwave is a slow mover but should move across the northern
sections during the overnight period with limited pop coverage.
This would setup the central zones as having the best chance for
pops on Wed. Models show moisture pooling from csg to mcn and
points southward with pws near 1.75 inches along with modest cape
values of 1500 j/kg. Still some residual cool air aloft so cannot
rule out some isolated strong storms during the afternoon hours.
/issued 315 PM EDT Tue Sep 19 2017/
long term /Thursday through Tuesday/...
only slight changes have been made to the extended forecast. The
ridge pattern positioned over the area is expected to have broken
down by the beginning of the extended period and will be replaced by
weak upper-level troughing. This trough pattern will contain
multiple shortwaves embedded within. As a result of these upper-
level impulses, isolated to scattered diurnally favored showers and
thunderstorms can be expected in the area in the later parts of the
week and into the weekend. The highest pops will be on Thursday
and Friday afternoon, mainly in the 30 to 40 percent range. Pops
have been lowered on Friday from the previous forecast due to a
lowered confidence in surface-based forcing.
GFS/ECMWF/NAM/Canadian models all continue to keep any direct impact
from Jose/Maria far to the east of the area. The official forecast
from NHC reflects this as well. Maria is expected to force a drier
and more stable air mass into the area on Sunday which will remain
in place until Tuesday. This air mass will lead to more seasonal
temperatures and humidity, along with lower pops, starting during
the weekend and into the early parts of next week.
VFR expected through the period. Rain and a few embedded
thunderstorms moving east toward the Georgia/Alabama border continue to
dissipate into the state. At this time, have opted for vcsh at
kcsg, but no precip mentioned elsewhere tonight. For tomorrow,
isolated to scattered showers are expected generally after 18z,
and have gone with vcsh for all taf sites. West-northwest winds will be
light overnight, then increase to 4-6kt through the day. Slight
visibility reductions to MVFR are possible for kcsg and kmcn
//Atl confidence...00z update...
high on all elements.
Preliminary point temps/pops...
Athens 67 88 66 88 / 20 20 20 30
Atlanta 70 87 70 87 / 20 20 10 30
Blairsville 61 82 60 83 / 20 20 10 40
Cartersville 66 87 65 88 / 20 20 10 30
Columbus 71 90 71 90 / 50 20 20 40
Gainesville 68 86 67 85 / 20 20 10 30
Macon 68 90 69 89 / 20 20 20 40
Rome 66 88 66 88 / 20 20 10 30
Peachtree City 67 88 67 87 / 20 20 20 30
Vidalia 71 91 71 89 / 20 30 20 50