Scientific Forecaster Discussion
fxus62 kffc 230258
Area forecast discussion
National Weather Service Peachtree City Georgia
1058 PM EDT sun Oct 22 2017
A large area of rainfall with a few embedded thunderstorms over
Alabama is gradually pushing into Georgia at this time. Rain will
increase from the west through the remainder of the night into
Monday morning. With very little in the way of instability, strong
or severe thunderstorms are not expected overnight.
The focus for rainfall will shift eastward through Monday, with
the best opportunity for a few stronger thunderstorms Monday
afternoon across the eastern portions of the state. Rainfall
totals generally in the 1-3" range can be expected through Monday
afternoon. Drying will rapidly occur from west to east as the
surface front pushes through the area through the day Monday.
Previous discussion... /issued 749 PM EDT sun Oct 22 2017/
Previous discussion... /issued 303 PM EDT sun Oct 22 2017/
Short term /tonight through Monday night/...
cold front is currently moving across the lower Mississippi River
valley with a pre-frontal trough analyzed just east of the
Mississippi River. Surface high pressure has finally begun to push
off the mid Atlantic coast. The precipitation shield associated with
the trough/front will continue to spread eastward overnight and
approach far western Georgia during the early morning hours.
The cold front should move through most of the County warning forecast area by the late
afternoon/early evening. The 12z NAM, GFS and European model (ecmwf) all support a
deep 500mb trough swinging through during the day...and all with a
negative tilt and open wave by the time it reaches Georgia. All have
varying strengths to the mid level system, with the GFS being the
strongest and a little further south with the forcing.
The European model (ecmwf) and the NAM take the best forcing just north of the cfwfa,
with some marginally steep lapse rates across the far north. Surface
instability values are a bit higher than they were yesterday, with
all of the cape along and ahead of the frontal boundary. Surface
instability across the north is slightly more concurrent with the
marginal lapse rates than in previous model runs. The best cape
values are expected across the southeast County warning forecast area across areas that
should receive the most sunshine. The best shear values are expected
across the northern County warning forecast area in the morning, but some marginal values
are possible across the southeast along the frontal boundary.
Isolated to scattered thunderstorms are possible tomorrow beginning
early in the morning in the west. Widespread severe weather is not
anticipated but isolated severe thunderstorms will be possible as
the system moves through. Locally heavy rainfall is also likely as
the cold front moves through tomorrow. Precipitable waters reach near 2" ahead of
the boundary. Ffg is rather high, so no widespread flooding is
expected but localized flooding will definitely be possible.
Rainfall amounts should average between 1" and 3", with locally
higher amounts will be possible.
Cooler temperatures and a drier airmass are expected behind the cold
front Monday night. Lows in the 40s and 50s are possible, but the
much cooler air will settle across the region into the long term
portion of the forecast.
Long term /Tuesday through Sunday/...
only tweaks to the long term based on the latest guidance.
Overall, much quieter weather expected.
heavier precipitation should be sweeping east of the forecast area as
the period begins Monday night into early Tuesday. Right now it
appears that moisture will be too limited Wednesday for pops as a
secondary upper trough and associated short wave move across. This
secondary system does push through another shot of good cold
advection with our coolest temperatures of the week expected
Wednesday and Wednesday night. Highly amplified and very progressive
upper pattern transitions the region back to southwesterly upper flow
quickly with a subsequent quick rebound in temperatures back toward
seasonal normals by the end of the week. The next upper trough/short
wave and the associated surface front sweep through next weekend.
ceilings this evening and into the overnight hours are expected to
lower through the MVFR range and into the IFR range by Monday
morning. Shra chances will also increase, becoming likely by
Monday morning. The best opportunity for thunder will be generally
between 10-14z at atl and csg area sites and a bit later at ahn
and mcn. Rainfall will depart from west to east through Monday
afternoon with skies gradually improving through Monday evening.
Winds will remain on the east side overnight, occasionally gusty
to near 20 knots. Winds will become gusty and shift to the west
as the attendant cold front pushes through the area on Monday.
//Atl confidence...00z update...
medium confidence on ceiling trends and convection timing.
High confidence on remaining elements.
Preliminary point temps/pops...
Athens 66 71 50 69 / 60 90 30 10
Atlanta 68 71 51 66 / 80 100 10 5
Blairsville 61 67 44 60 / 80 100 10 10
Cartersville 67 71 48 64 / 90 100 10 5
Columbus 71 75 54 70 / 80 100 10 5
Gainesville 66 69 51 65 / 80 100 20 10
Macon 70 75 51 71 / 50 80 30 5
Rome 67 71 48 64 / 100 100 10 10
Peachtree City 68 73 49 67 / 80 100 10 5
Vidalia 72 79 57 74 / 40 80 70 5