Scientific Forecaster Discussion
fxus62 kffc 250045
Area forecast discussion
National Weather Service Peachtree City Georgia
845 PM EDT Sat Mar 24 2018
Previous discussion... /issued 300 PM EDT Sat Mar 24 2018/
Short term /tonight through Sunday night/...
weak northwest flow in the mid and upper levels continues this afternoon
per water vapor imagery...with noted upstream shortwave trough
continuing to push southeast from Iowa into Illinois. This wave will dampen
as it traverses thru the northwest flow and towards NE Georgia/Carolinas
overnight tonight. Meanwhile sfc reflection as evidenced by sfc low
pressure south of the wave is moving into the Tennessee Valley. Sfc
analysis still reveals a cold front extending SW of the sfc low into
the Southern Plains and a warm front draped southeast into eastern Georgia.
Across the local area around 19z...clouds have begun to erode across
southern portions of the County Warning Area all the way towards Metro atl...while
overcast skies continue across north Georgia. Despite clearing for
many this afternoon...cloud cover will increase from north to south
overnight as sfc wave and weak upper level shortwave move towards
the area. This will also help increase rain chances...with highest
chances across north Georgia thru the evening and then pushing south
overnight tonight and continuing in the atl-ahn vicinity into the
morning. Shower coverage should decrease into early Sunday but do
feel some will make it as far south as Macon-Columbus. Enough
instability will warrant mention of isolated thunder as the precip
moves south-tho do not expect strong or severe development. As the
showers and weak low move into the state...a very strong wedge of
high pressure will dam against the Lee side of Appalachians and
build south into the County Warning Area. This will push the weak low and associated
precip south/southwest...with colder air filtering in the wake of
this wedge frontal boundary. Many locations will notice falling
temps and rather unpleasant conditions thru the day Sunday with
abundant cloud cover and most likely lingering light showers and
Sunday night will feature colder low temperatures as wedge really
sets into most of the County Warning Area. Clouds are expected to linger and as
850mb winds turn more southerly...weak warm air advection will increase atop
stable...cold sfc airmass. This will likely allow for an increase in
shower coverage across most of the area. Unfortunately...given
abnormally strong wedge airmass...Northeast Mountain locations will
likely dip around freezing...with perhaps slightly subfreezing
dewpoints. Given 12z NAM and GFS sounding data...there will be a
chance for light freezing rain/freezing drizzle across this area
after after midnight Sunday going into Monday morning. No winter wx
is expected elsewhere and impacts across the NE should remain
minimal. Wedge continues into the long term.
Long term /Monday through Saturday/...
no major changes in the long term. Still some timing differences on
the mid to late week system, however there is starting to be some
agreement in the models for late day Thursday and have a little more
confidence in the showers Thursday afternoon. Previous long term
The models are rather consistent indicating a cad airmass will
have or will be moving over the area to start the long term with
rain chances continuing through Monday as there is potential for
moisture to overrun the cad airmass to cause chances for light
rain and occasional drizzle. While rain chances seem to diminish
Monday night and Tuesday, the cad airmass will still be in place
and patchy or occasional drizzle can still be expected.
With the onset of the colder cad airmass later Sunday night and early
Monday, there is some potential for a rain/freezing rain mix over
the far Northeast Mountain counties. This will continue to be watched
for anything more significant.
The GFS and European are somewhat inconsistent with the timing
of the moisture with the next system with the GFS more progressive
and the European slower. In any event, a slow moving cold front
is forecast to move across the area on Friday as a short wave
catches up to the front and gives it a push through the area.
Rain chances increase over N Georgia Wed/Wed night and across much
of the rest of the area into Thursday night, with rain chances
diminishing on Friday, then a dry start to the weekend for Saturday.
Not a lot of instability is forecast with this system and just went
with a slight chance of thunderstorms on Thursday over portions of
north and West Georgia.
Temperatures start out near to below normal on Sunday night then
well below normal for the high temperatures on Monday. Temperature
will begin to moderate on Tuesday then warm to above normal Wednesday
precip beginning to push into the area this evening with ceilings
lowering and winds diminishing. Ceilings are still in the VFR
range but should see some MVFR ceilings at the atl area taf sites
by 03z-06z looking for ceilings to continue to fall into the IFR
range by 10z. Precip expected to move into the taf sites by 06z-
08z and continue off and on through the taf period. Winds are out
of the W to SW right now but will turn to the NE by day break and
then to the east Sunday afternoon as The Wedge builds down into the
area. Wind speeds will stay 10kt or less tonight then increase
again Sunday afternoon into the 10-12kt range gusting to 18z by
//Atl confidence...00z update...
confidence medium to high on all elements.
Preliminary point temps/pops...
Athens 47 49 41 49 / 70 50 50 30
Atlanta 53 56 42 50 / 70 50 50 40
Blairsville 46 50 36 50 / 80 40 40 20
Cartersville 54 57 43 51 / 70 40 50 40
Columbus 62 69 48 55 / 60 50 50 30
Gainesville 45 49 39 48 / 70 50 50 30
Macon 60 64 45 53 / 50 50 50 40
Rome 55 59 44 53 / 70 40 50 30
Peachtree City 57 58 44 51 / 60 50 50 40
Vidalia 61 65 45 55 / 40 50 50 40