Scientific Forecaster Discussion
Area forecast discussion...update
National Weather Service Peachtree City Georgia
838 PM EST Monday Dec 9 2013
area radars show an area of light to moderate rain across parts of
central Georgia along and ahead of a pre-frontal trough or warm front...
and this activity is drifting south and east as it diminishes.
Another area of light to moderate rain showers was developing over
northwest and west central Alabama...and this activity is along and ahead of the
cold front. Models agree on this area expanding and pushing across
north Georgia later tonight and into central Georgia early on Tuesday. Although
additional rainfall amounts across north Georgia overnight should be
around one half inch or less... still cannot rule out a few more
rivers reaching flood stage toward morning with the additional
rainfall...but nothing widespread or too significant is expected.
As for any wintery threat... still expect any light snow or mix to
remain mostly in Tennessee and maybe northwest-north central Alabama overnight where
the colder air may arrive in-time to produce some light wintry
snow/sleet before the moisture pushes south. Although cannot rule
out a few flurries across far northwest-north central Georgia later tonight...
do not expect anything to accumulate as moisture will be limited and
grounds are still way too warm. Will just forecast rain for now
since models and timing seem to agree this will be the prevailing
precipitation type tonight.
Have update zones to tweak probability of precipitation and lows just a tad... and removed
any mention of thunder for tonight. Otherwise... the forecast still
looks on track with no major changes expected at this time. /39
Short term /tonight through Tuesday night/...
/issued at 235 PM EST Monday Dec 9 2013/
models in fairly good agreement in the short term with bringing in
the next cold front. Current cold front has stalled over northwest
Georgia while the warm front has moved to nearly a csg-mcn to Louisville
line. The warm front has gone stationary as well. An area of thunderstorms
has developed over southeast Alabama and is currently moving into the
southwest corner of the County Warning Area. This will move northeast with the
thunder holding on until it reaches The Wedge...it should then lose
the support for thunder. While there could be a strong wind gust
this afternoon with the thunderstorms...severe storms are not
expected. The next wave of rain should develop along and ahead of
the next cold front...pushing into extreme north Georgia around midnight
or thereafter...spreading across the rest of the County Warning Area late tonight
and Tuesday. This area of rain should be rather narrow and move
quickly through the area. At this time the threat for heavy rain has
diminished. Much drier air and colder air will move into the County Warning Area
behind the front along with gusty northwest winds.
Long term /Wednesday through Monday/...
/issued at 235 PM EST Monday Dec 9 2013/
no significant changes made to the extended forecast grids. See
previous long term forecast discussion below.
Previous long term forecast discussion...
GFS and European model (ecmwf) are coming into better agreement through the extended
especially with respect to the weekend system. Extended begins with
high pressure over the Ohio Valley in control of most of the eastern
third of the country behind the early week frontal passage. Very dry
air in place but enough of a pressure gradient will remain in place
to keep winds from going calm overnight... which in turn prevents
temperatures from bottoming out early in the period. Weak wave pushes
through Wednesday night which may serve to increase clouds but should
not bring any precipitation to the area.
The bigger story will be toward the weekend. Ridging increases aloft
on Friday in advance of strong trough deepening over the Desert
Southwest. Surface low develops in the Lee of The Rockies in the
Southern Plains and as it works its way east...it overspreads
moisture and precipitation across the area especially on Saturday.
May have a weak hybrid cad in place depending on how far offshore the
surface high has moved by that point. Introduced a brief rain/snow
mix Saturday morning as current timing brings moisture in with temperatures
in the lower 30s across north Georgia. Have also increased probability of precipitation to
likely on Saturday based on model agreement...though European model (ecmwf) is just a
touch faster than GFS. Front moves quickly out Saturday night...
though European model (ecmwf) is advertising a secondary shortwave pushing through
Overall maximum temperatures look to be fairly close to average...with larger
swings in low temperatures...starting off on the cool side with dry high
pressure and place and gradually increasing toward the weekend with
the increasing moisture.
/issued at 635 PM EST Monday Dec 9 2013/
a pre-frontal trough near a csg to mcn line is providing the focus
for most of the shower activity... and this trend is expected to
continue tonight... with mainly LIFR-IFR ceilings with 2-4sm -radz br
expected to persist north of the trough across most taf sites
overnight. The main cold front will enter northwest Georgia later this
evening... then push across the Atlanta taf sites by 14-15z Tuesday. A
much drier airmass will spread in behind the front...with sky clear
expected by 18-20z Tuesday. West-northwest winds will be light tonight...then
increase from the northwest to around 12kts by 12-13z... with 15g25kts by
15z Tuesday. Strong gusty northwest winds will persist Tuesday afternoon... with
gusts ending by 00z Wednesday.
//Atl confidence...00z update...
medium confidence on all elements.
High on wind direction and speeds Tuesday.
Preliminary point temps/pops...
Athens 45 54 29 53 / 70 70 0 5
Atlanta 42 51 31 52 / 60 60 0 5
Blairsville 39 48 23 50 / 90 90 0 5
Cartersville 38 47 24 52 / 70 70 0 5
Columbus 51 57 32 58 / 60 60 0 5
Gainesville 42 51 30 51 / 60 70 0 5
Macon 54 61 29 57 / 60 50 0 5
Rome 39 47 24 50 / 90 90 0 5
Peachtree City 44 53 23 54 / 60 60 0 5
Vidalia 61 65 39 58 / 20 60 0 5