Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
940 PM EST sun Jan 25 2015
have updated forecast to bring rain farther south into western Georgia...and also
extended the mention of isolated thunder into those zones until around 05z.
No changes to the overnight period.
short term /today through Tuesday night/...
No significant changes to the complex short term forecast. Latest
model runs continue to be in good agreement with the track and
timing of strong upper trough tracking across the area tonight
through early Monday. The main concerns will be the potential for
wintry precipitation across north Georgia due to the cold core and strong
upper level forcing. Although portions of north Georgia are
expecting to see 0.5-1.0 inch of snow with locally higher amounts
/largely in the higher elevations/ other portions of north
Georgia will be too warm to promote any accumulations.
At this time...the onset of the precipitation has not changed
significantly. Still anticipate light rain to push into northwest Georgia this
evening...spreading eastward across north Georgia. Anticipate the
transition to a rain-snow mix to occur early Monday morning. Higher
elevations are expected to see the additional transition to all snow
Monday morning. Any accumulations will likely be in areas above 1500
feet and generally 0.5 to 1 inch or less. Some portions of the
northeast Georgia mountains could see higher amounts. Although the
precipitation will exit northwest Georgia by middle morning Monday...residual
moisture remains across northeast Georgia through the day...tapering
off to sprinkles or flurries by Monday afternoon. There is a chance
of another shot of precipitation into Tuesday morning...which is
discussed more in the long term discussion below.
Have gone ahead and issued a Winter Weather Advisory for the
expected snowfall for the northern two tiers of counties in the County Warning Area.
The advisory means that accumulations will be below warning criteria
/or below 2 inches/ but that inconveniences are anticipated. For
now...the metropolitan atl area is expected to remain in the middle to upper
30s...if not a degree or two warmer...and although a transition from
rain to a wintry mix early Monday morning is expected /particularly
across the northern and western suburbs/...no accumulations are
Gradual clearing is expected through Monday...though residual
moisture will continue to impact the far northern counties into
And on an entirely different note...have added slight chance thunder
to the grids through late evening tonight for portions of far north
Georgia. Models have just enough instability /100-200 j/kg/ that an
isolated thunderstorm can not be ruled out. Expect any thunderstorm
potential to diminish into the overnight hours and have not
continued the thunder mention beyond 03z. Do not anticipate any
strong or severe storms at this time.
Long term /Tuesday through Saturday/...
Main change from this time yesterday has been the development of a
secondary trough to move through...the result of a lobe of upper
level energy that rotates into north Georgia. Indications are that
this could result in additional snow showers across far north
Georgia that would not be limited to just the mountains as
profiles are more than cold enough to support snow. Quantitative precipitation forecast however is
very meager with this system and just not seeing any accumulations
past 12z Tuesday. More concerning will be residual moisture on roads
and the quick transition to below freezing temperatures. Elevated winds
will help in the drying process but continued low clouds will
not...not to mention any residual precipitation as well. May be
that a tier of counties will need to be added to current advisory
eventually for black ice potential and that overall advisory is
extended in time through Tuesday morning.
Otherwise...limited changes to the extended with continued
advertisement of light rain/snow over the northern tier once again
on Thursday night.
Previous discussion... /issued 139 PM EST sun Jan 25 2015/
Long term /Monday night through Saturday/...
Otherwise active pattern continues through rest of long term with
several other shortwave disturbances traversing along the stubborn
broad upper trough that just cannot seem to shake the east Continental U.S..
however...large discrepancies exist in the models with timing and
amplitude of disturbances. The next best chance of precipitation for now
looks to be Thursday into Thursday night...then again late Saturday.
The Thursday system looks to be a bit better organized and more of a
clipper system /ECMWF much more bullish and less progressive than
the GFS/...while the Saturday night impulse has much less amplitude
and more of a trailing cold front into the north. Column temperatures both
periods support possible snow mixing into the far north so have
included low chance mention at the moment. Confidence is very low at
the moment and future changes are likely due to the aforementioned
differences seen in the solutions. Please continue to closely
monitor the forecast.
VFR conditions through this evening will become MVFR and possibly
IFR overnight...generally 05-07z. Bands of rain developing and should
move across the taf sites this evening and overnight. In the northern
taf sites...mixed wintry precipitation possible mainly after 06z. No
accumulations are expected as the lowest 2-3kft of the atmosphere
will be above freezing. Expect improvement to MVFR by 17-18z. An
isolated thunderstorm is possible mainly northwest taf sites this evening.
West to southwest winds 5-8kt overnight. Northwest winds at 12-15kt
with gusts to 20-25kt expected by middle morning Monday.
//Atl confidence...00z update...
medium confidence on MVFR ceilings and mixed precipitation. Medium to high
on remaining elements.
Preliminary point temps/pops...
Athens 57 38 51 32 / 10 20 20 5
Atlanta 56 40 47 33 / 10 30 20 5
Blairsville 51 36 41 27 / 30 60 40 20
Cartersville 57 37 45 30 / 30 50 20 5
Columbus 60 41 51 34 / 5 10 10 0
Gainesville 53 38 46 31 / 20 40 40 10
Macon 60 40 53 32 / 5 10 10 0
Rome 56 37 44 29 / 40 50 20 5
Peachtree City 58 37 48 29 / 5 30 10 0
Vidalia 61 42 55 36 / 5 10 10 0
Winter Weather Advisory from 4 am to 7 PM EST Monday for the
following zones: Catoosa...Chattooga...Dade...Dawson...Fannin...