Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
636 am EST sun Feb 14 2016
Previous discussion... /issued 458 am EST sun Feb 14 2016/
Short term /today through Monday/...
complicated forecast on tap as classical cad wedge is building
into the County Warning Area from the parent 1034-mb surface high sliding into the middle
Atlantic... before overrunning moisture ahead of an amplifying
upper trough and developing translated surface low is prognosticated to
interact with The Wedge tonight through Monday. The diabatic
effects of parcel evap cooling may be the top reinforcing factor
to The Wedge going into Monday since the parent high quickly
pushes off the East Coast and the approaching low trends farther
north on its track. Therefore not confident on how quickly The
Wedge will erode and have overall stayed closer to the better
resolving NAM solution though still went cooler than guidance on
forecast temperatures. Given surface temperatures and prognosticated wetbulb temperatures from hi-res
solutions there is decent consensus on the northeastern majority
of the County Warning Area reaching freezing or slightly above by 12z Monday with
gradual warming from the southwest with wedge erosion. The bigger
question is how much of the area farther northeast /in current
Winter Storm Watch/ remains in a sub-freezing pocket into the
The second bigger question is how much isentropically forced quantitative precipitation forecast
results Monday morning ahead of the main frontal forcing later that
evening/overnight. Wpc guidance basically shows zero quantitative precipitation forecast for Monday
morning while local WRF solutions translate light amounts along The
Wedge. Based on forecast partial thicknesses and thermal profiles it
would be in the form of light freezing rain or freezing drizzle and
extend a bit farther south of the current watch area along and
slightly south of the I-20 corridor /while the far NE may start as a
snow/sleet combo. Wpc guidance and many other models have also
slowed the higher quantitative precipitation forecast values from the approaching front into Monday
night. This also resulted in less overall ice/snow totals for the
far north by late Monday. All considered have lowered the maximum ice
accretion totals to 0.1-0.2 inches ice in far NE and spread lighter
glaze amounts farther south of current watch area...and have also
lowered total snow accumulation maximum to 0.5-1.0 inches in far NE.
Given recent trend of less quantitative precipitation forecast and overall more uncertainty on
amounts...have opted to continue on current watch with the hopes of
gaining more confidence with daytime package for any possible
upgrade to product. This is also in agreement with NE neighbor gsp
weather forecast office. Please monitor the forecast as changes are likely in this
Also added slight thunder mention Monday afternoon given some
instability nosing into the SW portion ahead of aforementioned
front. While shear looks marginal the low level helicity is pretty
decent so cannot rule out a few stronger storms /spc day 2 outlook
has marginal zone not too far from our SW border/.
Long term /Monday night through Saturday/...
models generally taking the surface low across north Georgia and into
the Appalachians Monday night and then off the middle Atlantic coast
Tuesday. Enough warming taking place Monday night that precipitation type
should be all liquid. Have mentioned thunder for a portion of
central Georgia Monday night although instability looks weak. Rain
ending quickly from the west on Tuesday with the GFS a bit faster.
Another short wave dropping rapidly into the Tennessee and Ohio Valley
Tuesday night with the southern end of the moisture passing over
north Georgia. Have continued with low probability of precipitation across the far north
Tuesday night. Temperatures should be warm enough for all rain
except in some isolated areas there may be a rain/snow mix.
Wednesday through Friday look dry. Strong low pressure moving
across the Great Lakes should push a front into the Tennessee Valley by
Saturday. Low probability of precipitation were included for the far north Friday night
initial VFR conditions should persist through the afternoon
..while gradual decrease in conditions expected overnight into
Monday with MVFR ceilings building in after 04-06z for most sites and
then lower into the day Monday as precipitation and overrunning
moisture becomes more widespread. For now have introduced prob30
for -ra after 09z Monday for the northern sites. Any wintry
precipitation potential looks to remain north and east of katl though
kahn could have a mix of -ra and -fzra Monday morning. Winds
should be shifting NE to east this morning then be predominantly
east-southeast 7-10 kts later this afternoon.
//Atl confidence...12z update...
medium on precipitation timing/type.
High on all else.
Preliminary point temps/pops...
Athens 43 29 40 39 / 5 30 60 90
Atlanta 46 33 44 41 / 5 30 80 90
Blairsville 35 28 39 35 / 20 60 90 90
Cartersville 45 32 44 39 / 5 40 100 90
Columbus 54 38 56 46 / 5 20 60 80
Gainesville 40 29 37 37 / 5 40 80 90
Macon 51 35 54 46 / 5 20 40 80
Rome 44 33 45 39 / 10 50 100 80
Peachtree City 48 32 47 41 / 5 20 80 90
Vidalia 49 38 64 52 / 5 20 30 80
Winter Storm Watch from late tonight through Monday evening for
the following zones: banks...Barrow...Cherokee...Dawson...