Scientific Forecaster Discussion
fxus62 kffc 160455
Area forecast discussion
National Weather Service Peachtree City Georgia
1155 PM EST Fri Dec 15 2017
Update for aviation...
Previous discussion... /issued 1023 PM EST Fri Dec 15 2017/
high clouds have continued to scatter and clear across north
Georgia with temperatures also dropping quickly in these areas.
Saturday morning low temperatures were dropped a few degrees
across north Georgia to account for these trends. Otherwise,
forecast remains in good shape.
Short term /tonight through Saturday night/...
Fairly amplified large scale pattern will continue through the short
term. Currently...ridging persists across the rocky mtn states while
broad troughing exits across the eastern 2/3rds of the country. As
faster mid level flow continues across northern latitudes...a slow
moving closed low is meandering across western Mexico. At the
sfc...high pressure is dominating most of the southern states in the
wake of a cold front draped from the Carolina coast into the central
For the remainder of today and through tonight...Pacific
moisture along the subtropical jet will continue to stream into the
area through the afternoon and into the evening hours as the mid
level low continues to fumble around western Mexico. Most of this
will be in the form of mid and high clouds with some virga showing
up on local radar imagery. Consensus is that a vort ribbon stemming
from northern stream cyclonic energy will help push out the majority
of cloud cover through overnight as it passes from northwest to southeast. Sfc
high pressure will also continue to build into the region overnight
as the cold front continue south. Tight pressure gradient between
sfc high and baroclinic response of sfc low off the Carolina coast
will keep breezy conditions into the first part of the evening
tonight before the center of the high moves closer to the County Warning Area.
For Saturday...pesky Mexico closed low will be kicked into western
Texas as a digging trough dives into the S California/baja area. This will
induce a short wave/diabatic ridge across the southeast and make
for fairly mild temps as 500 mb heights rise noticeably. Although
moisture will surge north into the Southern Plains and lower MS
valley...sfc high pressure will not move offshore until the
beginning of the long term. Therefore...will stay dry and mild
through Sat night with lower level moisture gradually on the rise.
A quiet short term then gives way to an active long term.
Long term /Sunday through Friday/...
The GFS and Euro continue to struggle on keeping run-to-run
consistency and consensus with each other from Monday Onward with
extent of Gulf moisture axis and possible shortwave influences
through Wednesday. They at least both agree on some less
instability present Sunday so have taken thunder chance out then,
though include in portions of mainly central Georgia for Mon/Tue. Will
continue high end chance to likely chance for widespread showers starting
from the northwest Sunday then other areas thru tues, then limit to
slight chance pops Wed/Thu given uncertainty. Oddly enough they
both agree on the return of a broad SW Gulf moisture fetch by
Friday so have increased pops accordingly. Previous discussion
Previous discussion... /issued 321 am EST Fri Dec 15 2017/
Long term /Saturday night through Thursday/...
The long term period begins as a transition one as high pressure
continues to push offshore of the Carolinas and high amplitude mid
level trough begins to push east out of the 4 corners region.
Embedded shortwaves on the east side of this trough will move into
the Tennessee Valley Sat night and into Sunday. This will quickly
transition the nil pops early Sat night into likely rain chances
late Sunday. Given moisture and lift profile, would actually see a
large area of predominant showers but this is a good start this
far out. Given strength of the shortwave, it is likely we will see
some elevated thunder and perhaps even some surface based
instability. Will therefore continue to carry isolated thunder
chances in the grids.
With broad trough remaining west of the region through Wed, would
expect disturbed pattern to continue into mid week although models
differ on the details. Have utilized a blend for this forecast
which keeps a zone of likely pops in transitioning south of the
region by Tue night into Wed.
Another storm system on tap into late next week as we approach the
Holiday with models actually in good agreement this far out.
Despite good agreement, run to run consistency has been all over
the place and will therefore keep pops at chance for now.
VFR conditions will continue through the period with just varying
high clouds. Surface winds light west-north becoming west-southwest or light and
variable during the day Saturday.
//Atl confidence...06z update...
low confidence for wind direction after 00z.
High confidence for all other elements.
Preliminary point temps/pops...
Athens 51 29 55 36 / 0 0 0 5
Atlanta 44 29 55 38 / 0 0 0 5
Blairsville 32 21 53 31 / 0 0 0 10
Cartersville 37 25 53 35 / 0 0 0 10
Columbus 48 30 58 39 / 0 0 0 5
Gainesville 41 28 54 37 / 0 0 0 5
Macon 52 28 57 36 / 0 0 0 5
Rome 39 23 54 34 / 0 0 0 10
Peachtree City 45 28 56 36 / 0 0 0 5
Vidalia 59 33 58 38 / 0 0 0 5