Scientific Forecaster Discussion
fxus62 kffc 230501 aab
Area forecast discussion...updated
National Weather Service Peachtree City Georgia
1201 am EST Thu Nov 23 2017
Update for aviation...
Previous discussion... /issued 618 PM EST Wed Nov 22 2017/
Short term /tonight through Thursday night/...
broad area of high pressure over the central Continental U.S. Has pushed into
parts of north and central Georgia today. Northerly winds and lower
dewpts/humidity exist this afternoon with just some high clouds
streaming across the area from the southwest. Afternoon temps were
generally in the mid-upr 50s (northwest zones) to around 70f (far
south -- Cordele to Dublin to swainsboro).
Main player the next 24-36 hours will center around a surface wave
of low pressure and associated upr lvl trough currently digging
across the northern Gulf of Mexico. This "wave" is expected to
become better organized as it drifts slowly northeast. Models are in
pretty good agreement with movement/track of this low with the
exception of the NAM which shows a more northerly track. The
divergent solutions have more of an impact on forecast late
Thursday night into Friday (vs. Tonight/tomorrow) with placement
and intensity of rainfall.
All this said, expect a gradual increase in moisture across the area
tonight into Thanksgiving, especially south of I-85/I-20. This will
mainly result in mostly cloudy skies, but a few light rain showers
and/or drizzle could develop by daybreak, generally along and south
of a Columbus to Macon to Sandersville line. A piece of the low is
expected to track across North Florida Thursday night along with the
upr trough. This should gradually diminish the threat for any
rainfall across the southern counties by Friday morning.
Long term /Friday through Wednesday/...
at the beginning of the long term forecast period around 12z
Friday...the mid and upper level synoptic regime will be slightly
less amplified than during the short term...albeit only temporarily.
Tight...more quasi-zonal westerlies will exist across the northern
rockies into the northern plains as a shortwave ejects from the
Washington state coast into eastern Montana. Downstream from
this...loose and broad cyclonic flow will be in place across the
eastern US...with a nuisance trough affecting the southeast coast. At the
sfc...a wave induced by mid level vort maxes within the nuisance
trough will push northeast just offshore the Carolinas along a
pre-existing frontal boundary.
Friday forecast is a bit tricky as the 12z guidance has yet to get a
decent handle on the evolution of the eastern Gulf trough. Although
the southern stream flow is slower...an overall progressive pattern
would likely suggest keeping an open wave trough as the system
progresses northeast. This makes 12z NAM guidance a noticeable
outlier with a potent closed low moving across southern GA. For
now...have discarded this solution and trended more towards
ec/GFS/CMC. This will keep slight chance pops across far southeast counties
until midday Friday. Will have to watch trends closely over the next
24 hrs tho given the degree of disagreement. A stronger/closed low
would push rain chances farther north into the County Warning Area.
Once this system clears late Friday another cold front will push
through the County Warning Area Saturday. This front will be dry and the only
sensible weather effects will be increased cloud cover during its
passage. Temps Sat should reach into the 60s most areas with a shot
of slightly cooler air for Sunday /mid 50s north to mid 60s central/.
Post-frontal high pressure at the sfc will dominate Sunday through
Monday and keep things dry and pleasant...though the mid and upper
levels will become highly amplified again as a strong cyclone pushes
into the Pacific northwest and induces downstream ridging across the
With the upper pattern becoming more meridional...sfc high pressure
will move offshore by Tuesday. This will help advect moisture from
the Atlantic as flow begins to take on a more southerly component in
the lower levels. Weak upper ridging should be enough to shunt any
precip activity on Tuesday. By late Tuesday operational ec and GFS
diverge significantly but will trend toward the GFS for now given
its better resemblance to gefs and eps ensemble data. This would
argue for another fropa by mid week...although elongated nature
of the front as the parent cyclone remains across Canada points
towards a potentially dry passage. Have kept slight chance pops
across the north for now to compromise somewhat given this is 7
potential for MVFR-low VFR ceilings to develop this morning and
likely to affect central Georgia the most. Best rain chances east and S
of mcn. Light northwest-NE winds becoming east-northeast 10 kts or less.
//Atl confidence...06z update...
low confidence for lower ceilings.
Medium to high confidence for all other elements.
Preliminary point temps/pops...
Athens 67 41 56 38 / 0 0 0 0
Atlanta 61 42 58 42 / 0 0 0 0
Blairsville 59 32 56 32 / 5 0 0 0
Cartersville 59 36 58 36 / 0 0 0 0
Columbus 68 46 62 44 / 5 5 5 0
Gainesville 64 40 56 38 / 5 0 0 0
Macon 70 47 58 42 / 5 10 10 5
Rome 59 34 58 34 / 0 0 0 0
Peachtree City 64 40 59 38 / 0 5 5 0
Vidalia 70 50 59 46 / 5 20 20 30