Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Peachtree City Georgia
638 am EST Friday Dec 13 2013
Previous discussion... /issued 321 am EST Friday Dec 13 2013/
Short term /today through Saturday/...
high pressure is centered across eastern Tennessee early this morning. Some
wispy cirrus is overhead portions of northern Georgia...but most of the
County warning forecast area is clear. Temperatures are between 5 and 10 degrees cooler than
this time last night.
High pressure will shift offshore early today...with surface winds
turning more NE/E. With the flow off of the western Atlantic...low
level moisture will begin to increase ahead of an approaching cold
The front is expected to move through the County warning forecast area on
Saturday...accompanied by widespread rains. For today and most of
tonight...the forecast will remain dry. Models have slowed down the
precipitation a bit. The GFS remains slightly faster than the NAM...but
both models concur that precipitation will begin approaching the northwest zones
after 06z Sat. The 00z run of the European model (ecmwf) is also in agreement on the
timing of precipitation.
The European model (ecmwf)...GFS and NAM all have a wave of low pressure developing
across the SW portion of the County warning forecast area and moving NE along the boundary
Saturday afternoon. South of the low center...thunderstorms will be
possible...while north of the boundary...precipitation is expected to be
more stratiform in nature. With high dewpoints and the possibility
of some heating south of the front...a few of the storms could
become strong to severe. Even though the instability will be
marginal...shear is expected to increase just along and ahead of the
front during the afternoon. However...any severe weather should be
isolated in nature as the chance of thunderstorms remains low.
Probability of precipitation will decrease on the northern side of the front. However...will
leave chance probability of precipitation behind the boundary as the middle level trough may
provide a mechanism for additional precipitation.
Long term /Saturday night through Thursday/...
a cold front will exit the area Saturday night with the main upper
trough over the middle U.S. The bulk of the deep moisture will have
shifted to central Georgia where the highest probability of precipitation will be. The GFS/NAM are
more aggressive moving the deep moisture east than the European.
Only precipitation chances to start Sunday will be over the far southeast. Upper
trough approaches the area with some moisture that could spit some
light precipitation over the far north counties but chances too low to include
in the forecast.
For Monday into Thursday...airmass and upper flow too dry for any
precipitation concerns even though there will be a couple of short waves in
the upper flow during the period.
Next system moves across the middle U.S. On Friday and more significant
moisture increases over the area then.
Temperatures will be transitioning to below normal starting Sunday
then back toward normal late in the week.
wind shift to the east/NE has already occurred this morning. Winds
will stay out of the east through the taf period. No ceiling/visibility
restrictions anticipated through this evening. Ceilings will begin to
lower to MVFR values between 08z and 10z Sat...then to IFR as
widespread rains move in after 12z. MVFR visibilities also anticipated
with the rain. Thunder should stay well south of atl.
//Atl confidence...12z update...
high confidence all elements through 12z Sat. High confidence
remaining elements through the period...except ceilings/visibilities medium
confidence after 12z Sat.
Preliminary point temps/pops...
Athens 53 40 50 42 / 0 30 100 30
Atlanta 53 43 55 43 / 0 40 100 30
Blairsville 48 35 45 36 / 0 70 100 30
Cartersville 52 41 54 41 / 0 60 100 30
Columbus 56 47 62 49 / 0 30 100 30
Gainesville 50 40 46 40 / 0 50 100 30
Macon 56 45 62 50 / 0 20 100 40
Rome 51 39 53 40 / 0 70 100 30
Peachtree City 53 41 58 43 / 0 40 100 30
Vidalia 58 48 66 55 / 0 10 100 90