Area forecast discussion...updated 
National Weather Service Peachtree City Georgia 
753 PM EDT Wednesday may 22 2013 




Update... 
quick update to grids. Appears coverage of thunderstorms and rain over eastern Alabama and 
western Georgia lower than model forecasts. Will back off on probability of precipitation. MLCAPE 
pretty Stout with values 1500-2000 j/kg and 0-6km bulk shear 
around 20-30kts. Apparently forcing and localized lift is lacking. 
Will continue to monitor. 


Snelson 


&& 


Previous discussion... /issued 350 PM EDT Wednesday may 22 2013/ 


Short term /tonight through Thursday night/... 
afternoon convection expected to increase in coverage and persist 
into the evening and overnight hours as upper level trough moves 
through the Mississippi Valley. Convection expected to become more 
organized as associated short wave focuses development. Models a 
little inconsistent with the development and/or progression of the 
organized precipitation...but with increasing 
instabilities...diurnal heating...and increasing shear across the 
area...feel there is enough to support good chance to likely 
probability of precipitation...especially across north Georgia. Have continued mention of 
possible severe storms...accompanied with gusty winds and small 
hail...in the grids through 02z tonight across north 
Georgia...generally north of the atl metropolitan area. Have also 
quickly tapered off evening and overnight probability of precipitation into Thursday 
morning...with generally slight chance probability of precipitation across the area through 
the day Thursday as short wave pushes into the Carolinas. 


As previously mentioned...the severe threat is primarily confined to 
north Georgia...though strong storms can be expected across much of 
the County Warning Area. The primary concerns in severe activity will be gusty winds 
to 60 miles per hour or higher...1 inch hail or higher...frequent lightning and 
periods of heavy rainfall. Gusty winds and small hail are also 
possible in the stronger storms. 


Pressure gradient tightens Thursday afternoon and into Friday...with 
winds 10 to 15 miles per hour with gusts near 20 miles per hour...especially across northern 
and eastern Georgia. 


For the temperatures..have generally gone with a guidance blend. 
Temperatures Thursday morning are expected to be in the 60s...and 
depending on the timing of the diminishing convection and clouds out 
of the area...this could impact morning lows by a few degrees. 
Temperatures will be back in the low to middle 80s Thursday afternoon 
before cooling by Friday. 


31 


Long term /Friday through Wednesday/... 
no major changes made to the extended portion of the forecast. A much 
drier airmass moves over the area Friday with dry northwest flow aloft 
and surface high pressure building over the Ohio/Tennessee valleys during 
the day. Gradient winds will increase getting close to Wind 
Advisory criteria(20 miles per hour sustained) for some areas. Dry conditions 
should continue through the weekend even with slight differences 
between the GFS and European model (ecmwf). The northwest flow aloft north of the area is 
expected to become more active with increased precipitation chances north 
of the state...but it should stay dry across Georgia. Looks like the 
better moisture finally moves in across the area by the beginning 
of next week so will slowly increase chances of probability of precipitation Monday through day 
7. Temperatures generally running within 5 degrees of normal 
through the period except Saturday ND Sunday morning lows are 
running 10-15 degrees below normal. 


01 


&& 


Aviation... 
00z update... 
confidence on widespread thunderstorms and rain dropping over much of the area. Will 
continue tempo thunderstorms and rain but based on trends...may have to pull this 
out later this evening. Any precipitation should end or be east of forecast 
points by 06z. Winds will shift to west after 07z and northwest after 
sunrise. Not much chance for radiational fog unless precipitation becomes 
more widespread. Have backed off on fog for most sites. Could see 
some gusts to 25kts Thursday afternoon with good vertical mixing. 


//Atl confidence...00z update... 
low confidence on likelihood of thunderstorms and rain this evening. 
Low confidence on radiational fog Thursday morning. 
High confidence on all other elements. 


Snelson 


&& 


Preliminary point temps/pops... 
Athens 65 85 59 79 / 60 20 5 0 
Atlanta 66 83 59 76 / 70 10 5 0 
Blairsville 61 78 54 71 / 70 20 10 0 
Cartersville 64 83 57 76 / 70 10 5 0 
Columbus 68 89 63 82 / 70 10 5 0 
Gainesville 64 82 57 75 / 70 10 5 0 
Macon 66 89 60 83 / 60 20 5 0 
Rome 64 84 57 77 / 50 10 5 0 
Peachtree City 64 85 58 77 / 70 10 5 0 
Vidalia 68 89 65 88 / 40 20 5 0 


&& 


Ffc watches/warnings/advisories... 
none. 
&& 


$$ 


Short term...snelson 
long term....Baker 
aviation...snelson