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Area forecast discussion...updated for aviation 
National Weather Service Peachtree City Georgia 
600 PM EDT Friday Jul 18 2008 


Short term /tonight through Sunday night/... 


The main excitement for the short term is the tropical low off the 
Georgia and South Carolina coasts which...if it remains over the 
Gulf Stream long enough...may become a tropical depression 
sometime tonight or early Saturday. However...unless a rain band 
manages to swing around the low...it should not affect our 
forecast area. Instead...we'll see the subsident flow around the 
outer edge of the system if it actually does develop into a 
depression (already seeing some signs of anticyclonic flow 
developing aloft). This may act to clear out some of our haze as 
we'll have a tropical airmass instead of a subtropical one...but 
we'll have to wait and see. 


The only other item of note is a very weak front that will 
approach the area on Sunday. Lots of convective feedback 
associated with the system as it traverses the upper Mississippi 
and Ohio valleys so not sure how strong it'll actually be as it 
reaches our area. The remnants of the tropical low will be 
absorbed by the approaching surface low Sunday into Sunday night 
and with the two combined it may produce some weak showers late in 
the day...especially in the mountains with the addition of 
orographic lift. Not particularly confident in any of this so only 
have probability of precipitation in the mountains at this time. 


Long term /Monday through Friday/... 


Weak...mostly dry...front pushes through the southeast Monday into 
Monday night. Will mostly serve to increase clouds but there may 
be some precipitation associated with it. Very weak flow aloft so not 
particularly impressed with the situation. Upper low develops and 
moves across the Great Lakes during the week...but extended 
models...as usual...disagree with this solution. GFS ends up with 
a strong positive tilt while the European model (ecmwf) has a weak negative tilt. In 
any case...a front should push into the Ohio and Tennessee valleys 
at some point and with the increased moisture we should have an 
increased chance of the typical afternoon showers and 
thunderstorms...especially toward the end of the week. 


&& 


Fire weather... 


No critical fire weather conditions are anticipated for the next 
several days...as relative humidities will not drop to critical 
levels between the tropical low off the Georgia coast and a weak 
front that will approach for the beginning of next week. 


&& 


Aviation... 
subsident region in place across forecast area this afternoon in 
association with surface high and proximity of low along the coast is 
keeping dry air in place and suppressing cumulus field for all taf sites 
except mcn. Dewpoints should recover slightly overnight and areas 
that typically see patchy radiational fog will likely see that 
occur tonight. May see MVFR visibilities at typical sites...with a few 
localized areas possibly going into IFR range between 06-13z. Wind 
shift should occur sometime tomorrow as coastal low lifts 
northeastward...however it appears that wind shift from easterly to 
westerly component at taf sites may hold off until Saturday 
afternoon. Cumulus field may be denser tomorrow as less subsidence will 
be in place...no middle/high level moisture to speak of during this forecast 
period. 


Msr 


&& 


Preliminary point temps/pops... 
Athens 68 94 69 95 71 / 5 10 5 10 10 
Atlanta 72 92 71 93 73 / 5 10 5 10 10 
Blairsville 61 88 63 86 65 / 5 10 5 20 10 
Cartersville 63 94 63 92 67 / 5 10 5 10 10 
Columbus 71 95 72 96 76 / 5 10 5 10 10 
Gainesville 69 92 69 92 71 / 5 10 5 10 10 
Macon 69 96 70 98 73 / 5 10 5 10 10 
Rome 65 94 66 92 68 / 5 10 5 10 10 
Peachtree City 63 93 62 93 66 / 5 10 5 10 10 
Vidalia 70 96 70 96 73 / 20 10 5 10 10 


&& 


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


$$ 


Tdp/22