Atlanta has a humid subtropical climate with four seasons and a long pollen season — the city consistently tops the American Asthma & Allergy Foundation's lists for spring pollen counts.
The best months are mid-April through mid-May and September through early November: daytime temperatures in the high teens to mid-20s C and the dogwoods and azaleas at full bloom (spring) or the trees turning (autumn). July and August are hot, humid, and frequently broken by afternoon thunderstorms — uncomfortable but not impossible.
Winter is mild by American standards (daytime highs around 11°C) with occasional ice storms; snow is rare. The week between Christmas and New Year is a quiet, pleasant time to visit if you do not mind closed restaurants.
The Atlanta Dogwood Festival runs in mid-April, Music Midtown in mid-September, and the National Black Arts Festival in summer.