National Weather Service United States Department of Commerce

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Some of the storm data is less affected by bias. For example, developing distributions of monthly and hourly frequencies is possible, since biases are distributed more or less equally across the data.

3. General Thunderstorm Climatology

Before presenting data on storms classified as "severe", it is appropriate to briefly discuss general thunderstorm climatology. Thunderstorms in Georgia are common, especially during Spring and Summer. The number of thunderstorm days per year ranges from around 50 in the mountains of northeast Georgia to around 55 across the southern extremity of Peachtree City's CWA (Local Climatological Data). A "thunderstorm day" is defined as a day during which thunder is audible from an official observing site.

Number of thunderstorm days
ATL 1.1 1.9 3.6 4.2 6.0 8.6 10.3 8.0 3.1 1.0 1.0 0.7
AHN 1.1 1.3 3.2 4.0 6.1 8.8 11.7 8.4 3.4 1.0 1.1 0.6
MCN 1.1 1.9 3.3 4.0 6.3 8.8 13.3 9.6 3.4 0.8 1.1 0.9

The table above exhibits the monthly distribution of thunderstorm days at a few key locations. Note that the only significant difference in thunderstorm frequency among the chosen sites is during the months of July and August when thunderstorms are more frequent at Macon (MCN), which represents the southern part of the CWA, than at Atlanta (ATL) or Athens (AHN) farther north. Note also that thunderstorms are more common in July than in any other month of the year. During December thunderstorms are at a minimum.

4. Severe Thunderstorm Climatology

a. Tornadoes

During the 44 year period from 1950 to 1993 the CWA averaged 6 tornado days per year - 2 of which involved tornadoes with an intensity of at least F2. Events involving "killer" tornadoes were infrequent, having occurred on average once every 2 years. In no year did killer tornadoes occur on more than 2 days. The records also show only one year where more than 3 counties reported tornado-related deaths (6 in 1974). Nevertheless, despite the rarity of killer tornadoes a total of 72 people perished, and almost 1700 were injured.

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