Lightning Climatology

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Where does lightning usually strike?

Lightning strikes the ground somewhere in the U.S. nearly every day of the year. Thunderstorms and lightning occur most commonly in moist warm climates. Data from the National Lightning Detection Network shows that over the continental U.S. an average of 20,000,000 cloud-to-ground flashes occur every year. Around the world, lightning strikes the ground about 100 times each second, or 8 million times a day. Ground-based systems don't tell us anything about lightning over the oceans, although a few science satellites have lightning detectors on them now. There are roughly 5 to 10 times as many cloud flashes as there are to cloud-to-ground flashes, so the total amount of lightning is quite a bit higher.

These conditions most often occur in summer. In general, the US mainland has a decreasing amount of lightning toward the northwest. Over the entire year, the highest frequency of cloud-to-ground lightning is in Florida between Tampa and Orlando. This is due to the presence, on many days during the year, of a large moisture content in the atmosphere at low levels (below 5,000 feet), as well as high surface temperatures that produce strong sea breezes along the Florida coasts. The western mountains of the US also produce strong upward motions and contribute to frequent cloud-to-ground lightning. There are also high frequencies along the Gulf of Mexico coast westward to Texas, the Atlantic coast in the southeast US, and inland from the Gulf. Regions along the Pacific west coast have the least cloud-to-ground lightning.

How often do positive cloud-to-ground strikes occur?

Worldwide, over an entire year, positive lightning strikes average 4-5%. Most storms start with mainly negative flashes, then have a higher ration of positives toward the end of their life cycle. In tornadoes and supercells, large numbers of positive flashes are common, and they appear to signal severe events. Positive ground flashes are often associated with the production of large hail.

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