Southeast Coastal Ocean Report 6 Figure 1.5. Mean annual flash (lightning) density from 1989- 1998 (http://www.srh.noaa.gov/mlb/ltgcenter/images/slide5.gif). Figure 1.6.  Number of days with thunderstorms.  In central Florida this is due to sea breeze interactions with warm, moist air, while along the eastern Gulf Coast this is due to warm, moist air from the adjacent Gulf of Mexico (http://www.iupui.edu/~geogdept/g112/clim_forecast.ppt). Other Severe Weather: lightning and thunderstorms   The highest frequency of cloud-to-ground lightning in the U.S. mainland occurs in the southeastern region between Orlando and Tampa, Florida (Figures 1.5 and 1.6).  This phenomenon is due to the presence of large moisture content in the atmosphere at low levels as well as high surface temperatures that produce strong sea breezes along the coast.  High lightning frequencies also occur along the Atlantic coast in the southeast and along the Gulf of Mexico coast westward to Texas.    Atmospheric instability and moisture work together to drive convective storms that can produce lightning. While the exact mechanisms are unknown, clouds become electrified when raindrops are carried upward until some of them convert to ice (around 15,000 to 25,000 feet above sea level). Interactions between ice crystals and supercooled water droplets produce electrical charges. In a cloud-to-ground strike, the charge builds up and then moves downward through the atmosphere in steps until it encounters something on the ground that is a good conductor, completing the cloud-to- ground circuit (http://www.nssl.noaa.gov/edu/ltg/).