Lightning ground flash density and thunderstorm duration in the continental United States: 1989-96

The mean annual flash density, thunderstorm duration, and flash rates were calculated using 121.7 million cloud-to-ground lightning flashes in the con tinental United States for the period 1989-96. Florida had flash densities over 11 flashes km(-2) yr(-1), while the Midwest, Oklahoma, Texas, and the Gulf Coast had densities greater than 7 flashes km(-2) yr(-1). There was a relative minimum in flash density (three flashes km(-2) yr(-1)) in the Appa lachian Mountains and Missouri. Thunderstorm duration values exceeded 120 h yr(-1) in Florida and 105 h yr(-1) in New Mexico, Arizona, and the Gulf Co ast. The maximum annual flash rates exceeded 45 flashes h(-1) in the Midwes t, along the Florida coasts, and along the mid-Atlantic coast with the mini mum flash rates, 15 flashes h(-1), over the Appalachian and Rocky Mountains . The relationship between thunderstorm duration and flash density is Flash (-)Density = 0.024(Flash(-)Hours)(1.29) producing expected flash densities that are within 30% of the measured densities for over 70% of the nation, w ith the greatest errors, over 80%, in the intermountain region of the Rocki es.