Lightning Ground Flash Density and Thunderstorm Duration in the Continental United States: 1989–96

Abstract

The mean annual flash density, thunderstorm duration, and flash rates were calculated using 121.7 million cloud-to-ground lightning flashes in the continental 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 Appalachian 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 Coast. The maximum annual flash rates exceeded 45 flashes h?1 in the Midwest, along the Florida coasts, and along the mid-Atlantic coast with the minimum 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, with the greatest errors, over 80%, in the intermountain region of the Rockies.