What Causes Flash Floods?
When a violent thunderstorm breaks over the mountains and deserts of the southwest, runoff from the torrential rains cascades into the steep canyons in a matter of minutes. Walls of water sometimes 10 to 30 feet high swirl through the canyons and arroyos, picking up mud, boulders, trees and other debris. Plants, animals and sometimes people are caught, swept along and battered in the onrushing torrent of the flash flood. Flash floods can result from thunderstorms centered over mountains many miles away. Flash Flood Seasons Flash floods can occur in the southwestern United States at any time of the year, but the predominant seasons are Summer and early Fall. They can occur as the result of: Isolated thunderstorms — late June to mid-September; Tropical storms or other general storms — mostly August to October. Thunderstorm Identification A thunderstorm cloud, called cumulonimbus, is a large towering cloud, frequently spreading out on top into the shape of an anvil. It usually appears d
