In winter, temperatures can often drop below freezing. Bring extra warm clothing. 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. 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 dark and threatening when viewed from below, but very bright and white when seen from the side at some distance. Protect Your Life Keep an eye and ear to the sky. Be alert for thunder or lightning in your vicinity and over nearby hills.