Hobbies And Interests
Snow and Early Spring
An especially heavy accumulation of snow over winter may threaten slow flooding over the length of a river or flash flooding when the melt is triggered by an unusual spell of warm weather or heavy rains. Such rains can also produce flash floods when the snow pack hasn't yet melted or the ground is frozen or saturated with snow melt. Flash flooding is usually more localized than a flood that can be watched and predicted, as the fast-accumulating water overwhelms small streams and pours into nearby roads. Flash floods in 2010 were responsible for almost twice as many deaths in the U.S. as the slower river floods.
Spring Melt
Lakes and deep rivers may not freeze solid, and their ice coating can break into floes before it melts entirely. These floes can jam up at outlet streams or narrower parts of a river and mix with downed trees and other debris to severely reduce the flow of water. When the weight of the water building up grows large enough and the jam gives way, a wall of water can rush downstream, carrying debris that multiplies its destructive force.
Summer Storms
The American Red Cross advises that slow-moving thunderstorms, such as those that form out of summer-afternoon humidity, are one of the most frequent causes of flash floods. Repeated heavy storms throughout an afternoon, especially when it has rained several days in a row and the ground is saturated with water, can also drop enough water to suddenly flood a stream or a road. Fatalities from all kinds of floods peak in July.
Storm in the Desert
Flash floods kill more people but cause less damage than river floods because they're so unexpected. Nowhere are they less expected than in arid places that see rain only a few times a year. Any gully or wash, and especially a deep, rocky canyon, channels the water and can create a flash flood from even a moderate rain. Rain from miles away can also rush through a canyon with deadly force.