Signs of warm weather are usually welcomed with enthusiasm--that is, except, when spring begins with immense flooding. After record snowfall in some areas, North Dakota experienced an early thaw, followed by a blizzard on April 5. The precipitation runoff was more than the Red River valley could handle. At its crest of 54.2 feet, the river was 26 feet above flood stage in the Grand Forks area, forcing the evacuation of the city's 50,000 residents. For what is being called a 500-year flood, damage and cleanup estimates range from $700 million to $1 billion.
Flooding can be as damaging as a drought is devastating. Fortunately, neither is the norm, and recorded precipitation averages are good indicators of what precipitation we can expect in a region on a yearly basis (see "Precipitation in U.S. cities," at left). Mt. Washington, N.H., has the highest average precipitation with 89.92 inches annually over approximately 209 days. On the flip side, Las Vegas averages only 4.19 inches in 26 days annually.
Temperature is a major influence in determining precipitation. Warm air rises, then cools. The condensation of atmospheric vapors form low-altitude clouds, called stratus or stratocumulus clouds, and rainfall. Precipitation usually occurs along the fronts. Generally, a warm front produces precipitation that is prolonged with moderate intensity, whereas a cold front typically produces a heavier and short-lived rainfall.
According to the National Climatic Data Center, the summer of 1996 ranked as the 34th warmest of the nation's 102 years of record. The temperature topped out at 0.6oF above the normal 72.3oF. Due to heavy precipitation in the Northeastern and South-Central states, the lower 48 states experienced an average precipitation total of 8.5 inches during the summer months, or 103 percent of normal. Washington, Oregon and Idaho averaged 64 percent of their normal precipitation, and California and Nevada reached just 40 percent of their normal average precipitation.
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