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Extreme storms 30 percent more common now than in 1948

(CBS News) A new report says it's raining more than ever over the United States, which paradoxically means there is also more dry weather that can lead to droughts.

Environment America, a national environmental advocacy group, released its report "When it Rains, it Pours: Global Warming and the Increase in Extreme Precipitation from 1948 to 2011" on Tuesday, which claims extreme rain and snowstorms are becoming more frequent. Collecting data from nearly 65 years of weather history, the report sees a 30 percent increase in the frequency of extreme storms.

"In other words," the report says, "heavy downpours or snowstorms that happened once every 12 months on average in1948 now happen every 9 months, on average."

"As the old saying goes, when it rains, it pours - especially in recent years as bigger storms have hit us more often," says Nathan Willcox, Federal Global Warming Program Director with Environment America.

Speaking with CBS News, Willcox explained the method of collating 65 years of nationwide weather history. The organization collected data from "3,700 weather stations across the country via the National Climatic Data Center."

Not only are big storms getting more common, they're also getting bigger. The report found that the largest annual storms produce 10 percent more precipitation on average than they did 65 years ago.

The report points to global climate change as the obvious culprit for the increased ferocity of storms. Warm weather allows the air to hold more water, as well as increasing evaporation, leading to larger precipitation.

A surprising counterpoint to larger storms is larger periods of dry weather.

"By increasing rates of evaporation from the land, warmer weather is making soils dry faster," Willcox told CBS News.

Greater evaporation means there could be longer periods of dry weather between heavy rainfall. 

U.S. Senator Dick Durbin of Illinois put out a news release along with Environment America's report.

"Illinois has seen it all in the last year - extreme flooding that forced residents of Cairo to evacuate, a severe blizzard in Chicago that shut down Lake Shore Drive and one of the worst droughts on record affecting the entire state," said Senator Durbin. "We are ignoring the obvious - our extreme weather events are getting worse, catastrophic in fact, and the federal government is unprepared. We need to begin to address the reality that there will be more extreme weather events and ensure that we are taking the necessary steps to protect our communities."

Looking on a state-by-state basis, the report found that extreme rainfall increased in 49 states since 1948. Only Oregon experienced fewer heavy rain and snowstorms. By region, New England and the Mid-Atlantic saw the largest increase in extreme storms. New England saw an 85 percent increase compared to rates in 1948. As the report restates, that means heavy rain or snowfall that hit New England every 12 months in 1948 now occurs every six and a half months on average.

Environment America is a national organization, based in Washington, D.C., that is made up of 29 state environmental advocacy groups.