The drought that swept across wide areas of the United States in the past year was historically unusual in its speed, its intensity and its size, climatologists at the National Drought Mitigation Center at the University of Nebraska-Lincoln report.



And, they said, those dry conditions are expected to last at least through winter.

Forecasts show little hope of quick improvement, deepening the negative effects on agriculture, water supplies, food prices and wildlife.



"We usually tell people that drought is a slow-moving natural disaster, but last year was more of a flash drought," said Mark Svoboda, a center climatologist and an author of the weekly U.S. Drought Monitor.

"With the sustained, widespread heat waves during the spring and early summer, coupled with the lack of rains, the impacts came on in a matter of weeks instead of over several months."



The result, according to year-end Drought Monitor data: More than 60 percent of the contiguous 48 states and 50 percent of the entire country was in severe to extreme drought for significant portions of 2012, Svoboda said.

Last year marked the first occurrence in the 13-year history of the monitor that all 50 U.S. states and Puerto Rico experienced drought.

In the past few months, it has receded slightly in the Midwest but remains entrenched in the Great Plains.



'Almost the perfect storm'



While the current drought has been brutal, it has been short from a historical perspective, said Brian Fuchs, also a monitor author and center climatologist.

But unique conditions earlier in the year set the stage for the unusually intense and widespread drought.



"It was almost the perfect storm last year, a mild winter without much precipitation and with early green-up, so plants were using moisture a month or more earlier than usual," Fuchs said.