Melting snowpack raises avalanche fears in Colorado

DENVER (Reuters) - A rapid thaw of Colorado's record winter snowpack has the potential to trigger destructive avalanches and debris flows on a scale not seen in decades, state forecasters warned on Friday.

Ethan Greene, director of the Colorado Avalanche Center, said unusually deep snowfall in the northern and central Rockies combined with unseasonably high temperatures forecast over the next several days could set dangerous snowslides in motion.

"The right conditions during May and early June could produce avalanches larger than we have seen in 30 to 100 years," Greene said.

Snowpacks statewide are running at 160 percent of average, with some basins reporting twice the normal levels, he said.

Last week, an avalanche destroyed century-old trees and an electric transmission tower built in the 1970s in the Peru Creek basin near Montezuma, Colorado.

Lisa Kriederman, a meteorologist with the National Weather Service in Boulder, Colorado, said the pattern of heavy winter snows, followed by rapid runoff in early spring is typical of La Nina conditions currently in effect.

In La Nina years, cooler surface temperatures in the equatorial Pacific Ocean alter the jet stream to produce more moisture in the Rocky Mountains west of the Continental Divide, she said.

Down-sloping winds wring moisture from the air west of the divide as weather fronts pass over the mountains, leaving the prairies of eastern Colorado with drier-than-normal conditions.

Ranchers in four southeastern Colorado counties already are eligible for federal assistance for grazing losses due to drought, according to the U.S. Department of Agriculture.

(Editing by Greg McCune)