La Niña could give Colorado wet winter

Forecaster 'optimistic' for good snowpack in mountains

Colleen Slevin | The Associated Press

11/19/2008 -

DENVER — Colorado's northern and central mountains could get normal or above-normal snowfall this winter, a federal climatologist says.

Colorado is headed toward a La Niña winter, which tilts the odds toward more snow. The downside is La Niñas — long-term wind patterns tied to cooler Pacific Ocean temperatures — also can bring a dry fall and spring, said Klaus Wolter, a climatologist at the National Oceanic and Atmospheric Administration in Boulder.

Wolter said Wednesday he was "guardedly optimistic" the winter will deliver enough snow to make up for a dry fall and produce a "near-normal" snowpack. But he also said it's too early to tell if the La Niña pattern will continue into spring.

Colorado's overall snowpack dropped to 49 percent of average on Wednesday after being in the 60-percent range last week.

Since snowfall amounts are relatively small so early into the season, one or two storms in coming weeks could boost those percentages, said Mike Gillespie, snow surveyor supervisor for the federal Natural Resources Conservation Service.

This November hasn't been as dry as last November, when some ski resorts delayed their openings until after Thanksgiving.

Snowpack in the North and South Platte basins, which provide much of the water to the populous Front Range, is at 65 percent and 64 percent of average, respectively. On Nov. 19, 2007, those percentages were 52 and 44 percent.

The Colorado River basin snowpack is at 60 percent, compared with 46 percent a year ago, Gillespie said.

"We're well ahead of last year, but last year was one incredibly dry start to winter," he said.

Last year, the storms started rolling in December, and Wolter predicted at the time they wouldn't continue.

Luckily for Colorado, he was wrong. Although he had predicted a La Niña effect, he also took other factors into account that led him to predict dry weather the second half of winter. On top of that, Wolter he said, most storms on the La Niña track hit Colorado.

This year, his forecast is more streamlined, based mainly on typical La Niña conditions. Wolter doesn't think the state can count on the odds of being hit by so many storms again.

La Niña is the opposite of El Niño, which is caused by warm waters in the tropical Pacific.

La Niña winters tend to be colder and stormier across the northern United States. Wolter said the Southwest, including southern Colorado, usually gets less snowfall than northern Colorado.

There's no scientific consensus that La Niña conditions exist this year, and Wolter acknowledges that water temperatures haven't dropped enough by NOAA guidelines. But his model takes into account trade winds and the movement of tropical thunderstorms, and he said his findings show that there is a weak to moderate La Niña taking shape.

La Niña winters can also bring frigid temperatures from Alaska or Canada, but that is tough to predict, Wolter said.