December 2007

Despite storm, forecasters worried about dry weather

By Jim Mimiaga

Weather’s capricious nature makes it a challenge to predict accurately, a case in point this month.

Snow finally arrived Dec. 1, after weeks of unseasonably warm, dry days. Long-term forecasts are an inexact science, to be sure, proving perhaps that you really don’t need a weatherman to tell which way the wind blows.

But, anyway, much-needed moisture finally arrived in the Four Corners, making it the proper start of the winter season. For the Montezuma Valley, the southern snow squall dropped more than 1 inch of precipitation in the first eight hours of December, quickly exceeding the month’s total average, reports Jim Andrus, a local observer for the National Weather Service.

The mix of rain and snow brought the year-to-date average to 89 percent, with a whole month to go to reach the average annual 13.21 inches.

Prior to the rain and snow, many people had been enjoying the mild temperatures of this year’s extensive Indian summer. But according to the National Weather Service, such warming trends are a bad sign for winter snowpack levels.

“We’re pessimistic this year, but we would be happy to be wrong,” commented forecaster Joe Ramey.

The NWS Grand Junction office predicts below-average winter snowfall this season for the San Juan Mountains, Southwest Colorado and southeastern Utah.

They blame La Niña, a still-unexplained climate phenomenon that causes significant cooling of the Pacific off the coastline of Peru. Climatologists say that this occasional drop in sea temperature at the equator forces the jet stream to push storms farther north.

“We are heading into a moderate La Niña winter, and that means storms will likely track along the Pacific Northwest and Northern Rockies, leaving the Southwest and Four Corners dry,” Ramey said, adding that the pattern is already happening.

The impacts of La Niña, and her brother El Niño (the opposite effect where the equatorial Pacific warms, causing more snow locally), are seen less in Colorado than in northern and southern regions.

Weaker La Niña patterns don’t affect us much, Ramey explained, but this one looks stronger because the Pacific cooling has been occurring steadily since last spring, and is expected to last into March.

“The Four Corners area has a fairly strong correlation to drier-than-normal conditions under moderate to strong La Niñas like this one.”

Yet Mother Earth doesn’t always comply. In 2001-02, for instance, there was no El Niño or La Niña, yet it was one of the driest years on record, fueling the destructive Missionary Ridge, Hayman and Coal Seam fires in Colorado. Then in 2003-04 there was an El Niño winter (Pacific waters warmed) but instead of a huge winter like the model predicts, the San Juans had below-average snowpack.

“With climate change starting to influence everything, we’re not quite sure what normal means now,” Ramey noted. “There is always the chaotic nature of weather. The probability is that it will be below normal this winter, but it is not guaranteed.”

In arid Colorado, often just one storm can bring precipitation averages back to normal levels, as was the case Dec. 1.

That storm dropped 2 feet at Telluride, 20 inches at Purgatory and 40 inches at Wolf Creek. The sudden accumulation prompted avalanche warnings and control measures.

Durango received 1.95 inches of precipitation and Cortez received 1.1 inches of rain.

The last moderate La Niña winters like the one now happening were in 1998-99 and 1999-2000. Both years had below-average snowfall.

Locally, precipitation averages were down significantly for October and November, which featured a run of 70- degree days, very little rain and one small snowstorm Nov. 23.

Andrus reported that October and November were particularly dry, showing 25 percent and 7 percent of normal respectively. Those warmer-than-normal conditions have forecasters concerned.

“I’ve got strong misgivings this year. It could be as bad as the winter of 2002,” Andrus said.

In addition to hurting agriculture and causing wildfires, La Niña conditions can hit wildlife hard as well. Bears are expected to suffer higher cub mortality this year from lack of sufficient food resources prior to hibernation, said Andy Holland, a wildlife biologist with the Division of Wildlife’s Durango office.

“It’s a tough year for bears,” he said. “They were involved in more road accidents because they had to roam into populated areas searching for food. And we expect the population to take a hit from food failure and lower reproductive rates. But they’re adaptive and will be there when conditions improve.”

Ironically, it was a late spring frost, not drought, that destroyed the berry and acorn crops relied on by bears. But drought conditions deplete vegetation critical for the omnivores’ longterm health.

Even with no snow, bears still hibernate, Holland explained. “Lack of food in the winter months triggers the hibernation, but with so little snow and warmer temperatures they went in later and may wake up and wander in and out of their dens a bit more.”

In the short term, elk and deer benefit from milder winters. This hunting season went especially well for them and harvest numbers were way down.

“They were scattered everywhere this year,” reported David Peterson, a local hunting and wildlife author. “There was no snow up higher to push them to lower feeding grounds.”