Warm weather not sign of easy winter

Despite a warmer-than-normal November and scarcity of snow, don't expect anything less than an average Sierra Nevada winter, say California and Nevada weather officials.

"I think the winter will be fairly normal, in my opinion," said Bill Mork, California state climatologist. "But really no one can know for sure."

As far as snowfall is concerned, the month of November may not end up that far from normal once a storm system expected to hit Monday night and today makes its way through the Tahoe area.

"It looks like we're on a fairly normal storm track - and not too far from normal in the northern Sierra," Mork said. "We've got two good storm systems moving in right now."

Kelly Redmond, regional climatologist for the Desert Research Institute in Nevada, said weather patterns so far haven't given any good indicators about what the winter will be like.

"In general, I think it's as close to a coin toss as it can be," he said. "There isn't much of a signal we've been able to look at. There isn't a strong signal either way."

Despite that, however, both Mork and Redmond said there are a variety of factors that can be taken into consideration.

n La Nina.

Like last year, this is a La Nina year.

Typically during a La Nina winter, Southern California is drier than normal and the Pacific Northwest including Oregon and Washington, are wetter than normal. U.S. Highway 80 is about where the dividing line is, and therefore the Lake Tahoe region can go either way.

Last year that was the trend, and Tahoe received above-average snow. However, some La Nina winters are extremely dry. The winter of 1975 to 1976, a La Nina winter, was one of the driest of the century.

Las Ninas also increase the likelihood of sporadic heavy precipitation events. While a normal winter may have regular snow but no several-day dumps, La Nina may bring dry periods with occasional six- to 10-day strong storms.

"Let's say in a normal year in the northern Sierra, there's a 20 percent chance of having a really wet precipitation event that will last six to 10 days," Mork said. "That goes to 30 percent now. It rises slightly in a La Nina year."

n Six wet winters?

The northern Sierra has had five consecutive wet winters, a string unprecedented this century, according to climatologists. A string of six wet winters hasn't happened since the early 1800s and likely has happened only about three times since the 1500s, Redmond said.

Snowboarders and skiers shouldn't panic yet, however.

"Some people are thinking that the odds of getting another wet winter are not likely because we've had five in a row. I would say there is just as much likelihood to get the sixth wet winter than to not get it," Redmond said.

n Other factors.

During the past five years, there have been a La Nina year and an El Nino year, both bringing above-average snowpack to the region. However, during the drought period earlier in the 1990s - one of the driest periods ever, Redmond said - there were also both La Nina and El Nino years.

Additionally, an unusual trend so far this season is that temperatures are higher than normal, which Redmond said could mean more rainfall this season than in winters past.

"A sort of an unusual thing going on is it's awfully warm this year - not just in Nevada, all over the West," Redmond said.