LAKE TAHOE – Finally, snow.

After weeks of waiting, mountain residents awoke to their first glimpse of winter on Dec. 13, a few fluffy inches of powder that clung to the tops of boulders like chefs' hats.

More fell over the past two weeks, enough to bury the camel-colored meadow grass and wine-red willows in a deepening blanket of white. The magic, though, came late, just days before Christmas – one of the tardiest winter debuts ever.

How much more snow will fall is anyone's guess. A winter storm just hit Thursday, dumping several feet of snow, to the relief of snow-starved resorts. But in the late arrival of this year's snow season – and increasingly early spring snowmelt from the mountains – scientists and state officials are finding more than the signature of a natural drought. They believe they detect the fingerprint of climate change.

The implications could be enormous. After all, the snowcapped Sierra is more than a skier's paradise. It is a giant water faucet in the sky, a 400-mile-long, 60-mile-wide reservoir held in cold storage that supplies California with more than 60 percent of its water, much of it when it's needed most: over the hot, dry summer months.

Not only are warmer temperatures thawing that mountain snow sooner, they are changing the nature of the precipitation as it falls – turning more Sierra snowflakes to sleet, slush and rain. Now 10 percent smaller than a century ago, the Sierra snowpack is expected to retreat dramatically in coming decades, posing major challenges for water managers and the climate-dependent ski industry.

Ski areas already are feeling the heat. This fall, temperatures were so toasty around Lake Tahoe that many resorts missed planned Thanksgiving weekend openings, despite major investments in energy- intensive snowmaking operations. Alpine Meadows did not open for the season until Dec. 19 – one of its latest starts ever.

"The fact that snow is coming later is clearly having a major economic impact," said Art Chapman, president of JMA Ventures, which owns Alpine Meadows and Homewood ski areas. "I think everybody in the ski industry is very concerned about climate change."

As the peaks warm, some ski areas are moving beyond snow and skiing – and sometimes kicking up controversy as they do, particularly with high-end real estate development ventures.

At Mammoth Mountain, guests no longer simply slide downhill on skis. They ride mountain bikes, golf, fish, even scale an artificial climbing wall.

"We absolutely recognize the problem. Seasons are changing. Shorter winters mean longer summers," said Greg Dallas, a Mammoth vice president, at a recent climate change conference in Bishop.

"Our strategy is to pump more guests through in what we call the mud seasons, the shoulder seasons," he said. "We need to be able to … weatherproof our business."

More moisture a false hope

Unfortunately, weatherproofing is not possible at lower elevations where massive state reservoirs – all fed by snowmelt – have dropped to their lowest levels in more than a decade following two years of drought and the driest spring and summer on record.

"The forecast is that by 2050 we'll have 25 to 40 percent less snowpack than today," said Lester Snow, director of the California Department of Water Resources. "That's like losing 6 million acre-feet, six Folsom Reservoirs – so it's a major amount of storage."

Even more worrisome is that California's dams were built on the belief that climatic conditions of the past 150 years, one of the coolest, wettest periods of the millennium, would portend the future. Scientists now know that's not true – and many say global warming is sure to sharpen the pain of natural drought cycles.

"What we consider to be normal wetness today is a chimera," said Scott Stine, a professor at California State University, East Bay.

Stine's research has shown that two century-plus droughts parched the Sierra in medieval times, allowing forests to grow on what are now the bottoms of mountain lakes.

Call The Bee's Tom Knudson, (530) 582-5336.