Courtesy Westwide Avalanche Network.

Let's start with the basics: To have an avalanche, you need snow and you need slopes -- generally between 30 degrees and 45 degrees. (You can buy an inclinometer to tell you the exact slope.)

Duh. Like, what else?

Suddenly, we go from the obvious to the sublime -- the judgment realm. Here are some signs of avalanche, in no particular order.

Recent avalanches in the area.

Avalanche tracks -- chutes where sliding snow has removed the trees.

Warnings from avalanche centers

A whoomping! sound from the snow, indicating a small- - or large -- failure.

But it's not just nincompoops who die under the snow. Alex Lowe, a mountaineer who was called the best in the world, was killed in 1999 in a giant avalanche in Tibet, where he was planning to ski down Shisha Pangma, an 8,000 meter peak!

Finally, a note for snowmobilers: It's dangerous up there! In the past few years, the machines have been getting faster, leading to a competition called "highmarking," where the winner reaches the highest point on a snowfield.

Through such progress, getting avalanched on a noisy sled has joined falling through the ice as a deadly hazard of the gasoline-powered sport: Forty percent of 1998-'99 avalanche deaths in the United States were snowmo riders. Snow physicist Colbeck says word is gradually getting out to snowmobile riders: "When enough of your friends die, you learn that it's not much fun."