Tuesday's massive Category 5 avalanche outside Aspen, which cut all the way down to the rock, is known as a deep-slab avalanche and is one of two types that forecasters have been watching recently.

Deep slab avalanches typically set up on north-facing slopes, where the late-afternoon sun doesn't shine. Over the course of the winter, wind hardens various layers of snow, "kind of like an Oreo cookie," said John Snook, a forecaster with the Colorado Avalanche Information Center.

Lately, he said, deep-slab conditions have developed across Colorado's mountains. "They're pretty isolated, but those slides are large," Snook added.

Avalanches tend to happen late in the day. "The key is to get out of the backcountry after noon," said Jeff Lumsden, Pitkin County Sheriff's spokesman.

The other kind of avalanche Colorado is seeing is a "wet avalanche," which happens on south-facing slopes in the springtime.

Five people have died in Colorado avalanches this season, compared with four last winter, according to the center. The average is six per year.

The other avalanche deaths this season were a skier outside Snowmass on Dec. 21, a snowmobiler in southwestern Colorado's San Juan Mountains on Feb. 4 and a snowshoer south of Idaho Springs on March 3.

A large avalanche shoved two cars off U.S. 40 at Berthoud Pass on Jan. 6, but no one died.