Last Sunday, 38-year old pro skier Jamie Pierre died in Utah’s Little Cottonwood Canyon. He was skiing inbounds at Snowbird, a resort in the Wasatch Range which hasn't opened or begun avalanche control work. While his partner watched, Pierre dropped into a shady, northwest-facing 40-degree slope. The snow immediately cracked through to the ground, releasing an avalanche with a 150-foot-wide crown. It barreled Pierre 800 vertical feet down through a landscape of trees and small cliffs, according to the UAC incident report.

Area avalanche bulletins for the day rated the risk of avalanche activity at considerable to high based on the thin snowpack and base layers of loose, so-called faceted snow and crust. Pierre’s slide started when a slab released on a buried layer of faceted, unstable snow. (When snow first falls, it is usually as classic small, symmetrical snowflakes, but under certain conditions the flakes can grow into weaker, irregularly shaped crystals that don’t bond well.) Many skiers were out touring in the vicinity of Pierre’s accident, and numerous skier-triggered slides were reported.

All the slides ran on the same weak, faceted interfaces near the ground. “Everything at Alta that had a slope angle had a crown,” says Drew Hardesty, a forecaster at the Utah Avalanche Center and one of the investigators of the fatal avalanche.  

The reality that last weekend’s events in the Wasatch made clear is that despite the hype of another La Niña, this season’s snowpack is not shaping up to be the stable, deep powder heaven of the past couple of seasons. Throughout the Intermountain West, states like Montana, Wyoming, and Colorado have seen similar weather patterns as in Utah: early snows followed by cold, clear weather. Observations of the volatility of the weak layers under the snow—such as this one, taken by the American Avalanche Institute off Teton Pass, Wyoming—have many avalanche and backcountry experts worried about skiers with early-season powder fever and the effect on the rest of ski season.

Dangerous, weak, and persistent snow layers near the ground form what is called an upside-down snowpack—a loose configuration of crystals that must support the weight of all successive snowfall. Facets, such as the one that caused Pierre’s fatal slide, form when exposed snow is subjected to the extreme temperature gradient between the warmer earth and colder air for periods of time between storms. This creates an unstable base that may remain under the snow for the rest of the season. The weight of more snow, or a skier, can cause these weak layers to fracture—imagine trying to build a brick house on a base of styrofoam peanuts. Varying temperatures early this season have also led to melt-freeze crusts. Snow from subsequent storms won’t be able to form strong bonds with this slick material.

The winter of 2008–09 was the most recent season with an upside-down snowpack. The early-season layers proved to be incredibly unstable. Even in-bounds avalanche control did not reign in it, resulting in three fatalities inside ski resorts. But the extreme volatility kept many out of the backcountry altogether, and the season's 27 fatalities remained near the U.S. average of 25, according the Colorado Avalanche Information Center.

In general, the past few seasons in the Intermountain West saw a right side-up snowpack, where continuous snowfall didn’t allow for dangerous layers to form. Successive mid- and late-winter storms piled on top of that sturdier base. This season, forecasters have been observing facets and slick crusts near the bottom layers of this season’s snowpack—which isn’t entirely unusual. Some seasons, these heal up with the right temperatures and storm conditions, says Hardesty. But sometimes they persist, creating widespread instabilities through the winter.

In this kind of upside-down situation, “no matter how good the snowpack builds above it, it is still on a poor foundation,” says Don Sharaf, co-owner of the American Avalanche Institute. “It’s too early to write off the winter season, but it merits caution.”