Snowpack List: Avalanche assessments from around the U.S.: Week of December 11

Deep slab avalanches are occurring across the western U.S., so exercise caution when traveling out of bounds. To stay safe, don’t leave without the proper avalanche safety gear and up-to-date information from your local avalanche center about the day’s conditions.

Crested Butte Avalanche Center (CBAC)/Colorado Avalanche Information Center (CAIC)

In the Front Range of Colorado, the CAIC cautions skiers and riders to be aware of a weak layer near the ground that, when combined with formation slab layers above, is proving to be reactive.

“Over the last five days, we know of six people who triggered and were caught in avalanches in the Front Range Zone,” they explain on their website. “Observers have reported some very large and destructive natural avalanches. Avalanche activity is decreasing, but careful snowpack evaluation is mandatory before you travel in or below avalanche terrain today.”

The avalanche danger is rated as considerable near and above treeline and moderate below for this region.

In the Vail and Summit County region, there is considerable danger near treeline with moderate above and below. This is a result of hard slab layers left by wind near treeline. The CAIC recommends staying away from any wind-affected slopes in the area at this time, as avalanches could be triggered in a wind-affected slope above a skier or rider and then step down to buried weak layers.

In other areas of Colorado, similar problems in the snowpack exist, but to a lesser degree. Slabs formed by wind-drifted snow are leading to instabilities primarily near and above treeline, and the avalanche danger rating for those zones remains moderate for Wednesday, December 14.

The Crested Butte Avalanche Center reiterates the information presented by the CAIC.

“Monday’s snowmobile burial in Washington Gulch and a handful of avalanche results by CB Ski Patrol over the weekend exemplify the kind of avalanche that is possible to trigger today,” CBAC explains on their website. “You are most likely to release a dangerous persistent slab avalanche on a windloaded slope near and above treeline, where last weekend’s storm and subsequent winds have added stress to weak layers in the middle and bottom of the snowpack. You can trigger a persistent slab avalanche from beneath the slope, or it could propagate unusually wide distances, two reasons to give suspect terrain an extra wide berth in your travels. On isolated slopes below treeline, you may encounter a smaller, more manageable version of the problem. Use caution in extreme or high consequence terrain at these lower elevations.”

To find out more about Colorado avalanche conditions, visit avalanche.state.co.us, and cbavalanchecenter.org. 

Northwest Avalanche Center

A recent storm bringing two-to-four feet of snow came through the regions under the purview of the NWAC, and buried a suncrust layer and surface facets that had previously formed. A natural avalanche cycle occurred over the past few days and has begun to settle out, but avalanche danger ratings remain at moderate for all zones below, near and above treeline.

“Overall, the avalanche danger will be less on Wednesday than the past few days,” says the NWAC, “but small areas of new wind slab might be possible depending on the strength of the east to southeast winds.”

To find out more about conditions in the Pacific Northwest, visit www.nwac.us.

Utah Avalanche Center

The primary concern for regions under the purview of the UAC today are wind-drifted slopes facing north, above treeline. Northeasterly aspects are of the utmost concern and are rated as moderate with small pockets of considerable, and pockets of low avy danger around and below treeline.

But the UAC cautions, “Destructive deep slab avalanches failing near the ground are possible on some steep upper elevation north facing slopes. The snow is becoming more stable after last weekend’s storm, but you still might trigger persistent slab avalanches in steep terrain.”

To find out more about conditions in Utah, visit utahavalanchecenter.org.

Gallatin National Forest Avalanche Center

Across the region covered by the GNFAC, facets on dirt or on an ice crust near the ground are causing the primary instabilities in the snowpack. While the weight of the snowpack is supported, and natural avalanches are not being seen, human triggered avalanches are likely, and the avalanche danger is set at considerable throughout the GNFAC area. There has not been a lot of new snow in the last few days, but with a storm in the forecast, the danger rating could change.

The GNFAC warns, “Before you enter avalanche terrain, put your shovel in the snow to see if the slab is undermined by these weak facets. If so, stay away from steep slopes.”

With a recent death in the Cooke City area, forecasters want to make sure travelers in the backcountry understand the gravity of the instabilities in the snowpack. The staff of the GNFAC have put together a video explaining the dangers that can be viewed below.

To find out more about conditions in Montana, visit www.mtavalanche.com.

Bridger Teton National Forest Avalanche Center

South of Montana, a similar weak layer toward the bottom of the snowpack is creating dangerous instabilities. Deep slabs sit on top of a rain crust in addition to a persistent weak layer. The BTAC cautions that these slides could be very big and a skier/rider is unlikely to survive once triggered. The avy danger rating across the region is listed as considerable.

“These dangerous slides could be triggered by the weight of a single person even after an avalanche starting zone or slide path has been crossed multiple times by others,” the BTAC warns on their website. “Surface slabs also present a hazard at the mid and upper elevations. Conservative terrain choices are essential for safe travel in avalanche terrain today.”

To find out more about conditions in Wyoming, visit www.jhavalanche.org.

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As the winter progresses, it is important to keep an eye on snowpack trends and instabilities. This is not a complete guide to avalanche forecasts, so stay informed and educated by visiting local avalanche forecasting websites and get educated about avalanche safety through programs like Know Before You Go, the Mountain Academy hosted by Solomon and Atomic and through courses offered by the American Institute for Avalanche Research and Education (AIARE) offered nationwide.