Colorado Avalanche Bulletins

This bulletin is from the CAIC, which is an agency of the State of Colorado.

Colorado Avalanche Information Center (CAIC) Advisory

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Issued 03/11/2010 7:05 AM by Brad Sawtell

Highlights

Favoring both sides of the 10-Mile Range, between one and six inches of new snow is reported across the zone. Winds have been redistibuting this new snow to East and Southeast aspects. Slabs will be tender today. Avalanches have been stepping down to deeper weak basal facets, growing into larger sized ones.

An avalanche fatality occurred on March 10, 2010 in the backcountry west of Arapahoe Basin Ski Area. A male snowboarder triggered and was caught in an avalanche in Steep Gully #1. The victim died of trauma after being carried into a stand of trees at the terminus of the path.

This is the fourth avalanche fatality in Colorado this season.

For more information:

The avalanche danger has risen.

The avalanche danger in the Vail and Summit County zone has risen to on most aspect above treeline including N-NE-E-SE-SW. New snow and forecast winds will load and cross load most slopes. Pockets of danger can be found on W-NW aspects above treeline and all aspect near treeline. Tender slabs will form in areas where winds speeds slow, depositing more snow. Deep slab instabilities lurk on all aspects and elevations. Be leery on steep, cross-loaded terrain features. Below treeline the danger is .

Snow & Avalanche Discussion

Since the 8th of March, there have been seven skier or snowboard triggered avalanches, including yesterday's tragic fatality. Most of these have occurred in wind loaded pockets, near rock bands, some with widely spaced trees. Additionally, their location is closest to the "near treeline" elevation band. Most have stepped down to the basal facets. Although, most of the recent avalanche activity has occurred near the Eastern side of the zone, South of Loveland Pass, one large skier triggered avalanche and a suspected natural avalanche has occurred fitting the above description in the East Vail backcountry.

The snowpack structure varies quite a bit throughout the zone. But, all of the triggered releases have the same weak layer in common: basal facets. Stability is very misleading these days. We tend to be drawn closer to areas where most snow has blown in, such as steep cross loaded gullies, concavities and lee slopes. Below the recent new snow is a mix of soft slabs, and depending on aspect and in some cases, elevation, the slabs are separated by either more, or less dense slabs, sun affected crusts, thin layers of small faceted grains and even wind crusts. These mid pack layers are sitting above the bigger issue which is the deep slab instability composed of large, weak basal facets. Most locations, these have grown into large depth hoar grains. This problem is real and will continue to be a problem through the winter season.

Continue think about where likely trigger points would be and avoid those areas. Well spaced trees, convex roll-overs, exposed rocks and near rock bands should be treated as suspect areas. We have hit a new level with this current unsettled weather pattern. Due to additional snow, water weight and forecast winds, the avalanche danger has risen.

Also of note there have been moments of increased convection in the atmosphere, which can rapidly increase precipitation rates over a small area. Add a little wind and we have a rapid loading event over a short time period. Available snow and forecast winds could build slabs 2-4 feet deep. The end result is awareness levels should be heightened if you venture into the backcountry.

Weather Discussion

Mountain temperatures were cold last night, and most mountain locations picked up several inches of new snow. Light snowfall will continue through the morning as the closed low moves off to the east. Clearing will begin mid morning in the west, and extend east through the day as a steep upper level ridge moves into the area. Northerly flow is established and mild, dry weather follows through Saturday evening.

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