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Wed, February 12th, 2014 - 7:00AM
Thu, February 13th, 2014 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

We continue to have a  MODERATE  avalanche danger on all aspects above treeline. Human triggered soft slab avalanches remain possible on slopes where a slab 12-20 € thick sits on a thin layer of weak faceted snow. Most suspect areas are those that have seen prior wind loading. In locations where the slab has weakened and is comprised of very loose snow, sluffing should be expected in steeper terrain.

Below 2,000 feet the avalanche danger is  LOW  and triggering an avalanche will be unlikely where 3-15 inches of loose snow is resting on either a frozen ground or a stout crust.

Wed, February 12th, 2014
Above 2,500'
2 - Moderate
Avalanche risk
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

It was a quiet day in the backcountry yesterday (avalanche-wise) though many folks were out continuing to enjoy the sunny weather and Friday’s unexpected 14-18” refresher. The last avalanche reported on the Pass was Monday, two days ago, where a snowboarder triggered a soft slab in Seattle Creek. Otherwise, there have been a few reports of remote triggered shallow slabs Sunday and Monday north of the Pass (20mile area) as well as south (Grandview region).

The main concern for today continues to be triggering one of these persistent soft slab avalanches. These slabs have been in the 12-20″ range and are sitting on a thin layer of faceted snow over a crust. It is interesting how spatially variable both the slabs are as well as the thin layer of faceted snow underneath. Many areas simply have no slab at all, only loose unconsolidated snow. Yet in other areas, people are still finding snow with just enough slab character to trigger an avalanche. If you didn’t read it yesterday, check out this great article on spatial variability by Ron Simenhois (inventor of the very popular ECT test). This is one of those set-ups that can lull us into complacency. Just because the ridge next to you was tracked-out without incident doesn’t necessarily mean yours is good to go. Every slope should be evaluated on its own, especially if you are venturing into steeper and more complex terrain where triggering even a small slab could have higher consequences. Watching for cracking or collapsing as well as performing hand pits, proper ski cuts and having an escape route planned are ways to manage this issue.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Loose snow avalanches, or sluffs, are becoming easier to initiate as the top foot+ of snow continues to become looser by the day. The past four days of clear and cold conditions are eating away (or faceting) Friday and Monday’s snow. Sluffs yesterday were mainly low volume, predictable and confined to slopes around 40 degrees and steeper. With continued cold temperatures, watch for these to start entraining more snow and run further.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

The deep slab issue is still of concern in the upper most elevations of our forecasting zone. The likelihood of triggering a full depth avalanche breaking in weak snow near the base of the pack is low but the consequences remain high.

This problem is not a concern below 3000ft where the previously water saturated layers have now frozen into a very strong and stable layer.

Wed, February 12th, 2014

Sunshine, light variable winds and single-digit temperatures prevailed again yesterday. Overnight, skies have remained mostly clear and the temperatures have plummeted – minus single digits are being seen at all elevations: -5 to -10F at sea level and -2F on the ridgetops. Winds are still light from a Northerly direction around 3-5mph.

For today, mostly clear skies will be replaced with clouds and a chance for a falling snow crystal or two. Temperatures will continue to be cold and may even reach the minus double digits in valley bottoms – burrr. The good news for anyone venturing out today is the wind will be light from the North, ~5mph or less. This may not help to warm things up however if the clouds keep the sun at bay.

For tonight and into tomorrow there is a chance for snowfall as a large area of low pressure develops in the Northern Gulf spreading small amounts of moisture our way. However, the temperatures remain below 0F which is not an ideal set up for snow accumulation. But, we can hope for the best, which would be around 4-5″ by Thursday night.

Check out this graphic by the NRCS. It shows general snowpack depth for the state as of February 1st. Yes, too much red…  

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.