Turnagain Pass

With long days and sunny weather ahead, many folks may be thinking about summertime activities – however, winter is still alive in the mountains. Dry settled powder covers aspects on the North side of the compass at the mid and upper elevations and these zones are the exact places we are concerned about deep slab avalanches. A layer of buried surface hoar exists anywhere from 2-6′ below the surface and is still producing concerning stability test results. This layer was also the culprit weak layer in many human triggered deep slab avalanches over last weekend. This problem is one of low probability but high consequence as these are large and potentially unsurvivable slides. Over time, the likelihood decreses but has not gone away – by any means. Points to think about if you are getting out this week:

• Because the weak layer is deep, it is tough to effect and therefore tough to trigger. It will take someone hitting a ‘thin spot’ in the slab, often where rocks sit just under the surface, or a large trigger such as a snowmachine and/or groups of people.
• These slides can be triggered remotely, for example, from a ridge or bench on the top/side or below. 
• There may be no signs of instability before the slope shatters 
• Several tracks may be on a slope before it releases

If wishing not to roll the dice on this deep slab possibility, one can always stick to slopes under 35 degrees on these shaded aspects with nothing steeper above you.

Photo: Deep slab avalanches that were believed to be snowmachine triggered several days ago on April 7th or 8th in Main Bowl/1st Bowl of Seattle Creek. Older photo, but this gives an idea of the deep slab avalanche issue we are dealing with. Crown heights are 3-6 feet. 

 If you haven’t seen it yet, this video shows a snowpack stability test at a thin spot in the slab – likely trigger point. This test was done near a sub-ridge where slabs often are thinner due to scouring during storms.

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As the day warms up – into the 50’sF in the parking lots possibly – expect the Southerly aspects and lower elevation snowpack to become so wet and saturated it is unsupportable to snowmachines, skis or boots. When the pack gets this loose then it’s time to head to a different aspect as slopes steep enough to slide become suspect for wet snow avalanches. Human triggered wet loose slides and wet slabs are a possibility late in the day and nothing to mess with.

Springtime melt-freeze cycle (Southerly aspects): We are moving into what we call a melt-freeze cycle. Low avalanche danger in the morning, Moderate to Considerable danger in the afternoon. When the snowpack is frozen in the morning from nighttime cooling, it’s stable. During the course of the day the pack warms to the point it is punchy and unsupportable, this is when the avalanche danger rises with the chance for wet snow avalanches. Wet avalanches can be small to very large. For today, keep an eye on Southerly slopes and see if any new wet loose avalanches release from under rocks or other dark features.