Turnagain Pass

The natural avalanche activity slowed down as temperatures cooled Sunday and Monday and the freeze was more pronounced. Today and tomorrow it will still be important to pay close attention to how the warming is affecting the pack. We are in a melt-freeze cycle on Southerly slopes – hard frozen crusts in the morning, which turn to unsupportable mushy and unstable snow by the afternoon/evening. Choosing what aspect to travel on, paying attention to the time of day and how long the slope you are on has been exposed to direct sunlight are essential to staying out of trouble.  Zones with thin snowpacks have been particularly active where free water is interacting with old weak snow. Wet loose snow avalanches may also trigger deeper slabs.  Rocky areas that are absorbing more heat should be avoided.

 If heading out for a fun day in the sun keep these points in mind:

• Once the snowpack becomes so wet it is unsupportable and ‘punchy’ to skis, snowmachines or boots – it’s time to head to a cooler aspect. 
• The steeper the Southerly slope, the more it will warm and the more dangerous it will be.
• Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down. 
• The recent wet avalanches seen have been large enough to injure, bury or kill a person. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope.

Temperature trend from late last week until this morning. The natural wet avalanche activity peaked during the warmest days Friday, April 14th and Saturday, April15th. 

Natural wet slab avalanche that occured on Friday afternoon on Seattle Ridge. 

Yesterday around 5 pm, a skier triggered a slide on a West aspect in Triangle Bowl on the backside of Seattle Ridge. The skier was the 4th person on the slope and triggered it in a thin spot. They were able to ski off of the slab. The bed surface was reported as the rain crust from the April Fool’s storm. In this springtime transition it is important to remember on the shaded and cooler side of the mountains (Northerly aspects: NE – NW – W), a cold mostly dry snowpack still exists. Afternoon warming may also influence how easy it is to trigger weak layers that are buried anywhere from 2-5′ below the surface. As folks venture out looking for “cold, soft snow” this remains a concern. Shaded aspects (NE – NW – W) in the mid and upper elevations that haven’t avalanched already are the most suspect places for triggering a deeper slab.  

This problem is one of low probability but high consequence as these are potentially large and unsurvivable slides.

Keep these points in mind:  

• It will take someone hitting a ‘thin spot’ in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall.. 
• There may be no signs of instability before the slope shatters 
• Several tracks may be on a slope before it releases
• Stability tests may not produce any notable results

Triangle Bowl a few minutes after the avalanche was triggered. Thanks to the party involved for sharing the photo and information.

Several small glide avalanches have released on Southeast facing Seattle Ridge and Eddies Ridge over the past week. We expect this trend to continue with the warm days ahead. Keep an eye out for glide cracks, full depth cracks in the snow, and limit time underneath them. 

Glide cracks in Eddies continue to open. Glide avalanche occured on Wednesday April 12th. 

Cornices: Cornices are large and likely hanging close to their tipping point. Direct sunshine, a person, or a group of people on top these could be enough to cause one to break. An observer in Seattle Creek noted a large cornice fall on Friday. Cornice crevasses have also been noted (opening slots where the cornice is pulling away from the ridge but has not broken off. Give cornices a wide berth from above and limit exposure under them from below. 

Cornice in Summit Lake with old slab crown below.