Turnagain Pass

Blue skies and warm days will continue to be the theme for today and into the workweek. As the mountains continue to heat up a bit more each day, they will become more and more dangerous. It is 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. Each night the re-freeze is a bit less and the melt phase is a bit longer, creating a longer period of heightened avalanche conditions. 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. 

Over the past few days many natural wet avalanches have occured. The activity looks to be starting around 12:00 pm and continuing into the evening hours, as late as 8 or 9pm. Natural avalanches were witnessed on the front and backside of Seattle Ridge, in Girdwood, in Placer and in Whittier on Friday. In the Lost Lake area several wet avalanches have been seen this past week. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope. 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.   

 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 (due to more warming but also because it’s simply steeper).
• 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 avalanches seen have been large enough to injure, bury or kill a person. Extra caution is advised. Natural avalanches are happening. Get Out of Harm’s Way! 

   

Large wet slabs on the Southwest face of Cornbiscuit – released sometime over the weekend (4/15 or 4/16). Mike Davidson Photo.

Natural avalanche that occured Friday around 5:30 pm on Ragged Top mountain in Girdwood Valley, Southeast facing slope.

Natural wet slab avalanche in the Lost Lake and Snug Harbor zone from earlier in the week (Photo: Troy Tempel). This areas is out of our forecast zone, but it is the type of avalanche activity we have been seeing on Southerly aspects – including the Seattle Creek drainage.

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On the shaded and cool side of the mountains (Northerly aspects) dry snow still exists. There are several weak layers anywhere from 2-5′ below the surface. As folks venture out looking for “cold 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 deep slab. 

This problem is one of low probability but high consequence as these are large and potentially unsurvivable slides. As the snowpack continues to adjust, triggering will become more stubborn and less likely with time. Keep these point 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.
• 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
• Stability tests may not produce any notable results

Several small glide avalanches have released on Southeast facing Seattle Ridge and Eddies Ridge over the past few days. 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. 

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. 

Glide avalanches and glide cracks near the Seattle Ridge up-track. 

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