Turnagain Pass

Today marks one week of elevated avalanche danger due to continuous stormy weather following a cold and dry March. A fast moving warm front will impact Southcentral, Alaska this morning, causing Easterly ridgetop winds to build into the 40’s (mph) with gusts in the 60’s (mph). Up to 6” of snow is forecasted to fall above 2000’; this is .45” of rain at lower elevations. Natural wind slab avalanches up to 1-2’ thick are likely today in the alpine due to blowing snow overloading steep slopes.This is on top of 2-4′ of snow that has incrementally fallen across our region over the last week. These storm related wind slabs have the potential to step down to an older layer in the snowpack, and run further than expected. (More on this below.) Avoiding all avalanche terrain, slopes steeper than 30 degrees, is the only way to manage this problem today. This includes giving run out zone plenty of space, and avoiding trails like Johnson Pass and Lynx Creek, where an avalanche could cross the trail. 

One of the many debris piles along the East face of Seattle Ridge over the last few days. This is a good example of how far things have been running in Turnagain, and reminder that today’s strong winds could be creating bigger slabs – increasing their run out distance. 

On Saturday rain falling on dry snow caused a cycle of wet slab avalanches below 1500’. Over the last two days an additional 6-12” of snow fell across our region insulating a layer of wet snow. Today another cycle of rain, up to a half an inch of water is forecasted below 2000’. This is a perfect recipe (rain falling on dry snow) to intiate another round of natural wet avalanche activity. To compound this, an avalanche in the alpine has the potential to run into the lower elevation band and intiate a wet slab avalanches – increasing the overall volume.  Again it will be important to avoid steep terrain and maintain a conservative distance from all runout zones. 

A wet slab that occurred between 1 and 2pm on Eddies on Saturday, 4/1/17. It was roughly 1-2′ thick and 300′ wide. The crown is near ~1500′ and was triggered by rain on the new snow from this week. However, if you look closely, it almost seems like it could have broken in an old weak layer that was not near the top of the pack. Photo by Wendy Wagner. 

Snowpit at 1500′ yesterday on Sunburst shows about 3″ of wet saturated snow perserved below yesterday’s new snow. 

Several old layers of weak snow (near surface facets and surface hoar) sit buried in the snowpack. Avalanches releasing in the storm snow have the potential to ‘step down’ into them. Snowpack tests are still showing propagation potential in these layers and today’s strong winds and precipitation are likely to tip in the balanche in the upper elevations. An avalanche occuring in one of these older layers could be as deep as 3-5′, and run the entire length of slide path. 

A persistent slab avalanche triggered by a skier on Manitoba yesterday in Summit Lake. Luckily no one was cuaght or injured. Photo by Matteo Calcamuggi

A snowpit at Sunburst yesteday shows several weak layers (buried surface hoar and the March facets) that are sitting under this week’s snow. Snow totals in the alpine are estimated to be closer to 3-4′ where the snow has remained dry.