Turnagain Pass Avalanche Forecast

The National Weather Service has issued a Winter Weather Advisory from Girdwood to Seward beginning at 0800 this morning. After 11 days with nearly no new snow and strong northwest outflow winds wreaking havoc on Wednesday, snowfall this weekend is a welcomed relief. The current snow surface is less than ideal, described in yesterday’s reports as “scoured, boney, pretty terrible, difficult to find any soft snow”, I’ll stop there. Snowfall should begin midday with 1-4″ falling by sunset, with more possible in favored areas such as Portage Valley. An additional 4-8″ is expected overnight. Snow should make it to sea level with the cool temperatures in place. 

Today is a ‘watch for changing weather’ day. Avalanche danger will increase in sync with new snowfall and wind. The hard existing snow surface will make inital bonding with the new snow poor. Once snow piles up to a good 4-6″ we can expect easily triggered sluffs on steep slopes and shallow wind slabs along ridgelines. With lower snow amounts today, fresh wind slabs should be in the 6-10″ range, relatively small. As temperatures climb and when new snow accumulates to over 6″, we could start seeing storm slabs in areas out of the wind. This issue is more likely to be seen overnight and into Sunday. 

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Roughly 1-3′ below the old hard wind affected surface sits a layer of buried surface hoar and in some areas facets. The layer of buried surface hoar was responsible for several large avalanches triggered a couple weeks ago and has slowly become unreactive. New snow this weekend and more through the week will be adding a load, and hence additional stress, onto these buried weak layers. Our concern is, will these layers become reactive again? In areas near Summit Lake the potential is higher for triggering a large slab breaking in old snow due to a weaker snowpack. As we move forward with new snow and stoke, we can’t forget there are some hidden dragons, especially in thin snowpack zones. 

If you’re headed into the mountains and visibility is good enough for travel above treeline, keep in mind:

1. Wind loaded steep features, large connected and unsupported slopes are the most suspect.
2. There is more potential for triggering a large slab in Summit Lake, Johnson Pass and Lynx Creek due to a generally thinner and weaker snowpack.
3. Use safe travel protocol. Expose one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready.

Alaska Avalanche School’s Level 2 snowmachine course investigates the currently unreactive layer of buried surface hoar in God’s Country of Seattle Ridge. The photo on the right is also from the course and illustrates the hard wind affected surface that this weekend’s new snow will be falling on (don’t be fooled, those tracks are raised anit-tracks!).

Glide cracks are still on the move. Two glide cracks released into avalanches this week, one near the Hope Wye and another in Girdwood Valley. Several cracks threaten popular routes on the South facing slopes of Lipps and Magnum. There is also a new glide crack opening on Seattle Ridge on Repeat Offender. Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.

Big thanks to Tom Enzi for capturing this photo of a large glide crack on SW facing Magnum ridge yesterday (2/15). This crack has been slowly opening for several weeks.