Turnagain Pass

As we move away from a storm that ended Tuesday and into a sunny day be aware of the temptation to push into steeper terrain. This is a situation where the weather is rapidly improving, but snowpack is slow to follow. Triggering a large high consequence avalanche remains a real possibility due to a reactive layer of buried surface hoar 2-4’ below the surface. Recent natural avalanches occured this week and numerous remote triggered avalanches last weekend were initiated on this layer in Seattle Creek drainage.

What makes this buried surface hoar layer different than previous layers this season? This layer is widespread, large in size, and has been found intact under the snow along some ridgeline. This is why remote triggered avalanches are possible. Strong winds have created variable slab thicknesses across any given slope. This means trigger spots, thinner areas of the slab, will be impossible to identify until the weight of a person or snowmachine collapses the weak layer. An additional challenge exists across the region due to varying storm totals. In Girdwood, where more snow fell, average slab thickness is estimated around ~3’ thick. In Turnagain Pass the average slab depth is ~2’ and in Summit Lake its 1-1.5’ thick.

This type of avalanche problem is tricky to navigate and requires a good deal of skepticism when making decisions. Please keep mind:

1. The larger the slope the bigger the consequences.
2. Previous tracks on a slope do not mean its safe. The 3rd, 4th or 8th person could find a trigger spot.
3. “Whumpfing” may not be present until committed to a steep slope and a large avalanche releases.
4. Be aware of other groups above or below you. The more people in any given area = more triggers.

Winds/Wind Slabs: Ridgetop winds are expected to be 5-20mph from the Northwest. Whittier and Portage pass will see stronger outflow “gap winds” today. Remember any active wind loading and blowing snow could form tender wind slabs or overload a deeper more dangerous problem. Wind loading is an obvious sign to avoid all avalanche terrain. 

South of Turnagain – Johnson Pass/Summit Lake zone: Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present, including buried surface hoar. A storm that ended on Tuesday triggered numerous large avalanches including a notable cornice triggered avalanche on Spirit Walker. If Northwest winds pick up today in this area, natural avalanche will be possible. Also keep in mind that an avalanche triggered in these zones could step down into deeper weak layers.

Recent natural avalanche in the Twenty Mile drainage on a SW aspect. Note the wind sculpted snow texture on the slope adjacent that didn’t avalanche.

Although a little tricky to make out in this picture. There are three separate avalanches with large crowns. It is suspected these were triggered by natural cornice fall near or after the last storm. 

Large cornices are present along many ridgelines across the region. These ridgtop hazards can be difficult to see and can break further onto a ridge than expected. Triggering a cornice could initiate a large avalanche on the slope below. Keep in mind any active wind loading could trigger natural cornice fall. Avoid traveling on or underneath these unpredictable hazards. 

Sun: We are just starting to see minor solar radiation happening on steep Southeast aspects in the form of small wet-loose point releases. Today radiation is not expected to increase the avalanche danger, but it is an additional factor in the unpredictable nature of cornices.