Turnagain Pass

New snow overnight with an additional 3-6″ expected today along with strong ridgetop winds are overloading the tenuous snowpack. If you’ve been following along, you’ll know that a weak layer of buried surface hoar sat 1-3′ below the surface before this new snow. The layer was highly reactive during last weekend’s clear skies and resulted in nine human triggered avalanches. Today, we will see how reactive it still is with another shot of stress by new snow and wind loading. 

Total snowfall as of 6am this morning for the past 24-hours:

• Turnagain Pass – SNOTEL (1800’):  4″ at station, 6-8″ estimated above 2,500′
• Girdwood – Alyeska Midway (1700’):  5″ at station, 10-12″ estimated above 2,500′
• Portage – Bear Valley Tunnel (100’):  1.7″ of rain, 16″ – 2′ estimated above 2,500′
• Summit Lake – SNOTEL (1400′):  4″ at station, 5-6″ estimated above 2,500′

Wind loaded slopes above 1,500′ are the most suspect for both naturally occurring avalanches and human triggered avalanches. Below 1,500′ the snowpack is composed of mostly crusts and avalanches are unlikely. Although fresh wind slabs and cornice falls may be the most common avalanche today, the more dangerous avalanche is the one that breaks deeper in the snowpack. If you are headed into the mountains and skies clear enough for travel above treeline keep in mind:

1-  Large avalanches have the potential to occur naturally and send debris to valley floors
2-  Fresh wind slabs and cornice falls may step-down and trigger a large avalanche
3-  Sticking to lower angel slopes, less than 30 degrees, with nothing steeper above you is a way to avoid these dangerous avalanche conditions. 

Storm snow avalanches from last week’s storm cycle in Lynx Creek Drainage (1/25). The debris in these slides covered the route into the upper portion of the valley. Additional slides like this are expected off steep ridgelines today. 

The thin gray line easily seen about a foot deep in the pit wall is the MLK buried surface hoar responsible for the rash of human triggered avalanches last Saturday and our worrisome weak layer being overloaded today. (Lynx Creek Drainage, 1/27/19, 2,800′ north aspect)

Ridgetop winds have been blowing strong out of the east (20-35mph) for the past 24-hours. We can expect fresh wind slabs and cornices to be forming as winds transport not only the new snow but older soft snow. Wind slabs are likely to be in the 1-2′ foot deep range and easily triggered. This is also a prime condition for step-down avalanches. Meaning a fresh wind slab that triggers a deeper slab underneath. One that breaks 2-5′ deeper in the pack creating a much larger and dangerous avalanche.