Yesterday we received a report of a remotely triggered large slab avalanche in Warm-Up Bowl of Seattle Creek. This avalanche was triggered by a snowmachine from Seattle ridge without incident the day before (Wednesday.) The weak layer in question was confirmed to be buried surface hoar. We have been tracking this layer since it formed on Christmas Eve and have found its size and distribution to vary across the region with no consistent pattern. This is a tricky problem to manage. Multiple people could ride or ski a slope before someone finds a pocket or just the right trigger spot. The incident on Tuesday is proof that this layer is reactive and a slab could be large enough to bury or kill a person. Obvious clues like whumpfing may not be present. Digging a test pit adjacent to a slope may or may not be representative of the presence or reactivity of this weak layer.
As we move away from the New Years Storm that brought hurricane force winds and 2-3’ of snow, we must be diligent with our terrain choices and travel protocols. This means avoiding terrain traps, identifying safe zones and traveling one at a time in avalanche terrain.
South of Turnagain: The New Years storm caused some notable avalanche activity throughout Summit Lake on many West and South aspects. This isn’t a big surprise. Observers over the last month have been tracking a poor snowpack structure in this region. Buried weak layers of facets associated with crusts sit near the base of the snowpack and buried surface hoar has also been found similar to Turnagain Pass. The Lynx Creek and Johnson Pass area are also suspect for deeper instabilities and also warrants a cautious mindset. Evaluate terrain and snow as you travel and remember ‘whumpfing’ and recent avalanches are obvious clue of instability.
Remotely triggered avalanche on a North aspect of Warm-up Bowl in Seattle Creek that occured on Wednesday. Photo taken yesterday by Wendy Wagner.
Crown profile of Warm-up bowl avalanche.
Several glide cracks have avalanched over the last few days and we expect more to release through the weekend. Glide cracks have been seen in popular ski and snowmachine terrain and some are covered by new snow from the New Years storm. If you see a glide crack the best way to manage this problem is to avoid traveling under them. They can release at any time and are not typically associated with human triggers. Known glide avalanches have occurred on Lipps, Seattle Ridge, Penguin Ridge, Lynx Creek and Johnson Pass this week.
There are also some very large cornices along many ridgelines across our region. Give them lots of space and similar to glide cracks avoid being directly under them.
This glide crack on Lipps continues to release chunks of the slab. Photo taken yesterday.
Yesterday: skies were clear and sunny. Temperatures dropped from the low 20F’s into the single digits throughout the day at Turnagain Pass. Areas near the coast remained in the 20F’s most of the day. Westerly Ridgetop winds were light, 5-10mph. No precipitation occurred.
Today: Expect clear and sunny skies in the alpine with valley fog. Temperatures will be slightly inverted with cooler air (single digits) at lower elevation and in the teens F near ridgetops. Winds should remain be calm to light from the West.
Tomorrow: An arctic high is positioned over mainland, AK and will continue to bring cold, clear and dry conditions through the weekend. Expect temperatures to range from single digits to teens.
*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||15||0||0||62|
|Summit Lake (1400′)||2||0||0||21|
|Alyeska Mid (1700′)||16||0||0||48|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||15||*N/A||*N/A||*N/A|