A buried layer of surface hoar may sit 2-3′ below the surface of the snow. Zones that saw prior wind effect (especially in the Alpine) are most concerning where the buried surface hoar is potentially sandwiched between layers of harder snow. This was the set-up in the one known human triggered avalanche on this layer that occurred on Wednesday, Jan. 2nd on Seattle Ridge. As time passes, high pressure and cold temperatures continue and more information is gathered, we are finding that being able to trigger a slab avalanche breaking 2-3′ deep is becoming less and less likely. Most snowpack tests and pits have shown the layer to be either generally unreactive or not present. The spooky part is that it has been found in a few pockets with the hard snow above and below and the potential to initiate an avalanche. Signs of instability will likely not be present.
When there is a buried surface hoar in the snowpack it is always important to consider the consequences if part or all of the slope does release. Is there a terrain trap below? Remember to use safe travel protocols: watch your partners, expose one person at a time and have an escape route planned.
Buried surface hoar sandwiched between hard layers of snow. 1-2-19.
South of Turnagain – Lynx Creek/Johnson Pass/Summit Lake zone: A poor snowpack structure exists in these areas. The buried surface hoar mentioned above exists as well as facet/crust combinations in the bottom of the snowpack. The New Year’s storm overloaded a variety of these weak layers as can be seen in photos from the avalanche activity throughout Summit Lake. If you’re headed this way, the snowpack becomes more complex – evaluate terrain exposure and the snowpack as you travel.
Glides cracks have been observed in all the hot spots on Turnagain: Seattle Ridge, Lipps, Tincan, Eddies, Lynx Creek, Johnson Pass, Sunburst, Corn Biscuit and Magnum. “Gliding” is the whole snowpack is slowly sliding down the mountainsides and can release into an avalanche at anytime. This is a completely unpredictable situation and one where a human does not play a role. Glide cracks have been releasing into large avalanches over the past week. Please don’t be caught in the wrong place at the wrong time and limit/avoid exposure under any crack you see. The most recent glide avalanche we know of was on the south face of Eddies where the glide debris covered fresh ski tracks. Cracks maybe white and look like bergshrunds at first before progressing to the brown frown and the snow sometimes looks like a wrinkled sheet on the slope below. Glide cracks have now been observed in both the Alpine and Treeline elevation bands.
Glide cracks in the Library, 1-6-19. Photo: Andy Moderow
Glide cracks in Petersen Creek, 1-6-19. Photo: Alan Abel
Yesterday: The pattern of cold temperatures, clear skies and valley fog continued yesterday. Highs were in the low teens to single digits and lows were below zero with a slight inversion.
Today: Another cold, clear day with valley fog is forecast. Highs will be in the teens at upper elevations and lows will be in the single digits. Winds will be light and southerly. Temperatures will slowly rise with a chance of light precipitation overnight.
Tomorrow: Partly to mostly cloudy skies and a chance of snow showers with temperatures in the high teens. On Wednesday the pattern goes back to clear, sunny. Warmer temperatures and snow are in the long-term forecast for the weekend.
*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||0||0||0||57|
|Summit Lake (1400′)||-7||0||0||20|
|Alyeska Mid (1700′)||3||0||0||46|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||3||*N/A||*N/A||*N/A|