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Mon, February 15th, 2021 - 7:00AM
Tue, February 16th, 2021 - 7:00AM
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE today. Triggering a slab avalanche on a layer of weak snow, buried 1-2’ deep, is still possible in steep terrain. Assess the snowpack as you travel, identify areas of concern and evaluate terrain consequences. Give cornices a wide berth, limit time spent under glide cracks and watch your sluff.

Mon, February 15th, 2021
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Triggering an avalanche on a buried layer of weak snow is the main concern today. The big question is whether or not there is a slab over the weak snow. Slopes that were loaded during the wind event last Thursday (2.11) are most suspect due to the potential for a more substantial slab.  Since January 28th we have been talking about a layer of buried surface hoar and near surface facets, and the possibility of triggering an avalanche if you travel on a slope that has a slab over this layer. In addition, there have been subsequent small snow events, a few wind events (from different directions) and more surface hoar and near-surface facet formation. In some terrain there is now more than one layer of weak snow and more than one layer of wind affected snow. During the Thursday wind event there was a natural avalanche cycle with avalanches failing on buried weak snow. There were a couple of small human triggered avalanches reported yesterday and there were a handful on Friday and Saturday. With that data in mind there are a few other things to remember in as you make your travel plan for the day today. Areas with more snow over the January 28th layer like Placer, Skookum and Grandview could have deeper slabs. Additionally, there is a melt-freeze crust buried below weak snow from sea level to somewhere between 1200-2000′ depending on location. This crust facet set-up combined with a slab on top could be a recipe for a larger, more connected avalanche. When you are out today watch for cracks shooting out from your snowmachine or skis, smooth rounded pillows of snow, and ‘punchy’ feeling stiff snow over weaker snow. Steep slopes with wind affected snow should be approached with extra caution. Slabs will mostly likely be found near ridges, on wind-loaded slopes and in cross-loaded gullies. Even shallow slabs can be quite dangerous in high consequence terrain and hard wind slabs may break above you as you travel out onto the slope. Look for signs of signs of instability, choose terrain carefully and use good travel protocol.

Loose Snow Avalanches (Sluffs):  In steep terrain that has been sheltered from the wind be aware of your sluff, especially if you are above terrain traps like cliffs, rocks, trees, or gullies.

Cornices: When traveling along ridgelines be sure to give cornices plenty of space, and minimize the amount of time spent traveling below them. Cornices could fail under the weight of a person on skis or a snowmachine, and might trigger an avalanche if the slope below is wind-loaded.

Natural wind triggered avalanches from the 2.11 wind event on Eddies, 2.13.21. Photo: George Creighton. Wind-loaded terrain like this is still suspect today.  

Slab failing on a layer of buried facets, Pete’s North 2200′, 2.13.21. 

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks have opened up throughout the area and there was a recent glide avalanche observed yesterday from Girdwood. This type of avalanche is unpredictable, involves the entire season’s snowpack and can be large and destructive. Avoid spending time below glide cracks. If you see any new glide activity, please let us know here.

Glide avalanche above Sunrise Creek, 2.14.21.

Mon, February 15th, 2021

Yesterday: Skies were overcast becoming broken in the afternoon. Winds were light and easterly and temperatures were in the teens to low 20°Fs at upper elevations and high 20°Fs to low 30°Fs at sea level. Overnight skies were mostly cloudy with temperatures in the teens to low 20°Fs and winds were light and variable.

Today: Skies will be mostly cloudy with a chance of snow showers late in the afternoon. Temperatures will be in the 20°Fs and winds will be light and variable. Overnight skies will be cloudy with light snow, 1-3″ to sea level. Temperatures will be in the low to mid 20°Fs. Winds will be light and easterly.

Tomorrow: Mostly cloudy skies and snow showers in the morning. Light easterly winds and temperatures in the 20°Fs. After a few weeks of not much precipitation, a more potent storm looks to be on track to impact the region Wednesday. However, there is still some uncertainty with temperatures and precipitation amounts. Stay tuned and as always think cold thoughts! #snowtosealevel

PRECIPITATION 24-hour data (6am – 6am)

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24 0 0 116
Summit Lake (1400′) 21 0 0 42
Alyeska Mid (1700′) 23 0 0 109

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16 E 6 23
Seattle Ridge (2400′) 19 E 6 18
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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.