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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 20th, 2016 - 7:00AM
Expires
Thu, January 21st, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is  MODERATE  at and above Treeline today where it is possible for a skier or rider to trigger a wind slab in steep, wind-loaded terrain. As the next pulse of snow and rain moves through today pay attention to changing conditions and active wind loading.  In the mid-elevation band (at Treeline), glide cracks continue to pose a significant threat.  Avoiding time spent under glide cracks is the best way to mitigate this particular avalanche problem.

A  LOW  avalanche danger exists below 1000′ where triggering an avalanche is unlikely.

Wed, January 20th, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

The wind picked up again last night and was strong enough move snow. There was snow available to transport from the Monday night storm and a there is more snow forecasted to fall today. This combination of wind and snow creates the potential for wind slabs in steep, leeward terrain that could be triggered by the weight of a person or a sled. Be on the look out for shooting cracks, hollow feeling or sounding snow and stiff snow over softer snow. Remember a small pocket of wind slab in can be very hazardous in high consequence terrain. Cornices and pillowed slopes will help indicate wind-loaded areas.

The winds and new snow will continue to build already large cornices. Avoid spending time underneath or on them. They tend to break farther back from ridgelines than expected.

Practice safe travel techniques in avalanche terrain: ride one at a time, watch your partners, have an escape route planned, park or stop in safe zones and always consider slope consequences.

Wind-loaded slopes and cornices: Tincan Proper.

 

Avalanche Problem 2
  • 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

Today at Treeline (the 1,000’ – 2,500’ elevation band) on all aspects, pay attention to and avoid glide cracks. These can lead to glide avalanches that are very unpredictable as we have seen over the past few days. There is no discernable pattern to predict a failure as they tend to fail naturally and on their own schedule. Warm temperatures can trigger them and so can cooling temperatures. Cracks can form and release in seconds or days later or sometimes a glide crack won’t release at all. The new snow has made it harder to see the existing cracks and glide releases in the terrain. 

It is best to give glide cracks a wide berth.  Avoid spending time underneath and if skiing or riding in terrain with glide cracks, try and map them out before your travels so as not to end up directly on top of or inside one.  Remember, when these do fail, they tend to be destructive, failing to the ground and bringing the entirety of the snowpack with them. 

Recent glide release on Wolverine.

Weather
Wed, January 20th, 2016

Yesterday was mostly overcast with a few breaks in the high clouds. Winds were light during the day and picked up overnight into the 20s, gusting into the high 30s.  Temperatures were in the low-30Fs at 1,000′ and mid-20Fs at ridgeline.  

Today will be mostly cloudy with rain and snow showers. New snow accumulation of 1-5 inches possible. Snowline is forecasted to be around 2000′. Winds will be easterly, 15-30mph with stronger gusts. Temperatures will be in the low to mid 30Fs.  

Showers will continue into the evening with a drying trend overnight as the region has a short break before the next wave of precipitation moves in.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31    0  0  86
Summit Lake (1400′)  31  0  0 26  
Alyeska Mid (1700′)  32  0  0  26

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26    ENE 12    39
Seattle Ridge (2400′) 27  n/a n/a   n/a  
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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.
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