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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 13th, 2016 - 7:00AM
Expires
Mon, March 14th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is MODERATE today above 1000′. Human triggered wind slabs and wet loose avalanches will be possible on solar aspects where radiation from the sun will be weakening the snow. On shaded aspects triggering a wind slab and dry loose snow will be possible on slopes steeper than 35 °.   Glide cracks continue to release naturally and without warning and threaten a lot of mid elevation terrain. Avoid putting yourself in the runout of a glide crack.

*If you are headed to the Summit Lake area don’t forget to check  Summit Lake Summary.

Special Announcements

Yesterday morning there were numerous car accidents on the North side of Turnagain Pass. No serious injuries were reported, but several vehicles were on their side. Please drive safe and be aware of black ice in the morning and evening.

Sun, March 13th, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

Yesterday several skier-triggered and snowmachine-triggered wind slabs were observed in the mid and upper elevation zones following a storm that dumped 12” of new snow in the alpine on Friday. Most of these slides were small, with the exception of a skier triggered wind slab on the North side of Cornbiscuit that was big enough to bury a person. Luckily the terrain allowed the debris to fan out at the bottom and the ski tracks didn’t look like the person was caught. If anyone has info about this avalanche or any others consider sending in an observation, by clicking HERE.

Triggering a wind slab will be possible on slopes steeper than 35° and could easily take you for a ride in undesirable terrain. On solar aspects pay attention to how the sun is warming the surface snow and avoid steep slopes when the surface becomes damp. Active roller balls or water dripping from cornices are obvious signs the snow is becoming unstable. On shaded slopes ease into terrain with caution and avoid terrain with high consequences (terrain traps, rocks, and usupported slopes) where taking a ride could have a poor outcome. 

A few other concerns to be aware of:

Loose snow: Don’t be surprised by loose snow sluffing on shaded aspects. Sluffing could be fast moving with the ability to entrain a significant amount of surface snow in big terrain. 

Cornice falls: Very large cornice features loom over many ridgeline and have a tendency to break further back than expected. Give them lots of space, and limit time under them. 

 

Skier triggered wind slab on the North side of Cornbiscuit as seen from the Sunburst parkinglot around 1:30pm yesterday. 

 

Snowmachine triggered windslab on West aspect of Seattle Ridge. Photo by Graham Predeger

 

Skier triggered wet loose avalanche just above the ‘uptrack’ on Seattle Ridge. 

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

There were several new glide avalanches seen yesterday in Turnagain Pass and Girdwood, including a very large glide release on the North side of Eddies and a smaller one on the South side of Sharks Fin. Glide cracks cover all aspects within the mid elevation band and remain a significant threat to popular terrain. This avalanche problem is impossible to predict and is not associated with human triggers. As long as glide cracks continue to open up, move and release, we will stress the importance of avoiding them. AVOIDANCE IS THE ONLY WAY TO MANAGE THIS AVALANCHE PROBLEM.

Recent glide release on the North side of Eddies. Click HERE for more pictures of recent glides.

 

 

Natural Wind slab on South Face of Lipps along side a growing glide crack. Photo by Liz Repetto 

Weather
Sun, March 13th, 2016

Yesterday skies were sunny and temperatures reached a high of 44.5F at Center Ridge Weather Station by 12pm.’ Winds were light from the East switching to the West by the afternoon. No precipitation fell yesterday.

Overnight temperatures dropped into the mid 20’s F. Ridgetop winds became East with a sudden increase from Light to Moderate this morning.

Today Easterly ridgetop winds are expected to be light and skies will be mostly sunny. Daytime temperatures could easily reach the high 30’s F to low 40’s F by early afternoon. There may be some valley fog in Turnagain Arm.

Tomorrow looks like another repeat of today; partly cloudy, warm daytime temps, and freezing temperatures overnight. Winds are expected to remain light.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   0   0   138  
Summit Lake (1400′) 30   0   0   42  
Alyeska Mid (1700′) 32   0   0   107  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   Variable   5   27  
Seattle Ridge (2400′) 28   Variable   5   30  
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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.