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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, March 20th, 2014 - 7:00AM
Expires
Fri, March 21st, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Weather continues to be calm and sunny.  The snowpack has gotten more stable since the last storm.  However, the possibility still exists to trigger deep slab avalanches up to 5 feet deep in terrain over 35 degrees.  

A  MODERATE  danger can be found in areas above treeline in steep terrain.  The likelihood of triggering a deep slab pocket is low, but the consequences to your health would be significant.

Below treeline the danger is  LOW.  

Thu, March 20th, 2014
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

It has been 5 days since we have had reports of major avalanche activity.  This is a good sign, as time goes on people are getting on increasingly agressive slopes and the snowpack is trending towards stable.  

Anyone riding in big, steep terrain must understand the possibility of a large avalanche still exists.  The slab/weak layer combination that caused the big avalanches last weekend is still present.  Both the slab and weak layer have gained strength over time, making it more difficult to trigger this problem.  But remember, this isn’t our typical snow year.  The snowpack is shallow, and multiple crust layers have led to persistent weaknesses.  Click here for a writeup of the big avalanche in Seattle creek last weekend.

Steep terrain should be approached with a conservative mindset.  Ask yourself, “What would happen if this slope avalanched?”  

Avalanche Problem 2
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices are as big as we’ve seen them this year.  The photo is from last week of a section that dropped spontaneously, triggering a slab on the slope below.  

Check out this video for a good perspective of a close call with a cornice.

 

Weather
Thu, March 20th, 2014

Perfect March weather would be accurate for the last few days.  Sunny skies, minimal wind, and comfortable temperatures.  

Today will bring more of the same.  Some clouds will roll in by the afternoon.  Wind will be calm, and temperatures rising with the sun exposure.  

For the long-term, we don’t see any significant storms from now through the weekend.  A ridge across mainland Alaska is keeping the low pressure at bay.  

Observations
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Date Region Location
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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.