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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, January 12th, 2014 - 7:00AM
Expires
Mon, January 13th, 2014 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The general avalanche hazard is MODERATE above and below treeline.   However, dense slabs up to 3′ in depth could be triggered in steep upper elevation terrain.   In these areas the avalanche hazard is CONSIDERABLE due to the potential for avalanches to be large.  

The likelihood of triggering avalanches will increase if people venture onto steep slopes, rollovers or convexities.   The likelihood will become greater in this type of terrain where the snowpack is shallow.   It is in these spots where humans are more likely to affect weak layers and produce avalanches.   The consequences, or result of an avalanche have the potential to be severe.   Consequences will be greater in the higher elevations where the overall slab depth is greater.

Sun, January 12th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
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
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.
More info at Avalanche.org

It has been a week since significant precipitation or loading has occurred in the area.  All of our information over the past seven days has come from tests in snow pits in the mid and lower elevations.  The general trend in our tests has shown us that it is slowly becoming more difficult to trigger an avalanche.  The one variable that has remained the same is the potential for avalanches to propagate across entire slopes.  This fact alone has kept us tip toeing around the mountains lately.  Travel into the more suspect areas (e.g. upper elevation starting zones and steep terrain) has not happened.  This makes it more difficult to truly have a comprehensive understanding of the snowpack.

The foundation of the snowpack is weak.  Faceted snow near the ground is prevalent throughout the area.  The slab that has formed over the past month is between 1 and 3 feet deep, depending on elevation (deeper in the higher elevations).  This slab is strong enough in many areas to support the weight of a person or snowmachine.  The areas where that is not the case are:

Steep rollovers & convexities.
Steep open slopes, generally above 35 degrees and certainly above 40 degrees.
Thin spots in the slab.  Areas with shallow snow that are connected to areas with deeper snow, commonly found along ridgecrests.

It is worth avoiding these areas for the time being.  The weak snow near the ground simply needs more time to adjust to the slab above it.

Weather
Sun, January 12th, 2014

In the past 24 hours the mountains around Eastern Turnagain Arm have received no new snow.   Temperatures have averaged 12 degrees F at ridge tops.   Wind direction has shifted overnight and is currently blowing out of the East.   The 24 hour average wind speed was 5mph with gusts to 23mph.

Today will bring another uneventful day in terms of weather in the mountains.   Temps at 1,000′ will reach the mid 20s F.   Winds will remain light out of the East.   There is a slight chance for snow during the day with little accumulation expected.

The beginning of this coming week looks to bring continued clouds and light precip to the area.   The long term outlook is starting to show the potential for more significant precipitation by the middle of the week.

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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.