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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, March 19th, 2014 - 7:00AM
Expires
Thu, March 20th, 2014 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger is MODERATE in terrain over 35 degrees above treeline today.   Deep slab avalanches up to 5 feet in depth have the potential to release in steep terrain.   This is a low likelihood/high consequence situation.   Conservative terrain selection is the best practice for this specific avalanche concern.

Below treeline and on slopes under 35 degrees the avalanche danger is LOW today.

Special Announcements

Our deepest condolences go out to the family and friends of Aaron Karitis. He passed away from injuries sustained following a recent avalanche in Haines, AK.

http://freeskier.com/stories/heli-guide-aaron-karitis-dies-following-haines-avalanche

Wed, March 19th, 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. Dangerous avalanche conditions. 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 4 days since any avalanche activity has been reported.  This most recent activity involved deep slab avalanches pulling out on layers buried 3-5 feet below the surface.  While the likelihood of triggering this type of avalanche is waning, the consequences remain high.  Slabs up to 5 feet in depth have the potential to pull out across entire slopes and do a significant amount of damage.

What’s tricky with this avalanche problem is that you will not encounter it everywhere.  The slab that built up last week is now strong and able to hold a lot of weight.  Because of this it is possible to get onto steep terrain without incident.  Now is not the time to let your guard down.  We know that some areas still harbor weak reactive snow below the March slab.  (See VIDEO and OBSERVATION for a more detailed desrciption)

Areas where you would be more likely to trigger a deep slab are in rocky areas, transition zones between wind scoured and wind loaded, steep terrain, and slopes with an overall shallower snowpack.  Avoiding these areas is the best way to tip toe around this problem.

Photo below: Deepest part of the crown face (8′) of the Widow Maker avalanche (March 15); a prime example of a deep slab avalancheWendy Widow Maker Crown

Click HERE for a detailed write up of this avalanche.

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 have become sufficiently large over the course of the winter.  It is difficult to predict when these monsters will release themselves.  Strong solar radiation and an absence of wind are two factors that can encourage cornices to drop onto slopes.  Avoiding being on or under cornices is a good habit to get into.  Know where the cornice begins and the underlying terrain ends.  If you are traveling below cornices, spread your group out and only expose one person at a time.

Additional Concern
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

The sun will be strong today on mainly South through West facing terrain.  Daytime heating will last into the evening hours, given that sunset is now after 8pm.  Low volume loose snow avalanches will not be a concern on their own.  In steep terrain above terrain traps it will be important to be on the lookout for wet loose avalanches, as they have the potential to knock you off your feet and into trees, gullies or over cliffs.

Weather
Wed, March 19th, 2014

In the past 24 hours no new precipitation has fallen.   Temperatures at the Sunburst station (3,812′) have averaged 19 degrees F.   Winds there have been light, averaging 7mph out of the Northwest with a max gust of 23.

A pleasant day in the mountains is on tap.   Expect clear skies, winds out of the North at 15mph and temperatures at 1,000′ reaching into the high 30s F.

A large area of high pressure is establishing itself over most of the state.   This will bring clear and dry conditions over the next several days.

Observations
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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.