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Mon, February 24th, 2014 - 7:00AM
Tue, February 25th, 2014 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE today above and below treeline.   It will be possible for snowmachiners, skiers and snowboarders to trigger wind slabs 1-3′ in depth that formed yesterday on a variety of aspects and elevations.   A layer of weak snow deeper in the snowpack also has the potential to release slabs anywhere from 2-4′ in depth in steep terrain.

Avoiding wind loaded features and steep terrain are your best bets for staying out of trouble today.

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Mon, February 24th, 2014
Above 2,500'
2 - Moderate
Avalanche risk
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
  • 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

Strong and gusty winds created very sensitive wind slabs during the day yesterday (see video & observation HERE).  An ample amount of light density snow was moved easily by these winds and formed slabs 2-3 feet thick.  We received one report of a snowmachine triggered avalanche in one of these wind loaded areas yesterday.  details HERE.  Natural and human triggered avalanche activity was observed and reported by multiple parties over the weekend.

Snowmachine triggered avalanche in a wind loaded starting zone in Triangle Bowl.  No one was injured or buried. (Photo: Kolin Smith)

Triangle Bowl

Today expect the sensitivity of these slabs to be on the decline.  It will still be possible to trigger slabs in many areas, as the winds affected slopes above and below treeline yesterday.  It’s important to learn how to recognize wind slabs.  Gullies that have been cross loaded, cornices and wind lips at the top of slopes, and any snow that has a smooth, rounded or pillowy look to it are worth avoiding today.

Avalanche Problem 2
  • 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

Weak faceted snow that is sitting between the late January crust and the snow that has fallen in February continues to hold the potential for deeper slabs to release.  This layer has been slowly gaining strength but still warrants your attention.  Combine this problem in areas where newly formed wind slabs are up to 3 feet on their own and the consequences (volume and depth of debris) are potentially unsurvivable.

Choosing lower angled terrain, <35 degrees, is the simplest way to avoid triggering slabs up to 3’ in depth.  Avoiding spots where slab depth quickly changes from thin to thick (i.e. starting zones, cross loaded gullies) will also help in avoiding trouble today.

Mon, February 24th, 2014

The most significant weather factor contributing to instability over the last 24 hours was wind.   Wind data from ridgetop stations were the following:
Sunburst– 13 avg   – 55 gust out of the East
Seattle– 22 avg         – 53 gust out of the South
Fresno– 18 avg         – 40 gust out of the North

Temperatures over the last 24 hours averaged 17 degrees F at the Sunburst weather station. It has been 6 days since the last precipitation has fallen.

Today expect sunny skies.   Winds speeds will remain elevated, averaging in the 20-30mph range out of the Southeast.   Temperatures at 1,000′ will be in the high 20s to low 30s F

A ridge of high pressure over most of Alaska is preventing moisture from reaching our area.   There is a slight chance for some light precipitation tomorrow, but much of that depends on the ability of that high pressure ridge to prevent low pressure from the south and west to move over us. The rest of the week looks to be dry and clear with slightly warming temperatures as high pressure will continue to dominate.

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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.