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Sat, January 26th, 2013 - 7:00AM
Sun, January 27th, 2013 - 7:00AM
Kevin Wright
Avalanche risk The Bottom Line

A MODERATE danger lingers above treeline for shallow windslab, unstable cornices, and stubborn deep slab.   The windslab and cornice are avoidable and manageable problems in moderate terrain.   Deep slab avalanches are becoming less likely, but high consequences remain if one is triggered.   Below treeline is a solid supportable crust, making the avalanche danger LOW below 2000 feet.

Sat, January 26th, 2013
Above 2,500'
2 - Moderate
Avalanche risk
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
  • 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

The last couple days have brought steady stiff wind, and combined with light snowfall it has created a subtle stiffer layer of snow on multiple aspects.  Yesterday we took a closer look at a couple small windslabs on the south side of Tincan.  The small, isolated windslabs were becoming less likely to trigger.  There is no persistent weak layer associated, but the subtle structure differences in the layering are just enough to make it break at an interface 1 foot deep.

This kind of windslab is manageable in the right terrain.  It should be expected near ridges, under cornices, and may be easy to trigger the small low volume pockets.  The manageability of this problem is directly related to the terrain.  If you get surprised in steep, high commitment terrain it could very well be dangerous. 

Cornices are building and may be unstable.  One of the small slabs at Tincan was triggered by a naturally failing cornice.  We can expect other cornices around the region to be large and easy to collapse under the weight of a person, snowmachine, or dog. 

Avalanche Problem 2
  • 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

The deep slab is getting to be less of a problem.  However, the high consequence of a large deep slab avalanche is still affecting my own travel decisions despite the low probability of triggering one at this time.  Causing one today will require the right combination of a steep slope and shallow trigger point. 

Sat, January 26th, 2013

Temperatures have dropped dramatically over the last 2 days, and despite sunny weather today, it’s going to be a cold one.   The highest temperature we see this morning is 10 degrees in Portage and it drops as you get to higher elevations.   Above 3000 feet is negative temperatures.  

Wind has been strong and steady at the ridgetops and in Turnagain Arm recently, a trend which will continue today.   The wind chill factor up high will be quite cold.   We can expect snow plumes blowing off the mountains, building windslabs and creating cornices.   Some areas will see a strong northwest wind through channeled terrain.  

Below treeline the combination of recent thawing temperatures and the deep freeze yesterday has created a solid supportable crust from 0-1500 feet elevation.   There is good skate skiing potential on the crust today around Turnagain Pass.

Wendy will issue the next advisory Sunday morning, January 26th.

Recent Observations for Turnagain Pass
Date Region Location
12/06/23 Turnagain Observation: Eddies
12/05/23 Turnagain Observation: Sunburst
12/04/23 Turnagain Observation: Lynx Creek
12/04/23 Turnagain Observation: Sunburst, 2400′ – 3100′ NW ridge common uptrack.
12/03/23 Turnagain Observation: Center Ridge
12/03/23 Turnagain Observation: Magnum
12/03/23 Turnagain Observation: West ridge of Tincan Peak and Peak 4400
12/03/23 Turnagain Observation: Lipps
12/02/23 Turnagain Observation: Seattle Ridge
12/02/23 Turnagain Observation: Tincan South Side
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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.