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Wed, January 9th, 2013 - 7:00AM
Thu, January 10th, 2013 - 7:00AM
Kevin Wright
Avalanche risk The Bottom Line

Sunny skies today after 2 solid weeks of stormy weather will make today the most likely day for somebody to die in an avalanche.   Another large avalanche was triggered late yesterday in Turnagain Pass on the snowmachine route up to Seattle Ridge.   The snowpack is still reactive to human triggers, and despite a decreasing possibility of causing an avalanche, if one is triggered it will be large, deep, and deadly.   A CONSIDERABLE hazard can be found above treeline, meaning human triggered avalanches are likely.   Conservative route choices are essential.    

Wed, January 9th, 2013
Above 2,500'
3 - Considerable
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
  • 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

Last night we got reports of an avalanche on Repeat Offender, the site of the large fatal avalanche in 1999.  A group of snowmachiners had just started descending the standard trail from Seattle ridge when it released remotely 100 yards away.  Initial reports estimate the size as 600-1200 feet wide.  It undoubtedly took the entire depth of the snowpack, breaking on old October and November weak layers.  Reports say that Main Bowl also slid on the west side of the ridge.

The deep slab problem is difficult to understand because it won’t show signs of instability until it avalanches in a big way.  You also won’t see a lot of slopes avalanching on the same day, meaning that the mountains will look good and enticing.  The problem is that when you find a trigger point, the resulting slide will be much bigger than you want.  This is a low frequency, but very high consequence problem that is difficult to predict.

We have compiled ample evidence to show that the mountains are ripe for this to happen again.  Over 10 feet of new snow in the last 2 weeks has already brought down a number of large avalanches including at Tincan, Seattle ridge, Johnson Pass, Portage, and elsewhere.  This is the most dangerous persistent deep slab problem we’ve had in our region in a number of years.  The only way to avoid becoming a statistic is to alter our behavior and choose conservative, lower angle terrain.

Avalanche Problem 2
  • 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

Yesterday we found a small reactive wind slab in the top 6 inches of surface snow at treeline.  Wind deposit areas may have this layer of stiffer, less stable snow.  Compared to the deep slab issue, this is a relatively minor and manageable problem. 

Wed, January 9th, 2013

A few inches of colder snow fell yesterday with light wind in the mountains.   Today is likely to be the first day since December 22nd without any snowfall.   Expect sunny skies and light wind in the mountains with slightly colder temperatures.  

The clear weather will give way to another weak storm tonight, with snow expected again tomorrow and a return to warm and moist flow by the weekend.

Recent Observations for Turnagain Pass
Date Region Location
12/02/23 Turnagain Observation: Seattle Ridge
12/02/23 Turnagain Observation: Tincan South Side
12/02/23 Turnagain Observation: Eddies up track
12/01/23 Avalanche: Sunburst
12/01/23 Turnagain Observation: Eddie’s trees
12/01/23 Turnagain Observation: Turnagain – God’s Country
11/30/23 Turnagain Avalanche: Tincan Trees
11/27/23 Turnagain Avalanche: Tincan Ridge
11/26/23 Turnagain Observation: Road report: Slide with dirt on Repeat offender
11/26/23 Turnagain Observation: Pete’s North
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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.