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Wed, April 12th, 2017 - 7:00AM
Thu, April 13th, 2017 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

The overall avalanche danger is  MODERATE  at all elevations. There are two main avalanche problems to deal with: 1) The possibility remains for triggering a large and dangerous deep slab avalanche (3-6′ deep) on slopes over 35 degrees. Most likely slopes are those above 1,500′ with a Northerly aspect and harboring cold dry snow. 2) A very warm day is on tap and wet snow avalanches are possible, and may even be likely, this afternoon. These could be wet slab avalanches and/or wet loose avalanches on Southerly aspects as well as all aspects below 1,500′. The danger could  rise to CONSIDERABLE  in shallow snowpack zones where wet snow avalanches may occur naturally.

Hiking in Portage Valley and on summer trails around the Advisory area (including the Turnagain Arm Trail a.k.a the bike path).   Extra caution is advised during the afternoon and evening hours for triails that cross under avalanche paths. Avalanches are still possible at the higher elevations that could send debris over snow-free hiking trails.

Summit Lake:   See the  Saturday Summit Summary  HERE  and observations from the last few days  HERE.


Special Announcements
  • Due to low snow cover, Twentymile drainage is now closed to snowmachines. You can check the status of riding areas at the bottom of this page.
Wed, April 12th, 2017
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. 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

With long days and sunny weather ahead, many folks may be thinking about summertime activities – however, winter is still alive in the mountains. Dry settled powder covers aspects on the North side of the compass at the mid and upper elevations and these zones are the exact places we are concerned about deep slab avalanches. A layer of buried surface hoar exists anywhere from 2-6′ below the surface and is still producing concerning stability test results. This layer was also the culprit weak layer in many human triggered deep slab avalanches over last weekend. This problem is one of low probability but high consequence as these are large and potentially unsurvivable slides. Over time, the likelihood decreses but has not gone away – by any means. Points to think about if you are getting out this week:

  • Because the weak layer is deep, it is tough to effect and therefore tough to trigger. It will take someone hitting a ‘thin spot’ in the slab, often where rocks sit just under the surface, or a large trigger such as a snowmachine and/or groups of people.
  • These slides can be triggered remotely, for example, from a ridge or bench on the top/side or below. 
  • There may be no signs of instability before the slope shatters 
  • Several tracks may be on a slope before it releases

If wishing not to roll the dice on this deep slab possibility, one can always stick to slopes under 35 degrees on these shaded aspects with nothing steeper above you.

Photo: Deep slab avalanches that were believed to be snowmachine triggered several days ago on April 7th or 8th in Main Bowl/1st Bowl of Seattle Creek. Older photo, but this gives an idea of the deep slab avalanche issue we are dealing with. Crown heights are 3-6 feet. 


 If you haven’t seen it yet, this video shows a snowpack stability test at a thin spot in the slab – likely trigger point. This test was done near a sub-ridge where slabs often are thinner due to scouring during storms.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

As the day warms up – into the 50’sF in the parking lots possibly – expect the Southerly aspects and lower elevation snowpack to become so wet and saturated it is unsupportable to snowmachines, skis or boots. When the pack gets this loose then it’s time to head to a different aspect as slopes steep enough to slide become suspect for wet snow avalanches. Human triggered wet loose slides and wet slabs are a possibility late in the day and nothing to mess with.

Springtime melt-freeze cycle (Southerly aspects): We are moving into what we call a melt-freeze cycle. Low avalanche danger in the morning, Moderate to Considerable danger in the afternoon. When the snowpack is frozen in the morning from nighttime cooling, it’s stable. During the course of the day the pack warms to the point it is punchy and unsupportable, this is when the avalanche danger rises with the chance for wet snow avalanches. Wet avalanches can be small to very large. For today, keep an eye on Southerly slopes and see if any new wet loose avalanches release from under rocks or other dark features.  

Wed, April 12th, 2017

Sunny skies and very light Westerly winds were over the region yesterday. Temperatures were warm – between 45-50F at 1,000′ and below, along ridgelines in the 30-35F range. During the past 24-hours ridgetop winds have been 0-10 mph from the West.

Overnight, clear skies have dropped lower elevation and valley bottom temperatures into the 20’sF while upper elevations have remained warm (~30F) due to a warmer air mass that has moved in. Today, temperatures should climb rapidly to near 50+F with direct sunshine in the lower elevations while ridgetops cloud push into the 35-40F range. Skies should remain blue and ridgetop winds light, in the 5-10mph range from the Northwest with some stronger gusts on the peaks. This could be the warmest day of the season.

Long, warm and sunny days look to be in our future until Friday.  

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0   0   71  
Summit Lake (1400′) 36   0   0   24  
Alyeska Mid (1700′) 37   0   0   66  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29   W   4   12  
Seattle Ridge (2400′) 33   NW   4   19  
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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.