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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 9th, 2017 - 7:00AM
Expires
Fri, February 10th, 2017 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger above 1500′ in Turnagain Pass remains MODERATE due to a poor snowpack structure where triggering a large slab avalanche (2′-5′ thick) that breaks near the ground is possible. This is a low probability, but high consequence situation and it is critical that safe travel protocols are executed and avalanche rescue gear is carried. This means only one person on a slope at a time – in the event an avalanche is triggered, there are people capable of rescue. Additionally, there are some normal caution problems to keep an eye out for today, these are: shallow fresh wind slabs, sluffs in steep terrain and cornice breaks.  

Below 1500′ the avalanche danger is LOW where triggering an avalanche is unlikely.  

Summit Lake and Girdwood:   A poor snowpack structure  exists in these areas as well and human triggered avalanches breaking near the ground are possible. Make sure and check the Saturday Summit Summary  HERE.

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Thu, February 9th, 2017
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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 6 days since two separate snowmachine triggered avalanches occurred in Turnagain Pass zone, one in Seattle Creek and the other in Lynx Creek. Sunny weather this week has allowed many people to venture far and wide, testing a lot of terrain without incident. The likelihood for someone to find and trigger a large slab is decreasing as the snowpack adjusts, but the poor snowpack structure remains and the consequences are scary. For example the avalanche in Lynx Creek had a crown that was 1000’ wide and ran 1500’ into a large terrain trap. The slab was 1-4’ thick and was sitting on weak faceted snow near the ground. Both near miss avalanche accidents last week were triggered in thinner areas of the snowpack, on slopes that already had tracks on them. The tricky part about this particular avalanche problem is that it is very difficult to assess. Obvious signs like whumpfing and shooting cracks are unlikely and stability tests may not be reactive. Just because a slope has tracks on it does not mean it is safe. Likely places to trigger a deep persistent slab will be near rocks or in scoured zones. Likely triggers are large: snowmachines, groups of people or cornice falls. Identify and avoid terrain traps (like large gullies,) and always practice safe travel protocol, by only exposing one person at a time on steep slopes. 

Click HERE to read the detailed near miss report about the Seattle Creek avalanche where one snowmachiner was fully buried, and a quick rescue by his partners saved his life. Click HERE for the initial details about the Lynx Creek avalanche where luckily no one was caught. Stay tuned as we will be posting more info about this avalanche soon.

A photo of the crown on a NE aspect of Seattle Ridge avalanche near the Headwall. Photo taken 2/6/17 by Wendy Wagner

  

 

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

Wind slabs: Light flurries today combined with Easterly ridge top winds 10-20mph are expected and may form small isolated wind slabs on leeward features. There is also up to 8” of older loose snow available for transport. These wind slabs could from on a hard sun crust on Southern aspect and may be extra tender. Keep an eye out for blowing snow and pay attention to which slopes may be more loaded. Avoid pillowed or drifted snow or areas with stiff snow over soft snow on high consequence terrain.

Loose snow: With 4-8″ of loose snow on the surface over a dense base and possibly a few inches of light dry snow today, watch your sluff. 

Sun: It’s that time of year again. Although the sun is not expected today, should it appear, it has the potential to weaken the surface snow and make wind slabs and loose snow easier to trigger. 

Sun crust found on a SE aspect of Tincan early this week. Photo courtesy of Brooke Edwards

Additional Concern
  • 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

This weekend cornice cracks were reported along the back bowls of Seattle Ridge making some of these cornices extra sketchy. A few chunks have been triggered this week. Also these features can be difficult to see in poor visibility. Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche on the slope below. Give cornices extra space and avoid being under them. 

 

Weather
Thu, February 9th, 2017

Yesterday clear skies became overcast by early afternoon and winds were light from the East, 5-15mph. Temperatures averaged between 15F to 20F at all elevations. Snow flurries have been observed this morning at the Turnagain Pass DOT web cam, but no measurable amount has accumulated.

Today expect light snow flurries throughout the day, 1-3 € by this evening. Southeast ridge top winds are expected to be in the 10-20mph range and temperature are forecasted to drop throughout the day into the single digits (F) by this evening. A similar pattern is expected through tomorrow.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 17   0   0   49  
Summit Lake (1400′) 17   trace   .1   24  
Alyeska Mid (1700′) 21   0   0   45  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 15   E   3   13  
Seattle Ridge (2400′) 16   E   5   16  
Observations
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Riding Areas
Updated Mon, December 02nd, 2019

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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