Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 28th, 2017 - 7:00AM
Expires
Fri, December 29th, 2017 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

There is a  MODERATE  avalanche danger today in the alpine, above 3,000′ where triggering a large and dangerous deep slab avalanche is possible due to weak snow near the ground. Additionally triggering a hard wind slab is still possible on leeward, steep, unsupported slopes in the alpine.  Evaluate snow and terrain carefully.

The avalanche danger is LOW at Treeline. LOW danger does not mean NO danger. Pockets of unstable snow are not out of the question on isolated terrain features below 2500′.  

There is no hazard rating below 1,000′ due to a lack of snow.  

*Please remember your safe travel practices! This includes, exposing one person at a time in avalanche terrain, watching your partners, being rescue ready and having an escape route planned.

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Thu, December 28th, 2017
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
No Rating (0)
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

If this is your first day reading the advisory this winter it is important to know that deep slab avalanches have been a concern in the advisory now for two weeks. If you have been following along all season we are not trying sound like a broken record but the message is the same. This snow pack set-up continues to warrant elevated caution and respect. It is a high consequence avalanche problem that is impossible to outsmart. The ingredients for a deep slab avalanches have been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche in the early December storm cycle. There is a hard slab, 3-5+ feet thick sitting on top of weak sugary snow (basal facets) near the ground. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations.

 

When dealing with a deep slab avalanche problem, keep in mind:

  • Large snow covered slopes that do not have piles of old debris under them are all suspect 
  • Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks   
  • It is possible to trigger this avalanche from below and it could run further than expected 
  • Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
  • Thicker areas (3-5+’ thick) will be difficult to trigger and several tracks may be on a slope before someone finds a trigger point

 

 

An avalanche on the NW face of Pastoral was triggered one week ago by a party of two skies traveling on the low angle terrain below. They were very lucky and were able to get out of the way of the debris. This avalanche also triggered a second avalanche on an adjacent slope over 1000 feet away. Deep slabs can linger for long periods of time and warrants extra caution in places that have not avalanched. 

 

 A view of the North facing terrain of Corn Biscuit taken yesterday from Magnum. Some old debris can be seen on looker right side, lower North Chutes, but much of the upper elevation terrain of Corn Biscuit and Super Bowl are still intact and didn’t have evidence of much avalanche activity from mid December. 

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

As we move further away from a wind event that ended on Dec.24th wind slabs are becoming more difficult to trigger. Cold temperatures are making the snow more brittle, and instead of seeing high energy shooting cracks we’re seeing wind boards crumble underfoot. Triggering an old wind slab is still possible in very steep terrain with more potential in the alpine zone. Places you might trigger an old wind slab will be in steep couloirs, large unsupported terrain features, or in thin rocky areas. Triggering a wind slab in the Treeline zone is becoming less likely, but isn’t out of the question on isolated features. The tricky part about this problem is that it will be hard to evaluate a steep slope before committing to it. The other big risk is the possibility of initiating a much larger and more dangerous avalanche if you are above 3000’. Identify features that have fat, smooth, pillow-type shapes and be suspect of any slope that may harbor a more dangerous deep slab problem. 

 

Steep wind loaded gullies adjacent to thin rocky areas on a SE aspect on Seattle Ridge. This is one example of where triggering a wind slab is possible.  

Weather
Thu, December 28th, 2017

Yesterday skies were clear and temperatures along ridgetops averaged in the teens with pockets of single digit (F) temps found at valley bottoms. Winds were light from the East. No precipitation was recorded.  

Today looks similar with mostly clear skies, light and variable winds, and temperatures averaging in the teens to low 20F’s. No precip is expected.  

A pattern change is in the forecast for this weekend beginning Sunday with a series of low pressure systems moving into our region. This storms should bring warmer temperatures, precipitation (snow and possible rain) and strong winds. At this point it is uncertain how these storms will track across the region, but stay tuned for more info as we move closer to the weekend.  

*This 1″ recorded at Summit Lake is likely from ice crystals in the air and not from snow falling from the atmosphere.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 20   0   0   30  
Summit Lake (1400′) 5   *1   *0.1   12  
Alyeska Mid (1700′) 21   0   0   25  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16   ENE   5   17  
Seattle Ridge (2400′) 21   SE   7   17  
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Riding Areas
Updated Wed, December 11th, 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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