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Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, February 17th, 2016 - 7:00AM
Expires
Thu, February 18th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger remains  MODERATE  today in the Alpine (above 2500′) where lingering wind slabs 1-3′ deep may prove reactive in steep terrain greater than 35 degrees. Skiers/snowmachiners, direct sun or cornice fall are all likely triggers, particularly later in the day when daytime temperatures peak.  

In the Treeline elevation band (1,000′ €“ 2500′) the danger is also  MODERATE,  where the potential for glide avalanches continues to be an issue.  

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Wed, February 17th, 2016
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
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
Moderate (2)
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
  • 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

Lingering wind and storm slabs will still be possible to trigger in steep (>35 degree), wind-loaded terrain. Observations yesterday identified a weak interface in the snowpack at the boundary of the most recent storm and the snow surface it landed on, approximately 15-20″ below the surface. Preserved precipitation particles remain sandwiched between stiffer snow layers above and below and were still reactive in stability tests. We suspect this structure combined with rapid warming and sunshine were reason the skier triggered wind slab avalanches in Goldpan area occurred on Monday and what the cornice triggered slab avalanches are running on as well. Avalanching has not been widespread and in general the snowpack has shown good bonding. However, this particular set-up needs to be considered, especially later in the day. In the Girdwood Valley, a thin rain crust was observed up to 3100′ as the bed surface of wind/storm slabs that released during avalanche mitigation.

We have reached the time in Alaska where sun is a now a factor. ‘It feels like spring’ has been the general sentiment. Pay attention to increased solar input, warm ambient temperatures and changing surface conditions in the terrain you are traveling through. Warming may make slabs easier to trigger with the weight of a skier or snowmachine. Increased rollerball activity is a good indicator of the snowpack heating up rapidly and a sign that the surface is weakening. Avoid steep (>35 degrees), leeward slopes (South and West) late in the afternoon when the sun is at its strongest. 

Loose snow avalanches: There is the potential for wet loose avalanches on steep southerly slopes and dry loose avalanches on steep northerly slopes. Remember these will release at your feet but may gain momentum and catch you from behind as you travel downhill.  Avoid being knocked off your feet in steep high consequence terrain. 

Another look at at the skier triggered avalanches in Goldpan on 2/15.

 

Avalanche Problem 2
  • 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

Yesterday we were able to get a closer look at the cornice fall on the South side of Magnum. It ran all the way to the drainage below and had pulled pockets of slab out with it. It covered the region where the skin track often goes. There were a number of reports from the advisory area of other large cornice falls that triggered the slopes below. Cornices will continue to be tender and travel on or below should be avoided. Remember they can break farther back than expected. Warming temperatures in the afternoon and direct sunshine may increase the hazard for both natural and human triggered cornice fall. 

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

The glide avalanche problem continues. We observed two recent releases yesterday and glide cracks grow daily. All that needs to be said is avoid travel underneath glide cracks.

 

 

 Glide avalanche on Seattle Ridge.

Weather
Wed, February 17th, 2016

Yesterday was mostly clear with periods of valley fog. Temperatures were in the low 20Fs to mid 30Fs. Winds were light and variable. Skies were mostly clear overnight.  

Today will be mostly sunny with a chance of valley fog. This afternoon may become partly cloudy. Temperatures will be in the mid 20Fs to mid 30Fs and winds will be Easterly 15-25 mph.

Tonight will be partly cloudy with another day of sunshine on tap for tomorrow as we sit under a ridge of high pressure for a couple days.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24    0 0   103  
Summit Lake (1400′) 22  0 0 30  
Alyeska Mid (1700′) 25  0 0 85

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  22 variable   7   19  
Seattle Ridge (2400′)  28  n/a n/a   n/a  
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Riding Areas
Updated Fri, May 01st, 2020

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

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Closed as of May 1. Thanks for a fun, safe season!
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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.