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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, November 24th, 2016 - 7:00AM
Expires
Fri, November 25th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains  CONSIDERABLE  for all slopes near and above treeline. Due to a buried layer of surface hoar human triggered slab avalanches 10-20″ thick are likely and may release on lower angled slopes.  These can also release remotely from ridgelines or break above you.

A  MODERATE  danger exists in the trees where triggering a slab avalanche is possible on open slopes or debris running from an avalanche above may occur. Extra caution and safe travel protocol is advised if venturing in the backcountry.  Avoid travel underneath glide cracks.  

***Observations from the Summit Lake area on the Kenai are showing a similarly unstable snowpack. Weekly summaries will begin on December 2nd.

Special Announcements

We are thankful for snow in the mountains and sunshine but please don’t be a turkey and get caught in a holiday avalanche!  The CNFAIC forecasters  really appreciate all the observations submitted in the past week! Thank you! Have a safe and happy holiday weekend!  

Motorized use on Turnagain Pass is closed due to insufficient snow cover.  Please see riding area status at the bottom of this page for the most up-to-date information.

Thu, November 24th, 2016
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

A widespread layer of surface hoar (that formed on November 15th/16th) is buried 10-20″ below the surface and continues to be reactive. Human triggered avalanches were reported again yesterday. That makes a full week of avalanches… persistent slab avalanches. Yesterday an observer noted being able to get out onto the slab and having it break above as them well as triggering a slope that already had multiple tracks on it. They also noted that it was hard to escape the fast moving slide. These are all reasons to have your guard up, not trust the snowpack and choose your terrain wisely. In addition, folks venturing to Magnum also triggered avalanches in terrain that has not seen traffic yet this season. There are still many slopes that could potentially slide in the Turnagain Pass area. Don’t let your quest to find fresh tracks lure you into a consequential avalanche. If you do go out today pay attention to the surface conditions. What will be buried by new snow? There is a new layer of surface hoar forming and the surface snow is also being weakened(faceting) due to the colder temperatures. 

Again, things to keep in mind for the sunny day forecast:

The snowpack is still unstable, remote triggering is possible. Be on the lookout for shooting cracks.

  • The larger and more connected the slope is, the larger the avalanche = higher consequences
  • Slabs can break above you, making it more difficult to escape
  • Be aware of OTHER groups and WHO IS BELOW YOU

Here is a little more information on Persistent Slabs and Travel Advice. This comes from the Utah Avalanche Center’s Avalanche Problem Toolbox, authors: Drew Hardesty and Wendy Wagner!

Skier triggered slide yesterday on Sunburst. Slope had previous tracks on it. Photo: Mike Records

Avalanche Problem 2
  • 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

There were two glide avalanches reported in the past two days and glide cracks are visible in the other pieces of terrain. Give these wide berth, minimize time spent underneath glide cracks and remember these are totally unpredicatable. They are not triggered by humans and are the entire snowpack releasing. 

 

 

 

Sunburst glide avalanche and glide crack. This released sometime between Tuesday afternoon and Wednesday morning. Photo: David Evans

 

Weather
Thu, November 24th, 2016

Yesterday was a clear sunny day in the mountains. Winds were light and temperatures were in the mid 20Fs. Overnight the temperatures dipped into the teens in valleys and winds remained light and variable.  

Today will be similar with clear skies and temperatures in the 20Fs. WInds will pick up to 10-20mph from the NW. There will be increasing clouds overnight and a chance of snow showers.  

Tomorrow will be mostly cloudy with snow showers, 0-3″ possible. This system is forecasted to linger and bring snow to the region into next week.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  24 0    0 18  
Summit Lake (1400′)  14 0 0 2  
Alyeska Mid (1700′) 27   0 0 2

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24  variable 3    12
Seattle Ridge (2400′) 26    variable 3    9
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Riding Areas

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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.