Turnagain Pass RSS

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Mon, January 30th, 2017 - 7:00AM
Tue, January 31st, 2017 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE in the Turnagain Pass area. On slopes over 35 degrees and above ~1,500′ there is the possibility for triggering a large (2-3′) slab avalanche that breaks lower in the snowpack. The most suspect areas are on the South end of Turnagain Pass where the snowpack is shallower and there has been little traffic this season. In addition, watch for fresh shallow wind slabs to be formed, and possibly easy to trigger, due to an increase in winds along ridgelines. Last, cornice falls are still a concern along with glide avalanches.  Below 1,000′ the danger is LOW where surface crusts exist.

Girdwood Valley:   A shallower snowpack exists in the Girdwood Valley. Slab avalanches have the potential to be larger, over 3′ thick, and break near the ground.  

Summit Lake:   Dangerous human triggered slab avalanche conditions persist in the Summit Lake zone. Check out the Saturday Summit Summary  HERE.  

**The probability of triggering one of these large slabs is decreasing but the consequences remain high. This is more reason to be sure to carry your rescue gear and practice safe travel protocol – such as exposing one person at a time, grouping up in safe zones, having escape routes planned and watching your partners!  

Special Announcements

Dangerous avalanche conditions persist in many areas around Southcentral Alaska
including the  Southern Kenai Mountains,  Hatcher Pass and  Anchorage Front Range

  • A preliminary report is out with a few photos regarding the snowmachine avalanche fatality in the Snug Harbor area on Saturday. The final report with finalized details on the events, rescue and snowpack analysis will be posted in the next couple days. Our thoughts continue to be with the victim’s family, friends and rescuers.
  • The  Southern Kenai Mountains, including Snug Harbor and Lost Lake zones continue to have dangerous avalanche conditions. This region is out of the advisory area but large human triggered slab avalanches 3-5 thick are possible on slopes over 35 degrees.  Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential.
  • Click  HERE  for the Hatcher Pass Avalanche Center advisory and  HERE  for recent snowpack observations.
Mon, January 30th, 2017
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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
  • 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

It has been just over 3 days since the tail end of the January 26th warm storm event added 2-3′ of snow to the upper elevations. This event overloaded a variety of weak layers in the pre-existing snowpack and caused a widespread avalanche cycle in the region. The good news is the snowpack in the heart of Turnagain Pass is showing signs of adjusting to the load, the bad news is other areas are not. This can make for difficult snowpack assessment as the weak layers of concern (depth hoar, facets and buried surface hoar) are lurking anywhere from 2-4+ feet below the surface. Thicker snowpacks, as found at Turnagain Pass and on the North end of the Pass had a stronger snowpack to begin with and this has been a big factor in the area beginning to adjust quicker. This is opposed to the persisting unstable snowpack found South of Turnagain Pass and the Girdwood Valley.

In general – this is a high consequence but low probability situation. If choosing to ride or ski the steeper terrain, we recommend using safe travel protocol, especially exposing one person at a time and grouping up in safe zones. If a large slab is triggered it may run further than expected and wrap around terrain features taking out mid-slope relative safe zones. Since the weak layers in question are fairly deep, it will likely take finding a thin spot in the slab or a big trigger to initiate an avalanche.

A few points to consider today if visibility holds enough for travel to the high elevations:

  1. Obvious signs of instability may not be present (such as whumphing and shooting cracks)
  2. Large groups of people and/or snowmachines could initiate a failure and trigger an avalanche (or cornice fall)
  3. Cornice falls may trigger large slabs 
  4. Again, areas surrounding the main Turnagain Pass zone are the most suspect for these large slides, though Turnagain is not completely out of the woods.
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

With Several inches of soft settled powder on the surface, watch for winds today to take this and form soft wind slabs along ridgelines and potentially cross-load upper elevation gullies. These fresh slabs could be sensitive to human triggers and likely to be on the shallow end, up to a foot thick. Watching for recent wind loading, stiffer snow over softer snow, cracks that shoot out from you and performing quick hand pits are all good ways to assess whether you have found a wind slab. 

Winds have already impacted the Eddies ridge, to some degree, yesterday (photo: Andy Moderow)

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

For those traveling in the Seattle Ridge area, there are a few glide cracks opening up above the flats along the Northern side facing the road. There are also a few cracks on the backside. Watching for these and limiting time underneath them is recommended.

Glide cracks on the North side of Seattle Ridge (photo: Andy Moderow)

Mon, January 30th, 2017

Mostly sunny skies filled the region yesterday before clouds began filtering through later in the day. Ridgetop winds were light to moderate from the West before switching to Easterly mid-day and remaining light with gusts near 20mph. Temperatures warmed a few degrees, into the mid teens F at all elevations yesterday.

This morning, we are expecting clouds to begin filling in as a frontal boundary heads our way associated with a low-pressure system in the Bering. Snow, falling to sea level, is expected to begin later today with only 1-3″ expected by this evening. Another 2-6″ of snow is forecast for tonight into tomorrow morning (also falling to sea level). Ridgetop winds will bump up today into the 15-25mph range from the Southeast and bump up again into the 20-35mph range overnight. Temperatures should continue to climb to ~30F at sea level, the mid 20’sF at the higher elevations.

For Tuesday into Wednesday, the front is expected to stall and weaken, this will bring a chance for another few inches of snow and decreasing winds. Later in the week, high pressure builds bringing clear sky conditions with cooler temperatures.

*THANK YOU to whomever cleared the rime off the Seattle Ridge weather station  yesterday!!!!  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 17   0   0   62  
Summit Lake (1400′) 10   0   0   25  
Alyeska Mid (1700′) 20   0    0 52  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14   E   7   23  
Seattle Ridge (2400′) 15   SE   13*   26*
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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.