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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, December 27th, 2013 - 7:00AM
Expires
Sat, December 28th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Continued red flags, including whoomphing (collapsing) in the snowpack are keeping the danger rating at  MODERATE above treeline. Steeper slopes should be approached with caution, as the slab/weak layer problem is well understood.  Despite the duration we’ve had without new snow, lingering instability is keeping us wary of steeper terrain.

Snow is forecasted for this evening, meaning a small increase in the avalanche danger is expected tomorrow.  

Special Announcements

Check out this Kickstarter project for an all female ski movie.   The project will include filming within our own Chugach National Forest, and will have local talent in the cast.  It will be used as an educational tool for avalanche awareness trainings with SheJumps.  The project is soliciting support and has 20 days to the deadline.

Fri, December 27th, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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. 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

The poor structure of the snowpack is the culprit behind the collapsing that’s keeping us worried.  The most reactive layers we’ve been seeing are the facets above the early December “drizzle” crust (see pit profile here).  This layer is showing a tendency to propagate in some pit tests, and we believe it is the big player in most of the recent natural and skier triggered avalanches. 

Check out Fitz’s video for a discussion of managing the Moderate problem on Thursday.

 

 

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

There remains some evidence of wind slab avalanche activity from the wind storm on Monday.  On Thursday we found numerous mid slope crown lines near Crow Pass from avalanches that presumably happened during that wind event.  We can expect some areas to be holding stiff wind slab that didn’t slide spontaneously, but may be triggered by a person hitting a trigger point.  

Weather
Fri, December 27th, 2013

Weather has been consistently benign since Monday with cold, clear, and calm conditions.  Temperatures are a little warmer at the ridgetops today, so don’t let cold Anchorage temperatures keep you at home today.  

Look for increasing clouds today, and snowfall is expected to commence tonight in Eastern Turnagain Arm.  Up to 4-8 inches of snow is in the forecast for tonight!  

The storm will be short lived as the front sweeps across southcentral Alaska, with snow tapering Saturday morning and ending.

Observations
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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.