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Fri, December 19th, 2014 - 7:00AM
Sat, December 20th, 2014 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger continues to be CONSIDERABLE in the alpine today.   Dense slabs up to 3′ in depth could be triggered by skiers and riders between 2,500-4,000′ in elevation.   Avoidance of terrain over 35 degrees and trigger points such as steep rollovers and areas with thin snow coverage will be critical today.

In the treeline elevations, between 1,000-2,500′, the danger is MODERATE.   Slabs up to 2′ in depth could be triggered in steep terrain and areas where the overall snowpack is more shallow.   Avalanches initiated in the higher elevations have the potential to run down into this elevation band today.

Below treeline zero to a few inches of snow sit on the ground.   Rocks, stumps and open water are the main issues you will encounter at this elevation.

Yesterday a skier triggered an avalanche on the Southwest face of Sunburst.   The skier was caught, carried and fully buried.   Fortunately the skier and his partner were able to dig him out and walk away without injury.   Similar avalanches are possible today as a layer of buried surface hoar sitting under 2-3′ deep slabs holds the potential to propagate across large areas.

Sunburst skier triggered 12-18-14

click HERE, HERE and HERE for more detailed info on this incident.   Stay tuned for a more thorough write up on this incident.

Fri, December 19th, 2014
Above 2,500'
3 - Considerable
Avalanche risk
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. 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

Our main avalanche concern today is one that will not go away quickly.  Surface hoar that formed a week ago has been preserved and is sitting below 1-3’ slabs.  Typically surface hoar gets knocked over and blown around before a slab builds on top of it.  That is not the case with our current snowpack.  The snowfall that began on December 13th came in with very little wind and allowed this layer to be buried intact.  We have been investigating this layer over the last several days and we have found it in all pits above 2,700’.

The tricky part with this set up now is that it is gradually becoming more difficult to trigger an avalanche.  We know this based on our test results in snow pits.  Unfortunately, it will be possible to test this layer by traveling in steeper terrain and not get results (NOT RECOMMENDED!)  Exceptions to this were found on Sunburst and in the Summit Lake region, where skiers remotely triggered an avalanche from 50’ away.  In areas such as this where the snowpack is thinner, it will be easier to initiate an avalanche today.

The nature of buried surface hoar is such that it persists as a weak layer in the snowpack for many days, sometimes weeks after it becomes buried.  Because of this we will be tip toeing around the mountains for the foreseeable future.

In order to stay out of trouble it is best to avoid steep terrain.  Terrain on all aspects over 35 degrees should be treated as suspect.  Avalanches, if initiated have the very real potential of propagating across large areas, making escape difficult at best.  There is plenty of evidence to support this and the problem will potentially take a long time to go away.  

Below 2,500’ in elevation the likelihood of triggering a slab avalanche 1-2’ in depth will be less than in the higher elevations.  A crust that has formed in the middle of this newest slab will make it harder to trigger any buried surface hoar that survived the rain and wet snow.  We cannot rule out the potential for triggering slabs in this elevation band and it will be important to keep slope angles low until we see more signs of this layer becoming non-reactive. 

Paying attention to what is above you, including other groups, when in this elevation band (bewteen 1,500-2,500′) will be important as avalanches initiated in the higher elevations could run into the mid elevations today.

Fri, December 19th, 2014

In the past 24 hours the precipitation has shut off and the temperatures have cooled – see table below.   Winds have picked up slightly overnight along ridge tops and are averaging in the 20mph range out of the East at Sunburst this morning.

Today expect light snow showers with 2 € accumulation possible.   Temperatures at 1,000′ will be in the high 20s to low 30s F range.   Winds will be out of the Northeast at 10-20 mph.

The extended outlook is showing some potential for more precipitation as a complex series of Lows move through the Gulf and along the Aleutian chain over the next several days.   There is a high level of uncertainty as to the timing and track of these systems with the next best chance for snow coming Sunday into the early part of next week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  28  0 0  28
Summit Lake (1400′)  24  0  0  4
Alyeska Mid (1700′)  27  0  0  18.5

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  25  ENE  11 42
Seattle Ridge (2400′)  22 N/A  N/A  N/A
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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.