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Sat, December 13th, 2014 - 7:00AM
Sun, December 14th, 2014 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger is LOW in the treeline and alpine elevations.   New snow arriving today will not be quite enough (3-5 €) to bump up the danger except for in isolated pockets on steep upper elevation leeward slopes.   On these terrain features the avalanche danger will be MODERATE; expect small pockets of slab up to 6 € deep to be very sensitive to human triggers and low in volume.

Below treeline, between sea level and 1,500′, there is little to no snow on the ground and no danger rating.

Firm snow surfaces between 1,500′-2,500′ require careful travel today.   Early season hazards such as stumps, rocks and open water will begin to be covered with a thin layer of snow.   Pay attention to these obstacles in these areas in order to avoid injury.

Sat, December 13th, 2014
Above 2,500'
1 - Low
Avalanche risk
1 - Low
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
  • Normal Caution
    Normal Caution
Normal Caution
Normal Caution means triggering an avalanche is unlikely but not impossible.
More info at Avalanche.org

It has now been 5 days since the last precipitation fell.  During this past week temperatures have cooled and allowed a once rain soaked surface to refreeze between 1,500′-2,500’.  As you might guess the snow surface in this elevation band is firm to say the least.  “Boilerplate” and “coral reef” are terms that come to mind when thinking about this rain crust.  Once above this elevation band, you will find enjoyable and mostly stable snow.  Significant slope tests in the form of cornices were witnessed on Thursday with minimal avalanche activity.  A lack of buried persistent weak layers in the snowpack in the higher elevations has allowed instability to be confined to during and immediately after this most recent (now not so recent) storm.

New snow amounts today will be in the 3-5” range and are not enough to create slabs big enough to be of concern.  You may find exceptions to this on steep wind loaded slopes in the higher elevations.  Paying attention to areas that are receiving enough snow and wind to build slabs over 6” will be important today.  Keep in mind that these areas will be few and far between.  Volume of any potential slabs today should be very low.  Any new snow falling today will be touching down on a layer of surface hoar in many areas and consequentially will be sensitive to human triggers.

Other hazards in the mountains today will be traveling in the mid elevations on firm surfaces (hint: sharpen your edges), exposed rocks, stumps, and open water.

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

We are tracking several areas in the forecast zone that have glide avalanches.  Tincan trees, Eddies, and the East face of Pyramid all have glide avalanches of varying size.  No new movement was observed yesterday.  As always steer clear of any open cracks you see on the snow surface.  These avalanches are moving in super slow motion but could change speed without the normal warning signs that we typically associate with avalanche release.

Sat, December 13th, 2014

Over the past 24 hours no new snow has fallen in the forecast area.   Winds have been light out of the East.   Temperatures have averaged in the mid 20s F at ridge tops.

Today expect light snow to begin by midday.   Accumulations look to be light, in the 3-5 € range.   Winds will be out of the Southeast at 15 to 25 mph.   Temperatures will be just below freezing (32F) at 1,000′.

The extended outlook is calling for continued snow showers overnight and through the rest of the weekend.   The most intense precipitation should arrive tonight with another dose coming Sunday night.   Temperatures over the next few days look to fluctuate and warm enough for rain/snow line to climb into the 1,000′-2,000′ range.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26  0  0  18
Summit Lake (1400′) 17  0  0  4
Alyeska Mid (1700′) 27  0  0  12.4

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22  E  10  21
Seattle Ridge (2400′) 25  ENE  8  25
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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.