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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 20th, 2014 - 7:00AM
Expires
Fri, February 21st, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

In the past 24 hours we have not heard of any new avalanche activity.  However, the well documented weak layer above the January crust is still demonstrating problems.  

MODERATE avalanche danger is widespread across our forecast zone.  Careful terrain management is still warranted because of the known weak layer.  Natural avalanches will be unlikely today, human triggered avalanches are very possible in areas with steeper terrain.  The depth of potential avalanches is getting to be significant – 3 feet or more in wind loaded areas.  

Specific areas of  CONSIDERABLE danger may still be present where the last storm deposited the most snow (Girdwood valley and other locations).  In these areas human triggered avalanches may be likely and careful terrain management is essential.

We cannot forget all the skier triggered avalanche activity that’s happened in the last 2 weeks.  More snow has buried the weak layer deeper, apparently making triggering less likely.  Consequences of triggering will be greater with deeper and possibly wider avalanches when somebody finds the trigger point.  

Special Announcements

All motorized areas in Chugach National Forest are OPEN!  

Thu, February 20th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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 faceted weak layer on top of the January melt/freeze crust is definitely the most concerning part of the snowpack.  It has been responsible for widespread collapsing and avalanche activity over the last 2 weeks.  

The sensitivity of this weak layer seems to be waning, but probably because it is now buried more than 2 feet in most places, and over 3 feet in some wind loaded areas.  With that much snow insulating the problem layer, triggering will be more difficult.  

This problem needs to be considered when you venture onto steeper terrain today.  Consider the consequences of the slope releasing and the terrain in the runout below.  

Crystal card grid is 3mm spacing.  These facets produced an ECTP 14 – propagation under a moderate force.  Location – Sunburst, south aspect, ~3200 feet.

Weather
Thu, February 20th, 2014

The last snowfall was 2 days ago.  Storm totals varied widely depending on location.  The upper mountain of Alyeska received 22 inches, while Turnagain pass only had about 2 inches.  Snowfall at Turnagain pass since February 7th has been 51 inches!

Weather yesterday partly cleared in the afternoon.  Wind has been light since the last snowfall ended.  Temperatures remain cold with single digits at ridgetop stations and teens at sea level.  

A clearing trend is expected today.  Partly cloudy in the morning and mostly sunny in the afternoon.  Expect a north to west wind 10-20mph.  High temperatures in the mid 20s.  

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.