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Wed, March 6th, 2013 - 7:00AM
Thu, March 7th, 2013 - 7:00AM
Kevin Wright
Avalanche risk The Bottom Line

In the absence of sun today, the danger will be generally LOW.   Warmer temperatures are expected for low elevations today, and combined with a small amount of rain we may see some minor wet loose activity below treeline.   Above treeline we are still finding a lot of mature overhanging cornices that can fail spontaneously at random times.   Overall our snowpack right now is strong, with only a couple weak anomalies that are very difficult to trigger by a person.  

Wed, March 6th, 2013
Above 2,500'
1 - Low
Avalanche risk
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. 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
  • Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices throughout the region are getting to be very large in most areas, including Turnagain Pass.  The largest natural avalanches in the last 5 days have been as a result of cornice falls.  In Haines a heli-ski guide was killed over the weekend when his party collapsed a cornice.  We got a report of a natural avalanche in the Placer river region yesterday that may have been a cornice failure.

Cornice safety relies on managing exposure.  This means you should limit the time you spend directly underneath overhanging features, especially if temperatures are warm or they are in direct sun exposure.  Traveling directly on ridge tops can be safe, as long as you give a wide berth to any overhanging sections.  When standing on a ridge it can be very difficult to know how far back a cornice might break.  In general, the breaking point is much further back than you might expect. 

The good news related to cornices is that they are one of nature’s best slope stability tests.  We get a lot of information from cornice failures when the slope underneath gets pummeled by thousands of pounds of hard cornice chunks.  Based on our observations of cornice failure, the current snowpack is showing minimal reactivity to large triggers.  This means that backcountry travelers are unlikely to trigger a slab avalanche in the backcountry today.

The one recent exception was a cornice that triggered a deep slab on the mid elevation ice crust in steep terrain in the Girdwood valley on Sunday.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Yesterday’s sunny skies were hammering southerly slopes with solar radiation.  Temperatures overall were not much above freezing, so the warming effect was minimal but still noticeable.  Some direct south facing slopes at low elevation showed a small amount of loose wet avalanche activity.

Sun is not in the weather forecast today, but temperatures are expected to reach into the low 40s at sea level.  This may be enough to melt the surface crusts and cause more minor loose avalanche activity by the afternoon. 

Wed, March 6th, 2013

Yesterday was sunny and calm with mild temperatures.   Our last big shot of moisture was 6 days ago, and the snowpack has been settling and strengthening since then.  

Today, rain and snow is in the forecast.   Actual amounts predicted are very minor, leading me to believe that new precipitation today will not have a significant effect on the avalanche danger.   The rain/snow line is predicted at 700 feet today.   Temperatures may reach into the low 40s at sea level.   Expect light wind to 15mph from the south.  

Tomorrow a larger storm system is moving into our region with high wind, rain, and snow forecasted.   We can expect the avalanche danger to increase for Thursday and Friday as a result of this coming storm.

Graham will issue the next advisory on Thursday, March 7th.

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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.