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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 30th, 2013 - 7:00AM
Expires
Thu, January 31st, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Avalanche danger today is mostly associated with the recent snow and wind slab.   A MODERATE danger exists above treeline from the several inches of new snow in the last few days and moderate wind.   A small amount of new snow today will keep the danger at moderate, but it may rise tonight with up to a foot of snow possible.   Below treeline is LOW, with a strong supportable crust underneath the recent few inches of loose snow.

Wed, January 30th, 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. 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
  • 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

All recent reported avalanche activity is related to a shallow wind slab in steeper terrain.  That trend continues today with more wind slab expected with today’s weather.  If you travel above treeline today, watch for wind drifting patterns related to slope aspect.  One recent report indicated that the shallow wind slab wasn’t a major problem if anticipated.  The danger will become greater as the depth and mass of those wind slabs increases today.

As the snowfall picks up today, combined with rising temperatures and wind, the chance of finding more wind slab will increase.  By later tonight the storm snow by itself could be enough to cause concern without the wind component.  The timing on the greater amounts of snow is expected for late tonight and tomorrow morning. 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

The deep slab problem has not been evident in more than a week.  We believe it still warrants a minor discussion.  Triggering deep slab at this time will require perfect placement and an element of bad luck.  However, if that happens the consequences could be very bad.  It’s worth considering this possibility in steep, shallow, and rocky terrain above treeline. 

Weather
Wed, January 30th, 2013

The last couple days have brought just a few inches of snow, but enough to maintain moderate avalanche concerns.  

A weak front is moving across southcentral Alaska today, bringing snow to the mountains of Turnagain Arm.   Temperatures are expected to rise, bringing mixed rain and snow to sea level this afternoon.   Snowfall rates will increase this afternoon into Thursday morning, bringing between 8 and 18 inches to the mountains by tomorrow.   Southeast wind will reach into the 30s and 40s up high.  

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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.