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Fri, January 18th, 2013 - 7:00AM
Sat, January 19th, 2013 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The hazard above treeline today is MODERATE, where it is still possible for a person or snowmachine to trigger a large destructive avalanche.   Below treeline the hazard is LOW today, where it is unlikely for humans to trigger avalanches.   Remember that ‘LOW’ does not mean ‘NO’. The main concern below treeline is being under large, open terrain that has the potential to produce high volume avalanches that can run into the lower elevations.

Fri, January 18th, 2013
Above 2,500'
2 - Moderate
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
  • 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

Deep slab avalanches are the primary concern for today.  Large, dense and potentially deadly slabs continue to sit on a weak foundation.  Clear and cold weather for much of October, November and the first half of December created thick layers of weak, faceted snow.  The steady stream of moisture beginning around Christmas formed the deep slab that we are worried most about.

At this point, it is getting more and more difficult to trigger these avalanches.  But make no mistake; getting tangled up in one of these avalanches has the potential to do a lot of damage.  It is common for this type of avalanche problem to lay dormant for extended periods of time.  It has been 4 days since any natural avalanche activity and 3 days since any human or explosively triggered avalanches have been reported.  With clearing skies and good visibility it will be tempting to venture onto steep terrain.  Do not forget what is down below your feet or sled-weak rotten snow capable of producing very large avalanches.  It is unlikely that the normal warning signs of recent avalanches, shooting cracks or collapsing will be present prior to a deep slab avalanche releasing.

Pit tests over the last several days continue to illustrate this problem well.  The weak layer is hard to impact, but the outcome once it is affected translates to large avalanches propagating across wide areas.

Avalanche Problem 2
  • 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

Very small shallow (<6″) wind slabs formed yesterday in the higher elevations, where light density snow was easily transported by light to moderate winds.  We witnessed very small shooting cracks in the surface snow above treeline yesterday.  While this problem is relatively minor, it is worth paying attention to today in upper elevation starting zones.

Fri, January 18th, 2013

Precip, winds and temps have not done anything dramatically in the past 24 hours to change our avalanche problems for today.
Light veering winds overnight have given way to current temps in the single digits at ridgetops and mostly clear skies.   No new snow has been recorded in the past 24 hours around Turnagain Arm.
The weather for today looks to be partly cloudy and cooler, with winds out of the NW at 5-15 mph, temps in the teens and no precip expected.
The extended outlook is calling for the next chance of snow on Saturday, as a low pressure system to our SW moves towards the region.


Kevin will issue the next advisory tomorrow morning, January 19th.

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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.