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Fri, February 7th, 2014 - 7:00AM
Sat, February 8th, 2014 - 7:00AM
Graham Predeger
Avalanche risk The Bottom Line

Increased winds and a modest amount of snow in the forecast today will raise the avalanche danger below treeline to MODERATE today.   If the forecasted precipitation arrives expect shallow wind slabs to be reactive at all elevations throughout the day.

The persistent slab and deep slab problems are of secondary concern today as fresh wind slabs form in the upper elevations, resting on a variety of surfaces.

€œSlide for life € conditions will continue to be a serious concern in the mountains around Eastern Turnagain Arm, especially in steep terrain below 3,500′.   Slick, hard crusts are making it very difficult to arrest a fall.

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Fri, February 7th, 2014
Above 2,500'
2 - Moderate
Avalanche risk
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. 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

With literally no snow available for transport in lower elevation terrain (it’s all locked up as one thick crust below 3,000’) the depth of any fresh wind slab will be directly linked to the amount of snow we receive throughout the day in the lower elevations. Expect bonding to be particularly poor between the surface and any new snow, as it will be falling on a very slick and stout crust or surface hoar that has formed over the last week.  If fresh wind slabs build they will be possible to trigger in terrain greater than about 30 degrees today.  With winds predominantly from the north and east, south and west aspects will prove most suspect.

Below 1,000’ any new snow today will be falling on either ice or frozen vegetation where we are essentially building our snowpack, literally from the frozen ground up.

Avalanche Problem 2
  • 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

In terrain above 3,500’, the last storm cycle laid down mostly snow (as opposed to rain).  Terrain above this elevation is harboring old wind slabs up to a foot in depth resting on weak interfaces.  Add to that more wind and a fresh shot of snow today and it will be possible to awaken a persistent slab.  Again, leeward slopes on the south and west tilt of the compass should be treated as suspicious if you make it into upper elevations today.

Additional Concern
  • 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

Slabs 3-6 feet thick are sitting on weak snow near the ground in the upper elevations.  It is less likely to trigger a deep slab today in comparison to a more shallow wind slab or persistent slab.  However, the possibility remains for triggering a slab that can pull out snow to the ground.  Unlike the persistent or wind slab concern, deep slabs have the potential to move large volumes of snow.  Avoiding likely trigger points, especially areas where slabs are thinner, will lower the likelihood of triggering a deep slab avalanche today. 

The deep slab problem is not a concern below 3000 feet where the previously water saturated layers have now frozen into a very strong and stable crust layer.

Fri, February 7th, 2014

Increasing mid and high level clouds yesterday were indicative of an imminent change in weather for our region.   Temperatures were in the mid 20’s with light winds from the north.   Some folks may have even seen a snowflake or two falling at sea level yesterday though it did not add up to more than a trace.

Today the National Weather Service has issued a Blizzard Warning until 7PM for Whittier, Girdwood, Seward and Moose Pass.   Winds from the north and east are expected to pick up throughout the day blowing 40-60 mph and usher in 5-12 inches of snow.   Temperatures look to be in the mid-20’s at 1,000′ and low-teens to single digits at ridgetop locations.   Expect blowing snow to reduce visibility and make travel difficult today.

This pulse of moisture looks to be brief with a return to cold and dry conditions by tomorrow and for the weekend.

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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.