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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, December 25th, 2012 - 7:00AM
Expires
Wed, December 26th, 2012 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Merry Christmas!   Skiers and riders got a big Christmas present today in the form of the biggest storm of the year…   Unfortunately it’s too much to play with today.   Girdwood and Turnagain Pass are trying to adjust to 2-3 feet of new snow in the last 24 hours, which has the avalanche danger pegged at HIGH.   Even playing below treeline is going to be difficult and potentially dangerous with this much new snow.  

We are issuing an Avalanche Warning today, meaning HIGH avalanche danger can be found across a wide region.   Backcountry travel is not recommended.

This morning, natural avalanches have been reported along the Seward Highway and in Girdwood.   It’s undoubtedly avalanching spontaneously across the region, but the storm is too thick for us to see much yet.   Open your Christmas presents, relax, enjoy the day off, and be safe.

Tue, December 25th, 2012
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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
  • 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

Wind has been blowing into the 60s at the ridgetops along with all that new snow.  Natural avalanche activity started sometime yesterday and got bigger overnight as the new snow piled up.  Despite a taper expected this morning in the storm intensity, the possibility of natural and human triggered avalanches will remain high this morning.   With this much snow we can expect large avalanches to run down into valley bottoms, making safe areas difficult to determine even below treeline.  The best travel advice today is to stay away from the Kenai peninsula or go to Alyeska. 

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Areas below treeline that are less wind affected will still have a huge amount of new snow.  All this new weight is sitting on a very weak base from early winter.  There is nothing good about this combination…  The stress of the new snow will be exceeding the strength of the underlying foundation.   Let’s give it time to go through the natural avalanche cycle before we go play in the new snow.

By mid afternoon yesterday the backcountry in Turnagain was already so deep that it was difficult to ski.  The snow depth has doubled since then…  Again, the best advice is to stay away until the snowpack has time to adjust to this massive new load. 

Weather
Tue, December 25th, 2012

24 hour storm totals as of 5am

Turnagain Pass – 24-30 inches snow, 2+ inches of water

Alyeska – 25-36 inches snow, 3+ inches of water

Wind reaching over 60 mph at most ridgetop weather stations.

Temperatures have risen during the storm, with some rain at low elevations.   The storm is expected to taper this morning both in wind and precipitation.   Tomorrow morning another pulse is expected to hit with more heavy snow and high wind across our region.   The Blizzard Warning is canceled, but the storm is not over.  


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).

Wendy will issue the next advisory Wednesday morning December 26th.

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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.