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Mon, April 6th, 2015 - 7:00AM
Tue, April 7th, 2015 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The danger is MODERATE on steep slopes in the Alpine.   Fresh wind slabs 8-12 € thick could be triggered on leeward slopes approaching 40 º.   North facing slopes are also suspect and have dense slabs 2-3′ thick that could be triggered by skiers and riders.

The danger is LOW at Treeline where avalanches are unlikely.

Mon, April 6th, 2015
Above 2,500'
2 - Moderate
Avalanche risk
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

Winds will move around the 3-6” of loose snow that is currently sitting in the higher elevations.  Slabs will build as thick as 1 foot on leeward slopes in the Alpine.  With more snow available for transport in the Girdwood Valley expect slabs to be thicker there than on Turnagain Pass.  Another 2+” of snow falling today will help to slightly increase the size of wind slabs.  These slabs will be most sensitive as they are forming.  Be on the lookout for snow that is stiff, feels upside down or produces shooting cracks.  These slabs will exist in small pockets and will become more of an issue if triggered above terrain traps or on large steep (>40º) slopes.

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

Steep north facing slopes in the Alpine have a setup that hold the potential for large avalanches 2-3’ deep to release under the weight of a person or group.  This concern reared its ugly head last week and has since quieted down.  Despite the lack of activity on these deeper layers over the weekend, it is still worth keeping in mind that there exist pockets of dense slab sitting on layers of weak faceted snow. If you find yourself in steep North facing terrain make sure you take precautions to minimize your exposure – travel one at a time, identify escape routes and communicate your decisions and plans well within your group.

Additional Concern
  • 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

If visibility improves enough for travel in the Alpine, expect terrain sheltered from the wind to have enough loose surface snow to produce low to medium volume sluffs.  This will be a minor issue, but like wind slabs will become more serious when travelling above terrain traps such as cliffs, gullies and trees.

Mon, April 6th, 2015

Over the past 24 hours temps have remained mild with averages in the mid 20s F at ridgetops and low 40s F at sea level.   Precipitation in the form of snow fell yesterday morning with Girdwood Valley receiving 3 € and Turnagain Pass picking up just a trace.   Winds were generally light but have picked up into the 20 mph range this morning at ridgetop level.

Today a mix of snow and rain will fall as a large and broad low pressure system moves in from the Bering Sea.   Accumulation will be light during the day with up to 2 € expected.   Rain/snow line will be around 1,500′.   Ridgetop winds will be moderate, in the 15-25 mph range out of the East.   Temps will climb into the low 30s F at ridgetops.

The system responsible for stormy weather today will pick up in intensity tonight and into tomorrow.   Snow accumulation will be in the 8-10 € range in the higher elevations by tomorrow morning.

Looking further out we can expect a continuation of unsettled weather through the middle part of the week with generally light precipitation through Wednesday.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 trace 0 58
Summit Lake (1400′) 34 0 0 10
Alyeska Mid (1700′) 33 3 .25 33

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 12 35
Seattle Ridge (2400′) 25 n/a 17 39
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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.