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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, April 10th, 2013 - 7:00AM
Expires
Thu, April 11th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Several inches of light dry snow covers the surface in most areas of our region.  The areas we covered yesterday did not show signs of avalanche potential besides minor sluffing of the dry surface snow.  

Watch for areas with older stiff wind slab that may have formed over the weekend.  A few more inches of cold snow may fall today, but with only minimal wind expected it should not contribute to the avalanche potential.  

Recent snowfall has brought more snow to the Anchorage area, so don’t expect to find deeper powder by driving south.

Wed, April 10th, 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
  • 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

Sluffing was easy to initiate yesterday with the ultra dry layer on the surface.  Steeper confined terrain like chutes and couloirs could likely entrain enough volume to knock someone off their feet.  

From the avalanche perspective, loose snow is a manageable concern.  Use the terrain to let the sluff fall away and to the side of your line, stop periodically to allow it to pass, or keep enough speed to stay in front of it.  

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

Wind appeared to be strongest overnight through the channeled terrain of Turnagain Arm.  Sunburst station showed relatively little wind.  In those areas that saw gusting into the 20s we may have wind slab at higher elevations.  The dry nature of the recent snowfall makes that snow easy to pick up and move around by the wind.  Many of the weather stations showed a northwest wind direction, meaning that south and east facing slopes are most likely to have wind slabs.  

Besides the surface snow, the underlying bed surface may contribute to the problems.  Southerly faces and anything that got sun exposure in the last week will have a thick crust under the new snow.  That crust may contribute to poor bonding of other layers and complicate the issues.  

Weather
Wed, April 10th, 2013

Temperatures dropped overnight, with ridgetop temperatures near 0 degrees or colder in some areas.  Sea level is in the mid teens, and we will see some daytime increase.  

A small amount of snow is in the forecast and some areas got a few inches overnight.  Expect any snow to be very light and dry.  

Northwest wind will stay minimal, less that 10mph.


Fitz will issue the next advisory tomorrow morning, April 11th.

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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.