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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, April 11th, 2013 - 7:00AM
Expires
Fri, April 12th, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

There is a MODERATE avalanche danger above treeline today for wind slab and loose snow avalanches. Winds slabs 6-10″ deep, sitting just off ridgelines and rollovers, will be possible to trigger on upper elevation slopes over 35 degrees. Additionally, moderate sluffing in the weekend’s new snow should be expected on all aspects in the steeper terrain. In the event skies remain clear and the sun warms the surface snow, damp sluffs and shallow slabs are possible on southerly aspects.

Thu, April 11th, 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. 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

Despite the light winds the past couple days, shallow and very sensitive slabs have been able to form in scattered areas along ridgelines (shown in the photo below). This is mainly due to the weekend’s snow being so light and easy to transport. They didn’t pack much punch yesterday but a bump in wind overnight with plenty of low density snow available for transport will likely have continued wind slab development. Watch for these to be 6-10″ thick and on a variety of aspects – winds have been blowing from various directions due to our region being in the heart of a low pressure system. Keeping an eye on the snow texture as well as for shooting cracks from your skies/board or sled will be key.

 

Avalanche Problem 2
  • 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

Loose snow avalanches are expected to be prevalent again today. These are both in the dry snow category and the wet/damp snow category (pending clear skies):

Dry snow: The very cold overnight temperatures will add to the looseness of the surface snow (and to the good riding/skiing conditions). This should keep dry sluffs something to plan for on steep slopes.

Wet/damp snow: If the skies remain clear today, the sun should have ample time to warm southerly aspects. Watch for dampening of the snow surface to turn a small low volume dry sluff into a larger heavier damp sluff. Shallow slabs are also possible with daytime warming on southerly aspects. These sluffs and slabs have the potential to release naturally if we do get intense sunshine today.

Weather
Thu, April 11th, 2013

Under mostly clear skies this morning, temperatures have plummeted to the single and minus single digits. Winds have remained light from the north and west with a slight bump overnight to the 15-20 mph range. Yesterday, mostly cloudy skies limited much daytime heating and 24-hour average temperature at the Sunburst wx station was +1F while winds averaged 4mph with gusts to 16.

Today, a few clouds are likely to stream through but the sun should have time to warm things up a bit. Temperatures should reach the mid 20’sF at sea level up to treeline and the low teens on the ridgetops. Winds will be light and slowly backing to the SE where they look to pick up tonight to the 15mph range.

Beautiful spring weather consisting of sunny days, cold nights and light to moderate northerly winds are on tap for the remainder of the week and into the weekend.


Kevin will issue the next advisory tomorrow, April 12th.

Observations
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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.