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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 6th, 2013 - 7:00AM
Expires
Thu, February 7th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

 Aging wind slabs at high elevation keep our concern at MODERATE above treeline.   The stability trend today is steady, with a small amount of snow in the forecast.   Small avalanches are possible in specific steep terrain.   Below treeline several hard melt/freeze layers are locking the snowpack in place and keeping the danger LOW.   We have few reports of avalanche activity from the last several days, but a blizzard watch for tomorrow will keep our stability short lived.

Special Announcements

We have a few spots open in our non-motorized backcountry observer training day this Saturday, February 9th.   Check our calendar page for more information.   Join the forecasters for a day in the backcountry and learn how to contribute snow and avalanche observations to your local avalanche center.

Wed, February 6th, 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

The pictures below show an example of our primary concern.  Wind slabs have been reactive to natural and human triggers over the last few days.  After yesterday’s calm weather it will be less likely to find this problem today.  It may be possible to find reactive wind slabs in steep and complex terrain greater than 35 degrees. 

Patterns of recent wind slabs have shown mostly small avalanches, breaking 6-18 inches deep.  A mid-elevation band between 2000 and 2500 feet places the wind slab on top of a slick melt/freeze crust.  I’m more concerned about terrain above 3000 feet today because that’s where we find more of our steeper pitches.  Cross loaded steep gullies in consequential terrain on all aspects should be treated with respect.

Cornices are another form of windslab, with an unsupported overhanging nature.  Now that we’ve reached mid winter, cornices are getting large and mature.  As always, they should never be trusted and only approached with caution.  The wind slab in the pictures was likely triggered by a naturally failing cornice.

 

Weather
Wed, February 6th, 2013

No snow yesterday, mostly sunny skies, pleasant temperatures in the mid to high 20s, and light wind made for a great day in the mountains.  

Today, a few inches of snow is forecasted this morning.   Temperatures should be just below freezing at sea level.   Wind is expected to be 10mph or less.   Snowfall will decrease this afternoon leaving mostly cloudy skies.

A blizzard watch is in effect starting Thursday afternoon.   Stay tuned as we track the development of this storm.

Graham will issue the next advisory tomorrow morning, February 7th.

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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.
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