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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 8th, 2014 - 7:00AM
Expires
Thu, January 9th, 2014 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

The avalanche danger today remains at CONSIDERABLE above treeline where the potential exists to initiate large slab avalanches 2-3′ deep.   An avalanche triggered today has the potential to propagate across entire slopes in surprising and unpredictable ways.   Cautious route finding and conservative decision-making will again be essential elements to a fun, safe day in the backcountry.

Below treeline the danger remains MODERATE due to the continued, around the clock above freezing temperatures and weak snow found near the base of the snowpack.

Special Announcements

For anyone who has taken an Avalanche Level 2 course and interested in a refresher check out the  Alaska Avalanche School’s €œLevel 2 refresher/Observer Workshop €. The course will be a lot of fun and taught by CNFAIC’s Wendy Wagner and AAS’s Eeva Latosuo.

Wed, January 8th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
  • 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

We haven’t heard of any new avalanche activity since Sunday, when a substantial natural avalanche cycle occurred in addition to a second-hand report of snowmachine-triggered avalanche activity near Seattle ridge.  This most recent cycle has a common theme in the fact that all of these avalanches have been quite large, propagating across entire slopes with faceted snow near the ground proving the common and persistent weak layer. Recent results from the snowpit show these weak layers have been slow to gain strength as Fitz’s video here points out.  This is a great example of the persistent slab problem that has dominated our primary concern over much of the last three weeks.

As few people have been venturing into the backcountry since the Jan. 5th storm, our information is limited.  What information we do have, points toward a snowpack hanging in the balance with a poor structure, moderate strength and high energy.  In a nutshell this means that if a fracture is initiated on or below a slope steep enough to avalanche (> 35 degrees) there is good potential that the crack will propagate far and wide, creating a large and unmanageable avalanche.  Likely trigger points include thin spots in the slab or near rocks and trees mid-slope.

Maintain astute situational awareness and be mindful of any obvious signs of instability if you travel into the backcountry today.  Conservative terrain selection and proper travel protocol will be key.

In areas below treeline where the surface snow is still wet, exists a very poor snowpack structure with free water percolating throughout.  Once overnight temperatures maintain below the freezing mark, this lower elevation snowpack will ‘lock-up’ and we’ll likely see Low danger in this elevation band.

Weather
Wed, January 8th, 2014

Southeast flow continued yesterday ushering in warm temperatures and intermittent bands of rain through the eastern Turnagain arm region with no measurable snow accumulation to speak of.   Winds have been light to moderate predominantly from the East and temperatures remained in the 20’s at ridgetop locations and mid-30’s at 1000 feet.

Today looks to be the start of a gradual cool down with temperatures moderating back to near normal values by the weekend.   Cloudy skies and 28-33 degrees should usher in 2-3 € of snow above 1000 feet today with slightly warmer temperatures and a rain/ snow mix at sea level.   Winds will be out of the East at 15-25 mph and look to  decrease to single digits from the North by tonight.

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.