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Issued
Mon, December 10th, 2012 - 7:00AM
Expires
Tue, December 11th, 2012 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Above treeline, a CONSIDERABLE avalanche danger will linger today.   The 10+ inches of snow combined with high wind over the weekend built very touchy wind slabs on top of the super weak snow from November.   We found the wind slabs to be very reactive to human trigger yesterday with remote and sympathetic avalanches in numerous places.   This trend is likely to diminish slightly today, but conservative terrain management   will still be important.

Mon, December 10th, 2012
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. 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 storm snow by itself didn’t seem to be creating very reactive or connected avalanches yesterday.  Adding wind loading to the mix built the stiffness and tension required to build a slab.  Wind loaded areas steeper than 35 degrees should be approached with caution today.  Any areas with this combination in high consequence terrain should be avoided completely.  Check out the observations from yesterday for some more examples of skier triggered wind slabs.

Likelihood – human triggered likely

Trend – decreasing since yesterday

Distribution – Widespread above treeline

Size – small to medium

Watch a video of the avalanche in the picture HERE.

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Below treeline where wind did not affect the new snow, the snowpack behaves differently.  We found very little difference in density between the fresh light powder and the underlying weak facets.  However, I wouldn’t rule out the possibility of finding unstable storm snow below treeline.  If you find the right combination of an open steep slope at lower elevation, it may be able to avalanche as a slab or as a loose sluff.  This should be less dangerous than the wind slabs found up higher. 

Weather
Mon, December 10th, 2012

The storm Saturday to Sunday morning dropped about 10 inches across Turnagain Pass.   Winds were strong from the east, reaching gusts over 70mph.  

Today looks like calm weather that won’t contribute to avalanche problems.   A chance of snow is in the forecast with little accumulation.   Light wind and mild below freezing temperatures in the mountains.   The next chance of significant snow looks to be Wednesday.  


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).  

Wendy will issue the next advisory Tuesday morning, December 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.