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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, December 8th, 2016 - 7:00AM
Expires
Fri, December 9th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

A MODERATE avalanche danger exists on all aspects above 2000′ where triggering an avalanche 1-2+’ thick is possible on slopes steeper than 35 degrees. Triggering an isolated wind slab avalanche is also possible today near ridgetops that have been loaded by winds over the past week.  Below 2000′ in the trees where the snow is loose and unconsolidated the avalanche danger remains  LOW.

If headed to Summit Lake check out the Summit Lake Summary  HERE.

***Out of area:  Click HERE to check out an observation about a human triggered avalanche in the Anchorage Front Range on Dec. 5.

Special Announcements

Planning on taking an avalanche class? The Friends of the CNFAIC is offering two avalanche scholarships through the Rob Hammel fund. Both scholarships are for $500. One is for avalanche professionals and the other is open to anyone!  The deadline for both scholarships is Dec 15th! For more information click this link  HERE.  

Thu, December 8th, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • 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

A 1-2+’ slab sitting on top of a widespread layer of buried surface hoar continues to warrant caution in the alpine throughout Turnagain Pass. This layer was formed in mid November and was the cause of  dozens of human triggered avalanches over several weeks. Observers continue to find this layer on all aspects above 2000’ and many stability tests still show propagation potential.  However without any major weather factors adding stress to the snowpack this layer is becoming more stubborn and difficult to trigger with time. The places most suspect are large steep slopes (>35 degrees) that haven’t avalanched. Since we don’t have X-ray vision of the entire snowpack and evidence of natural avalanche activity was limited during several storms, uncertainty exists in terrain that hasn’t seen much traffic. The presence of surface hoar within the snowpack should be part of your slope choices today especially if you are venturing into steeper untracked areas. Consider the consequences of an avalanche before committing to a route and always use safe travel protocols. 

  • Expose one person at a time
  • Group up in safe zones
  • Have an escape route planned
  • Watch your partners and be aware of other groups around you

 The two photos below are examples of where the buried surface hoar continues to be reactive in test pits. Check out observations from Dec.6 at Sunburst and Dec.5 at Tincan.  

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

Several wind events over the last week have formed wind slabs near and below ridgetops on a variety of aspects.  Stiff supportable wind slabs formed in thin rocky areas may pop once you are out onto the slab. Be wary of hard over soft snow, hollow sounds and steep slopes with obvious deposition in the start zone.

Weather
Thu, December 8th, 2016

Yesterday was overcast with low temperatures around 15F and highs around 23F. Winds were calm. No new precipitation was recorded in Turnagain Pass, and an inch of snow fell in Girdwood overnight.  

Today skies will be mostly sunny with a chance of light snow showers. Expect light ridgetop winds to be shifting from the East to a more Northerly direction and temperatures will be in the teens (F) to low 20F’s.  

A similar pattern is expected into the weekend with temperatures dipping back into the single digits and possibly cooler.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 21   0   0   19  
Summit Lake (1400′) 16   0   0   4  
Alyeska Mid (1700′)  18 .05   1   8  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   ENE   4   17  
Seattle Ridge (2400′) 23    ESE 1   2  
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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.