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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, December 3rd, 2016 - 7:00AM
Expires
Sun, December 4th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

A MODERATE avalanche danger exists in the mountains surrounding Turnagain Pass at all elevations above 2,000′ and on all aspects. Wind slab avalanches around a foot thick will be possible to trigger on slopes loaded by blowing snow. Larger slab avalanches are also possible in areas less traveled where a weak layer remains in the snowpack 2-3′ deep. Safe travel protocol will be essential this weekend.

Caution is also advised in periphery areas like Portage Valley where windslabs are possible on ice climbing routes.  

*** Summit Lake weekly summary can be found HERE.

Special Announcements

Tonight is the 8th Annual Alyeska Ski Patrol Auction, a fundraiser to benifit the Alyeska patrol avalanche canines. The event will be in Girdwood at the Sitzmark, 8-10pm. For more details click HERE.

Sat, December 3rd, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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
  • 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

Don’t forget your down jacket, mittens, and thermos today. Moderate Northwest winds (15-30mph) and single digits (F) temperatures could easily bring the windchill factor near -20F, especially in the upper elevations. These same winds could also be adding stress to an early season snowpack.  Watch out for isolated windslabs near ridges or a wind slab that could be sitting on the Nov 16 layer of buried surface hoar. If this is the case, a ‘typical’ wind slab avalanche could step down and trigger a much larger slide releasing 2-3′ deep. Keep in mind, these could pop out mid-slope. Be aware of your exposure and avoid pillow shaped snow on steep unsupported terrain features. Snow that feels supportable, hollow or drumlike is suspect and cracking will be an obvious sign that this snow is unstable.   

Be prepared for cold weather, travel one at time between safe zone, and adjust your plans if an area becomes too crowded.

A normal weekday on the popular ski track up Sunbursts SW shoulder. Photo taken yesterday, Dec.2 at 12:30pm.

Avalanche Problem 2
  • 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 layer of buried surface hoar, 1-3′ deep, still remains on many slopes throughout Turnagain Pass and in the Summit Lake area. During the past two weeks, many popular slopes have avalanched (removing the weak layer), and been covered again by recent snow. This makes it really hard to know the full extent of which slopes still have this weak layer set-up, especially in places that haven’t seen much traffic.   

Keep these questions in mind today before committing to a route or descending: 

  • “What are the consequences if this slope avalanches?” 
  • “Are there other groups above me or below me?”
  • “What is my plan if this slope avalanches?”
Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

It’s been roughly a week since we have seen or heard of a glide crack releasing – but the cracks continue to widen despite the cold weather. Once again, limiting your exposure under these is highly recommended. 

Weather
Sat, December 3rd, 2016

Yesterday was mostly cloudy with temperatures in the low to mid 20F’s. A generally NW wind direction was recorded at ridge tops. Sunburst weather station recorded light NW winds while Seattle Ridge weather station experienced sustained moderate winds (15-25mph.)

Overnight temperatures have been falling into the single digits in the upper elevations and low teens (F) along the road corridor.   No new precipitation was recorded in the last 24 hours.  

Today looks similar. Temperatures should remain in the single digits with a high of around 10F at lower elevations. Northwest Ridgetop winds are expected to remain moderate (15-25mph) with a chance of isolated snow showers in the afternoon.  

Northwest flow are expected to bring cold arctic air and moderate ridgetop winds to Southcentral, Alaska throughout the weekend. Anticipate clear skies tomorrow.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 14   0   0   23  
Summit Lake (1400′) 17   0   0   4  
Alyeska Mid (1700′) 15   0   0   12  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 7   NW   3   15  
Seattle Ridge (2400′) 10    NW 11    35
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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.