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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, November 21st, 2015 - 7:00AM
Expires
Sun, November 22nd, 2015 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Saturday, November 21st UPDATE:

After a much-anticipated series of storms rolled through the past several days, the Girdwood, Turnagain and Summit areas have picked up a total of 6-10″ of new snow. Last night’s pulse added roughly 6″ at the mid-elevations in Girdwood Valley and 4″ in the Turnagain and Summit areas. Winds have been moderate to strong from the North and East, yet have switched to the West this morning. Throughout the weekend, the Westerly winds should be strong enough to transport snow and load slopes – as well as usher in colder air.


Yesterday we had our first reported ‘human triggered’ avalanche on the Chugach National Forest this season.  This was a  skier triggered slide in the Summit Lake area of the Kenai (Tenderfoot Ridge). See link for a great report sent in of the avalanche.

Photo: 8″ thick x 50′ wide wind slab, skier triggered on the South face of Tenderfoot Ridge, ran to valley floor (photo credit: Chad Saetre)

AVALANCHE OUTLOOK FOR THIS WEEKEND:

Due to new snow and wind, human triggered avalanches will be possible this weekend.  These are most likely to be on upper elevation  steep slopes where winds have deposited new snow into slabs (~6-12″ thick). There are a variety of old surfaces  out there, how much snow has piled up and how well it sticks to these surfaces will be the thing to watch for.

Although the snow cover is shallow, it can still be unstable (as seen in the Tenderfoot slide). Sugary facets formed during the cold snap sit at the bottom of the snowpack in certain areas. In this case, an avalanche triggered may break at the ground taking the whole, albeit thin, snow cover.

*Safer areas to recreate will be on slopes that have seen little wind effect and smaller amounts of new snow.

Things to keep an eye out for:

– Watch for cracking in the new snow, especially where winds have stiffened the snow
– Quick hand pits are good ways to assess how the new snow is bonding with the old snow
– Look for recent avalanches and listening for ‘whoomphing’, the big Red Flags for unstable snow

Special Announcements

ADVISORIES?
We will begin issuing daily avalanche advisories for Turnagain Pass on Thanksgiving Day. Until then, we will continue to post intermittent updates.

Avalanche conditions OUTSIDE our forecast zone:
Up to 2′ of snow has fallen in the past couple days at Hatcher Pass. This area continues to have dangerous avalanche conditions. PLEASE see  hatcherpassavalanchecenter.org  for  the Saturday morning report!!

Sat, November 21st, 2015
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
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.
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

Glide avalanches:

Several glide cracks remain on Seattle Ridge, Eddies Ridge and Tincan. These could become more active with the warmer temperatures this weekend. Although most are just cracks, some have avalanched. Limiting time under glide cracks is prudent as there is no way to know if/or when they may release.

Below are photos of a glide crack on Tincan: Left image is from Nov 10th (crack roughly 3-5′ wide). Right image is the same crack from a week later, Nov 17th, which has grown (10-15′ wide, although recent snowfall on the ground makes the crack more difficult to see).

     

Image below is from a glide avalanche on Tincan that released around Nov 11th/12th.

Observations
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Date Region Location
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04/11/24 Turnagain Observation: Tincan
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04/10/24 Turnagain Avalanche: Tincan
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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.