ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, November 23rd, 2016 - 7:00AM
Expires
Thu, November 24th, 2016 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line
The avalanche danger remains CONSIDERABLE for all slopes near and above treeline. Human triggered slab avalanches 10-20″ thick are likely and may release on lower angled slopes. These can also release remotely from ridgelines – see reports from yesterday below. Most suspect slopes are those that have not been skied or ridden in the past week.
A MODERATE danger exists in the trees where triggering a slab avalanche is possible on open slopes or debris running from an avalanche above may occur. Extra caution and safe travel protocol is advised if venturing in the backcountry.
***Observations from the Summit Lake area on the Kenai are showing a similarly unstable snowpack. Weekly summaries will begin on December 2nd.
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Wed, November 23rd, 2016
Alpine Above 2,500'
Considerable (3)
Treeline 1,000'-2,500'
Moderate (2)
Below Treeline Below 1,000'
No Rating (0)
Alpine Above 2,500'
Considerable (3)
Treeline 1,000'-2,500'
Moderate (2)
Below Treeline Below 1,000'
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
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.
Yesterday was the fifth day in row that skiers and snowboarders have triggered a minimum of three avalanches per day on Turnagain Pass. Three avalanches were triggered on Sunburst yesterday and one on Tincan.
The video below is from an avalanche on Sunburst triggered remotely from the ridge. There was a group of four that were riding on the looker’s right slope of this avalanche. The first two rode that slope, each triggering a small avalanche (one of which can be seen on the right side). Just as the third person was about to descend, the larger avalanche released and caught on video by the two people below. Discussions with all groups involved concluded that the avalanche in the video was unintentionally triggered from the ridge by another group. More details HERE.
Photo below: Same avalanche as in the video from a different perspective.
Photo below is from Hippy Bowl on Tincan that also was reported to have been triggered remotely from the ridge.
If you have been reading the advisory lately, you’ll know this is all due to a layer of highly reactive buried surface hoar sitting 10-20″ below the surface (under the snow from last Thursday and Monday). Slabs have been relatively shallow and soft, yet debris has been running far. Few people have been getting caught, which is mainly because these have ‘mostly’ been releasing at peoples feet or remotely, meaning the avalanche occurs either next to you or below you.
Things to keep in mind for the sunny day forecast:
The snowpack is still unstable
Although slabs are soft and shallow – the larger the slope, the larger the avalanche
Slabs can break above you, making it more difficult to escape
Be aware of OTHER groups and WHO IS BELOW YOU
Is there any good news with this tender snowpack? So far slabs are soft and relatively shallow – not good news per se but better than hard and thick slabs. Another thing to consider is where you are riding – take Sunburst ridge for example: much of the popular West slopes of Sunburst have already avalanched and been filled in with Monday’s snow – folks are now riding these slopes without incident. Bump up a little further along the ridge and boom – there are many slopes, or portions of slopes, that have not slid and are lying in wait.
Avalanche Problem 2
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.
On the South end of Turnagain Pass a few glide avalanches have released. One of these was on the South face of Pete’s North. Additional cracks are opening on Sunburst and Tincan. With so much focus on the buried surface hoar issues – don’t forget to keep an eye out for glide cracks and limit time under these.
Weather
Wed, November 23rd, 2016
Yesterday greeted backcountry travelers with partly cloudy skies, light and variable winds and no precipitation. Overnight, winds have been light from the East and temperatures in the 20’s F.
Today, another nice day is on tap with mostly sunny skies and light Easterly winds. For Thanksgiving day, skies should remain mostly sunny but the winds are expected to bump up slightly and shift Northerly bringing in cooler temperatures.
Our next chance for snow looks to be Friday and into the weekend – stay tuned!
Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff.
Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations.
Riding area questions contact: mailroom_r10_chugach@fs.fed.us
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.
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