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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, November 28th, 2016 - 7:00AM
Expires
Tue, November 29th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  in both the alpine and at treeline on all aspects due to a widespread layer of buried surface hoar. Human triggered persistent slab avalanches 1-2 feet thick are possible today. Triggering an isolated wind slab to is also possible on steep features near ridgetops.  Caution and safe travel protocol is advised if venturing in the backcountry.  Avoid travel underneath glide cracks.

***Observations from the Summit Lake area on the Kenai are showing a similar snowpack. Weekly summaries will begin on December 2nd.

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Mon, November 28th, 2016
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
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 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

It is now been over 10 days since the November 16th surface hoar layer was buried and it remains reactive and our primary layer of concern. Yesterday skiers reported triggering small slides in Main Bowl (Seattle Ridge) on the buried surface hoar layer in steeper terrain (40 degrees). One skied off of the slab and the other was carried but stayed on top. It is important to remember that this widespread layer of buried surface hoar is sitting below 1-2 feet of snow and that observers keep finding this layer on all aspects and elevations throughout Turnagain Pass. Stability tests also continue to show that is slab/weak layer combination has the potential to avalanche. Up until a few days ago human triggered (including remote triggered) avalanches were happening daily with a couple dozen avalanches reported over a 7-day period. These avalanches have been small to medium in size; just large enough to bury a person or seriously injure you in a ride. Larger and/or steeper, more wind-loaded slopes that haven’t been ridden still have the potential to avalanche and could fracture once onto the slope. Be aware of the consequences below you and keep an eye out for recent wind loading, shooting cracks and whumphing sounds (RED FLAGS).  Practice safe travel techniques like regrouping in safe zones and only expose one person at a time in avalanche terrain. This can be challenging to practice in crowded areas, thus be extra aware of other groups who may be traveling above or below you. Don’t forget buried surface hoar is a persistent weak layer and human triggered avalanche are still possible. This layer has not gone away and should be a major factor in slope choice today.

Skier triggered slides in Main Bowl, Photo: Eric Dahl

Shovel Tilt Test showing the slab over the buried surface hoar from pit near Hippy Bowl. 

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

The snow that fell Saturday night was light and fluffy and will easily be transported with moderate winds. Early this morning there was a few hours where the winds picked up on Seattle Ridge gusting to 30 mph. The Sunburst weather station is down so it’s hard to determine if this was the same across the Pass. There was some increase in wind speeds at road level as well. It will be important to watch for signs of recent wind loading and if the snow feels stiffer underfoot. Look for shooting cracks. Triggering a small wind slab is possible in steep leeward terrain near ridgetops. This wind loading may add stress onto the buried surface hoar layer. Pay attention to changing conditions and choose terrain carefully. 

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

Several glide avalanches have released this week including one observed Saturday morning on the West face of Pyramid. Several glide cracks have been noted in popular terrain like Tincan’s Common bowl and the SW face of Sunburst. If you see glide cracks give these a wide berth, minimize time spent underneath, and remember these are totally unpredictable. They are not triggered by humans and are the entire snowpack releasing. In places like Tincan Common this could be over 4′ of snow.

 

Weather
Mon, November 28th, 2016

Yesterday was partly cloudy with light winds and temperatures in the high teens/low 20Fs. Overnight temps dropped a little into the mid teens(F). The winds were northerly and there was a minor spike in winds speeds early this morning gusting up to 30mph.  

Today will be mostly sunny and cold with temperatures in the teens(F). NW winds should be light to moderate. Overnight there is a slight chance for snow and skies will be mostly cloudy. Temperatures stay cold and winds may increase depending on the track of the low in the Northeastern Pacific.  

Tomorrow will be mostly cloudy and cold with light to moderate NW winds. There will be a window of clearing on Wedesday again and then the likelihood of snow increases into the weekend but the timing and amounts are still TBD.  

***Sunburst Weather Station has not been recording weather data since Nov. 25th. We are currently assessing and hope to get it repaired soon.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  20 0    0 20  
Summit Lake (1400′)  22 0  0    3
Alyeska Mid (1700′)  22    0  0  5

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) n/a*** n/a*** n/a*** n/a***
Seattle Ridge (2400′)  16  N 9   31
Observations
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Riding Areas
Updated Wed, December 11th, 2019

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

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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