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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, January 7th, 2016 - 7:00AM
Expires
Fri, January 8th, 2016 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

Today the avalanche danger is MODERATE both at Treeline and in the Alpine. Triggering a fresh windslab 4-8 € thick is possible today near ridgetops and on leeward features. Be on the look out for hollow sounding snow, shooting cracks, and blowing snow. Be aware of large cornice features and recent glide crack movement and avoid putting yourself on or under these unpredictable hazards.

Below 1000′ the avalanche danger is LOW where triggering an avalanche on a hard supportable crust is unlikely.

*Outside of our forecast zone in Summit Lake where a generally thinner snowpack exists triggering a slab 3′ thick is a concern. Cautious route-finding and careful snowpack evaluation is advised.  

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Thu, January 7th, 2016
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
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
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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

Overnight Easterly winds increased into the 20’s with gusts in the 30-40’s mph and moderate winds are expected to continue today. With 6-10” of low-density surface snow available for transport, isolated winds slabs are possible on leeward features. These slabs are expected to be small (4-8” thick), but if triggered in steep terrain, could send you for an unintentional ride.

Older winds slabs from the holiday storm event may still be lingering in very steep terrain, but otherwise this problem is becoming less likely as we move away from the storm. Yesterday a generally stable snowpack was observed where older wind affected snow was stabilizing quickly.

Ease into steep terrain today and pay attention for hard hollow sounding snow and shooting cracks. If you see snow being transported off of ridges be very aware of the consequences below you. 

Avalanche Problem 2
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Today’s secondary concern is Cornice Fall and Glide Cracks!

Very large cornice features have formed throughout the region as a result of a two-week storm that deposited ~9’ of snow and was accompanied by very high winds. Cornices have the potential to fall naturally or be triggered by the weight of a person or machine and can be very dangerous. Travel under or on them should be avoided. They have the tendency to break farther back from the ridge than expected and can trigger an avalanche on the slope below by adding a lot of weight quickly. As you approach ridgelines and the entrances to backcountry bowls make sure you aren’t accidently traveling on overhanging snow. 

Glide cracks are appearing throughout the forecast region (Girdwood to Turnagain Pass.) These cracks appear to be opening fast and are very unpredictable. Similar to managing a cornice, it is best to avoid traveling on or under slopes with glide cracks. Although triggering one of these is uncommon, should one release above you, consequences would be high. 

Significant moat at least 5 meters back from cornice on Seattle Ridge near the top of uptrack. At least one sled track took a quick dip. Photo by Paul Forward

 

Ski tracks above two glide cracks on Lipps SW face. These glide crack have recently opened and were not present a week ago.

 

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

In some parts of the advisory area 5-7′ of settled storm snow is sitting on a layer of old faceted snow on top of the Thanksgiving Rain Crust. This still needs to be a consideration as you travel into the backcountry today. This is a low probability, very high consequence set-up.  It is important to use safe travel practices and do not overload slopes with multiple skiers, boarders or snowmachines. Limit your exposure time spent underneath large paths.

On the Sourthern periphey of our forecast zone such as Johnson Pass and Lynx Creek we have limited snowpack information. But we do know in Summit Lake, the snowpack is shallower and harbors more weak layers under the recent storm snow.  See Wendy’s observation and write-up from a snowboarder-triggered avalanche (Saturday) that failed on a buried surface hoar layer.

Watch for signs of instability: recent avalanches, shooting cracks, collapsing and whumpfing. Pay attention to snow depth and trigger points. Deep slabs are most easily triggered from shallow spots where the weight of the traveler can more easily affect the weak layer. 

Weather
Thu, January 7th, 2016

Yesterday skies were clear and temperatures were in the 20’s F. Light ridgetop winds were from the West.

Overnight Easterly winds increased into the 20’s mph. This morning increasing temperatures were 32F at 1000′ at Turnagain Pass. No precipitation was recorded overnight.

Today showery conditions are forecasted for mountain areas near the coast. This will likely be light rain below 1000′ near Girdwood and Portage and periods of light flurries are possible today in Turnagain Pass. Not much accumulation is expected. Easterly Ridgetop winds will remain in 15-30mph range throughout the day.

Friday night into Saturday another storm is expected to bring warm temps and more precipitation.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   0   0   83  
Summit Lake (1400′) 25   0   0   26  
Alyeska Mid (1700′) 28   0   0   61  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23    NE 11   40  
Seattle Ridge (2400′) 25   n/a   n/a     n/a    
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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
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South Fork Snow River Corridor
Closed
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Summit Lake
Closed
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