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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, December 9th, 2012 - 7:00AM
Expires
Mon, December 10th, 2012 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

There is a CONSIDERABLE avalanche danger today for storm and wind slab avalanches, both above and below treeline. Recent new snow and strong wind has created an extremely unstable snowpack and dangerous avalanche conditions exist.  Very weak faceted snow sits under the new storm snow and wind slabs making it difficult for any new accumulation to stick to the mountain sides. Human triggered slab avalanches are LIKELY today on slopes steeper than 30 degrees above and below treeline. The wind, snow and natural avalanche activity has abated but the snowpack remains teetering on the edge of release. If you are not certain where avalanche terrain exists, in order to avoid it, travel in the backcountry is not recommended.

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Sun, December 9th, 2012
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
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

High winds yesterday afternoon through midnight, sustained around 40mph with gusts over 70mph, raked the mountains, scouring windward slopes and depositing a combination of new snow and existing snow onto leeward slopes and catchment zones. Even the mid and lower elevation snow saw substantial wind transport. There was likely a peak in natural wind slab acivity and HIGH danger at the tail end of these strong winds overnight.

Wind slabs that were just starting to be formed yesterday were 4-10” thick, very sensitive and could be cracked out and released with the slightest touch. Because these slabs have formed on very weak sugary snow they are not likely to bond anytime soon.

Steering clear of ANY wind deposited snow on slopes over 30 degrees will be prudent. These areas may not be obvious as 1-3” of new snow forecast with little wind today could mask these monsters. Remotely triggering a slope (i.e., from below or a flat area) is possible. Collapsing and cracking should be widespread – if you are on a slope steep enough it will probably avalanche.

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Though the forecast for 2 feet of snow by this morning was a bust and yesterday evening’s quick and dirty onslaught was finished around midnight, the 8-12” of new dense snow above treeline is highly unstable. Not only did the storm come in cold and leave warm (creating an unstable upside down storm layer), it fell on extremely weak faceted snow – ball bearings – that will have little chance of allowing the new snow to stick to the sides of the mountains. Hence, areas lacking a wind slab will still be likely to avalanche with just the new layer of storm snow.

Weather
Sun, December 9th, 2012

Snowfall numbers (storm total as of 6am 12/9):
Turnagain Pass SNOTEL 1880′:   9 € snow,  .7 € water
Summit Lake SNOTEL 1400′:   3 € snow,   .3 € water
Alyeska mid mtn:   10 € snow,   .8 € water   (1.2 € water at 2800′)

The leading edge of the first “real” storm system for over a month moved through quickly yesterday evening with strong easterly winds (sustained 40mph, gusting 70’s) and heavy snowfall in Eastern Turnagain Arm. As the storm weakens today there is a chance for another 1-3 € as well as a few more inches for Monday. The easterly winds have decreased substantially since midnight and should be in the 10-20mph range on the ridgetops today. Temperatures around treeline increased from ~20F yesterday to the upper 20’s today where they should remain. There is a light rain/snow mix this morning at sea level along Turnagain arm with slippery roads.


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).  

Kevin will issue the next advisory Monday morning, December 10th.

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Riding Areas
Updated Fri, May 13th, 2022

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 as of May 1 per Forest Plan.
Placer River
Closed
Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage
Closed
Closed as of April 1st per Forest Plan.
Turnagain Pass
Open
Open. Extended opening through May 31.
Twentymile
Closed
Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake
Closed
Closed as of May 1 per Forest Plan.
Lost Lake Trail
Closed
Closed as of May 1 per Forest Plan.
Primrose Trail
Closed
Closed as of May 1 per Forest Plan.
Resurrection Pass Trail
Closed
Closed as of May 1 per Forest Plan.
Snug Harbor
Closed
Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor
Closed
Closed as of May 1 per Forest Plan.
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Closed as of May 1 per Forest Plan.

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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.