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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 23rd, 2015 - 7:00AM
Expires
Thu, December 24th, 2015 - 7:00AM
Forecaster
CNFAIC Staff
The Bottom Line

The avalanche danger is  MODERATE  at and above treeline in the backcountry surrounding Turnagain pass.  The possibility remains for a person, or group of people, to trigger a large and dangerous slab avalanche that breaks 2-4′ deep on a layer of near surface facets and/or buried surface hoar within the snowpack.  This is a low probability but a high consequence situation and results in a tricky snowpack that cannot yet be trusted.  The periphery areas (for example:  Johnson Pass, Lynx Creek, Summit Lake and Girdwood Valley)  of the forecast zone are particularly suspect due to a shallower snowpack and a more pronounced slab/weak layer set-up. Choose terrain wisely, do not put multiple snowmachines or skier/riders on or under steep slopes all at once, and watch for shooting cracks and recent avalanches.

 Below treeline the danger is  LOW  where there has been less snow and less wind.    

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Wed, December 23rd, 2015
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
  • 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

The weak snow that formed in early December sitting over the Thanksgiving Rain Crust or old hard snow is now buried under 2-4′ of snow. This combination is our current cause for concern and heightened caution in the backcountry. Many large avalanches ran during the storm Saturday. The crowns were long and connected, indicative of a persistent slab problem. Smaller human and cornice triggered avalanches have also run on these buried weak layers during the past few days on Turnagain Pass and in Summit Lake. Yesterday we received reports of a snowmachine triggered avalanche up Lynx Creek (possibly remotely triggered) and shooting cracks from snowmachines up towards Johnson Pass proper. These are both signs that the snowpack is still reactive. Many people have gotten out into steep terrain with no issues but these conditions warrant continued respect. These slides may be harder to trigger but very dangerous if you happen to hit the wrong spot. Being very careful to not overload the slope is crucial. Multiple sleds or skier/riders in or under avalanche terrain should be avoided. This type of avalanche often can be triggered from shallower areas where weight can transfer to the weak layer more easily. Pay attention to slopes above you and look for signs of instability. 

Silvertip Creek: Long continuous crown at top of ridge extending out of sight from our perspective. 1-2 miles long? Photo: Joe Connelly

Additional Concern
  • Announcement
    Announcement

There are multiple additional concerns to look out for today. Mostly clear skies should provide good visibility.

CORNICES: Cornices grew during the recent storm and as always travel on top of these should be avoided. They often break further back than expected and can trigger avalanches on the slopes below. Be careful not to accidently drive your snowmachine out onto them or have your ski lunch break in the wrong spot.

WIND SLABS: There was a lot of snow moved around by the wind during the storm. Stiff, pillowed, sculpted snow may indicate old wind slab that is still possible to trigger. Listen for hollow sounds and look for shooting cracks.

LOOSE SNOW:  The surface conditions have become less cohesive during the cold snap, loose snow avalanches are likely in very steep and rocky terrain. They may not be big enough to bury you but could be hazardous if they push you off of a cliff, flush you through rocky areas or into terrain traps.

 

Weather
Wed, December 23rd, 2015

Yesterday valley fog lingered throughout the day. There was mostly clear skies and sun shining above this layer. Temps were in the teens at ridge tops and single digits at valley bottoms. Winds were very light.  

Today will be a mixture of clouds and sun with the colder temperatures continuing. Winds may increase during the day blowing from the NW 10-20 mph. Tonight will be cold and clear.  

Tomorrow the weather pattern will begin to shift with clouds and warming temperatures as a low moves into the Gulf and brings our next chance for snow over the holiday weekend.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 13    0 0   50  
Summit Lake (1400′)  0  0 0   18  
Alyeska Mid (1700′)  15 1.5   .06   36  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 10   W   5    10
Seattle Ridge (2400′) 9    NNE  4  8
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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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