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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, December 23rd, 2015 - 7:00AM
Expires
Thu, December 24th, 2015 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk 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.    

Special Announcements

Looking for a special Christmas gift? Pick up a F-CNFAIC raffle ticket!  Awesome prizes from our sponsors at Alaska Airlines, Alyeska Resort, Chugach Powder Guides, Talkeetna Air Taxi and Ortovox.  Drawing to be held Feb 26th at TapRoot.  Contact the Friends group through Facebook if you’re interested!

The Chugach National Forest has opened Johnson Pass trailheads (North and South) to motorized use as of yesterday.  Please see the “Riding Areas” table at the bottom of this page for current info on areas open to snowmachines.

Wed, December 23rd, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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
Observations
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Date Region Location
02/25/24 Turnagain Observation: Kickstep NE Bowl
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02/22/24 Turnagain Avalanche: Lynx Creek
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02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
Riding Areas

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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.