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Thu, February 23rd, 2017 - 7:00AM
Fri, February 24th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

There is a MODERATE avalanche danger on all aspects above 1,500′ where triggering a large propagating slab avalanche 2-3′ thick is possible and could have high consequences. In addition there are a handful of other avalanche concerns to be aware of including fresh shallow wind slabs, cornice fall and loose snow point releases. Also keep in mind that warming temperatures combined with periods of sun could make it easier to trigger a deeper instability on solar aspects.  

Below 1,500′ there is a LOW danger where triggering an avalanche is unlikely due to a snowpack consisting of hard crusts.

 In Summit Lake, Girdwood, and near Johnson Pass triggering a deeper more dangerous avalanche near the ground is still possible but will be hard to trigger. If headed to Summit Lake please check out the weakly summary  HERE.

Special Announcements

Southern Kenai mountains;  including the  Seward zone (Lost Lake/Carter/Snug Harbor/etc):  Heavy precipitation, strong winds and warm temperatures last week have added several feet of new snow to these areas.  Cautious route-finding is recommended as  avalanche conditions may still be dangerous.

Other regions throughout Southcentral, AK continue to have heightened avalanche conditions including  Chugach State Park  and  Hatcher Pass.  

Thu, February 23rd, 2017
Above 2,500'
2 - Moderate
Avalanche risk
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
  • 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

Wind slabs: Loose surface snow combined with Easterly ridgetop winds in the 10-20mph range could form shallow wind slabs on leeward features. The snow may feel “upside down” with slightly stiffer snow over softer snow. Look for areas of pillowed or drifted snow and identify steep features like convexities or gullies where the snow may be more loaded. Triggering even a small wind slab could have high consequences in the wrong terrain. Blowing snow and shooting cracks will be obvious clues to look for today. 

Loose snow: Yesterday small natural point releases were observed during the heat of the day as well as some human triggered sluff. The top 6” of surface snow is loose and may be easy to initiate and fast moving on steep features protected from the winds. 

Cornices: Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche on the slope below. Give cornices extra space and avoid being under them. 

Glide avalanches: There is a new glide crack above the flats along Seattle Ridge, just looker’s left of the up-track and Repeat Offender slide path. Avoid hanging out under this crack and any others you may see – these release without warning and are very destructive.

Sunshine: Today skies are expected to be partly sunny and solar warming may trigger loose snow avalanches in steep Southerly aspects. Sun combined with warm temptures could also make it easier to trigger a cornice or deeper instabilty (persistent slab) on Solar aspects. 


Cross loading pattern along South facing gullies on the SE face of Seattle Ridge as well as scoured ridgeline in the foreground. A good example of where wind slabs may be tender.


Skier triggered sluff on Tincan SW aspect just below CFR ridge, captured yesterday 2/22 on the DOT time lapse web cam. 


Avalanche Problem 2
  • 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

Clear skies over the last two days have allowed more folks to push further into the mountains with no reports of avalanches being triggered since last weekend. Unfortunately poor structure is still a concern throughout our region and triggering a large propagating slab 2-3’deep is still possible. A weak layer of buried surface hoar and/or faceted snow remains a concern on all aspects and elevations surrounding Turnagain Pass and Girdwood. A dense slab sitting on this weak layer has been slowing adjusting making this problem more and more stubborn to trigger with time. This means the probability of triggering a large avalanche is decreasing, but the consequences remain high, should someone find a trigger spot. Trigger points are often where the slab is thinner, near rocks or scoured areas. Also keep in mind, these slabs can break above you, and release after the 3rd, 5th, or 10th person has been on a slope. The trickiest part about our current snowpack is how difficult it is to assess due to the spacial variability of the weak layer, the slab thickness, and even the bed surface in some places. Be aware that snow pits and stability tests may not be representative of the actual slope you are trying to assess. A helpful way to think about this problem is to consider the consequences of a slope if it slides and indentify terrain traps (gullies, cliffs, or trees below.) Then decide is it worth the risk. Remember the steeper the terrain the higher the likelihood for triggering. 

In this snowpit on SW aspect of Sunburst buried surface hoar was found ~3′ below the surface and was very difficult to trigger in stability tests. 


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 places within our forecast zone at the bottom of the snowpack are various layers of facets with varying degrees of strength. In the Summit Lake zone and some areas in Girdwood Valley and Johnson Pass depth hoar has been found. The Valentines Day Storm cycle tested these layers with only a few avalanches occurring near the ground in (Girdwood Valley, and Summit Lake). Similar to the problem above these layer will be stubborn to trigger, but a possibility remains in places with this structure. The more likely scenario is where an avalanche occurring in the upper layers of the pack has the potential to step down and release the entire snowpack. If this does happen the volume will be large and could run long distances. 

Thu, February 23rd, 2017

Yesterday overcast skies and light flurries in the morning were replaced with partly cloudy skies. Moderate Easterly winds (15-30mph) shifted late morning to more of a Westerly direction and decreased to 5-15mph. Temperatures were on the rise increasing from ~10F yesterday morning to ~20F overnight.  

Clouds have moved back into our region this morning and temperatures will continue to rise as warm front moves in and may reach the low 30F’s by this afternoon. Skies may range from mostly cloudy to partly sunny. Westerly winds will shift again to the East and ridge tops are expected to be in the 10-20mph range. Precipitation is expected to start this evening favoring Anchorage and northward, with a possiblity of a mix of rain and snow for Turnagain Arm and the Kenai.  

Friday expect a similar pattern with warm temps, light precipitation, and temperatures hovering around freezing (32F).  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 19   0   0   68  
Summit Lake (1400′) 18   1   .1   34  
Alyeska Mid (1700′) 22   trace   .05   65  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16   Var.   7   29  
Seattle Ridge (2400′) 19   n/a    n/a   n/a    
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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.