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Mon, February 27th, 2017 - 7:00AM
Tue, February 28th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is  MODERATE  above 2,000′ in the Alpine where triggering a fresh wind slab is possible today. There also remains a possibility of triggering a more stubborn, and more dangerous avalanche 2-3′ deep on all aspects. If winds increase beyond the forecasted 10-25mph range today, avalanche danger may increase to CONSIDERABLE in the Alpine. Be prepared to change plans if conditions worsen. In addition be aware of cornices, surface sluff, and a glide crack that has formed on Seattle Ridge.  

Below 2,000′ there is a  LOW  danger where triggering an avalanche is unlikely due to a snowpack consisting of hard crusts.

In Summit Lake, Girdwood, and on the southern end of Turnagain near Johnson Pass triggering a deeper more dangerous avalanche near the ground is still possible, but will be hard to trigger.

Check out the Saturday Summit Summary HERE.

Special Announcements

Elevated avalanche danger exists in Hatcher Pass. Click  HERE  for a several reports about a human triggered slab avalanche near Hatch Peak on Saturday. Click  HERE  for the Hatcher Pass Avalanche Center weekend advisory and more info about the snowpack.

Friends of the Chugach National Forest Avalanche Center is an  official Pick. Click. Give. organization. When you apply for your PFD please considering supporting your public avalanche center!!

Mon, February 27th, 2017
Above 2,500'
2 - Moderate
Avalanche risk
1 - Low
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

Today expect ridgetop winds from the Northwest to steadily increase this afternoon ranging from 10-25mph with gusts reaching the 30-40’s mph. This wind direction can funnel through parts of Turnagin Pass from more of a Southerly direction. Be aware that loading may occur on a variety of aspects depending on which side of the road you are on. There is about 6 inches of snow available for transport and wind slabs are anticipated to grow to 10 -12” range.  Watch for pillowed or drifted snow or where the snow may feel stiff and ”upside down,” and identify steep features like convexities or gullies where a shallow wind slab could knock you off our feet. The avalanche danger will depend on how much snow is being transported. If large plumes of blowing snow are observed, this could add stress to existing weak layers deeper in the pack, and make it easier to trigger a deeper more dangerous slab. More details in Secondary Concern below. Be prepared to change plans if you see any obvious signs of instability; shooting cracks, recent avalanches or collapsing “whumpfing” sounds. 

Typical loading patterns of wind slabs

Skier triggered “sluff” on Corn Biscuits West face and a good example of the top 6″ of loose surface snow that is available for transport if winds pick up today. 


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

Above 2000′ a widespread layer of buried surface hoar remains a concern on steep slopes, where triggering an avalanche 2-3’ deep has become stubborn due to a stabilizing snowpack. Relatively calm weather this week has allowed for folks to push further into the mountains with no reports of avalanche activity since last Saturday (2/18). However, increasing winds today may add additional stress and triggering a persistent slab avalanche could have high consequences. Triggering this avalanche will be more possible in steep terrain and in places where the snowpack is thinner – near rock bands or on more scoured features. Also, these slabs can break above you, and release after several tracks are on a slope. 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 identify and avoid terrain traps (gullies, cliffs, or trees below). Change your plans and avoid steep terrain should you see rapid loading due to blowing snow. 

Deep Persistent Slab: We continue to find various layers of weak faceted snow and depth hoar near the bottom of the pack in certain areas. This includes Summit Lake zone, and some areas in Girdwood Valley and towards the Southern end of Turnagain near Johnson Pass. Similar to the problem above, these layers will be very tough to trigger, but a possibility remains in places with this structure.

Additional Concern
  • 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

Cornices: Winds today may add stress to already large 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. 

Loose snow avalanches: The top 6” of surface snow is loose and sluffs may be easy to initiate and fast moving on steep terrain features protected from the winds. 

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.

A large cornice above Magnum’s SW face. Photo taken yesterday by Aleph Johnston-Bloom. 

Mon, February 27th, 2017

Yesterday skies were mostly sunny and temperatures reached the mid 30F’s during the heat of the day. Westerly winds were observed throughout our region averaging around 10mph with gusts in the 20’s mph. Low valley fog moved into Turnagain Arm towards Portage Valley late afternoon along with cooler temperatures overnight.    

Today skies are expected to become cloudy causing valley fog to lift. There is a chance for light flurries. Northwest ridgetop winds (10-25mph) are expected to increase throughout the day. Sustained winds could reach the mid 20’s mph by mid afternoon, with gust in the 30-40’s mph. Temperatures will start drop by late evening, and may reach the single digits overnight.  

Cold off shore flow is expected to continue over the next few days bringing more sustained ridge top winds and cold temps as high pressure settles in over interior Alaska. This pattern is expected to dominate Southcentral, AK for the next week. Today’s weather discussion warns; €œOld man winter is going to make a forceful return, reminding Alaskans that Spring is most definitely not here yet. €

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   0   0   65  
Summit Lake (1400′) 26   0    0 31  
Alyeska Mid (1700′) 27   0   0   60  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   W   8   23  
Seattle Ridge (2400′) 25   NW   10   33  
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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.