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Wed, February 18th, 2015 - 7:00AM
Thu, February 19th, 2015 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2000′ today in the Alpine.   There is currently a weak layer of old snow sitting under a fresh new load from Feb. 16th. Triggering an avalanche 1-3′ thick is likely on terrain steeper than 35 °. Below 2000′ the avalanche danger is MODERATE where a different snowpack structure exists and a breakable crust is present.

We would like to stress the need for patience and abstaining from temptation. Today obvious signs of instability are likely as you travel into the Alpine. Watch for recent avalanches and listen for whoomphing sounds. Even if you do not observe these signs don’t be tempted to ski/ride in terrain steeper than 35 °.

Wed, February 18th, 2015
Above 2,500'
3 - Considerable
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

Tincan Feb.17, 2015 ETC

Two days ago a warm and windy storm produced hurricane force winds leaving the Kenai Mountains and Western Chugach mountaintops coated with a thick layer (1-3′) of new snow in the Alpine above 2000’. Temperatures were warm during this two day storm and rain/snow line fluctuated between 1500-2000’ causing snow below this elevation band to become saturated by rain. Sunburst weather station experienced several hours of 80 mph winds from the East, with a gust measuring 129 mph, which damaged the Sunburst anemometer.

Snow totals from this two-day storm averaged 2’ in the Turnagain Pass area with closer to 3’ in the upper elevations of Girdwood and the Portage area. Summit Lake received slightly less snow, but even 1’ of new snow still warrants a similar level of concern. Slab depths are variable, 1-3′ deep, depending on terrain features and its exposure to the wind.  You will also find places where the wind has left some features scoured.  

This is not your typical Chugach maritime snowpack! A very unstable weak layer of faceted snow is buried beneath this1-3’ slab. This weak layer is widespread above 2000’ throughout our region and has shown significant propagation potential after the storm ended on Sunday night. Three remote triggered avalanches occurred simultaneously on a Southern aspect at about 2500 of Tincan’. A skier-triggered avalanche was also reported on Tincan yesterday, lower in the trees near 2100’, with a 1.5’ slab that propagated 20-30’ across a small terrain feature. Luckily no one was caught or injured. These two separate incidents confirm that a human is enough to tip this delicate balance. This problem will not be going away quickly and is the reason we will need to refrain from tempation and stay off of slopes steeper than 35° in the coming days as this weak layer adjusts to it’s new load. 

These three remote triggered avalanches occured while digging a snow pit on an adjacent lower angle slope on Tincan’s South face. Photo by John Sykes

Travel Advice:

Remotely triggered avalanches are possible today and could be triggered from both above and below. Pay attention for other groups and be aware of run-out distances.

In areas with short steep rollovers, watch out for terrain traps.  A slab if triggered on a small slope in the wrong place, could be enough to bury a person.  

Large collapsing sounds will be your first red flag warning sign. If you hear “woomphing” sounds this is a sign that your weight is enough to collapse the weak layer below and reinforces your decision to stay off of all slopes greater than 35° today. 

Additional Concern
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

The combination of new snow, warmer temps, and sun affect could be enough to heat up the surface snow on Southern aspects today. On steeper slopes this could produce moist loose point-releases. If you are keeping it under 35° this will be an additional hazard to observe from low consequence terrain. Rollerballs and snow sticking to the bottom of your skins will be the first signs that surface snow temperatures are heating up.  

Natural slab avalanche activity is unlikely today, but should a moist loose avalanche pick up enough volume, it could trigger a slab in steep terrain. 

Wed, February 18th, 2015

No new precipitation was recorded yesterday. Cloudy skies in the morning became mostly sunny in the afternoon. Winds were light to moderate averaging 15mph from the South on Seattle Ridge. Sunburst wind data was not available yesterday due to damage caused from high winds the day before. We will try to get this fixed when it becomes safe to access this terrain.  

Overnight temperatures were in the 20’s F and no precipitation was measured. Wind data was not available after 10pm last night when Seattle Ridge weather station wind sensor malfunctioned.

Today Sunny skies are anticipated for today and temperatures could reach the mid 30’s F with solar affect from the sun. Winds are expected to be light to moderate (10-20mph) from the South. Precipitation is unlikely.

*Wind data from Seattle Ridge weather station was not available after 10pm on Feb.17.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30   0   0   43  
Summit Lake (1400′) 28   0   0   8  
Alyeska Mid (1700′) 32   0   0   24  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   N/A   N/A   N/A  
Seattle Ridge (2400′) 25   *S    *15 *31  
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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.