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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, February 19th, 2016 - 7:00AM
Expires
Sat, February 20th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

Overall generally stable avalanche conditions exist in the advisory area but with the widespread glide cracks in popular recreation terrain in the  Treeline (1000′-2500′) elevation band and continued reports of large naturally occurring cornice falls in the Alpine, the hazard remains at MODERATE. In addition, lingering pockets of wind slab and loose snow avalanches may be triggered in steep terrain. Practice safe travel techniques and take inventory of surface conditions as a storm approaches for the weekend. Watch for changing conditions if snow and winds pick up earlier than forecasted.

*Shallow snowpack zones: South of Turnagain Pass and the Summit Lake area have old weak layers in the snowpack where triggering a much larger avalanche is possible. This is something to keep in mind if you are headed to these zones. Click  HERE  for a recent photo of large Natural avalanche between Lynx Creek and Silvertip Creek.  

Special Announcements

Saturday, February 20th  Hatcher Pass Avalanche Center is having their annual fundraiser at the Government Peak Chalet near Hatcher Pass. This event will feature a slide show by local climber and ski mountaineer, Kirsten Kremer,  a Silent Auction, Live Music and FUN!  Click  HERE  for more info.

Fri, February 19th, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
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
  • Cornice
    Cornice
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

There has been no reports of human triggered avalanches since Monday. Overall temperatures have cooled throughout the week and winds were light yesterday. Observers have reported good stability and slope testers have been in steep terrain without incident. However, there have been a few large naturally cornice triggered avalanches in steep Alpine terrain. Avoid traveling on or underneath cornices. They may break much farther back than expected and could trigger a large avalanche on the slope below. Falling on to a slope with a refrigerator to school bus sized piece of snow would be bad news. There have been significant cornice cracks observed along ridgelines. You do not want to end up on the wrong side or take a dip into one of the wide ones on your snowmachine or skis. 

In addition, watch for any lingering wind slabs on leeward slopes and loose snow sluffing. Both of these could be quite hazardous in steep, high consequence terrain.

As always practice safe travel techniques: ride slopes one at a time, park and regroup in safe areas, have escape routes planned and watch your partners. 

Cornice crack on Magnum ridge. Photo: Amanda Goss

 

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks continue to appear, grow and release throughout the Treeline (1000′-2500′) elevation band. They are on all aspects and are still totally unpredictable. The best way to minimize the risk is to avoid travel underneath. There was a new crack observed on Lipps yesterday in skiable terrain. 

 

 

Glide crack in Main Bowl (1st Bowl).  February 9th.                                                                                                            

 

The same glide crack on February 18th.

Weather
Fri, February 19th, 2016

Yesterday was partly cloudy with light winds and temps in the mid 20Fs to low 30Fs.  

Today will partly to mostly cloudy with a slight chance of snow showers during the day. Temperatures will be in the mid 20Fs to mid 30Fs and winds will be Easterly 5-15 mph. Clouds will increase overnight and with 1-4″ of snow possible as the first front affects the area.  

Tomorrow snow showers and winds will increase as the next storm really moves into the region. The National Weather Service is decribing this as a robust front. Stay tuned for more details as the jury is still out on the timing, temperatures and the form of precipitation it will bring.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 22   0    0 101  
Summit Lake (1400′) 20 0  0 30
Alyeska Mid (1700′) 24 0  0 85  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   E   5   13  
Seattle Ridge (2400′) 23  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.