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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 26th, 2016 - 7:00AM
Expires
Sun, March 27th, 2016 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A  CONSIDERABLE avalanche danger remains at the mid-elevations on all aspects for glide avalanches in the Turnagain Pass, Girdwood Valley, Summit Lake and surrounding mountains. Glide cracks continue to release and produce large and destructive slides. Avoiding time under glide cracks is recommended.

At the upper elevations (above 3,000′) there is a MODERATE avalanche danger where shallow wind slabs 6-8″ thick may be found and possible to trigger. Watch for, and limit time under, cornices which are large and looming along ridgelines. Last, the sun may warm the surface enough for human triggered wet loose avalanches on southerly aspects.

*If you are headed to the Summit Lake area don’t forget to check this morning’s  Summit Lake Summary.

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Sat, March 26th, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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. Dangerous avalanche conditions. 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
  • 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

The snowpack continues to fall apart at the ground. Yesterday, another large glide crack released on the face of Seattle Ridge. If you are headed to Turnagain Pass this weekend you can’t miss it, it’s front and center, just across from the motorized parking lot. If you have not been to the ‘Pass’ for a while, you may be surprised at how many cracks litter the mid-elevations and how many of these have released. It goes without saying, staying out from under glide cracks is HIGHLY recommended! 

 

*With the unseasonably warm temperatures over the past week, the springtime melt-down (or shed-cycle) is closing in upon us. We do have cooler temperatures for today, and likely tonight, that will form surface crusts as high as 2,500′, but it is good to remember that undreneath the pack is very wet and unsupportable at these mid-elevations. This ‘rotten’ soft snow, so to speak, is a red flag for not only the glide problem but for the potential for large wet slab and wet loose avalanches. 

Wet Loose Slides today? Southerly slopes seing direct sunlight may warm enough to melt the surface crust. In this case, wet loose slides could be triggered by people. Keep tabs on the surface conditions.

Avalanche Problem 2
  • 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

At elevations above 3,000′ (above the majority of the glide crack/avalanche hazard) fairly dry snow exists. There was roughly 2-5″ of new snow yesterday which sits on a mixture of old loose snow and old sun and wind crusts. Shallow wind slabs composed of mostly the new snow likely formed on leeward slopes during yesterday’s moderate Easterly winds. These slabs should be ~6-8″ thick and in pockets along ridgelines. Quick hand pits and watching the surface texture for smooth rounded wind pillows and drifts will help to find any relatively new wind slabs. 

Additional Concern
  • 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

With a chance for direct sunshine today (and tomorrow) watch for cornices to weaken and possibly fall naturally. We have not seen much cornice failure recently but we do know these large features will begin to start calving soon. Limiting and avoiding time under cornices will be key as we head into springtime hazards.

If skies clear for travel above treeline, take stock of the slope or couloir you wish to ride/ski – is there a large cornice looming over you while you ascend/descend?

Weather
Sat, March 26th, 2016

Yesterday’s weather consisted of overcast skies with some light precipitation in the morning hours. Around .5″ of rain fell up to 2,000′ and between 2-5″ of snow fell above 2,000′. Ridgetop winds were moderate, averaging to 20mph with gusts to 40mph from a generally East direction. Temperatures were in the mid-30’s at 1,000′ and upper 20’s at 3,000′. Overnight, winds have died down substantially and temperatures have cooled off several degrees and move into a break between storms.  

For today, we are expecting partly cloudy skies, which could become quite clear by noon before a chance more clouds might move in later today (tough sky cover forecast). No precipitation is expected and winds are slated to be light to moderate from a Northerly direction, averaging 5-15mph. Temperatures should begin to climb again today as the sun comes out and reach up to 40F at 1,000′.

Sunday looks to be nice: mostly clear skies and light Northerly winds as a quick high pressure ridge builds before another low pressure system moves in Sunday night.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   rain    0.5 124  
Summit Lake (1400′) 35   rain   0.3   41  
Alyeska Mid (1700′) 33   rain   0.3   105  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24   NE   11   40  
Seattle Ridge (2400′) 27   SE   12   23  
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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.