Turnagain Pass RSS

ARCHIVED - Forecasts expire after 24 hours.
Wed, March 2nd, 2016 - 7:00AM
Thu, March 3rd, 2016 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE in the Turnagain Pass area today for slab avalanches, cornice falls and glide avalanches. It will be possible for people/snowmachines to trigger slabs 1-2′ thick at elevations above 1,000′. These are most likely on the steep sunlit slopes, more than 35 degrees. Cornice falls are possible as well, and could trigger slabs below. Last, glide avalanches remain a concern at the mid-elevations.  Easing into terrain will be key. Pay close attention to Red Flags: warming by the sun, recent avalanches, ‘whumphing’, and cracking in the snow.

*There is little information for areas South of the Pass, such as Silvertip, Summit Lake and Johnson Pass zones. More reason for a conservative mind-set.  

**Remember a MODERATE danger means human triggered avalanches are possible:

Wed, March 2nd, 2016
Above 2,500'
2 - Moderate
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
  • 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

After a 10-day storm deposited between 10 and 15 feet of snow at the upper elevations, yesterday was our first day with no precipitation and today will be our first clear sky day. Many of us have been eagerly awaiting this window of high pressure to travel places other than the low angle trees and flats. After two days of snowpack analysis, one day on Seattle Ridge and one day on Tincan, we have few data points to pull from. However, from these we have found both stable and unstable results. The stable results were from Tincan (more on that HERE) and the unstable result was from Seattle Ridge (that can be seen HERE). That said, we should head into today with a conservative approach. Although large connected avalanches are not expected, pockets of wind slab and old lingering storm slabs could be triggered. Keep in mind, these pockets can be large enough to ruin your day.

Warming by the sun is expected to help destabilize slabs that remain tippped on the balance. That makes two trigger mechanisms for lingering slabs and cornices, sun and people. Keep an eye out for warming snow surfaces and roller balling. These are signs the snowpack properties are changing and triggering an avalanche more likely.

Wind Slabs: Strong winds Monday night have formed wind slabs and wind crusts along ridgelines and in exposed areas. 

Storm Slabs: Lingering storm slabs are possible where fluctuations during the storm created layers of crusts, strong snow and weak snow. This is what Graham found on Seattle Ridge on Monday. These storm slabs are most likely to be found at the mid-elevations.

Sluffs: Sun induced loose snow avalanches are possible. These will likely be damp heavy snow and could push you around on steep sunny slopes.

We want to hear what you are seeing!! Please pass on photos/videos/a few sentences of what you see today/tomorrow. We are trying to map out the post-storm snowpack.

Avalanche Problem 2
  • 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

Cornice fall may one of the larger hazards today with sunshine acting to weaken these already tenuous bombs. Cornices right now are LARGE – some bigger than a semi-truck. Limiting time spend under these is key. With amount of snow from the last storm, discerning how far back from the ridge you should travel could be difficult, err on the safest side possible as they really can break much farther back than expected!

Photo: Cornice fall on the Tincan Ridge (CFR). This large cornice fell just after the end of the storm cycle, possibly Tuesday. It triggered a wind slab below and ran around 700′ down the slope out of view. This is one the smaller cornices seen in the area.

Additional Concern
  • 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 are moving and coming out of hiding after they were covered by wind and snow during the storm cycle. Although it has been several days since the last glide crack we know of released and avalanched, they are still on the move. Limiting time spend under cracks is crucial, as they will mow anything down in their path if one does release.

Wed, March 2nd, 2016

Yesterday, the mountains surrounding Turnagain Pass saw overcast skies with some sunshine breaking through. Over the past 24-hours there has been no precipitation, winds have been light out of the East on the ridgelines and temperatures have been mild (~32F at 1,000′ and in the low to mid 20’s at 3,500′). Temperatures in valley bottoms have cooled overnight to the low 20’sF.

Today, we are scheduled for our first sunny day in just about two weeks; yet, this could be in conjunction with some valley fog. Winds are forecast to be light, 5-10mph out of the East along the ridgelines. Temperatures should be warm, up to 30F at 3,000′ and 35F at 1,000′.

Thursday another nice and sunny day is on tap before clouds begin to move in Friday ahead of a possible weekend storm system. Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   0   0   143  
Summit Lake (1400′) 29   0   0   42  
Alyeska Mid (1700′) 30   0   0   106  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24   NE   8   31  
Seattle Ridge (2400′) 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.