Turnagain Pass RSS

ARCHIVED - Forecasts expire after 24 hours.
Tue, February 24th, 2015 - 7:00AM
Wed, February 25th, 2015 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains  CONSIDERABLE  on all aspects and slopes above 2,000′. Wet slab avalanches up to a foot thick will be possible to trigger in the short elevation band from 2,000′-~2,500′. Dry slabs, 1-3+’ thick, will also be possible to trigger above roughly 2,500′. On top of these slab avalanche problems, daytime warming and solar radiation may induce wet loose slides on steep Southerly slopes.  

Although natural avalanche activity is not expected today and human triggered avalanches are only possible as opposed to likely, which is the definition of a  MODERATE  avalanche danger rating, today’s rating is based on the “Travel Advice” column of the danger scale – stated above in orange. We have very little information for Turnagain Pass and the surrounding mountains. As we head into a relatively clear sky period and travel into the backcountry and the upper elevations is possible, know that there is a layer of weak faceted snow under a variable slab 1-3+’ thick. Careful snowpack evaluation, cautious route finding and conservative decision-making will be key for a safe outing.  

A fun day skiing or riding can be had in the dry snow by sticking to slopes 35 degrees or less and avoiding steep rollovers on the ascent through the mid-elevation wet and crusty snow.

Special Announcements

If you haven’t heard – the first annual SNOWBALL is around the corner!! A “more formal than normal” night of music, door prizes, raffle and fun is on the schedule at the Taproot this Friday.  Please join the Friends of the Chugach National Forest Avalanche Information Center and Alaska Avalanche School  in an effort to support local avalanche education and information!

Tue, February 24th, 2015
Above 2,500'
3 - Considerable
Avalanche risk
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. 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
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Following in step with our unprecedented warm winter, during the past several days we have seen rain falling on snow up to 2,000′, and as high as 3,000′ in places. Water amounts have accumulated to ~.7″ on Turnagain Pass and up to 2″ in the Girdwood Valley since Saturday. Not only has this been raising the snow line (which is currently around 1,500′) but it has more importantly induced a mini wet slab cycle in this small elevation band. Technically, warm temperatures and sunshine has helped to tip the balance for some of these wet slabs after the rain, but regardless, there is a poor snowpack structure in the top 1-2′ and this is why we are seeing wet slabs. Below are some shallow slabs seen yesterday in the Portage Valley – these are similar to the shallow slabs on Seattle Ridge two days ago

For today, skies have been clearing the temperature dropping which will start freezing the pack from the surface down and decrease the wet slab potential. But, only a shallow re-freeze on the surface should not be mistaken for good stability. Sometimes a shallow re-freeze can act to strengthen the slab enough to increase triggering potential before it does indeed freeze enough to be safe; something to keep in mind when moving through the mid-elevations to get to the drier snow above.

Portage Valley shallow wet slabs likely from Sunday 2/22 (Maynard Mtn, West facing ~2,000′).

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

In the dry snow, which begins roughly just above 2,500′, we continue to be concerned with the well documented layer of faceted snow that sits under a slab 1-3+’ thick. The slab is highly variable due to the extreme winds seen a week ago. From the little information we have been able to gather, high variability does exist in the slab depth as well as the weak layer depth and strength. This variability can be helpful in breaking up the slab/weak layer combo and minimize the ability for an avalanche to propagate across entire slopes. However, a 3′ slab is nothing to mess with even if it does just release in a pocket and not over an entire slope. 

If you are getting out in search of dry snow today:

  • Watch for RED FLAGS – collapsing (whoomphing) will be most likely
  • Be aware this set-up is the type where NO Red Flags may be present until a slope avalanches
  • Stability tests may not be representative due to the variability of the slab (and possibly the weak layer)

  • Practice safe travel protocol!!! Exposing only one person at a time, watch your partners and have an escape route planned if choosing to enter terrain over 35 degrees
Tue, February 24th, 2015

Partly cloudy skies, some sunshine and intermittent rain showers covered much of the region yesterday. Around 0.2″ of rain fell below 2,000′ with a dusting of new snow above this. Ridgetop winds were 5-10mph from the Southwest while temperatures were in the upper 30’s F at 1,000′ and in the upper 20’s F on the Ridgetops.

Overnight, skies have continued to clear and temperatures have cooled slightly at each station (ridgetop as well as valley bottom). Valley fog is likely today with partly sunny skies above. Temperatures should warm back up to the mid 30’s at 1,000′ and the upper 20’s on the ridgetops and feel quite warm in areas with sunshine. Ridgetops winds are expected to be in the 5-10mph from the East.  

We look to remain between storms with mostly sunny skies and light winds through Friday; a low pressure does brush to our South on Wednesday, which should only bring some high clouds and moderate East winds. The weather models are showing our next shot of precipitation on Saturday with another dose of warm, wet and windy weather.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   rain   0.1   40  
Summit Lake (1400′) 30   rain   0.1   6  
Alyeska Mid (1700′) 33   rain   0.17   22  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   N/A   N/A     N/A    
Seattle Ridge (2400′) 27   N/A     7   18  
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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.