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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, April 15th, 2017 - 7:00AM
Expires
Sun, April 16th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The overall avalanche danger is  MODERATE  in the morning but will rise to CONSIDERABLE and maybe go to HIGH on steep Southerly facing slopes later this afternoon and evening. As the sun heats up and softens solar aspects during the day, triggering a wet slab or wet loose avalanche will be likely and naturals are possible.  Paying attention to aspect and time of day are crucial. On Northerly aspects where dry snow exists, there is still the possibility of triggering a deep slab avalanche 2-5+’ thick.    Watch for changing conditions. Avoid travel on or under cornices and give glide cracks a wide berth.  

 ***The mountains are heating up a little more each day. It is important to pay close attention to how the warming is affecting the snowpack. If you see any avalanche activity today or over the weekend please let us know!    On  steep  Southerly slopes with a  thin  snowpack, such as where rocks are protruding the danger could trend towards HIGH =  natural wet avalanches likely, human  triggering very likely.  Avoid travel in Southerly avalanche terrain in the afternoon and steer clear of runout zones.  

Hiking on summer trails (including the Byron Glacier trail, Turnagain Arm Trail a.k.a the bike path, etc).    Extra caution is advised during the afternoon and evening hours for trails that cross under avalanche paths. Avalanches are still possible at the higher elevations that could send debris over snow-free hiking trails.  

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Sat, April 15th, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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

Timing is everything…

It’s that time of year where clear skies freeze up the snow surface at night and then the sun and warm air temperatures turn hard crusts into slop later in the day.  A MODERATE danger in the morning transitions to a CONSIDERABLE or even HIGH danger in the afternoon and into the evening hours. Choosing what aspect to travel on, paying attention to the time of day and how long the slope you are playing on has been exposed to direct sunlight are essential to staying out of trouble. Remember to avoid the runout areas of Southerly slopes as well as things heat up. 

Yesterday observers saw natural wet avalanche activity start around 12:30 pm and continue into the evening on Southerly slopes. Natural avalanches were witnessed on Seattle Ridge, in Girdwood, in Placer and in Whittier. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope. This stepped down to the ground. Wet activity has been observed all week on Southerly slopes and zones with thin snowpacks have been particularly active where free water is interacting with old weak snow. Wet loose snow avalanches may also trigger deeper slabs.   

 If heading out for a fun day in the sun keep in mind these things:

  • Once the snowpack becomes so wet it is unsupportable and ‘punchy’ to skis, snowmachines or boots – it’s time to head to a cooler aspect. 
  • The steeper the Southerly slope, the more it will warm and the more dangerous it will be (due to more warming but also because it’s simply steeper).
  • Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down. 

All of the avalanches in the pictures below are large enough to injure, bury or kill a person. Extra caution is advised. Natural avalanches are happening. Get Out of Harm’s Way! 

Sunburst avalanche that was triggered around 4:30 pm on Thursday afternoon.

Natural avalanche on Seattle that was witnessed around 4 pm yesterday. Avalanche path in center of photo that has dirty debris. 

Natural that occured yesterday around 5:30 pm on Ragged Top mountain in Girdwood.

Wet loose that triggered wet slabs and ran to the ground on Corbiscuit. Photo: APU Snow Science Class

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

On the shaded and cool side of the mountains (Northerly aspects) dry snow still exists. While wet snow issues are not a problem here, deep slab issues are. There are several weak layers anywhere from 2-5′ below the surface. The most notable is the March 27 buried surface hoar and/or facets; these layers were buried by 3-6′ of snow during the 10-day April Fools storm.  As folks venture out looking for “cold snow” this remains a concern. Shaded aspects (NE – NW – W) in the mid and upper elevations that haven’t avalanched already are the most suspect places for triggering a deep slab. 

This problem is one of low probability but high consequence as these are large and potentially unsurvivable slides. As the snowpack continues to adjust, triggering will become more stubborn and less likely with time. Keep these point in mind:  

  • It will take someone hitting a ‘thin spot’ in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall.
  • These slides can be triggered remotely, for example, from a ridge or bench on the top/side or below. 
  • There may be no signs of instability before the slope shatters 
  • Several tracks may be on a slope before it releases
  • Stability tests may not produce any notable results
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

Small glide avalanches have released on Southeast facing Seattle Ridge the past couple days. On Wednesday a larger glide released on the South aspect of Eddies ridge. We expect this trend to continue with the warm days ahead. Keep an eye out for glide cracks, full depth cracks in the snow, and limit time underneath them. Most cracks appear to be small and in areas less traveled, but a glide avalanche can also release with little warning when a crack is not visible prior. 

Cornices: Cornices are large and likely hanging close to their tipping point as the warming trend continues. Direct sunshine, a person, or a group of people on top these could be enough to cause one to break. An observer in Seattle Creek noted large cornice cracks/crevasses along some of the ridgelines. Give cornices a wide berth from above and limit exposure under them from below. 

 

Glide avalanches and glide cracks near the Seattle Ridge uptrack. 

 

Weather
Sat, April 15th, 2017

Yesterday was another warm spring day with clear, blue skies and warm temperatures. Highs were in the 40-50Fs and winds were light and variable. Temperatures dropped just below freezing last night and winds stayed calm.  

Today looks to be very similar with temperatures in the 30-40Fs at higher elevations and 40-50Fs at lower elevations. Skies will be mostly clear today and it will be partly cloudy tonight with temperatures in the low 30Fs.  

The current pattern is forecasted to continue until Thursday or Friday next week with a low-pressure system moving into the Gulf and bringing precipitation to the area.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 42   0   0   67  
Summit Lake (1400′) 35 0   0   23  
Alyeska Mid (1700′) 40 0   0 61

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  35  SW 5   12  
Seattle Ridge (2400′)  No Data  SE 6 13  
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Riding Areas
Updated Mon, December 02nd, 2019

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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