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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, April 16th, 2017 - 7:00AM
Expires
Mon, April 17th, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The overall avalanche danger is  MODERATE  this morning and will  rise to CONSIDERABLE on steep Southerly facing slopes this afternoon and evening. Wet slab and wet loose avalanches will be likely to trigger and natural avalanches will be possible as the sun heats up and softens Southerly aspects. Paying attention to aspect and time of day are crucial. On Northerly slopes, where dry snow exists, there is still a chance 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.  

 ***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 possible at the higher elevations could send debris over snow-free hiking trails.  

MONDAY AVALANCHE OUTLOOK:
No avalanche forecast will be issued tomorrow, Monday April 17th. The avalanche outlook will be the same message tomorrow as for today due to continued warm and sunny weather expected.

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Sun, April 16th, 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

Blue skies and warm days will continue to be the theme for today and into the workweek. As the mountains continue to heat up a bit more each day, they will become more and more dangerous. It is important to pay close attention to how the warming is affecting the pack. We are in a melt-freeze cycle on Southerly slopes – hard frozen crusts in the morning, which turn to unsupportable mushy and unstable snow by the afternoon/evening. Each night the re-freeze is a bit less and the melt phase is a bit longer, creating a longer period of heightened avalanche conditions. Choosing what aspect to travel on, paying attention to the time of day and how long the slope you are on has been exposed to direct sunlight are essential to staying out of trouble. 

Over the past few days many natural wet avalanches have occured. The activity looks to be starting around 12:00 pm and continuing into the evening hours, as late as 8 or 9pm. Natural avalanches were witnessed on the front and backside of Seattle Ridge, in Girdwood, in Placer and in Whittier on Friday. In the Lost Lake area several wet avalanches have been seen this past week. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope. 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 these points in mind:

  • 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. 
  • The recent avalanches seen have been large enough to injure, bury or kill a person. Extra caution is advised. Natural avalanches are happening. Get Out of Harm’s Way! 

     

Large wet slabs on the Southwest face of Cornbiscuit – released sometime over the weekend (4/15 or 4/16). Mike Davidson Photo.

 

Natural avalanche that occured Friday around 5:30 pm on Ragged Top mountain in Girdwood Valley, Southeast facing slope.

Natural wet slab avalanche in the Lost Lake and Snug Harbor zone from earlier in the week (Photo: Troy Tempel). This areas is out of our forecast zone, but it is the type of avalanche activity we have been seeing on Southerly aspects – including the Seattle Creek drainage.

 

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. There are several weak layers anywhere from 2-5′ below the surface. 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

Several small glide avalanches have released on Southeast facing Seattle Ridge and Eddies Ridge over the past few days. 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. 

Cornices: Cornices are large and likely hanging close to their tipping point. 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 a large cornice fall on Friday. Cornice crevasses have also been noted (opening slots where the cornice is pulling away from the ridge but has not broken off. Give cornices a wide berth from above and limit exposure under them from below. 

Glide avalanches and glide cracks near the Seattle Ridge up-track. 


Weather
Sun, April 16th, 2017

Over the past 24-hours skies have been clear and winds have been light along the ridgetops, in the 0-10mph range from an Easterly direction. Temperatures were a bit cooler than yesterday, but are still warm, climbing from the 20’s to the 50’s at sea level and rising to the mid 30’sF along the ridgelines.

Today and Monday, we can expect very similar weather – bluebird. Winds should remain light from an Easterly direction and calm at times. Temperatures are expected to rise to the 50’sF at elevations below 2,000′ and into the 30’s and 40F along the ridgetops.  

This stretch of high pressure and clear sky days should extend into the coming workweek.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 40   0   0    66
Summit Lake (1400′) 38   0   0   22  
Alyeska Mid (1700′) 41   0   0   61  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 33   NE   3   10  
Seattle Ridge (2400′)  No Data SE   7   15  
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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
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Turnagain Pass
Closed
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Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
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Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
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South Fork Snow River Corridor
Closed
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Summit Lake
Closed
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