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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, April 18th, 2017 - 7:00AM
Expires
Wed, April 19th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE above 1000′.    On steep Southerly facing slopes in the afternoon and evening, triggering wet slab and wet loose 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 deeper persistent slab avalanche 2-5+’ thick.    Watch for changing conditions. Avoid travel on or under cornices and give glide cracks a wide berth.  

Below 1000′ the avalanche danger is LOW.  The wet snowpack has been draining and getting a solid freeze at night. Due to a stout crust triggering an avalanche is unlikely. It is still important to pay attention to runout from higher elevation terrain.  

WEDNESDAY AVALANCHE OUTLOOK:

No avalanche forecast will be issued tomorrow, Wednesday April 19th. The avalanche outlook will be the same message due to a similar weather forecast.  

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Tue, April 18th, 2017
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
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

The natural avalanche activity slowed down as temperatures cooled Sunday and Monday and the freeze was more pronounced. Today and tomorrow it will still be 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. 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.  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.  Rocky areas that are absorbing more heat should be avoided.

 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.
  • 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 wet avalanches seen have been large enough to injure, bury or kill a person. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope.

Temperature trend from late last week until this morning. The natural wet avalanche activity peaked during the warmest days Friday, April 14th and Saturday, April15th. 

 

Natural wet slab avalanche that occured on Friday afternoon on Seattle Ridge. 

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

Yesterday around 5 pm, a skier triggered a slide on a West aspect in Triangle Bowl on the backside of Seattle Ridge. The skier was the 4th person on the slope and triggered it in a thin spot. They were able to ski off of the slab. The bed surface was reported as the rain crust from the April Fool’s storm. In this springtime transition it is important to remember on the shaded and cooler side of the mountains (Northerly aspects: NE – NW – W), a cold mostly dry snowpack still exists. Afternoon warming may also influence how easy it is to trigger weak layers that are buried anywhere from 2-5′ below the surface. As folks venture out looking for “cold, soft 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 deeper slab.  

This problem is one of low probability but high consequence as these are potentially large and unsurvivable slides.

Keep these points 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.
  • 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

Triangle Bowl a few minutes after the avalanche was triggered. Thanks to the party involved for sharing the photo and information.

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 week. 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. 

Glide cracks in Eddies continue to open. Glide avalanche occured on Wednesday April 12th. 

 

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. 

Cornice in Summit Lake with old slab crown below. 

 

Weather
Tue, April 18th, 2017

Yesterday skies were partly cloudy to mostly clear. Winds were light and Westerly. Temperatures were in the high 20Fs at upper elevations and 30-40Fs at lower elevations. Overnight temperatures dropped below freezing.

Today will be mostly clear and sunny. Winds will remain light. Temperatures will be in the 30-40Fs in the valleys and with high 20Fs to low 30Fs forecasted above 3000′. Tonight into tomorrow looks to be very similar with temperatures dropping at night and climbing back up during the day. Clouds may increase Wednesday evening. There is a pattern shift still in the forecast for the weekend. Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31    0 0   64  
Summit Lake (1400′) 30  0 0  21
Alyeska Mid (1700′)  32  0 0  58

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   W    3  9
Seattle Ridge (2400′)  No Data W    3    12
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Riding Areas
Updated Wed, December 11th, 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
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Skookum Drainage
Closed
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Turnagain Pass
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Twentymile
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Closed.
Seward District
Carter Lake
Closed
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Closed
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Closed
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Resurrection Pass Trail
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Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
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South Fork Snow River Corridor
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Summit Lake
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