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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, April 20th, 2017 - 7:00AM
Expires
Fri, April 21st, 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 (SE-S-SW) aspects. Paying attention to aspect and time of day are crucial. Watch for changing conditions as the sun affects colder aspects more and more each day.  On Northerly slopes, where dry snow exists, there is still a chance of triggering a deeper persistent slab avalanche 2-5+’ thick.  Avoid travel on or under cornices and give glide cracks a wide berth.  

Below 1000′ the avalanche danger is  LOW.  Triggering an avalanche is unlikely. It is still important to pay attention to runout from higher elevation terrain.  

FRIDAY AVALANCHE OUTLOOK:

No avalanche forecast will be issued tomorrow, Friday April 21st. The avalanche outlook will be the same message due to a similar weather forecast, however temperatures are creeping up each day with less and less of an overnight freeze. The danger could rise to CONSIDERABLE if temperatures do not go below freezing overnight tonight.  

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Thu, April 20th, 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

We have not observed or received any reports of natural avalanche activity with the exception of glide releases in the past two days.  The temperatures have been dipping below freezing every night but have been slowly climbing again over the past two days. Warmer temperatures and longer days with direct sunshine on slopes means that the melt-freeze cycle is slowly migrating to colder aspects (specifically W-NW). Today and tomorrow it will be important to pay close attention to how the warming is affecting the pack. We are in a melt-freeze cycle on Southerly (SE-S-SW) slopes – hard frozen crusts in the morning, which turn to unsupportable mushy and unstable snow by the afternoon/evening, the less of a freeze the greater the likelihood of wet avalanches. 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.  As colder aspects heat up remember cold snow, persistent weak layers and free water are a bad combination.  Watch for roller balls and natural wet loose avalanches indicating surface warming. 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.
  • Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down. 
  • Wet avalanches are hard to escape if you get caught and a small slide can be deadly if it pushes you into a terrain trap. 
  • Rocky areas that are absorbing more heat should be avoided.

Click HERE for a great dicussion from the forecasters at Avalanche Canada on managing spring avalanche conditions.

Magnum, Super Bowl and Cornbicuit from the heli. A good look at shaded versus solar aspects. Choosing aspect is crucial this time of year. Photo: Graham Predeger

Cornices: Cornices are large and likely hanging close to their tipping point due to warm temperatures. Direct sunshine, a person, or a group of people on top these could be enough to cause one to break. 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. 

Avalanche Problem 2
  • 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

Eddies south side looks similar to the glide carnage of last year. Several glide avalanches have released and existing cracks are opening each day.  Seattle Ridge is also littered with opening cracks as well as the south side of Tincan. There was a new glide release observed in Lynx Creek yesterday. We expect this trend to continue today and tomorrow. Keep an eye out for glide cracks and limit time underneath them. Remember they are the entire snowpack releasing to the ground without warning. 

 

 

Eddies RWIS camera capturing a glide release just after 7 pm last night

  

Eddies glide avalanches. Photo: Jessie Haffener & Sam Galoob

Tincan glide cracks. Photo: Jessie Haffener & Sam Galoob

 

Additional Concern
  • 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

In this springtime transition it is important to remember on the shaded and cooler side of the mountains, Northerly aspects, a cold mostly dry snowpack 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 in the mid and upper elevations that haven’t avalanched already are the most suspect places for triggering a deeper slab.  On Monday the 4th skier on a slope in Triangle Bowl triggered a slab that ran on the April Fool’s storm rain crust. As the solar effect creeps onto more northerly slopes the interaction between cold snow and melt water also become more of a concern. 

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
Weather
Thu, April 20th, 2017

Yesterday was mostly clear and sunny with a few scattered clouds. Temperatures climbed into the high 40Fs in the lower elevations and into the mid 30Fs at upper elevations. Easterly winds were 5-15 mph gusting to 20mph. Temperatures dropped to freezing or below overnight.

Today will be clear and sunny again. Temperatures will be in the high 40Fs at lower elevations and the mid to high 30Fs at upper elevations. Winds will be light and variable. Temperatures will again drop to the low 30Fs or below tonight.

Tomorrow looks to be similar if not slightly warmer. Clouds will start moving in Friday night with a chance of rain/snow showers on Saturday. A series of lows are forecasted to move into the Gulf bringing rain and snow to the area into next week.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 40   0    0 62  
Summit Lake (1400′)  34 0    0  20
Alyeska Mid (1700′)  36  0  0  56

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  30  E 6   12  
Seattle Ridge (2400′)  No Data SE   8   20  
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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
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
Closed.
Primrose Trail
Closed
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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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