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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, March 13th, 2018 - 7:00AM
Expires
Wed, March 14th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

CONSIDERABLE  avalanche danger remains above 1000′ on all aspects. Large slab avalanches 2-4+ feet thick are likely to be triggered on slopes steeper than 30 degrees.  These may be triggered from a distance or from the bottom of a slope.  Cautious route finding and conservative decision-making are essential.

MODERATE  avalanche danger exists below 1000′ where triggering a large slab avalanche is possible in areas with avalanche terrain like Portage Valley and Placer Valley.

A skier remotely triggered an avalanche on the skin track in Summit Lake yesterday – see Saturday’s  Summit snowpack and avalanche summary  and observations from yesterday  HERE.  

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Tue, March 13th, 2018
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
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. Small avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become large enough to bury, injure, or kill people, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Yesterday there were 3 reports of skiers and snowmachiners triggering avalanches across the region. A party of skiers triggered two avalanches on Sunburst, one on a deeper buried weak layer. The skier involved in the deeper avalanche was caught, carried, deployed their airbag and ended up off of the debris. A snowmachiner remotely triggered a slab in Grandview and a skier remotely triggered a slide from the skin track in Summit Lake. Today triggering a large and unmanageable slab avalanche 2-4′ thick remains our primary concern. Various layers of old faceted snow and buried surface hoar sit under the 2-4 feet of storm snow from Friday. These persistent weak layers have been well documented and are wide spread across our region. During the window of sunshine yesterday some folks ventured out into steeper terrain with no incident while at the same time others were triggering avalanches. Recreating in steeper terrain is a gamble at this point with high consequences if the house wins… 

If you are headed out into the backcountry today things to keep in mind are:

  • The mountains are still adjusting to the several feet of new snow that fell four days ago and there is poor snowpack structure
  • Warming in the afternoon yesterday may also have played a factor in the avalanches being triggered. If the skies clear pay attention to changing conditions.
  • Avalanches can be triggered from the flats or remotely from an adjacent slope – be extra cautious to avoid being in a runout zone 
  • Stick to slopes less than 30 degrees and ease into steeper terrain slowly. Evaluate the consequences if the slope releases; where will the debris go?
  • Listen for whumpfing (collapsing) in the snowpack, look for shooting cracks but realize you may not see signs of instability before the slope releases. 

Sunburst avalanches from below. Photo: Conor Roland

Sunburst avalanches from a different view. The upper one is harder to pick out. 

 Grandview avalanche that was triggered from below, lookers left side.  Photo: Sebastian Landry

 

Remotely triggered avalanche in Summit Lake. Photo Patrick McCormick

Additional Concern
  • 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

Loose Wet Avalanches: Several inches of low-density snow fell this weekend. Wet snow or rain falling could trigger loose wet avalanche activity especially at lower elevations. Radiation from the sun, if it clears later in the afternoon, could also be factor today.  Look for small loose wet sluffs on Southerly aspects in steep rocky terrain. On upper elevation slopes unaffected by rain, wind or sun loose dry avalanches (sluffs) are also possible in steep terrain. 

Wind slabs: Shallow wind slabs formed on some leeward features yesterday due to moderate Easterly winds in the Alpine. Triggering a wind slab will likely be shallow, but could step down to a deeper layer of the snowpack and create a much larger and more dangerous avalanche. 

Cornices: Cornices have grown and are suspect for breaking while traveling along ridgelines. Give these an extra wide berth and minimize any time below them. Cornice falls can trigger avalanches on slopes below.

Natural loose wet activity on Seattle Ridge in the afternoon yesterday. 

 

Weather
Tue, March 13th, 2018

Yesterday was mostly cloudy in the morning and became mostly sunny by the mid to late afternoon. Temperatures were in the 20Fs to low 30Fs. Easterly winds were blowing 5-15 mph gusting into the 30s in the morning and calmed down in the afternoon. Overnight temperatures cooled slightly and then started rising in the early morning. Clouds moved in and Easterly winds were light.  

Today will be mostly cloudy with snow/rain showers, 1-4″ of snow possible and rain below 800′. There is a chance of some clearing in the late afternoon. Temperatures will be in the high 20Fs to high 30Fs. Winds will be Easterly 5-15 mph with gusts into the 20s. It is forecast to be mostly cloudy overnight with a chance of snow showers.  

Tomorrow looks to mostly cloudy in the morning with clearing in the afternoon, light Northwest wind and temperatures in the high 20Fs to mid 30Fs. The next system moves into the area Thursday. Timing and details are still uncertain.

*Seattle Ridge anemometer (wind sensor) rimed over and not reporting

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  29 1      0.1 90  
Summit Lake (1400′)   27    1      0.1 36  
Alyeska Mid (1700′)  28  1      0.12 82  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  20  ENE  14 38  
Seattle Ridge (2400′)  23 n/a*    n/a* n/a*  
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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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