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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, March 21st, 2017 - 7:00AM
Expires
Wed, March 22nd, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is  CONSIDERABLE  in the Placer Valley and Portage Valley regions where up to 2 feet and more of snow fell on Sunday, March 19th. This new snow is sitting on a very weak base and human triggered slab avalanches 2-3′ thick are likely  on slopes 35 degrees and steeper. Warming afternoon temperatures could make natural avalanches possible again today. Cautious route finding and conservative decision-making are essential if you head to Placer Valley or find yourself in zones with over a foot of new snow.

In the Turnagain Pass zone, or any slope where around a foot or less of new snow fell, the avalanche danger is  MODERATE. Shallow soft slab avalanches will be possible to trigger on slopes over 35 degrees. In all areas, expect sluffs on steep slopes, avoid travel on or under cornices and give glide cracks a wide berth.  

Summit Lake:  Read the  Saturday Summit Summary  HERE.

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Tue, March 21st, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
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
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

Ah, springtime in the mountains. Warm daytime temperatures, longer days (now longer than our friends in the lower 48) and a fresh dose of snow. What more could we ask for? Possibly, a more stable snowpack… Sunday’s refresher storm that brought over 2 feet of snow to the Placer Valley and around a foot to Turnagain Pass and Girdwood fell on a very weak old surface of facets and surface hoar. In areas with greater snow amounts, triggering a slab avalanche is still very possible and even likely. Essentially, the places that are the most enticing for powder lovers (areas with up to 2 feet of new snow) will be the most likely places to trigger a large slab avalanche. In areas with lower snow amounts (a foot or less) triggering a smaller shallow slab is still possible.

There was a report of natural avalanche activity in the Placer Valley yesterday along with one snowmachine triggered slab avalanche. In the Turnagain Pass area, there was one report of a skier triggered avalanche on Magnum. Along with the avalanche activity, we had several reports of whumphing and shooting cracks. Interestingly enough, on our field day over on Seattle Ridge, we had a hard time finding unstable snow. The new snow here was quite shallow (10-12″) and light – just not enough snow to overload the old weak snow surface.

For today, things to keep at the forefront of our minds:

  1. How much new snow is there where you are traveling?
  2. The more new snow the higher the likelihood of triggering a slab avalanche.
  3. Is the day heating up? Warming can increase the chance for triggering an avalanche.
  4. RED FLAGS? Recent avalanches, whumphing, shooting cracks? All these signs point to unstable snow.

Shallow soft slab avalanche triggered by a skier on Magnum in the Turnagain Pass area yesterday. Photo: Jordan Bancroft

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Similar to the slab avalanche concerns above, expect the size of sluffs to be dependent upon the amount of new snow you find. That said, human triggered sluffs (loose snow avalanches) are likely in steeper terrain that were not affected by the sun yesterday. Natural damp or wet loose snow avalanches may still be possible with warming in the afternoon. Keep in mind, sluffs have the potential to initiate a slab lower on the slope

Dry loose avalanches on the West face of Eddies. Photo: Conrad Chapman 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

Persistent Slabs and Deep Slabs:  There are a variety of very old weak layers in our thin snowpack. The February 9th buried surface hoar sits 2-4+’ below the surface and faceted snow sits in the mid and base of the pack. These weak layers (with varying degrees of strength) have been in a ‘dormant stage’.  Although unlikely, an avalanche breaking deeper in the pack isn’t completely out of the question with the new snow load and warming temperatures. Areas such as Johnson Pass, Lynx Creek and on the Northern side of Girdwood Valley (near Crow Pass) are the most suspect and observers continue to find poor structure.

Weather
Tue, March 21st, 2017

Partly cloudy skies covered the region yesterday. Intermittent light snow showers and cloud cover added a few flakes here and there but no measurable precipitation was recorded at the snow stations. During the past 24-hours ridgetop winds have been light (5-15mph) with moderate gusts (10-25mph) from the East. Temperatures that warmed during the day to 30F at 1,000′ and 25F along ridgetops have dropped back down to the teens overnight.  

For today, we can expect another day of in-and-out cloud cover (partly cloudy skies) and no precipitation. Ridgetop winds should remain light 5-10mph from the East and Northeast with a possible bump to the 15-20mph range later this afternoon. Daytime warming will again let temperatures climb into the 25-30F range by the afternoon.

Looking ahead, mostly clear skies with warm days and cold nights is in our future.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18   0   0   65  
Summit Lake (1400′) 19   0   0   30  
Alyeska Mid (1700′) 23   0   0   61  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 15   8   NE   24  
Seattle Ridge (2400′) 20   6   SE   19  
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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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