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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, February 12th, 2017 - 7:00AM
Expires
Mon, February 13th, 2017 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is  MODERATE  for a variety of avalanche problems. First, fresh wind slabs formed by moderate to strong winds today will be possible to trigger on leeward slopes. These could be quite touchy and around 1 foot thick. They could create a large amount of debris if triggerd on larger sustained slopes. Triggering sluffs on the steeper slopes should be expected and these are likely to run far may entrain a large amount of debis. Lastly,  keep in mind that  due to poor snowpack structure, there is still a chance of  triggering a large slab avalanche (2′-5′ thick) that breaks near the ground.  

Summit Lake: Make sure and check the Saturday Summit Summary  HERE.

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Sun, February 12th, 2017
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

It was an active day for human triggered avalanches yesterday. All but one of these slides were loose snow avalanches or sluffs. The one that was not was a fresh, but hard, wind slab avalanche triggered in the Girdwood Valley zone on the headwall of the Raven Glacier. This wind slab was shallow, 6″ to a foot thick, and hard – allowing the person onto the slope before it released. See the write up in the link.

As far as sluffs go, they were long running and fast. As one observer remarked “sluffs got uncomfortable large”.  This is due to 6-8″ of new light snow that fell on a few inches of loose faceted snow and surface hoar (acting as ball bearings). The reason they are running so far is a hard base and/or crust underneath is acting as a slick bed surface. For today, sluffs should be just as concerning and far running – keep a close eye on your sluff.

Great video sent in by Kevan Dee of skier triggered sluffs on Sunburst yesterday:

Long running and fanning sluffs on the back Southerly slopes of Sunburst (Jonathan Rupp).

 

WIND SLABS:

Although sluffs are a concern, wind slab avalanches created by moderate/strong winds today are a much less manageable situation. With 8-10″ of loose snow on the surface, it will not take much wind to form slabs. Furthermore, slabs will be sitting on a slippery base, making them very touchy. If the winds really crank, we could see natural slabs as well. Due to the limited amount of snow available for transport, slabs should be around a foot thick. They are likely to initiate sluffing as they avalanche and large amounts of debris can be generated by even a small wind slab.

Watch surface conditions and wind patterns closely for areas that could becoming windloaded. Look for areas of stiffer snow over softer and quick hand pits are good ways to assess the bonding of any wind slab found.

Winds transporting snow along higher peaks yesterday (Andy Moderow).

  

Even in the trees and at lower elevations, shallow slabs and sluffs are possible. This is a shallow soft slab skier triggered avalanche on a steep but small slope in the Tincan Trees (Zachary Liller).

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

Weak snow (facets and depth hoar) in the lower layers of the snowpack lingers as an issue in our advisory area. It has been 9 days since the last human triggered avalanches on these layers. However, triggering a deep slab is still a possibility if you find the wrong spot and a concern due to the depth of slab overlying the weak snow. The likelihood for someone to find and trigger a large slab is decreasing as the snowpack adjusts, but the poor snowpack structure remains and the consequences are scary. Both near miss avalanche accidents last week were triggered in thinner areas of the snowpack, on slopes that already had tracks on them. The tricky part about this particular avalanche problem is that it is very difficult to assess. Obvious signs like whumpfing and shooting cracks are unlikely and stability tests may not be reactive. Just because a slope has tracks on it does not mean it is safe. Likely places to trigger a deep persistent slab will be near rocks or in thin zones where affecting the weak layer is more of a possibility. Likely triggers are large: snowmachines, groups of people or cornice falls. Identify and avoid terrain traps (like large gullies).

Weather
Sun, February 12th, 2017

It was a cold and sunny day in the region yesterday along with some valley fog that filtered in. Ridgetop winds bumped up to 15mph with gusts in the 20’s from the North and West. Temperatures sat in the single digits at all locations, valley bottoms to ridgetops. Overnight, some low-lying area are in the minus double digits!  

For today, clear skies this morning will give way to cloudy skies in the afternoon as a large low-pressure system moves into the Gulf. Light snowfall should begin as well this afternoon possibly adding another 1-2″ by 6pm. Ridgetop winds are expected to increase to the 15-25mph range from the East. Temperatures will warm with this system and flow direction – up to 20F at the parking lots and mid-teens on the ridgelines.

Beginning Monday and through the middle part of next week, a potent warm storm system will impact the area, bringing rain to sea level. Check back tomorrow to see how this storm is shaping up!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 1   0 0   57  
Summit Lake (1400′) -1   0   0   24  
Alyeska Mid (1700′) 4   0   0   52  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 4   W   9   22  
Seattle Ridge (2400′) 1   N   6   27  
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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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