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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, February 7th, 2018 - 7:00AM
Expires
Thu, February 8th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  above 2,500′ for triggering a slab 1-2′ deep. Additionally, watch for cornices along ridgelines and sluffs in steep terrain.

*For the periphery zones, such as Girdwood to Portage Valley, and Johnson Pass to Summit Lake, more caution is advised where a slab could be larger and more connected.

Check out the Summit Lake Summary  HERE.

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Wed, February 7th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
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
Low (1)
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
  • 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’s storm brought a few inches of snow to Girdwood and Turnagain Pass. Portage Valley near the lake got 8-10″. The winds died down in the early morning but the strong easterly winds from Monday night should not be forgotten today. We have been talking about the January 21st buried surface hoar layer for a couple weeks now. This layer has been responsible for the scattered avalanche activity over the past week and a half (including a large avalanche that occurred on Saturday on Twin Peaks). Slopes that got more wind effect/loading may now have a stiffer and more reactive slab over the buried surface hoar. Leeward slopes in the Alpine are the most suspect. The new snow may be may have covered up the surface signs of wind effect. It will be important to pay attention to where the snow feels stiff, looks pillowed or sounds hollow and watch for shooting cracks. Before committing to steep terrain, identify terrain traps like gullies, cliffs or rocks below and consider the consequences if even a small slab is released.  The new snow also fell on a fresh crop of surface hoar that developed last week. In Portage due to more new snow, even on lower elevation slopes, this February 5th surface hoar layer could be the layer of concern.  

*Deep Persistent Slab:  Weak snow can still be found near the ground at the upper most elevations in our forecast area, 3,000′ – 5,000′. Although triggering a Deep Persistent Slab is very unlikely, it is worth keeping in mind that poor structure does exist at the high elevations. 

The January 21st buried surface hoar found in a snow pit yesterday under some stiffer wind-affected snow. Photo: Sam Galoob

 One of the lower piles of debris from the Twin Peaks avalanche that occurred on February 3rd.

The February 5th buried surface hoar layer under a couple of inches of new snow at Turnagain Pass. Photo: Sam Galoob

 

Additional Concern
  • 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

Loose Snow Avalanches, ‘sluffs’: In most places the snow is very loose and ’sluffs’ easily on the steeper slopes. The new snow will add volume to these.  Watch your ‘sluff’ and be aware of the consequences below you.

Cornices: Cornices are unpredictable and can break further back along a ridge than expected. Give these features plenty of space.

Weather
Wed, February 7th, 2018

Yesterday was mostly cloudy and there were snow showers throughout the day. Temperatures were in the 30Fs at sea level and 20Fs at upper elevations. Winds were easterly and became light in the afternoon. Snow stopped in the evening and temperatures were in the low 20Fs.  

Cloud cover should diminish this morning and skies will become clear and sunny. There is the potential for some valley fog. Temperatures will be in the 20Fs and winds will be northerly 5-15 mph. Tonight temperatures drop into the teens and winds remain light and northerly.

Tomorrow and Friday should be clear and sunny with temperatures in the low 20Fs and light variable winds.   There is snow in the forecast for the weekend but the details are pretty uncertain. Stay tuned!  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28    2 0.1  64
Summit Lake (1400′) 24  2  0.2    20
Alyeska Mid (1700′) 25  2 0.09    52

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  21  NE 6   26  
Seattle Ridge (2400′) 22 ENE   2   12  
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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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