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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, February 14th, 2018 - 7:00AM
Expires
Thu, February 15th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is MODERATE above 1,000′ on all aspects. Triggering a shallow wind slab avalanche will be possible on wind loaded slopes and cross loaded gullies. There is also the possibility for a person to trigger a larger slab that breaks in weak snow 1-2′ deep. The danger is LOW below 1,000′ where triggering an avalanche is unlikely.

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Wed, February 14th, 2018
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
  • 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 sunny skies revealed what most of us powder lovers do not wish to see after a snowfall event…wind. Monday night and Tuesday morning North and West winds wreaked havoc on much of the terrain around Turnagain, Summit Lake, Portage and the Girdwood Valley. Wind scalloped many snow surfaces, scoured some ridgelines to the rocks and sastrugi was reported on Tincan. Along with the winds, no natural avalanche activity was seen in the Turnagain area, but the Summit Lake region saw several shallow natural wind slab avalanches along with one that appeared to step down into an older weak layer.

For today, our main avalanche concern centers around a person triggering a large persistent slab avalanche up to 2′ or more in depth. Below the storm snow and recent wind slabs (addressed below) sits the Jan 21 buried surface hoar we have been talking about for some time. This layer is roughly 1-2′ below the surface and with recent wind and snowfall adding stress to it, the possibility for a person to tip that balance and initiate a larger slab avalanche is possible. There is also the possibility that a small wind slab or cornice fall could trigger this layer. We are back in a regime where no signs of instability are likely to be present before one of these avalanches releases and snowpit tests become unreliable. Therefore, assessing your terrain and the potential outcome if an avalanche breaking deeper in the pack does occur is key. Are there terrain traps below you? Cliffs? Are your partners watching and rescue ready? As we head into another period of high pressure (after today) keep these things in mind.

Northerly winds creating plumes off of Tincan Proper yesterday morning. (Photos: Jessie Haffener)

Anti-tracks on Tincan 


Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

Watch for wind slabs to be lurking intermixed with the variable surface conditions on the steeper slopes. These will likely be shallow, up to a foot thick, and stiff. They should be easy to identify with a rounded shape and hollow feeling. Watch for shooting cracks and places the wind crust becomes thicker. Cross loaded gullies could be a good place to find and trigger a wind slab as winds did blow at all elevations

Image below of a shallow wind slab on Tincan yesterday. Small terrain, small avalanche – Large terrain, small to large avalanche with higher consequences.

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

Above 3,000′ in the Alpine zones, several old weak layers of facets and buried surface hoar sit near the ground and in the mid-pack. This structure is most pronounced in areas with a thin overall snow cover, such as the South end of Turnagain Pass and the Summit Lake area. Recent wind slab avalanches Monday on Fresno ridge (Summit Lake zone) look as if they ‘stepped’ down into older weak layers in the snowpack. This is noteworthy and a reminder not to forget there are lurking old layers that could ‘wake up’ if one hits just the wrong spot.

Pictured below are shallow wind slab avalanches on Southeasterly facing Fresno ridge that looked to have triggered a deeper weak layer and subsequent larger avalanche lower on slope in the trees. (Photo: Jessie Haffener)

Weather
Wed, February 14th, 2018

Sunny skies along with strong West the North ridgetop winds were over the region yesterday. Seattle Ridge weather station recorded averages at 50mph from the North with gusts to 68mph. Wind decreased significantly over the day and was light and variable overnight. No precipitation fell and temperatures were in the mid 20’s along ridgetops and near 30F at 1,000′.

Today, Wednesday, a weak front is moving in with associated cloudy/overcast skies. There is a chance for a few snow flurries, but only a trace of accumulation is expected. Ridgetop winds are expected to pick up slightly from the Southeast and blow in the 10-15mph range. Temperatures will be near 30F at 1,000′ and remain in the mid 20’sF along ridgetops.  

Sunny skies with generally light winds and cool temperatures are expected for Thursday and into the weekend. Northerly winds may pick up again on Saturday, stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   0   0   66  
Summit Lake (1400′) 22   0   0   25  
Alyeska Mid (1700′) 29   0   0   58  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   NW   8   36  
Seattle Ridge (2400′) 27   N    20 68  
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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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