Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, February 16th, 2018 - 7:00AM
Expires
Sat, February 17th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  MODERATE  above 1,000′ on all aspects. Triggering a slab 2+ feet deep remains possible. Watch for active wind loading, and be aware of shallow wind slabs on leeward slopes and cross-loaded gullies.  Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche.  Evaluate snow and terrain carefully.

The avalanche danger  below 1,000′ is LOW where triggering an avalanche is unlikely, but not out of the question. Be aware of terrain traps where pockets of unstable snow may be lurking.  

**If you are headed to Placer Valley, remember that very little snowpack information exists in this zone. Ease into terrain with caution and be aware of other groups in the same area. If you see or experience any avalanche activity please take a picture and send us an observation HERE.  

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Fri, February 16th, 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

Triggering a persistent slab avalanche 2′ deep remains possible across the region, and winds today may add additional stress. Several weak layers including widespread buried surface hoar (from Jan. 21) sits roughly 1-2′ below the surface. A person skiing or on a snowmachine may tip the balance and initiate a larger slab avalanche. Triggering a smaller wind slab or a cornice may also activate this layer. The snowpack is now at a point where no signs of instability are likely to be present before one of these avalanches is triggered. Assessing the terrain and the potential outcome of an avalanche breaking deeper in the pack is key. Are there terrain traps below you? Cliffs? Are your partners watching and rescue ready? 

Winds this weak have loaded some slopes and scoured others as seen yesterday on Seattle Ridge. Triggering a soft or hard persistent slab is possible with our current snowpack. 

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

Triggering an isolated wind slab is possible today and will be more likely in places where wind is actively transporting snow into steep terrain. Today Northwest winds may be moving loose snow along some ridgetops and forming new wind slabs on leeward features. Earlier in weak ridgetop winds loaded some slopes and scoured ridge lines. Pay attention to where the snow feels stiff, looks pillowed, sounds or feels hollow and watch for shooting cracks.  Hard wind slabs tend to break when you are out onto the slope and often fracture above you. Be aware of wind loading patterns in the terrain, especially cross-loaded gullies. Sometimes Northwest winds can funnel in from the South near Sunburst and on the Southern end of Turnagain Pass. 

Small wind slab triggered in the last few days on a wind loaded gully, SE aspect of Seattle Ridge at about 2300′. 

 

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

Deep Persistent Slab: 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.  As you plan your day, keep in mind that there are deeper persistent layers that could ‘wake up’ if you find the wrong spot.

Weather
Fri, February 16th, 2018

Yesterday was clear and sunny with no precipitation. Westerly winds became Easterly 5-15mph early afternoon. Temperatures along ridgetops were in the high teens (F) increasing to the low 20F’s during the heat of the day. Temps at sea level bumped into the high 20F’s and back into the teens F’s overnight. Patches of valley fog were present near Turnagain Arm.  

Mostly cloudy skies are forecasted for today. Temperatures should average in the 20F’s and dip down into the teens (F) overnight. Ridge top winds will start out light from the East, but will transition to the Northwest and increase to 15-20mph. No precipitation is expected.  

Clear skies are in the forecast for Saturday wth similar temperatures. Moderate Northwest winds will continue tomorrow, becoming light by late afternoon. Increasing clouds and warmer temperatures are expected Sunday evening into Monday with a possibility of a few scattered showers.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   0   0   64  
Summit Lake (1400′)  17 0   0   24  
Alyeska Mid (1700′) 23   0   0   58  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18   W–E   7   22  
Seattle Ridge (2400′) 21 W–E   10   25  
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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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