Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, February 12th, 2018 - 7:00AM
Expires
Tue, February 13th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

There is a CONSIDERABLE avalanche danger above 1,000′ due to snowfall overnight and strong winds. Natural avalanches within the new storm snow are possible and human triggered avalanches are likely. Fresh wind slabs up to a foot thick, and possibly 2 feet thick, should be expected on slopes with recent wind loading. Additionally, weak layers deeper in the snowpack may become overloaded and release, creating a much larger avalanche up to 3′ thick. Below 1,000′ the danger is MODERATE for wet loose sluffs.

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Mon, February 12th, 2018
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
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

Overnight saw a quick shot of snowfall that should give us a much needed refresher. This storm was on the warm side however. Along with new moist snow that fell at the mid and upper elevations, rain has fallen up to 200-500′ in places. For storm totals at mid-elevations as of 6am this morning:

Girdwood Valley:  8-10+” snow
Turnagain Pass:  5-7″ snow
Summit Lake:  6-8″ snow

This is clearly not a large storm for our standards, but what is notable is the variety of weak layers we have within, and on the surface of, our pre-existing snowpack. Although the new snow is moist and ‘sticky’ it will likely have a hard time bonding right away onto the surface – storm snow avalanche issues are below. What is possibly more concerning is what is lurking around 1-2′ deep in our snowpack. This is a layer of buried surface hoar from Jan 21 that remains intact in many areas and could be waiting for a slab to form on top of it to start producing large avalanches. This storm has likely created that slab. Hence, today is a day to be extra cautious and evaluate the snowpack carefully. Avalanches releasing in the Jan 21 buried surface hoar could be up to 3′ thick. Also, small avalanches within the storm snow could ‘step down’ and release a much larger and unmanageable slide. This issue is less of a concern on slopes that were heavily tracked out over the past two weeks, and much more on a concern on slopes seeing moderate to no traffic. 

Photo below is from a small wind slab triggered yesterday releasing on the recently buried surface hoar. This was on the North Chutes of Cornbiscuit. Note the crack in the bed surface at the bottom of the photo. This crack is believed to have stepped down to the Jan 21 buried surface hoar, yet that layer did not slide. With more load overnight, we may see avalanche ‘step down’ to this older weak layer, creating much larger than anticipated avalanches. (Thanks to Mike Records for the photo).

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

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

Storm snow instabilities associated with the new snow overnight and today will be likely. These come in many forms listed below and due to the lesser snow amounts, are expected to be on the smaller side. The most concerning for us however, are wind slabs as they will likely be larger and a less manageable storm snow problem. Bonding between the new and old snow is not expected to be good as the new snow has fallen on a new crop of surface hoar and near surface facets.

Wind Slabs:  Moderate to strong winds coupled with 6-10″ of new moist snow have likely formed soft wind slabs up to a foot thick or even two feet in places. Because these slabs are likely sitting on weak old snow, they are expected to be quite sensitive and easy to trigger. 

Storm Slabs:  Out of the wind, on slopes that have more than ~5″ of new snow, expect to see soft storm slab avalanches composed of the new snow.

Loose snow sluffs:  Sluffs on steep slopes are likely with the recent new snow.

Wet sluffs:  Below 1,000′ where rain is falling on snow, small wet sluffs are likely in the steep terrain.

Roof-a-lanches:  Watch for your roofs to avalanche with the warm temperatures and rain.

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

Today’s snowfall is only a small load on top of our generally weak snowpack structure in the Alpine (above 3,000′). However, even a small load and warming temperatures could help tip the balance for someone to trigger a large deep slab that breaks in the bottom half of the snowpack. It’s good to remember that multiple layers of old buried surface hoar, facets and crusts exist deep in the pack and near the ground. These are not likely to ‘wake up’, but it’s worth keeping in mind, as outliers can happen as with last week’s Twin Peaks slide.

Weather
Mon, February 12th, 2018

Overcast skies were over the area yesterday along with snowfall that began late in the day, peaked overnight and is decreasing this morning. Roughly 5-10″ of new moist snow has been recorded at mid-elevations with .5-1″ of water equivalent. The rain/snow line looks to have been 200-500′. Ridgetop winds were Easterly in the 15-30mph range with gusts to 50mph. Temperatures were mild, in the mid 30’s at sea level and the mid 20’s along the ridgelines.  

Today, we should see light precipitation possibly add another 1-3″ of snow above 500′ and light rain below this in some areas. Skies will also start to clear out in certain areas as well. Ridgetop winds are expected to decrease and blow from a Southerly direction in the 5-15mph range before shifting Westerly this evening. Temperatures will remain warm, mid 30’sF at sea level and mid 20’sF along ridgetops before cooling off tonight.  

Tomorrow, Tuesday, we should see mostly clear skies, cooler temperatures and moderate to gusty Westerly winds. Another chance for snow is possible Thursday before, what looks like, mostly clear skies for late in the week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30   5   0.4   65  
Summit Lake (1400′) 30   5   0.5   24  
Alyeska Mid (1700′) 30   6   0.8   57  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   NE   16   44  
Seattle Ridge (2400′) 24   SE   24   50  
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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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