Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 16th, 2021 - 7:00AM
Expires
Fri, December 17th, 2021 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE at all elevations. With higher wind speeds today and light snowfall forecast to start this afternoon, triggering a 1′ deep avalanche in wind loaded areas is possible. The larger concern is a deeper layer of weak sugary snow buried 3-5′ which could create very large avalanches that are possible to be triggered by a smaller wind slab or by a person. These deeper avalanches could be triggered remotely – from the bottom, sides, or above a steeper slope. Conservative terrain selection is the best way to avoid exposing yourself to the potential of triggering a large avalanche.

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Thu, December 16th, 2021
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
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Winds picked up into the teens overnight with gusts into the twenties out of the east as a weak storm system moved into the area. The combination of increased wind speeds, 1-4″ of new snowfall forecast this afternoon, and existing light snow on the surface in many areas will make wind slabs up to a foot deep possible to trigger today. On the lower slopes of Cornbiscuit yesterday we came across some wind slabs from the last wind event over the weekend that were still somewhat reactive, with about 6″ of firm wind slab on top of soft snow. With the potential for additional wind loading and new snow these could become easier to trigger today. Look for active wind transport, firm over soft snow, and shooting cracks to identify areas with reactive wind slabs. A small wind slab has the potential to step down into a deeper layer of buried facets and create a very large avalanche today (see problem 2 for more details).

Portage and Placer valleys are likely to receive more new snowfall today, with up to 4-10″ possible, which could result in bigger wind slabs forming in exposed areas.

Wind affected snow along ridgeline of Sunburst from 12.12.21

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "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. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

The deep persistent slab is still foremost in our minds when making decisions in the backcountry, and will remain there for the foreseeable future. Patience is critical for managing this type of avalanche problem because the consequences of triggering one of these is so high. This type of avalanche problem is known for providing little or no feedback, in terms of ongoing avalanche activity or stability test results, but has the potential to create very large and destructive avalanches. In Girdwood and Turnagain Pass the most common deep persistent weak layer is weak sugary facets over a melt freeze crust which are buried 3-5′ deep and have been most prominent in the 1500 – 3000′ elevation band. In areas south of Turnagain pass (southern end of Seattle Ridge, areas closer to Johnson Pass) the weak layers are not buried as deeply due to an overall shallower snowpack which could make them easier to trigger.

Luckily, the low angle powder is still quite appealing in areas that have not seen too much wind since the last storm. To avoid the risk of triggering a large deep slab avalanche we recommend keeping your slope angles below 30° and being aware of the terrain above you.

If you decide to venture into avalanche terrain you can reduce your exposure by using safe travel protocols, such as one skier/rider on the slope at a time and always spotting your partners. Remember that it is often not the first skier on slope to trigger a deep slab. Initiating a failure in deeply buried weak layers tends to be easier in thin areas of the snowpack and near rocks or trees.

Snowpack summary from Cornbiscuit yesterday, sorry for the vertical video orientation. We saw propagation in the faceted weak layer for the first time in awhile but it took a lot of force to initiate the failure in the extended column test. 12.15.21

Weather
Thu, December 16th, 2021

Yesterday: Skies started off largely clear but clouds moved into the area throughout the day. Temperatures also climbed throughout the day and leveled off in the mid-teens overnight. Winds were light during the day but picked up overnight, with averages around 10 – 15 mph and gusts to from 20 – 25 mph since 2 am. No new snow accumulation.

Today: Skies will remain cloudy today with snowfall starting this afternoon and about 1-4″ possible for Turnagain Pass. Greater snowfall is likely near Portage and Placer with up to 4-10″. Winds should be out of the southeast at 10-20 mph with gusts into the 30s. Temperatures should remain in the teens throughout the day.

Tomorrow: The majority of the snow is forecast to fall Thursday afternoon through overnight Friday, but some lingering snowfall could persist through Friday morning. Winds should shift back to the northwest and calm down as the snowfall ends early Friday morning. Skies will remain partly cloudy on Friday with temperatures in the teens.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 9 0 0 73
Summit Lake (1400′) 0 0 0.3* 22
Alyeska Mid (1700′) 10 0 0 44

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14 W until 1700, then E 7 23
Seattle Ridge (2400′) 8 E 6 15
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/07/22 Turnagain Avalanche: Tincan
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12/06/22 Turnagain Observation: Seattle Ridge- Main Bowl
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12/04/22 Turnagain Observation: Kickstep Glacier
12/03/22 Turnagain Observation: Seattle Ridge
12/03/22 Turnagain Observation: Seattle Ridge
12/03/22 Turnagain Observation: Superbowl
12/02/22 Turnagain Avalanche: Magnum/Cornbiscuit
11/30/22 Turnagain Observation: Tincan
Riding Areas
Updated Wed, December 07th, 2022

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
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Placer River
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Skookum Drainage
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Turnagain Pass
Closed
The Forest has issued a closure order for Turnagain Pass due to inadequate snow cover for resource protection. Conditions are being monitored daily. 22” of snow exists at the parking lot. Another storm on Sunday/Monday 12/11 may just do it.
Twentymile
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Seward District
Carter Lake
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Lost Lake Trail
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Primrose Trail
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Resurrection Pass Trail
Closed
Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
South Fork Snow River Corridor
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.
Summit Lake
Closed
The Forest has issued a closure order due to inadequate snow cover for resource protection. Conditions will be monitored daily. Scheduled opening would have been Dec 1st.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.