Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, December 13th, 2021 - 7:00AM
Expires
Tue, December 14th, 2021 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ today. Human triggered avalanches 1-3′ deep are likely in areas with recent wind loading. Very large avalanches on a layer of weak sugary snow buried 3-6′ deep are also possible to be triggered by humans or smaller avalanches. Triggering one of these larger avalanches will be more likely in areas with a thin overall snowpack depth. The high consequences of being caught in one of these large avalanches makes it necessary to practice conservative decision-making and terrain selection.

Below 1000′ the avalanche danger is MODERATE. In areas that saw wind loading yesterday it is still possible to trigger an avalanche. Identify wind loaded terrain and look for signs like shooting cracks to determine if conditions are reactive.

Summit Lake: The overall shallower snowpack in the Summit Lake area makes it more likely to trigger a persistent slab on weak sugary snow buried 2-5′ deep. This area also received very high winds yesterday and has the potential for large wind slabs and more reactive avalanche conditions due to the recent loading.

Lost Lake/Snug Harbor: Very strong winds observed yesterday have created sensitive avalanche conditions on top of a weak existing snowpack. There is a potential to trigger fresh wind slabs or a deeper avalanche in weak sugary snow buried 3-6′ deep. Cautious terrain selection and being aware of slopes above you is important because of the potential to trigger a large avalanche.

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Mon, December 13th, 2021
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)
Recent Avalanches

Girdwood: 4′ deep slab at ~1700′ triggered by Alyeska ski patrol during avalanche mitigation work. This avalanche released on a layer of buried facets on top of the halloween crust.

4′ deep avalanche at Alyeska triggered during avalanche mitigation using explosives. Photo 12.12.21 Alyeska Snow Safety

Turnagain Pass: A few small natural avalanches were observed on the south side of the pass on the Seattle Ridge side. This area had higher winds and active wind transport in the afternoon so it is likely that these are small wind slabs. It is possible that one or both of these avalanches were remote triggered from below on the deeper faceted weak layer.

Small natural avalanche on S face of Seattle Ridge across from the Sunburst parking lot. Photo: Peter Wadsworth 12.12.21

Second small natural avalanche on S face of Seattle Ridge (center of photo in Alders). Photo: Peter Wadsworth 12.12.21

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

The winds were fairly light in the northern portion of Turnagain pass yesterday (Eddies, Tincan, Sunburst, Cornbiscuit, Lipps), but there was a lot of snow being moved around on the southern end of the pass, Seattle Creek drainage, and other areas of the forecast zone. A few small natural avalanches released at lower elevations on the south face of Seattle Ridge which was receiving heavy downslope winds and active wind loading in the afternoon. In areas that saw wind transport yesterday it will be possible to trigger a wind slab today ranging from 1-3′ deep that could be composed of either soft or hard snow depending on how strong the winds were. Look for shooting cracks in recently wind loaded areas, such as gullies and just below ridgelines, to determine if wind slabs are reactive. A small wind slab has the potential to step down into deeper layers and create a very large avalanche 3-6′ deep on a layer of buried facets (see problem 2 for more details).

We have received winds from multiple directions since the last snowfall which makes it tricky to determine wind loading patterns just by looking at the snow surface texture. Travelling outside the beaten track will help you determine whether an area has been wind affected and you can use small test slopes to see how reactive those slabs are. It will be important to identify wind loaded features and consider the consequences of triggering a deeper avalanche on a layer of faceted snow 3-6′ deep before deciding whether to step into avalanche terrain today.

Wind transport evident in snow surface texture in the foreground and active downslope wind loading in the background on south face of Seattle Ridge. Photo: Peter Wadsworth 12.12.21

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

You might be getting tired of hearing about it, but there is still the possibility of triggering a very large avalanche on a layer of weak sugary facets over a stout crust buried 3-6′ deep. This layer exists across the forecast zone and has produced many large avalanches in the past two weeks. As we get further away from the latest loading event (12-24″ new snow last Thursday/Friday) and the layer gets more deeply buried the likelihood of triggering an avalanche is decreasing while the consequences remain very high. The likelihood of triggering an avalanche on this layer is higher in thin areas of the snowpack or in regions that have a lower overall snowpack depth, such as the south side of Turnagain Pass and Summit Lake.

Alyeska snow safety has been consistently triggering avalanches on this layer during their mitigation work, which is a great reminder that the layer remains reactive but that may require a larger load (explosives) to release. This is the type of scenario where the tenth or hundredth skier/rider on a slope could find the sweet spot and trigger a large avalanche. Conservative decision-making and terrain selection is paramount for managing this type of avalanche problem. Digging snowpits can be helpful to track the progression of this faceted layer and determine the structure in the area you are travelling, but it is buried deep enough that the results of stability tests are inconsistent and do not accurately evaluate the potential for triggering or propagation. The avalanche activity we have seen on this layer so far has been between 1500 to 3000′ in elevation.

Snowpack structure from a thin area on the south side of Turnagain Pass on lower slopes of Seattle Ridge. The total snowpack depth was variable but ranged from 2.5 to 3.5′. The faceted layer is partially scooped out at the bottom below the ‘CT 6’ line. Photo: Peter Wadsworth 12.12.21

Weather
Mon, December 13th, 2021

Yesterday: Temperatures stayed in the negative single digits to negative teens throughout the day. Winds were variable across the forecast area. On the northern portion of the pass and northern end of Seattle Ridge the winds were light to moderate out of the northwest. Further south (Pete’s, Peak 4940) the winds picked up substantially in the afternoon and transported a lot of snow. Skies remained clear throughout the day.

Today: Temperatures will start out below zero again today but should rise into the single digits in the afternoon. Winds will shift to east at 5-15 mph. Cloud cover should move into the area this afternoon.

Tomorrow: We could see a few inches of snow tonight and tomorrow morning, with cloud cover increasing and winds out of the east at 5-15 mph. Temperatures will stay in the positive and negative single digits. After the snowfall winds will shift back to the northwest.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -2 0 0 77
Summit Lake (1400′) -12 0 0 24
Alyeska Mid (1700′) -1 0 0 49

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -11 W 4 15
Seattle Ridge (2400′) -4 N 3 15
Observations
Recent Observations for Turnagain Pass
Date Region Location
11/28/22 Turnagain Observation: Pastoral
11/27/22 Turnagain Avalanche: Tincan
11/26/22 Turnagain Observation: Eddies
11/26/22 Turnagain Observation: Eddies
11/26/22 Turnagain Observation: Lipps
11/25/22 Turnagain Observation: Sunburst
11/25/22 Turnagain Observation: Sunnyside / Seattle Ridge
11/25/22 Turnagain Observation: Sunburst
11/25/22 Turnagain Observation: Tincan Trees
11/25/22 Turnagain Observation: Tincan
Riding Areas
Updated Sun, November 27th, 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
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Placer River
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Skookum Drainage
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Turnagain Pass
Closed
The Forest has issued a closure order for Turnagain Pass due to inadequate snow cover for resource protection. Conditions will be monitored daily. Between 16-20” of snow exists at the parking lot. The scheduled opening would have been the Wednesday before Thanksgiving per Forest Plan.
Twentymile
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Seward District
Carter Lake
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Lost Lake Trail
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Primrose Trail
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Resurrection Pass Trail
Closed
Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
South Fork Snow River Corridor
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.
Summit Lake
Closed
Scheduled opening Dec 1st per Forest Plan, contingent upon adequate snow depth for forest resource protection.

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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.