Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, January 2nd, 2022 - 7:00AM
Expires
Mon, January 3rd, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE on all aspects above 1,000′. Triggering a wind slab avalanche, up to a foot thick, will be possible on slopes that saw wind loading yesterday or may see active loading today. Small shallow sluffs will also be possible to trigger on steep slopes. Even a small wind slab or sluff could run further than expected due a crust that sits underneath.

The danger is LOW below 1,000′ where triggering an avalanche is unlikely.

SUMMIT LAKE / LOST LAKE:  Strong NW winds impacted the Summit Lake area yesterday and may again today. Watch for wind slabs on leeward slopes. These also are likely to be sitting on a crust.

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Sun, January 2nd, 2022
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
  • 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
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 ground blizzards in Girdwood were pretty ominous for what the mountains would be like during the northerly wind event yesterday. Sure enough, there was plenty of snow pluming off the the Western Chugach range, along Turnagain Arm (gap winds), along the western Kenai Mountains, Summit Lake, Seward, etc. Despite all this, Turnagain Pass itself looks to have escaped the majority of the damage. Although there was still plenty of wind to move some snow in Turnagain, especially on the Seattle Ridge side, we had no reports of avalanches and did not see evidence of any wind slabs that released from the ridgelines that can be seen from the road.

A big part of this is that there is just not much snow available for transport. Only 3-5″ of snow from Friday that is sitting on a crust to ridgetops. One report from Seattle Ridge yesterday described the snow surface as a mix of ‘polished up crust and wind drifts’. However, the non-motorized side of the Pass appears to be in a bit better shape. The NW winds have died off, but not completely. The forecast is for 10-20mph so some continued wind effect is possible today.

If you are headed out in search of some sheltered ‘dust on crust’ conditions, it should be fairly easy to suss out where the winds have been blowing and where slabs could be lurking. Watch for changes in surface texture, the most obvious being a wind pillow, drift, or larger wind loaded area intermixed with scoured crusts. Also look for cracking in the snow around you. Winds made it into the trees, so keep an eye out for slabs in these areas as well. Slabs should be fairly small in general unless getting into the bigger terrain where they could be up to a foot thick. On steeper sustained slopes, keep in mind even a small wind slab could run fast and far as debris will be sliding on a crust.

 

Cracking in a shallow wind slab near treeline on the front (road) side of Seattle Ridge near the up-track. Photo by Troy Tempel, 1.1.22.

 

Wind transport along the southern end of Seattle Ridge yesterday due to the channeled NW winds aloft. Photo Troy Temple, 1.1.22.

 

Wind plumes on the easterly facing slopes of Summit Peak, just south of the Turnagain forecast zone. 1.1.22.

 

Loose snow avalanches (sluffs):  Shallow sluffs could be easily triggered on the steeper slopes. As with the wind slabs, debris may run faster and further than expected due to the crust.

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

We are continuing to monitor those old November facets that sit under a dense slab of snow anywhere from 2-5′ thick; thicker on the north end of Turnagain and shallower on the south end. At elevations between ~1,200′ to ~3,000′ the facets sit on top of the Halloween crust. With the top of the snowpack now frozen from last week’s warm weather, changing the character of the slab and making it even more difficult for a person to impact this faceted layer, triggering a large slab avalanche is now very unlikely.

This problem is becoming what we call ‘dormant’ until there is a major change in the weather/snowpack to reactivate it again. This could be a big storm cycle, or the spring melt season.

Weather
Sun, January 2nd, 2022

Yesterday:  Partly cloudy skies, light to strong NW winds, and cold temperatures were over the region. The NW outflow winds averaged 5-15mph at Turnagain Pass, but as high as 30mph to the north, west and south of Turnagain. Temperatures dropped to the single digits is most locations.

Today:  Partly cloudy skies are forecast again today with the NW winds in the 5-10mph (some areas seeing up to 20mph). Temperatures are still falling and are -10 to 0F along ridgelines and the 0 to +10 in valley bottoms.

Tomorrow:  Mostly sunny skies, light variable winds and cold temperatures are expected for Monday and most of next week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 0 0 67
Summit Lake (1400′) 5 0 0 24
Alyeska Mid (1700′) 5 0 0 40

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -5 W 5 19
Seattle Ridge (2400′) -3 N 6 17
Observations
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Riding Areas
Updated Wed, June 01st, 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
Closed as of May 1 per Forest Plan.
Placer River
Closed
Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage
Closed
Closed as of April 1st per Forest Plan.
Turnagain Pass
Closed
Closed as of June 1st.
Twentymile
Closed
Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake
Closed
Closed as of May 1 per Forest Plan.
Lost Lake Trail
Closed
Closed as of May 1 per Forest Plan.
Primrose Trail
Closed
Closed as of May 1 per Forest Plan.
Resurrection Pass Trail
Closed
Closed as of May 1 per Forest Plan.
Snug Harbor
Closed
Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor
Closed
Closed as of May 1 per Forest Plan.
Summit Lake
Closed
Closed as of May 1 per Forest Plan.

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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.