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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 11th, 2021 - 7:00AM
Expires
Fri, February 12th, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ due to strong easterly winds, snow available for transport and weak faceted snow and surface hoar.  Human triggered wind slabs, 1-2′ deep, are likely in steep wind-loaded terrain, on unsupported slopes and cross-loaded gullies. Natural wind slabs are possible. Additionally, give cornices a wide berth and avoid travel under glide cracks. Watch for blowing snow, shooting cracks and recent avalanches. Cautious route-finding and conservative decision-making are essential.

***Portage Valley ice climbers and hikers: A MODERATE danger exists below 1,000′ where there is potential for avalanche debris, from a slide occurring above, to run through gullies. Avoiding gullies and runout zones is recommended.

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Thu, February 11th, 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)
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

More blow than snow…? Say it ain’t so… Unfortunately that appears to be the current situation. Easterly ridgetop winds have jumped up and are averaging in the 30s and 40s, with Sunburst recording a gust of 71 mph this morning. If you are thinking of heading out today, expect quite windy conditions and increasing avalanche hazard. Yesterday winds did not blow as high as forecast but were strong enough to move snow around in wind exposed terrain. Observers reported shooting cracks and touchy, shallow wind slabs. They also noted plenty of soft snow left to move around. With strong winds that ramped up last night forecast to continue today and continued snow showers, we expect the slabs to build even more, be easily triggered by a person on skis or machine and potentially release naturally. This means that paying attention to what terrain above you is also important.

What to watch out for if you’re headed out today:

  • Areas with current wind-loading (winds should blow all day, peaking this afternoon)
  • Slabs lower on slopes from cross-loading (Seattle Ridge is a good example)
  • Stiff snow over softer snow (punchy snow)
  • Cracks shooting from your skis or machine
  • Whumpfing (collapsing of the snowpack into the faceted snow underneath)

Remember, expect any wind slab you find to be sitting on weak faceted snow and/or surface hoar and poor bonding is likely. There is also still a chance a persistent slab avalanche could be triggered. There is an older layer of buried surface hoar that is sitting under old wind slabs from the NW wind event last Saturday. A wind slab triggered today may be able to step down to this layer and cause a deeper avalanche.

Sluffs: If there are steep slopes out of wind, watch your sluff. These continue to be easily triggered and high volume in steep sustained terrain.

Cornices: Cornices are large and strong winds today will be adding additional stress. Cornice falls may trigger wind slabs on the slope below. Give them extra space as they can break farther back onto a ridge than expected and limit exposure under them.

Cracking on a wind-loaded slope yesterday on Tincan, 2.10.21

Soft snow over buried surface hoar in mid-elevation pit on Tincan yesterday, 2.10.21. This set-up could be quite touchy with a more developed slab.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. New glide cracks are opening up around our region and existing ones are on the move. The most recent glide crack to avalanche was two days ago on Penguin Ridge. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.

Weather
Thu, February 11th, 2021

Yesterday: Skies were mostly cloudy with a few pockets of blue in the afternoon. Winds were easterly 5-15 mph gusting into the 20s. Temperatures were in the high teens to mid 20°Fs at upper elevations and mid 30°Fs at sea level. There were light snow showers on and off throughout the day with 1-2″ of accumulation. Overnight skies were cloudy with light snow showers early this morning.  Winds were easterly 20-40 mph gusting into the 50-60s with Sunburst hitting 71 at 4 am this morning. Temperatures were the teens to low 20°Fs at upper elevations and low 30°Fs at sea level.

Today: Skies will be mostly cloudy with light snow showers in the forecast, trace-3″ possible.  Temperatures will be in the teens in the Alpine and the high 20°Fs to mid 30°Fs at lower elevations. Winds will be easterly 20-40 mph gusting into the 50s and 60s. There is some uncertainty with the wind models today so they may be lower than forecast, as was the case yesterday. Overnight snow showers and strong easterly winds continue and then taper off around midnight. Temperatures will be in the teens and 20°Fs.

Tomorrow: Skies will start off cloudy and become mostly sunny in the afternoon. Winds will be light and easterly and temperatures will be in the teens at upper elevations and high 20°Fs at sea level. The sunshine, light winds and moderate temperatures look to continue on Saturday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 2 0.2 117
Summit Lake (1400′) 27 0 0 43
Alyeska Mid (1700′) 25 2 0.17 109

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16 NE 19 71
Seattle Ridge (2400′) 20 E 16 33
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/18/21 Turnagain Observation: Tincan Ridge
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04/25/21 Turnagain Observation: Sunburst
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04/23/21 Turnagain Avalanche: Lynx Ck Drainage
04/23/21 Turnagain Avalanche: Sunburst
04/23/21 Turnagain Observation: Center Ridge Turnagain pass
Riding Areas
Updated Tue, June 01st, 2021

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
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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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.