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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, January 31st, 2020 - 7:00AM
Expires
Sat, February 1st, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is CONSIDERABLE in the Alpine and MODERATE below. A very cautious mindset is required for travel in exposed areas above the trees today as large and dangerous slab avalanches may still be likely to trigger on steep slopes. These slabs are 2-4+feet thick and sitting on weak faceted snow. Lingering wind slabs, around a foot thick, and sluffs will be possible to trigger. These smaller slides could initiate a larger slab on steep terrain.

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Fri, January 31st, 2020
Alpine
Above 2,500'
Considerable (3)
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
Considerable (3)
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)
Recent Avalanches

The skies cleared just enough yesterday afternoon to get a look at some of the natural avalanche activity that occurred during the storm Wednesday night, just 36 hours or so ago. Several wind slabs released, around a foot thick, that were partially filled back in. The more concerning avalanches however, were several slabs that appeared to have released in deeper buried layers, around 2 feet thick. These were observed on Sunburst, Tincan and Magnum and are pictured below.

Sunburst’s lower north ridge. If you look close you can see the partially filled in ~2 foot crown just off the ridge and extending for several hundred feet. This character of this slab points to failure in a buried weak layer as opposed to simple wind loading.

 

Magnum’s west face. Despite many sluffs and shallow wind slabs on this face, the spooky avalanche is the one at the top, the pocket that pulled out just under the rocks. This slab is near the slide that was human triggered in weak faceted snow around 3 weeks ago and like Sunburst, is indicative of failure in older weak snow.

 


This slab, who’s crown is partially filled in by wind, is also suspect for failing in buried weak snow. Located on the north side of Tincan Ridge, the Tincan north chutes, and just over the ridge from Hippy Bowl.

 

Slab avalanche seen on the Penguin Ridge, SE facing in Girdwood Valley yesterday as well. This slab also has the character of releasing in older weak snow. 1.30.20. Photo: Mike Welch

 

A typical wind slab, around a foot deep, that released on Tincan’s CRF ridgeline, SW aspect. 

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
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

Skies are dawning cloudy this morning, winds are light and temperatures are in the single digits. For those of you headed out and hoping the skies open enough for travel above treeline- BEWARE. There is a lot of uncertainty as to how tenuous the snowpack is right now.

Sitting under all the low-density snow from the last half of January (2-4+ feet of soft powder snow), are weak sugary facets and buried surface hoar. The winds from Wednesday night not only affected the surface snow, but they also tipped the balance just enough to initiate some natural avalanches. Some were in the form of common wind slabs, but what is much more concerning, were the slabs that are suspected to have released in deeper layers in the snowpack. Although the natural avalanche cycle was not widespread, that also means many slopes could still be hanging in the balance, just waiting for a trigger.

Very conservative terrain choices are advised today as the snowpack adjusts. It is just 1.5 days after the end of the natural cycle and although the likelihood of triggering a large slab should be decreasing, patience is key. Things to keep in mind if travel is possible to the higher slopes:

  • Don’t forget there is funny business several feet below you…
  • No signs of instability may occur before a slope releases
  • It could be the 3rd or 10th person on a slope before someone finds a trigger point
  • Remote triggering is possible (triggering a slab from below, along the ridge or on the side)
  • Avoid heavily wind loaded slopes. These are more likely to release due to the additional weight on the weak layers.

One of many snow stability tests performed on Tincan yesterday. Results were varied and pointed to areas where the buried weak layers were showing signs of reacting and areas they were not.

 

Video link HERE

Avalanche Problem 2
  • 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

Lingering wind slabs from the strong winds Wednesday night may still be possible to trigger on steep slopes. These are expected to be around a foot thick and somewhat stubborn. The more concerning issue is if a small wind slab triggers a deeper weak layer and a larger slab avalanche occurs. This can make for a very unmanageable and dangerous situation.

Loose Snow Sluffs:  Expect sluffs on steep slopes in areas that were spared the winds. In the lower elevations, these sluffs could entrain a large amount of older storm snow and be larger than expected.

Weather
Fri, January 31st, 2020

Yesterday:  Mostly cloudy skies with light snowfall was seen yesterday morning before skies broke and the sun shown through during the afternoon. Up to an inch of snow fell during the morning hours in most locations with 3-4 inches in Portage Valley. Ridgetop winds were light from the east. Temperatures were in the single digits in the Alpine and in the teens at the lower elevations.

Today:  Mostly cloudy skies with a few snow flurries are expected today. Ridgetop winds are light and have just turned northwesterly this morning, where they should remain in the 5-10mph range. Temperatures cooled in valley bottoms overnight and are expected to reach into the single digits today. Upper elevation temperatures should remain in the single digits.

Tomorrow:  Mostly clear skies and cold temperatures are in the forecast for Saturday- BUT models are showing the northerly outflow winds to increase across southcentral. Right now it’s looking like 20-30mph winds along the ridges with stronger gusts in favored areas. How this will impact Turnagain Pass is unknown at this time. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 16 1 0.1 60
Summit Lake (1400′) 9 0 0 20
Alyeska Mid (1700′) 17 1 0.1 58

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 8 NE 6 31
Seattle Ridge (2400′) 12 E 3 8
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Riding Areas
Updated Fri, May 01st, 2020

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
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Closed as of May 1. Thanks for a fun, safe season!
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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.