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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
Sat, January 11th, 2020 - 7:00AM
Expires
Sun, January 12th, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger remains MODERATE above 1000′. Triggering a large avalanche on a weak layer buried 1-3′ deep is possible. In addition, there is the potential a person can trigger a lingering wind slab in wind loaded steep terrain or a sluff on steep protected slopes. Give cornices a wide berth and limit exposure under glide cracks.

*Yesterday afternoon there was a near miss avalanche incident along the Crow Pass summer hiking trail. We will be visiting the site today and publishing more details as soon as they become available. We are extremely thankful everyone is OK.

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Sat, January 11th, 2020
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)
Recent Avalanches

As mentioned in the Bottom Line, there was an avalanche triggered along the Crow Pass summer hiking trail yesterday. A backcountry rescue response was initiated and all parties were located and ok. We will update this link with details as they become available.

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

One more clear sky day and cold temperatures are in store before clouds head in along with some snow flurries possible tomorrow. The snowpack remains in its holding pattern of sorts with various weak layers sitting 1-3′ below the surface, possibly deeper, while the surface snow continues to loosen and facet in many zones.

What this means for us today is the possibility of triggering a slab avalanche needs to remain on our radar. Although we don’t have details on yesterday’s avalanche yet, this only highlights that dangerous slab avalanches are still possible to trigger. Generally speaking, there are faceted weak layers and a layer of buried surface hoar that are responsible for not allowing the snowpack to completely stabilize. We’ve found these layers mostly 1-3 feet deep and showing signs that they are becoming harder to trigger with time. This is a tricky problem because the snowpack might ‘seem’ stable even if it is not. Signs of instability are not usually present before a slope releases in this case and many tracks can be on a slope before someone hits just the wrong spot. Thin areas in the snowpack are the most likely places to trigger a slide, they are often near rocks and on top of rollovers. Watching our partners, exposing only one person a time and being aware of consequences if the slope does slide are all good ways to help stack the odds in our favor.

 

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

Light to moderate northwesterly winds have been over the region for the past several days and bumped up into the moderate range yesterday morning. Although much of Turnagain Pass has been spared the wind, other areas such as the Girdwood Valley and Portage Valley have seen just enough wind to transport snow along the higher peaks, as can be seen in the photo below.

Winds have quieted down to 5-10mph, where they are expected to remain through the day. Due to the light winds, fresh wind slabs are not likely to form. However, finding and triggering an older wind slab is possible. These slabs could be sitting on weak faceted snow, which can make them easier to trigger. Watch for areas that have been loaded by the winds, these often have a smooth rounded shape. Also feel for stiffer snow over softer snow, hollow feeling snow and cracking around you in the snow surface. These are all signs of a wind slab.

Wind transport along the higher terrain on Goat Mountain in the Girdwood Valley yesterday morning. 1.10.20.

 

Loose snow sluffs:  On slopes out of the wind the surface snow is becoming looser and looser by the day with the cold temperatures. Sluffs are getting larger because of this and gaining volume in longer sustained slopes. Watch your sluff.

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

Despite the very cold temperatures, glide cracks continue to slowly open in certain areas around the region. Although none have released into avalanches for several weeks that we know of, it is still wise to limit exposure under them as they are unpredictable and could release at anytime.

Glide cracks that are oozing open in the Peterson Drainage. 1.10.20. Photo: Turner Pahl

Close up of cracks and how the snowpack is buckling as gravity pulls it down the slope in slow motion. 1.10.20. Photo: Turner Pahl

Cornices:  Cornices are looming along ridges. As always, be sure to give them plenty of space and limit your exposure when passing beneath them.

Weather
Sat, January 11th, 2020

Yesterday:  Sunny skies and very cold temperatures were over the region again yesterday. The northwest winds picked up into the 10-15 mph range along ridgetops in the morning hours before quieting down midday. Temperatures were between -20 and -5°F at all elevations with valley bottoms being slightly colder than higher elevations.

Today:  Clear and cold weather conditions are on tap again today. The good news is warmer air is moving in at the higher elevations and stations are reporting temperatures in the positive (5-10°F). Valley bottoms remain frigid (-25 to -10°F) and should stay chilly through the day. Ridgetop winds have shifted around and are blowing from the east briefly this morning before forecast to swing back to the northwest and stay light, between 5-10mph.

Tomorrow:  Clouds, warmer temperatures and a few snow flurries are forecast for tomorrow as a front pushes through Southcentral. Only a trace to a few inches of snow is expected along with temperatures in the teens and a brief period of increased easterly winds. A return to cold and clear weather is expected for Monday and into the work week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -1 0 0 38
Summit Lake (1400′) -13 0 0 14
Alyeska Mid (1700′) -1 0 0 33

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 2 W 9 24
Seattle Ridge (2400′) 0 N 5 12
Observations
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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
Glacier District
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Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
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Carter Lake
Closed
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Closed
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Closed
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Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
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Closed

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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.