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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
Mon, January 13th, 2020 - 7:00AM
Expires
Tue, January 14th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is MODERATE above 1000′. It is possible to trigger a wind slab in wind loaded terrain and there is still the potential to trigger a large persistent slab avalanche on a buried weak layer. Watch your sluff in steep protected terrain and avoid travel on cornices and under glide cracks. Evaluate snow and terrain carefully.

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Mon, January 13th, 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)
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

Starting January 8th we have seen several upticks in the wind strong enough to transport snow. The light snow that fell during the New Year’s storm and was enjoyed by powder seekers has now been blown around. Stiff wind slabs have formed in the Alpine and in exposed terrain in the Treeline elevation band. Observers from Summit Lake to Crow Pass have found hard wind effected snow along ridgelines and through valleys that channel the wind. Small natural and human triggered wind slabs have been observed and the avalanche that occurred Friday evening on the Crow Pass trail was a large hard slab avalanche involving wind effected snow. The winds have also been shifting directions and loading different aspects. Overnight the winds shifted again from the east to the west and are forecast to be gusty during the day. About an inch of new snow fell yesterday. Today when traveling it will be important to notice where is snow is drifted, watch for cracking and areas that feel hollow due to hard snow over soft snow. Pay attention to whether or not your skis or machine are sinking into the snow or are you staying on top of very hard snow? Wind slabs can be tricky and let you travel out onto them before failing. Even a small wind slab can be dangerous in steep terrain. The wind effected snow is also most likely sitting on top of weak snow that formed during the stretch of cold temperatures. The wind slabs may linger and be more reactive due to this setup and eventually become another part of our persistent slab issue.

Increases in wind speed recorded at the Sunburst weather station over the past week were enough to transport snow.

Evidence of wind loading and wind slabs. Skier triggered wind slabs on Seattle Ridge and an avalanche on Colorado peak that was possibly skier triggered on the 9th or 10th. 

Avalanche Problem 2
  • 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

December 22nd we started talking about the buried surface hoar and buried faceted snow so you might be having a little message fatigue. However, these layers now 1-3’+ deep in the snowpack are still a concern… A “persistent” concern. Now there is potentially even more of slab sitting on top  of these weak layers in wind loaded areas. Additionally, this means there is a chance that a shallow wind slab triggered higher in the snowpack might step down to one of these old weak layers. Choose terrain wisely with consequences in mind if a large avalanche were to occur and use safe travel protocol.

Snowpack on Goat Mtn. Note the weak layer of small facets.

Additional Concern
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Loose snow sluffs:  On slopes out of the wind the surface snow is becoming looser and looser by the day with the cold temperatures. This is more pronounced at lower elevations due to the inversion. Sluffs are getting larger because of this and gaining volume on longer sustained slopes. One observer described almost having a close call with his sluff on Friday. Getting stuffed into the alders is no joke. Expect sluffing in steep terrain with loose snow.

Cornices:  Give cornices plenty of space and limit your exposure when passing beneath them.

Glide avalanches: Glide cracks continue to open but there have been no recent reports of glide avalanches. However, due to their unpredictable potential to release the travel advice remains the same: limit your exposure while traveling underneath glide cracks.

Weather
Mon, January 13th, 2020

Yesterday: Mostly cloudy skies and light snow showers with accumulation of around an inch of snow. Temperatures were in the teens and winds were easterly 10-20 mph gusting into the 30s. Overnight winds shifted to the northwest.

Today: Cloudy skies with a slight chance of snow in the morning becoming partly sunny later in the day. Temperatures will start in the teens and drop into the single digits to just below 0°F overnight. Winds are forecast to be northwesterly 5-15 mph gusting into the 20s. They may be stronger in channeled terrain as an outflow pattern sets up.

Tomorrow: Mostly clear skies with some patchy valley fog. Temperatures will be in the single digits and northwesterly winds will continue and could be gusty. Cold and clear looks to be the norm until later in the week. There is uncertainty in the long term discussion about about a possible pattern change for the weekend. Stay tuned and maybe do a snow dance???

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 17 1 0.1 39
Summit Lake (1400′) 15 1 0.1 14
Alyeska Mid (1700′) 15 1.5 0.06 35

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 10 NE 9 26
Seattle Ridge (2400′) 13 SE 8 18
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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

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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.