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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
Tue, January 14th, 2020 - 7:00AM
Expires
Wed, January 15th, 2020 - 7:00AM
Forecaster
Ryan Van Luit
The Bottom Line

Above 1000′ the avalanche danger is MODERATE. It’s possible for a human to trigger a wind slab in wind loaded terrain and to trigger a large persistent slab avalanche on a buried weak layer. Remain aware of sluff in steep exposed terrain and avoid travel on cornices and under glide cracks.

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Tue, January 14th, 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

Over the past several days, the region has experienced winds capable of transporting loose snow.  As a result, wind slabs have formed in many exposed areas of the Alpine and Treeline elevations.  Due to varying wind directions and localized geography, some areas have experienced this wind effect more than others.  Because of this it’s especially important to pay close attention to indicators of wind slab formation where you are and where you’d like to go.  These clues of wind effected snow could include: firm surface conditions, cracking, hollow or drum like sound/feel, and visual cues of recent wind activity such as pillowing and scouring.  If you find these indicators, it’s prudent to reassess the plan.

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.

Wind transported snow observed at Mt Adair south of the advisory area.  1.13.2020  Photo: Alex McLain

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

Persistent is defined as: “continuing to exist or endure over a prolonged period.”  Related and synonymous words include: dogged, insistent, patient, persevering, tenacious, assured, certain, dedicated, determined, firm, hell-bent, intent.

Whether you like it or not, persistent layers including buried surface hoar and facet layers exist within the snowpack.  These weak layers have been found 1-3′ deep and have a slab formed on top of them. It remains possible for a human to trigger a large slab avalanche.  With that said, the trend of this concern is moving toward unlikely. The confusing part is these weak layers cannot be found everywhere throughout the advisory area.  The only way to know if they exist where you’re located is to dig and test.  If this type of investigation is not within your skill-set, it’s probably sound to assume they exist.  As always, good travel practices are called for: minimizing exposure and traveling one at a time, or choosing routes with lower angles, and outside of the run out of an avalanche path.

 

In this non-windloaded test pit at Tincan, observers found good stability and no concerning weak layers.  1.13.2020.  Photo: CNFAIC Archive

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. Sluffs are getting larger because of this and gaining volume on longer sustained slopes. Expect sluffing in steep terrain with loose snow.  Remain mindful when traveling over cliffs and rocky outcrops.

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. Due to their unpredictable potential to release, the travel advice remains the same: limit your exposure while traveling under glide cracks.

Weather
Tue, January 14th, 2020

Yesterday: Cloudy skies with valley fog. Temperatures were in the teens and dropped into the single digits in the evening. Winds were northwesterly 5-15 mph gusting into the 20s.

Today:  Sunny trending to partly cloudy in the evening.  Today’s high temperature is expected at 6°F, with a low of -1°F. Winds are forecast to be from the northwest from 15 to 20 mph.

Tomorrow: Clear skies with a high temperature near 2°F, low of -2°F. Winds are expected to be from the northwest to north from 5 to 10 mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 10 1 0.1 40
Summit Lake (1400′) 8 0 0 13
Alyeska Mid (1700′) 11 1 0.01 35

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 10 W 8 18
Seattle Ridge (2400′) 8 NNE 3 7
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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
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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.