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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
Wed, January 15th, 2020 - 7:00AM
Expires
Thu, January 16th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

Above  2500′ the avalanche danger is MODERATE. In the Alpine triggering a large avalanche on a buried weak layer remains possible. Pay attention to surface conditions as very hard snow could indicate lingering wind slab potential and loose snow might sluff in steep terrain. Below 2500′ the avalanche danger is LOW and normal caution is advised. As always use safe travel protocol.

SUMMIT LAKE: This region is out of our advisory area. The overall snowpack is shallower, the weak layers are more developed and the wind effect is from the recent winds is more pronounced. Extra caution is advised.

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Wed, January 15th, 2020
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
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
Low (1)
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
  • 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

We have been talking about buried weak layers for a while. Let’s take a quick inventory of the state of the snowpack. It has now been two weeks since the New Year’s Eve storm and we have been in a mostly clear and cold weather pattern. Since that storm the soft surface snow has become faceted and recently we had almost a week of on and off wind. Due to the wind, the faceted surface snow was buried in some terrain by wind slab. The last human triggered avalanche was Friday evening in Crow Pass.  Where does this leave us now in relation to triggering an avalanche? Well… It is still possible and something to keep in mind if traveling in steep terrain in the Alpine. The level of wind effect has been different across the advisory area. This is a key factor in where the most hazard is. If you find yourself in a zone with very hard wind effected snow this could be sitting on very weak faceted snow below. This is the suspected set up in the avalanche on Friday. Lingering wind slabs are now persistent slabs because they are associated with buried facets. Additionally there are layers deeper in the pack (Solstice buried surface hoar and/or facets and facets with the December 9th rain crust) that have been indicating that it would be hard to trigger them at this point but not impossible. The best way to manage this uncertainty is to avoid steep slopes with hard snow over soft snow, use safe travel protocol and think about consequences. If you did trigger a large avalanche where would all the snow go? Look for signs of instability but realize you may not see them with this type of avalanche problem.

Propagation in a snowpack test on Manitoba at 2700′ on a weak layer of buried facets, 1.11.20. Photo: Alaska Avalanche School Pro 1 

Propagation in a snowpack test on Goat Mountain, 1.10.20. Photo: CNFAIC

 

 

 

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 avalanches (sluffs):  On slopes out of the wind expect sluffing in steep terrain.  The surface snow is becoming looser and looser by the day with the cold temperatures.

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

Glide avalanches: Due to the unpredictable potential to release, limit your time spent under glide cracks.

Weather
Wed, January 15th, 2020

Yesterday: Skies were partly cloudy with patchy valley fog and very light snow showers. Temperatures were in the single digits to low teens. Winds were westerly 5-10 mph with gusts into the 20s. Overnight temperatures were mostly in the low single digits while a few stations recorded temperatures just below 0°. Winds were light and westerly.

Today: Mostly clear skies with temperatures in the low single digits. The winds are forecast to be light and becoming calm in the afternoon. Overnight temperatures look to be slightly inverted with temperatures in the the single digits at upper elevations and around 0° or just below in valley bottoms.  Winds remain calm.

Tomorrow: Sunny skies, calm winds and temperatures in the single digits. This cold and clear pattern looks to persist into the weekend until skies become cloudy Saturday evening and with a chance of snow on Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 1 0.01 38
Summit Lake (1400′) 4 1 0.01 15
Alyeska Mid (1700′) 7 4 0.04 37

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 4 W 8 22
Seattle Ridge (2400′) 6 W 2 16
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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
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Closed
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Closed
Turnagain Pass
Closed
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.