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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, February 22nd, 2020 - 7:00AM
Expires
Sun, February 23rd, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

CONSIDERABLE avalanche danger remains at all elevations from Girdwood, though Turnagain Pass to Seward. There are many avalanche concerns, but the most dangerous is the potential that someone could trigger a large and deadly slab avalanche on slopes 30 degrees or steeper. These slabs are unmanageable and range from 3-6′ thick. They could be triggered from the ridge above a slope or below. Other concerns are triggering a fresh wind slab avalanche, around a foot thick, due to an increase in winds last night and older slabs composed of last week’s storm snow. In short, very cautious route-finding and conservative decision making is essential if headed into the backcountry.

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Sat, February 22nd, 2020
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

No new natural avalanches were seen or reported yesterday. Also, few folks were out in the backcountry yesterday and to our knowledge, people have stayed out of avalanche terrain and slopes have not been tested. However, artillery was able to trigger large slabs during AKDOT & PF’s avalanche hazard reduction work along the Seward Highway. Below are few more photos of the natural avalanche cycle that occurred Tuesday through Thursday (Feb 18-20).

A zoomed in look into Davis creek (between Magnum and Cornbiscuit) and the Superbowl area with Goldpan peak in the far distance. Note the multiple slab avalanches. These most likely released Wednesday night or very early Thursday morning (Feb 19 or 20). Photo taken on Feb 20 by Travis Smith.

Natural slab avalanche on Sunburst’s SW face. Note the debris further up valley in the shade. It appears that earlier in the storm a few additional sections of Sunburst avalanched as well. 2.20.20. Photo: Travis Smith

Various pockets of slab avalanches that occurred on Cornbiscuit’s west face. 2.20.20. Photo: Travis Smith

Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

With a clearing trend on the door step and 6-8″ of new snow from yesterday (on top of the 3-5 feet of new snow from Tues-Thur), the mountains will be quite enticing to powder lovers for the next few days. This is worrisome. Not only because the storm snow is still adjusting, but under all that amazing snow are weak layers that are proving to be reactive.

The natural cycle we had a glimpse of Thursday afternoon proves that the snowpack isn’t stable. Many of the avalanches had crowns 5-8′ thick, were rated ‘very large’ and stepped down into buried weak snow. Can someone charge up and onto slopes and trigger one of these monsters? Can a person be cautious traveling along a ridge and trigger one? What about triggering from below a slope? Everything we have seen so far points to YES, we can. We are in a ‘tip-toe’ situation because these types of avalanches are much too large to have any way of managing.

To avoid these issues, we can play in the powder in the flats or on slopes 30 degrees or less with nothing steeper above us.

If you are headed out into avalanche terrain today, things to remember:

  • Between 3-6′ below your snowmachine or feet sits various layers of weak sugary faceted snow
  • Very large avalanches could be triggered that take out the entire slope
  • Yes, many slopes have already slid, but these could have portions still intact and waiting for a trigger
  • There is no way to know how close a slope is to avalanching. It could be the first person or the 15th person that hits the trigger point.
  • Remote triggering is possible (initiating a collapse in the weak layer from the top, side or bottom on the slope resulting in an avalanche)

 

The photo above shows the weak facets around 3 feet deep. The image also shows a failure in the slab from a storm snow interface that is still bonding. Either way, unfortunately there is bad news in our snowpack.

Close up view of the Motorized up-track on Seattle Ridge and a portion of the Repeat Offender slide path has not slid. Another big thanks to Travis Smith for his photos.

 

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

Storm snow avalanche issues exist in the top couple feet of the snowpack. Keep in mind, one of these types of avalanches could ‘step down’ and trigger a much larger slide.

Wind slabs:  The wind picked up last night, blowing 15-20mph with gusts near 40mph from the east. With all this fresh snow, we can expect to find new touchy wind slabs around a foot thick. Additionally, older wind slabs from last week’s storm could be triggered, these would be several feet thick and very dangerous.

Storm slabs:  The storm snow from the past week is still bonding to the old snow underneath. Triggering a slab composed of the storm snow is still possible. The snow has settled just over a foot and these storm slabs are now in the 1-3′ thick range.

Cornices:  These have grown substantially over the past week and could easily be triggered. If making it to the ridgelines, be sure to give these features a very wide berth.

Loose Snow avalanches:  Sluffs in the loose surface snow are likely. If getting on slopes this steep, there are much larger avalanche problems to deal with.

Weather
Sat, February 22nd, 2020

Yesterday:  Cloudy and obscured skies filled the region through the day and cleared out over night. Snowfall during the day added between 6-8″ of very low density snow to sea level is most areas with interior Kenai and Summit Lake seeing only 2-3″. Ridgetop winds were calm until 6pm when they picked up from the east averaging 15-20mph with gusts near 40mph during the overnight hours. Temperatures dropped from the 20-30°F range to the teens and single digits along ridgelines overnight as well.

Today:  Partly cloudy skies are forecast as a weak low pressure spins areas of clouds overhead. A chance for a few snow flurries is possible with no accumulation. Ridgetop winds should remain out of the east in the 10-15mph range with gusts to 25mph. Temperatures look to keep dropping and reach the single (or minus single) digits tonight at most elevations.

Tomorrow:  Some cloud cover may be over us again tomorrow, but we are generally in a clearing trend until Monday night. Ridgetop winds look to stay light to moderate from variable directions Sunday into Monday and temperatures cold.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 23 7 0.4 84
Summit Lake (1400′) 20 3 0.2 30
Alyeska Mid (1700′) 23 6-8 0.44 94

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12 E 10 38
Seattle Ridge (2400′) 19 *N/A *N/A *N/A

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.

Observations
Recent Observations for Turnagain Pass
Date Region Location
05/06/20 Turnagain Avalanche: Pastoral Peak, north face
04/10/20 Turnagain Avalanche: Wolverine
04/10/20 Turnagain Observation: Eddies lookers right shoulder
04/09/20 Turnagain Observation: Bench Peak
04/04/20 Turnagain Observation: Tincan
04/04/20 Turnagain Observation: Pete’s North
03/26/20 Turnagain Avalanche: Tincan – Proper (SW facing)
03/26/20 Turnagain Avalanche: Seattle Ridge
03/25/20 Turnagain Avalanche: Sunburst Uptrack @ 2000′
03/24/20 Turnagain Observation: Turnagain – Road Observations
Riding Areas
Updated Mon, October 26th, 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
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
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.