Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, November 24th, 2020 - 7:00AM
Expires
Wed, November 25th, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is CONSIDERABLE today and likely to rise to HIGH danger tomorrow. Human triggered large avalanches remain likely in the mid and upper elevations on all aspects. Avalanches can be triggered by people on a slope or remotely, from the side or below. They could be up to 4′ deep and fail near the ground, taking the entire snowpack down the mountain. Several of these were triggered on Sunday with one person narrowly escaping.

Wednesday:  A High Wind Watch and Special Weather Statement has been issued for the Turnagain Arm region.

*Very dangerous avalanche conditions exist and extreme caution in warranted. Careful terrain selection in critical to avoid being on or under slopes 30 degrees or steeper.

Special Announcements

Motorized use:  The Forest Service will be assessing snow cover conditions today in anticipation of opening certain areas to motorized use this week. See the ‘Riding Areas’ tab below for the most up to date information.

  • Avalanche Center Operations:  We will be issuing forecasts today and Thursday with daily forecasts starting on Saturday.
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    Please see the ‘Scholarships’ page for more details and get your application in!
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Tue, November 24th, 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

Skies cleared on Sunday allowing for many people to venture into the higher terrain at Turnagain Pass. This was the first test of the snowpack since 16-24″ of snow fell on Friday night through Saturday. It didn’t take long for several large avalanches to be triggered by people. All but one was remotely triggered from either the side or top. Here is a rundown:

  • Tincan, Hippy Bowl:  Remotely triggered, no one caught. Broke in faceted snow near the ground (basal facets). Several hundred feet wide and running 2,500′ to the creek below.
  • Sunburst, SW face:  Skier triggered while skier was on slope. Skier was very lucky to have been able to ski off the slab to safety as avalanche broke above skier. Released in basal facets taking entire snowpack. Several hundred feet wide and running to valley bottom.
  • Eddies, mid elevation rollovers:  Remotely trigged, no one caught. Broke at the new/old interface in buried surface hoar, stepped down to basal facets in spots. Up to 1,000′ wide.

A big THANK YOU to the 10 people who passed along their information from these events. See all those reports HERE.

 

 


Tincan’s Hippy Bowl. Avalanche was triggered remotely by a skier on the low angle terrain on the looker’s left side. Skier was well out of the way and no one was caught. 11.22.20. Photo: Henry Munter

 



Close up of the crown, note how the weak layer failed across the entire slope taking multiple sections just below the ridge. 11.22.20



Close up of the sympathetically triggered pocket below Hippy Bowl, also released in the facets near the ground. 11.22.20


 

Sunburst, SW face, large avalanche that was triggered by skier on the slope. This avalanche also broke near the ground in facets. 11.22.20

 

Eddies avalanche in mid elevation rolling terrain, up to 1,000′ wide. This was remotely triggered from the side/top and no one was caught. Avalanche broke in buried surface hoar at the new/old snow interface and stepped down to the basal facets in places. 11.22.20. Photo: Andy Moderow

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

The proof is undeniable – we have a bad setup for human triggered large avalanches. Add to that, a lot of people, including myself, are stoked to start the winter and get into the backcountry. Several bullets were dodged on Sunday and the same conditions will persist through the Thanksgiving holiday.

It’s a HEADS UP situation. Several feet of recent storm snow sits on a very weak base of sugary faceted snow. This is keeping all the new snow from sticking well to the slopes and why people are able to trigger these large avalanches. Furthermore, a layer of buried surface hoar sits under last weekend’s storm snow and is likely to still be reactive. Hence slabs releasing around 2 feet deep are likely along with a slab that releases 3-4′ deep and near the ground.

Not only is watching out for RED FLAGS a wise decision, but simply letting the mountains do their thing and adjust to these new loads of snow. We all want to return back to the parking lots with high fives. Sticking to low angle slopes, and out from under larger slopes, is a great way to enjoy the new snow.

As a reminder, here are the Red Flags to look for:
– Recent avalanches
– Whumpfing (collapsing) of the snowpack
– Shooting cracks

Below is a look at the snowpack from Tincan on Sunday. Note the few inches of weak snow at the bottom of the snowpack.

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Roughly a foot of new snow fell yesterday, Monday, and another 6-10″ of snow is expected tomorrow, Wednesday. This has been, and will be, accompanied by strong easterly winds. That said, storm snow avalanches will be likely, especially tomorrow.

With temperatures rising during tomorrow’s snowfall, making for an ‘upside down’ storm, expect shallow storm slabs to form. This is due to denser snow falling onto lighter snow. Additionally, wind slabs will be forming tomorrow as well. If they begin to release naturally, could step down and trigger a much larger natural avalanche. More reason to avoid avalanche terrain for the time being.

Weather
Tue, November 24th, 2020

Yesterday:  Light snow fell through the day above 1,000 adding another 2″ or so to the 10″ that fell Sunday night. Winds cranked from the east in the 40’s mph with gusts to 81 Sunday night before decreasing through the day (teens with gusts in the 20’s mph) yesterday.

Today:  Mostly clear skis are forecast with light to moderate westerly winds (10-20mph). Temperatures should remain in the 20’sF above 1,000′.

Tomorrow:  Another system arrives tonight and by tomorrow night 8-12″ of snow is expected. This is a warmer system and the rain/snow line should rise to 1,000′ by midday Wednesday before cooling back down. Winds are slated to be strong – 40-50mph with gusts in the 80’s or more from the east.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 2 0.4 38
Summit Lake (1400′) 25 0 0 13
Alyeska Mid (1700′) 28 1 0.1 40

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 E 19 69
Seattle Ridge (2400′) 24 *N/A *N/A *N/A

*Seattle Ridge wind sensor is rimed over and not able to spin and record wind data.

Observations
Recent Observations for Turnagain Pass
Date Region Location
11/24/20 Turnagain Observation: Seattle Ridge Up-Track
11/24/20 Turnagain Observation: Eddies
11/24/20 Turnagain Observation: Sunburst
11/24/20 Turnagain Observation: Sunburst West Bench
11/24/20 Turnagain Observation: Tincan
11/24/20 Turnagain Observation: Eddy’s
11/22/20 Turnagain Avalanche: Tincan
11/22/20 Turnagain Avalanche: Eddies
11/22/20 Turnagain Avalanche: Sunburst
11/22/20 Turnagain Avalanche: Hippy Bowl, Tincan
Riding Areas
Updated Tue, November 24th, 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
Open
Turnagain Pass will open to motorized use on Wednesday 11/25.
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season
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.