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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, February 24th, 2020 - 7:00AM
Expires
Tue, February 25th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

We have issued a Special Avalanche Bulletin through the National Weather Service for the Turnagain Pass area and surrounding mountains. 

Today the avalanche danger is CONSIDERABLE above 1000′ due to the potential size and consequences of triggering an avalanche. It remains possible for a human to trigger a large and deadly slab avalanche 3-8+ deep on slopes 30 degrees or steeper. Watch for lingering wind slabs in leeward terrain and avoid travel on or under cornices. Conservative decision making and cautious route-finding are essential if headed into the backcountry.

SUMMIT LAKE TO SEWARD REGION: Expect the avalanche danger to remain elevated due to yesterday’s strong winds, recent precipitation and poor snowpack structure.

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Mon, February 24th, 2020
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Both human and natural avalanches occurred in Summit Lake yesterday. A party skinning on the ridge of Manitoba remote triggered avalanches on the slope below and an impressive series of natural avalanches triggered by the northwest winds were observed on Fresno from the highway.

Remote triggered avalanches on Manitoba triggered by a party skinning on the ridge. 2.23.20. Photo: Carleton Lane 

Crowns of the natural avalanches on Fresno seen from Manitoba. 2.23.20. Photo: Andy Moderow. See video in Avalanche Problem 1

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

Despite the lure of sunny skies and people starting to poke into avalanche terrain is imperative to keep the consequences of triggering a large avalanche in your mind today. It is still possible to trigger a deep, unsurvivable avalanche. This why we have issued the Special Avalanche Bulletin and why the avalanche danger remains at CONSIDERABLE. The travel advice advice associated with this danger level is the key to staying safe; cautious route-finding and conservative decision making are essential. Picture a large avalanche anywhere from 3-8+ feet deep on the piece of terrain you are thinking of traveling on. Before you head out today look at the observations from the past week and imagine triggering one of the avalanches pictured. Big thanks to everyone sending in information this weekend!

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

  • Between 3-8 + feet below your snowmachine or skis sits various layers of weak faceted (sugar) snow. This is why we have a deep persistent slab problem.
  • Direct sunshine is just starting to be a concern and could be a factor today. Slopes heating up later in the day may be easier to trigger. Watch for small roller balls from rocky areas.
  • In shallower snowpack zones such as Lynx Creek or Summit Lake, it could be much easier to initiate a large slab. As noted above there were both human triggered and natural avalanches in Summit Lake yesterday. Check out the video below.
  • Areas near rocks or shallower snowpack areas are likely trigger points. This could be hard to identify and why messing with a deep slab issue is such gamble.
  • Very large avalanches could be triggered that take out the entire slope and connect to adjacent slopes.
  • Many slopes have already slid but these could have portions still intact, just 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. Use safe travel protocol.
  • Remote triggering is possible (initiating a collapse in the weak layer from the top, side or bottom on the slope resulting in an avalanche) as was the case of the avalanche from the Manitoba skin track yesterday.
  • You can avoid exposure to this avalanche problem by remaining in the flats or on slopes 30 degrees or less with nothing steeper above.

Video Link: Fresno Basin Avalanche Procession 2_23_2020

Large avalanche in the Johnson Pass area seen from the air that likely occurred during the storm last week. 2.23.20. Photo: Graham Predeger.

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

Yesterday gusty NW winds created plumes off of the peaks, formed tender wind slabs and triggered avalanches in Summit Lake. Today it still possible to trigger a wind slab in steep wind loaded terrain. Northwest winds can be a bit funky and load from the south on the east side of Turnagain pass. Pay attention to wind hardened surface conditions. Look for drifting patterns and pillowed snow. Watch for cracking and listen for hollow sounding snow. Initiating a wind slab in the top couple feet of the snowpack could ‘step down’ and trigger a much larger slide that breaks in the deep weak layers discussed above.

Cornices:  These have grown substantially over the past week and could be triggered today.  Avoid travel on or underneath. Triggering a cornice fall could also initiate a deep slab on the slope below.

Loose snow avalanches: On slopes protected from the wind, soft snow may easily sluff in steep terrain.

Mid afternoon snow transport off Spirit Walker in Summit Lake. North winds transporting to the south. 2.23.20. Photo: Andy Moderow.

North winds pluming from the south on Tincan Ridge. 2.23.20.

Weather
Mon, February 24th, 2020

Yesterday: Skies were partly cloudy. Temperatures were in the single digits to low teens. Winds were northwesterly 10-20 mph gusting into the 30s. Overnight skies were mostly clear and temps dropped down to single digits and in some valley locations below 0°F. Northwest winds eased to 5-10 mph.

Today: Clear skies with temperatures in the single digits to high teens. Northwest wind 5-15 mph becoming calm overnight. Skies will be partly cloudy overnight and temperatures will be in the single digits and low teens.

Tomorrow: Skies will be mostly cloudy with snow starting in the late afternoon. Winds will start light and northwesterly and then shift to the east blowing 10-20 mph with gusts into the 30s. There is the potential for heavy snow and strong winds overnight into Wednesday with the storm ending Wednesday night.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 11 0 0 80
Summit Lake (1400′) 7 0 0 31
Alyeska Mid (1700′) 9 0 0 86

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 0 NW 10 30
Seattle Ridge (2400′) 5 *NA *NA *NA

*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 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
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
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.