Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, December 12th, 2021 - 7:00AM
Expires
Mon, December 13th, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′ as northwest winds continue to build sensitive wind slabs on top of a snowpack that harbors a layer of weak, sugary facets buried 4-6′ deep. A relatively small wind slab triggered near the surface can step down to create a large avalanche on that deeper weak layer. Large avalanches on those weak facets may be triggered from the side of or below steeper slopes, and they may be triggered on slopes that already have multiple sets of tracks on them. This is a tricky snowpack that requires cautious route finding, avoiding spending time on or below slopes 35 degrees or steeper.

The danger will be MODERATE below 1000′. It is still possible a person may trigger an avalanche in steep, wind loaded terrain. Be on the lookout for signs of dangerous conditions like collapsing or shooting cracks, and stick to lower angle terrain if you see any of the above.

SUMMIT LAKE/SNUG HARBOR/LOST LAKE/SEWARD: Northwest outflow winds are expected to be strongest in these areas, making wind slab avalanches larger and easier to trigger.

Special Announcements

We are sad to report the first U.S. avalanche fatality of the season near Crystal Mountain, WA yesterday. 6 people were caught and buried in an avalanche, 5 were rescued and 1 did not survive. Our sincere condolences go out to the family and friends of those involved. Preliminary details in this news article.

Sun, December 12th, 2021
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Recent Avalanches

Seattle Ridge: A group taking an avalanche course watched a natural avalanche on the front side of Seattle Ridge yesterday. They also experienced large collapses and got propagating test results in snowpits at and below treeline.

 

Natural avalanche on the front side of Seattle Ridge. Photo: Joe Stock. 12.11.2021

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Northwest winds will continue today at 10-20 mph, building fresh wind slabs that a person could likely trigger. These will be easier to find at higher elevations on the typical suspect features- just below ridgelines, convexities, or in gullies. The slabs formed by these moderate winds should be less than a foot thick, but there is a good chance that even a small avalanche triggered near the surface could step down to trigger a larger avalanche on weak snow buried 3-6′ deep (see more on this in problem 2).

Be skeptical of the terrain features mentioned above, and be on the lookout for signs of recent wind loading. This could look like a smooth, rounded pillow of snow or a rippled texture on the surface, and it will feel like stiff or punchy snow on top of softer snow. You may also notice warning signs of unstable snow like cracking or collapsing below fresh wind slabs. The dangerous setup below the surface will require treating these surface instabilities with a little extra caution.

Natural avalanche on a wind loaded slope at the top of  Zero Bowl on the back side of Seattle Ridge. This likely occurred a few days ago, but similar activity may be possible as winds blow today. 12.11.2021

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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

Those of you who have been following the advisories for the past few weeks are probably well aware of the persistent weak layers of sugary facets lurking 3-6′ below the surface. As this layer gets buried deeper it is becoming more difficult to trigger, but we still need to approach it with caution. We are about 48 hours out from a major loading event where we saw large avalanches throughout the advisory area (check out more details and photos from Girdwood, Seattle Ridge, and Magnum/Cornbiscuit).

These layers are tricky because they usually won’t give you any kind of feedback before you trigger a large avalanche. It can be easy to get a false sense of security by seeing previous tracks on a slope, but we have recently seen avalanches on this layer getting triggered by the third or fourth person on the slope. We’ve also seen these avalanches triggered remotely, meaning that a person can trigger an avalanche without actually getting out into steep terrain. This requires an extra level of awareness, especially paying attention to the terrain above you. At this point an avalanche failing on this weak layer has the potential to be really, really big. We’ve seen them propagating thousands of feet wide and 4′-6′ deep or deeper. With consequences that high, we need to be extra cautious and avoid playing on or below slopes steeper than 35 degrees.

Natural slabs seen across Seattle Creek from the weather station. These failed during or just after the 12/9 storm. 12.11.2021

Large natural avalanche lower down on A1. Hard saying how deep it was looking at it from over on Notch, but it looked to be in the 6’+ range. 12.11.2021

Weather
Sun, December 12th, 2021

Yesterday: Temperatures started in the single digits to low teens F, dropping through the day and overnight. Winds were blowing out of the Northwest at 5-10 mph for the core advisory area, and 10-20 mph near Summit Lake. Skies were mostly sunny.

Today: Temperatures are currently in the single digits below 0F, and expected to continue to drop through the day into tonight. Northwesterly winds are expected at 10-20 mph with another day of mostly sunny skies.

Tomorrow: After dropping down to the minus teens F tonight we will see temperatures start to slowly climb tomorrow, although they will struggle to get above 0F. Skies will once again be mostly sunny, but we may see clouds moving in later in the day. Westerly winds will continue but they are expected to die down a bit, blowing around 5-10 mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 5 0 0 80
Summit Lake (1400′) 2 0 0 24
Alyeska Mid (1700′) 6 0 0 51

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -5 WNW 5 20
Seattle Ridge (2400′) -1 WNW 2 14
Observations
Recent Observations for Turnagain Pass
Date Region Location Observer
10/27/24 Turnagain Observation: Tincan Michael Kerst
10/21/24 Turnagain Observation: Turnagain Pass Road Observation Trevor Clayton
10/19/24 Turnagain Observation: Tincan – Below Todds Run Andy Moderow
10/18/24 Turnagain Observation: Taylor Pass Eli Neuffer
10/15/24 Turnagain Observation: Tincan Common John Sykes Forecaster
10/14/24 Turnagain Avalanche: Tincan CNFAC Staff
05/13/24 Turnagain Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South H Thamm
05/13/24 Turnagain Observation: Turnagain Pass non-motorized side Amy Holman
05/12/24 Turnagain Observation: Warm up Bowl Tony Naciuk
05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs A S
Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.


Subscribe to Turnagain Pass
Avalanche Forecast by Email

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.
Become a Member
If you think a public avalanche center is important please support our organization.
Donate Now
Become a Sponsor
Supporting the CNFAIC proudly shows that your business or organization values the safety of our snow sports community.
Become a Sponsor