Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, November 29th, 2020 - 7:00AM
Expires
Mon, November 30th, 2020 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

Today’s avalanche danger is CONSIDERABLE. Winds have built sensitive slabs on top of a snowpack that sits on weak snow at the ground. It may be possible to trigger a large avalanche from above, to the side, or (most dangerously) below the slope. A relatively small wind slab avalanche triggered near the surface could step down to a very large avalanche at the ground. Although it will be tempting to step out into bigger terrain, we need to resist that urge, and use cautious route finding by avoiding slopes steeper than 30 degrees.

SUMMIT LAKE: The snowpack is generally thinner and weaker in the Summit Lake region. This means it will be even easier to trigger an avalanche near the ground, and extra caution is warranted.

 

Special Announcements

Want to learn more about forecasting mountain winter weather?? Join us and guest meteorologist Kyle Van Peursem this Tuesday night, Dec 1st from 7-830pm on Zoom for our first Forecaster Chat series!!

Avalanche Education Scholarships are available and the deadline is December 1st.
Please see the ‘Scholarships’ page for more details and get your application in!

Thanks to our sponsors!
Sun, November 29th, 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

Storm totals from our most recent storm cycle were around 3-4′. During the tail end of this storm, Friday night winds were blowing 40-50 mph with gusts in the 80’s, creating a heavy load and sensitive slabs. Here is what we know happened immediately following the storm:

  • Multiple medium sized avalanches released in paths along the Seward highway yesterday, some of which ran to the valley.
  • We received multiple reports of soft slab avalanches roughly 2′ deep that failed at lower elevations on Seattle Ridge sometime during the most recent storm (Friday or Saturday).
  • Riders were able to trigger small avalanches on wind-loaded test slopes in the Seattle Ridge flats yesterday.

Avalanche Problem 1
  • 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

Over the past 24 hours, average ridge top winds between 15-20 mph, with sustained periods between 40—50 mph, have drifted snow into sensitive slabs 3-5’ deep or deeper. Today it will be easy to trigger an avalanche on this layer. A fresh wind slab will feel denser and more consolidated than storm snow. It may also feel ‘punchy’, or hollow. You might notice cracks shooting out from your snow machine, skis, or snowboard as you approach one. Expect to find fresh wind slabs on the leeward (downwind) side of ridges or rollovers, and they are often deposited immediately below cornices. Pay attention to all of these signs, and give any suspect slopes a wide berth. The good news is that it doesn’t take very long for a wind slab to gain strength. For today, however, they will be easy to trigger, and they could be large. It is possible that a wind slab triggered by a person could step down to a deep weak layer near the bottom of the snowpack.

Cornices: We are starting to see some bigger cornices developing as strong winds have plenty of snow to move around after this week’s storms. These new cornices will be prone to breaking, and they have a tendency to pull back much farther up the ridge than you would expect. If you are unsure of where the ground ends and the cornice begins, look for visual cues like rocks or vegetation poking out of the snow.

Tincan. Plenty of snow to get loaded above treeline at Tincan. Photo: Tully Ward-Hamer. 11.28.2020

Avalanche Problem 2
  • 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

The weak layers at the bottom of our snowpack are now buried by 3-5’ of snow throughout our advisory area, and they may be as deep as 6-8’ in areas that have been wind loaded. As this layer gets buried deeper and deeper, it is becoming more difficult to trigger an avalanche near the ground. The scary thing is that the potential for destruction is increasing at the same time as the likelihood of triggering is decreasing. These avalanches have the potential to propagate very wide, and may be triggered remotely from below or adjacent to a slope. Further complicating the issue is that our typical stability tests (Extended column test, Compression test) are not equipped to give us any information on whether a person could trigger an avalanche on a weak layer more than about a meter deep. It is also unlikely that you would experience typical warning signs such as cracking or collapsing with a deep slab problem.

Given the difficulty of predicting just how sensitive a deep persistent weak layer might be on a specific slope, and considering the major loading event we have had (including fresh wind loading in the past 24 hours), the only way to manage this problem is to avoid playing on or below slopes steeper than 30 degrees. The most likely places to trigger a deep slab avalanche are areas where the snowpack is thinner. This may be near rocks or trees, or in areas that were previously wind scoured. Generally, as you move further south down the pass and towards the Summit Lake area, we are seeing a thinner snowpack with more sensitive weak layers at the ground. For now, we need to be patient and avoid playing on or below steep terrain until the deep weak layers have more time to heal.

 

Seattle Ridge. This weak snow at the ground has now been buried by an additional 4′ of snow. This is a scary setup. 11.26.2020

Weather
Sun, November 29th, 2020

Yesterday: We received another 4-8” snow yesterday morning before the storm tapered off. Easterly winds picked up on the tail end of the storm, with sustained speeds of 40-50 mph and gusts to 80 mph. Temperatures were just above freezing at lower elevations and in the high twenties above 1000′, with lows in the high teens to low 20’s.

Today: We will see brief periods of snow throughout the day today, with the highest accumulations of 2-4″ on the north end of Turnagain Pass. Light easterly winds this morning will increase to 15-20 mph this afternoon. Highs will be in the mid 20’s.

Tonight: We will get a trace of snow, with 5-10 mph winds out of the east and low temps in the teens. Our next storm system should move in tomorrow night.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 8 0.5 62
Summit Lake (1400′) 22 tr 0.1 23
Alyeska Mid (1700′) NA NA NA NA

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 ENE 17 80
Seattle Ridge (2400′) 24 NA NA NA
Observations
Recent Observations for Turnagain Pass
Date Region Location
01/23/21 Turnagain Observation: Seattle Ridge
01/23/21 Turnagain Avalanche: Tincan Trees
01/22/21 Turnagain Observation: JOHNSON PASS
01/20/21 Turnagain Observation: Sunburst
01/19/21 Turnagain Avalanche: Cornbiscuit
01/19/21 Turnagain Avalanche: Sunburst and Tincan
01/19/21 Turnagain Avalanche: Seattle Ridge
01/19/21 Turnagain Avalanche: Tincan 2900′ SW aspect below Hippy Bowl.
01/18/21 Turnagain Observation: Turnagain Pass Road Obs.
01/16/21 Turnagain Avalanche: Tincan Trees
Riding Areas
Updated Tue, January 12th, 2021

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
Open
No parking in turnaround at end of the road near the outhouse.
Placer River
Open
Early season conditions exist, including thin ice on rivers, swamps and lakes. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Skookum Drainage
Open
Early season conditions exist, including thin ice on rivers, swamps and lakes. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Turnagain Pass
Open
Twentymile
Closed
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Primrose Trail
Open
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Summit Lake
Open

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.