Support the forecast! Support the forecast!

Give to Friends of the Chugach National Forest Avalanche Info Center.

Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, February 14th, 2018 - 7:00AM
Expires
Thu, February 15th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is MODERATE above 1,000′ on all aspects. Triggering a shallow wind slab avalanche will be possible on wind loaded slopes and cross loaded gullies. There is also the possibility for a person to trigger a larger slab that breaks in weak snow 1-2′ deep. The danger is LOW below 1,000′ where triggering an avalanche is unlikely.

Thanks to our sponsors!
Wed, February 14th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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

Yesterday’s sunny skies revealed what most of us powder lovers do not wish to see after a snowfall event…wind. Monday night and Tuesday morning North and West winds wreaked havoc on much of the terrain around Turnagain, Summit Lake, Portage and the Girdwood Valley. Wind scalloped many snow surfaces, scoured some ridgelines to the rocks and sastrugi was reported on Tincan. Along with the winds, no natural avalanche activity was seen in the Turnagain area, but the Summit Lake region saw several shallow natural wind slab avalanches along with one that appeared to step down into an older weak layer.

For today, our main avalanche concern centers around a person triggering a large persistent slab avalanche up to 2′ or more in depth. Below the storm snow and recent wind slabs (addressed below) sits the Jan 21 buried surface hoar we have been talking about for some time. This layer is roughly 1-2′ below the surface and with recent wind and snowfall adding stress to it, the possibility for a person to tip that balance and initiate a larger slab avalanche is possible. There is also the possibility that a small wind slab or cornice fall could trigger this layer. We are back in a regime where no signs of instability are likely to be present before one of these avalanches releases and snowpit tests become unreliable. Therefore, assessing your terrain and the potential outcome if an avalanche breaking deeper in the pack does occur is key. Are there terrain traps below you? Cliffs? Are your partners watching and rescue ready? As we head into another period of high pressure (after today) keep these things in mind.

Northerly winds creating plumes off of Tincan Proper yesterday morning. (Photos: Jessie Haffener)

Anti-tracks on Tincan 


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

Watch for wind slabs to be lurking intermixed with the variable surface conditions on the steeper slopes. These will likely be shallow, up to a foot thick, and stiff. They should be easy to identify with a rounded shape and hollow feeling. Watch for shooting cracks and places the wind crust becomes thicker. Cross loaded gullies could be a good place to find and trigger a wind slab as winds did blow at all elevations

Image below of a shallow wind slab on Tincan yesterday. Small terrain, small avalanche – Large terrain, small to large avalanche with higher consequences.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

Above 3,000′ in the Alpine zones, several old weak layers of facets and buried surface hoar sit near the ground and in the mid-pack. This structure is most pronounced in areas with a thin overall snow cover, such as the South end of Turnagain Pass and the Summit Lake area. Recent wind slab avalanches Monday on Fresno ridge (Summit Lake zone) look as if they ‘stepped’ down into older weak layers in the snowpack. This is noteworthy and a reminder not to forget there are lurking old layers that could ‘wake up’ if one hits just the wrong spot.

Pictured below are shallow wind slab avalanches on Southeasterly facing Fresno ridge that looked to have triggered a deeper weak layer and subsequent larger avalanche lower on slope in the trees. (Photo: Jessie Haffener)

Weather
Wed, February 14th, 2018

Sunny skies along with strong West the North ridgetop winds were over the region yesterday. Seattle Ridge weather station recorded averages at 50mph from the North with gusts to 68mph. Wind decreased significantly over the day and was light and variable overnight. No precipitation fell and temperatures were in the mid 20’s along ridgetops and near 30F at 1,000′.

Today, Wednesday, a weak front is moving in with associated cloudy/overcast skies. There is a chance for a few snow flurries, but only a trace of accumulation is expected. Ridgetop winds are expected to pick up slightly from the Southeast and blow in the 10-15mph range. Temperatures will be near 30F at 1,000′ and remain in the mid 20’sF along ridgetops.  

Sunny skies with generally light winds and cool temperatures are expected for Thursday and into the weekend. Northerly winds may pick up again on Saturday, stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   0   0   66  
Summit Lake (1400′) 22   0   0   25  
Alyeska Mid (1700′) 29   0   0   58  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   NW   8   36  
Seattle Ridge (2400′) 27   N    20 68  
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

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.