Share your feedback! Share your feedback!

How’s our new website?
How can we better serve you?

Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, February 21st, 2020 - 7:00AM
Expires
Sat, February 22nd, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A CONSIDERABLE avalanche danger exists at all elevations region-wide, from Girdwood, though Turnagain Pass and the Kenai to Seward. Large and deadly slab avalanches will be likely to trigger on slopes 30 degrees or steeper. These slabs range from 3-6′ thick and are nothing to mess with. They could be triggered from the ridge above a slope or below a slope. Avoid runout zones as debris could run far into valleys. The snowpack needs time to adjust and patience is critical. It is another day to avoid avalanche terrain and very cautious route-finding is essential to do so if headed into the backcountry.

Thanks to our sponsors!
Fri, February 21st, 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

A widespread large natural avalanche cycle occurred over the past three days due to very wet and stormy weather. Clouds parted just enough yesterday afternoon for a quick look around at some of the carnage. Although we have a few photos below, avalanche activity on much of the terrain in the region is still unknown. If you are out and see crowns or signs of recent avalanches, please pass on your photos to us! We are mapping the extent of the cycle as best we can.

Large slab avalanche on the Repeat Offender slide path on SE facing Seattle Ridge. This slab extended well over 1,000′ to the left of the photo and was estimated at 3-5′ thick. 2.20.20. Photo: Travis Smith

 

Several slabs that released on Eddies west and SW face. Image from the RWIS webcams. 2.20.20

 

Very large slabs seen from the Tesoro station in Girdwood on the backside of Seattle Ridge. 2.20.20.

Avalanche Problem 1
  • 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

The mountains received a heavy blow from Monday night until yesterday morning. The stormy weather has moved out and a weak system is moving over us today, bringing a few inches of snow and light to moderate east winds. With the cloud cover and lower visibility, the significance of the natural avalanche cycle may not be well understood. As you can see from the photos above, the mountains are littered with large crowns, ranging from 3′ to over 10′ thick in the Portage Valley. Countless avalanches occurred and the snowpack needs time to adjust.

Storm totals from mid-elevation stations since Monday night, February 17th:

  • Alyeska Mid Station (1700′): 56″ of snow, 4.9″ SWE
  • Turnagain Pass, Center Ridge Snotel (1880′): 35″ of snow, 3.1″ SWE
  • Summit Lake Snotel (1400′): 10″ of snow, 1.0″ SWE

Large avalanches composed of the 3-5 feet of new snow (wind slabs, storm slabs, cornices and sluffs) are all likely to be triggered and dangerous enough on their own. These avalanches could also ‘step down’ into the older weak layers below, creating a much larger slide (more on that below). Not only are steep wind loaded slopes dangerous, but everything in between and down to the small slopes in the trees out of the winds.

What to keep in mind if you are interested in headed into the backcountry:

  1. Avoid slopes steeper than 30 degrees, it’s been less than a day since the storm ended.
  2. Slopes that have not avalanched are prime to do so. Any slope 30 degrees or steeper is likely to be triggered and could release into a much larger avalanche than expected.
  3. Even slopes that have slid have sections hanging in the balance that did not slide. If traveled on, these remaining areas could pull out and take one for an unpleasant ride.
  4. Slabs could be triggered remotely, from the bottom of a slope, the ridgeline or the side of a slope.
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

Under all the new snow sits weak faceted snow from January. These weak layers are anywhere from 3-6+ feet below the surface. Much of the artillery and naturally triggered avalanches appear to have either stepped down or released from the get-go in these deeper weak layers. This is something we will be tracking as we take stock of the aftermath of the cycle. How likely it is a person could trigger these deeper layers is a big question and due to the sheer size of the potential avalanche, is not something worth testing right now.

 

Check out this video of rapid snowfall followed by quick settlement at Turnagain Pass’s RWIS station during the past 24-hours.

Weather
Fri, February 21st, 2020

Yesterday:  Stormy weather in the morning gave way to clearing skies and calm weather in the afternoon and through the overnight hours. Until around noon, heavy snowfall and strong easterly wind impacted the region. From 6am yesterday morning, Turnagain and Girdwood picked up an additional 9-10″ of new snow at mid-elevations. Ridgetop winds gusted into the 70’s at Sunburst before quieting down to the 5mph range from the east. Temperatures have remained near 20°F in the higher terrain and near 30°F at sea level.

Today:  Cloudy skies and light snow showers are expected today as a trough of low pressure is swinging through from the west. Between 3-6″ of new snow is forecast with (.3-4″ water equivalent) by tomorrow morning. Ridgetop winds are light and variable this morning and should pick up this afternoon to 10-15mph from the east.

Tomorrow:  Partly cloudy skies, light winds and a chance for a few flurries are on tap for Saturday. As the series of storms moves out of Southcentral and high pressure moves in, skies should begin to clear late Sunday and into Monday. At this time, ridgetop winds associated with the clearing skies look to remain light and northwesterly.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 9 0.7 83
Summit Lake (1400′) 25 0 0 29
Alyeska Mid (1700′) 30 10 0.9 94

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 E 15 71
Seattle Ridge (2400′) 25 *N/A *N/A *N/A

*Seattle Ridge 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

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.