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Turnagain Pass Avalanche Forecast RSS

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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.

Special Announcements

From Alaska DOT & PF: There will be intermittent traffic delays Today February 21, 2020 on the Seward Highway for avalanche hazard reduction work. South of Moose Pass and North of Primrose along the Seward Highway between mile post 20 and 23. Motorists should expect delays of up to 45 minutes between 12:00 PM-3:00 PM. Updates will be posted on the 511 system.  http://511.alaska.gov/

REGION-WIDE Avalanche Hazard: Dangerous avalanche conditions extend north from our forecast area including Chugach State Park to Hatcher Pass.  Extra caution is advised.

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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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
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
02/20/20 Turnagain Avalanche: Turnagain Pass – (Sunburst, Magnum, Cornbiscuit)
02/20/20 Turnagain Avalanche: Turnagain Pass – Seattle Ridge, Pyramid, Eddies
02/20/20 Turnagain Avalanche: Seattle Ridge – Repeat Offender slide path
02/19/20 Turnagain Avalanche: Tincan
02/18/20 Turnagain Observation: Tin Can
02/17/20 Turnagain Observation: Cornbiscuit
02/16/20 Turnagain Avalanche: Eddies, Sunburst, Cornbiscuit
02/16/20 Turnagain Observation: Sunburst
02/16/20 Turnagain Observation: Pete’s North
02/16/20 Turnagain Avalanche: Sunburst
Riding Areas
Updated Thu, January 30th, 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
Open
Placer River
Open
Skookum Drainage
Open
Turnagain Pass
Open
Twentymile
Open
Open to over snow travel on 1/22.
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Open to over snow travel on 1/22. Please stay on trail to prevent resource damage
Primrose Trail
Open
Open to over snow travel on 1/22. Please stay on trail to prevent resource damage.
Resurrection Pass Trail
Open
Open for the 2019/2020 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Open as of 1/30
Summit Lake
Open

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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.