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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 8th, 2020 - 7:00AM
Expires
Sun, February 9th, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations today due to strong wind, a few inches of new snow and warming temperatures. Not only will fresh wind slab avalanches be likely for a person to trigger, but much larger and dangerous slab avalanches are lurking. These larger slabs are releasing in weak faceted snow 2-3′ below the surface. They could occur naturally or be triggered by a person. They may also be triggered remotely (from below or from a ridgeline). Cautious route-finding is necessary and conservative decision making is again advised for travel in the backcountry.

Below 1000′: Watch for wet loose avalanches in steep terrain along with larger avalanches above sending debris to valley bottoms in places like Byron Glacier trail.

*Roof Avalanches:  Warming temperatures are causing roofs to shed their snow. Pay attention to children, pets and where you park your car. Rain will also increase this hazard.

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Sat, February 8th, 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)
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

It was just after midnight last night when the easterly winds began to ramp up. As of this morning, they are blowing 35mph and gusting over 65mph along ridgetops. Although the bulk of the snowfall associated with this system is headed up cook inlet and toward Hatcher Pass, Girdwood and Turnagain Pass will hopefully squeak out 4-6″ of new snow today. That is on top of the 2-3″ that fell last night. With a lot more blow than snow, fresh wind slabs will be the new avalanche problem forming on top of the snowpack today. Under the snow surface however, we still have old weak snow that has been responsible for the many human triggered avalanches last week. More on that issue below.

Wind Slabs:  Watch for active wind loading and expect fresh wind slabs to be forming. The winds are likely getting into the mid elevations and could be loading slopes near the trees along with the usual places such as the lee of ridgelines and cross loading in steep gullies. Stiffer snow over softer snow and cracking in the snow around you are clues you’ve found a wind slab. Also, be mindful that these slabs could step down into deeper weak layers and create a larger avalanche.

Cornices:  Cornices should be growing with the wind and could break off easily. Even a small chunk of cornice falling could trigger an avalanche below.

Avalanche Problem 2
  • 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

As many of you know, there are multiple weak layers of facets and buried surface hoar lurking 2-3′ below the surface. These were formed during the cold January period and have created a ‘persistent slab‘ avalanche problem that is very slow to go away. Today’s weather will only add more stress to these layers. It is possible that slopes seeing additional weight from wind loading could overload the buried weak layers and a large slab release 2-3’ thick. It is also likely that a person could tip the balance and trigger one of these large slabs. Keep in mind, remote triggering has been a common theme and likely to remain so moving forward. This means triggering a large and dangerous avalanche from below a slope, above it or on the edges of a slope.

*That said, to avoid all these issues, sticking to lower angle terrain with nothing steeper above us will be key.

Additional Concern
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

At the lower elevations, rain and/or wet snow falling on colder snow is likely to cause some wet loose avalanches on steep terrain features.

This snowfall total graphic was provided by the NWS Anchorage Forecast office. 

Weather
Sat, February 8th, 2020

Yesterday:  Overcast skies and light snow showers (rain/snow mix at sea level) have been over the region. Just a few inches of snow has fallen with up to 6″ in favored areas in the Alpine that sit closer to the Portage Valley. Ridgetop winds averaged 10-15mph yesterday before increasing early this morning to 25-35mph with gusts hitting 70mph from the east. Temperatures have been in the mid 30’s°F at the lower elevations and the mid 20’s°F at the upper elevations.

Today:  The storm system over the region will continue to bring light snowfall above 800′ and a rain/snow mix below. An additional 4-6″ of snow is expected through the day. The easterly ridgetop winds are strong currently and expected to remain in the 25-35mph range with much stronger gusts. Temperatures also stay warm and may hit the mid 30’s°F at 1,000′ today.

Tomorrow:  Mostly cloudy skies, instability showers and decreasing winds are expected tomorrow as the system moves out. High pressure is forecast to build in for the beginning of the work week bring clear skies, cooler temperatures and possibly northerly winds.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 2 0.1 55
Summit Lake (1400′) 26 trace trace 20
Alyeska Mid (1700′) 29 4 0.3 56

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 NE 19 68
Seattle Ridge (2400′) 25 SE 13 28
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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

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Closed as of May 1. Thanks for a fun, safe season!
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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.