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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
Sun, January 28th, 2018 - 7:00AM
Expires
Mon, January 29th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

There is a  MODERATE avalanche danger at all elevations for wind slab and soft storm slab avalanches between 1-2′ thick. Thursday’s new snow is sitting on buried surface hoar and in areas the new snow is cohesive and stiffer (due to wind or settlement) triggering slabs will again be possible. Additionally, loose snow avalanches (sluffs) will be likely on steep slopes.   At high elevations, above 3,000′, there is still a chance someone could trigger a deep persistent slab avalanche.

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Sun, January 28th, 2018
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
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

A glorious sunny Saturday coupled with 20″ of new low-density snow two days prior and it was no surprise many folks were out enjoying themselves in the mountains yesterday. With many people on the slopes it is not big surprise many there were 8 reported avalanches at Turnagain Pass and one in the Girdwood Valley. As far as we know, no one was caught in any of these and many were remotely triggered. They ranged in size from very small to just large enough to bury a person and did not propagate very wide. They were all soft slabs 1-2.5′ thick, less than 100′ wide and composed of Thursday’s new snow. Please see the list of observations sent into us HERE as well as highlighted photos below – a huge thanks to all the folks taking the time to send us their photos and reports! 

The new snow is sitting on a layer of buried surface hoar that is inhibiting bonding to the old snow surface. This is creating a new persistent slab avalanche problem for our mountains that could linger for some time. The reason these slabs have not been propagating into larger avalanches is the slab is still very soft and generally non-cohesive. The areas the slab is cohesive is where triggering is possible, such as where winds have loaded/stiffened the snow, where the slab has settled and become cohesive on it’s own and it’s that time of year where the sun can create a slab by warming steep South aspects. Hence, if you are headed out today, and this week, keep these points in mind:

– Are the winds picking up enough to transport snow? This will be a big question moving forward for slab development!
– Quick hand pits are great ways to assess changes in the new snow character
– Watch for cracking and whumpfing – this was prevalent yesterday
– These avalanches may seem small now, but could start to propagate wider with passing time and/or fresh wind loading 

*Remember your safe travel protocol – expose one person at time, watch your partners, have escape routes planned

 
Fourth skier on slope triggered this slab avalanche on Max’s Mountain  pictured below, SW face at 3,000′. 

  

Two skier remote triggerd slabs on the upper SW face of Eddies Ridge  (Photo: Joe Engel)

 

 Snowmachine triggered wind slabs in Main Bowl (1st Bowl) of Seattle Ck drainage near the Widowmaker slide path (Photo: Bryan Pfaender)

 

Skier triggered slab with a ski cut on Tincan Proper, 1-2.5′ thick and 30′ wide (Photo: Meg Smith)

 

Small wind slab human triggered in Hippy Bowl on Tincan Ridge, westerly facing rollover (Photo: Heather Thamm)

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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

Loose snow avalanches ‘sluffing’ is possible on steep terrain features protected from wind. Small slabs may entrain loose snow below and could run faster and farther than expected. 

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

Triggering a deep slab is becoming difficult, but is still possible above 3000′ where a hard slab is sitting on a variety of weak layers in the mid pack and near the ground. The most likely trigger spots are in thin areas in the snow cover, often near rocks, or where the slope rolls over. The Southern end of Turnagain Pass to Johnson Pass is more suspect due to a thinner snowpack. Remember, this is a ‘low probability, high consequence’ situation. 

*** There is very little info in the Johnson Pass and Lynx Creek zone. If you’re headed to either of these areas and you observe any signs of instability: recent avalanches, shooting cracks, or whumpfing please send us an observations HERE

Weather
Sun, January 28th, 2018

Sunny skies and light variable winds were over the area yesterday. Temperatures were in the mid 20’s at all elevations. A thick valley fog below 1,500′ developed late in the day. Overnight skies have remained mostly clear above the valley fog.

For today, Sunday, sunny skies are expected again with winds shifting Northerly and slightly increasing to 5-10 and possibly 15mph in places. These winds will bring in a cooler air mass so expect temperatures to be trending to the chilly side, 5-10F along ridgetops. Overnight tonight, the wind could increase up to 20-25mph from the North.

This coming week, clear skies and cool temperatures are on tap. The winds will be the weather parameter to keep an eye on and we’ll be watching this. Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0   0   70  
Summit Lake (1400′) 8   0   0   20  
Alyeska Mid (1700′) 18   0   0   54  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17   NE   3   7  
Seattle Ridge (2400′) 20   SE   4   10  
Observations
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Riding Areas
Updated Mon, October 26th, 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
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Closed
Seward District
Carter Lake
Closed
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Closed
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Closed
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Closed
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Closed
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Closed
Summit Lake
Closed

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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.