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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 7th, 2016 - 7:00AM
Expires
Thu, December 8th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  on all slopes near and above treeline.  Triggering a slab avalanche 1-2+’ thick is still possible and the likelihood goes up as one travels to areas  that have had less traffic this season.  This is due to a buried layer of surface hoar that remains reactive. Additionally, triggering a wind slab avalanche is also possible today on steep slopes that have been loaded by winds over the past week.

Below 2000′ in the trees where the snow is loose and unconsolidated the avalanche danger remains  LOW.

If headed to Summit Lake check out the Summit Lake Summary  HERE  and a recent observation from Fresno Ridge on Sunday, Dec.4,  HERE.

***Out of area:  Click HERE to check out an observation about a human triggered avalanche in the Anchorage Front Range on Dec. 5.

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Wed, December 7th, 2016
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

The buried surface hoar remains a nagging concern in the snowpack. Don’t forget this layer is on all aspects and continues to show propagation potential in test pits above 2000’. The other important thing to note is the slab character is becoming denser with recent wind events, which means the slab could break above you once well onto the slope.  During the past two weeks, many popular slopes have avalanched (removing the weak layer), and been covered again by recent snow. This makes it really hard to know the full extent of which slopes still have this weak layer set-up, especially in places that haven’t seen much traffic. Most of this activity has been on the popular Southwest slopes of Sunburst and Tincan and little is known about places less traveled. Yesterday digging on a section of terrain that hasn’t slid on Sunburst but has seen some skier traffic showed the surface hoar was still easy to distinguish in the snowpack and still reactive. The presence of the surface hoar should be part of your slope choices today and be something you keep in mind when we get our next loading event.  Manage your terrain and use safe travel protocols. 

  • Expose one person at a time
  • Group up in safe zones
  • Have an escape route planned
  • Watch your partners and where other groups are around you

Buried surface hoar in a snow pit at 3200′ on Sunburst, December 6th.

 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

The winds yesterday calmed down by mid-day. Monday night into Tuesday morning they were strong enough to transport soft snow around, filling in tracks and depositing snow on the leeward side of terrain features. Today two types of wind slab are still possible and warrant caution if venturing into steep wind loaded terrain. Softer more tender pockets of wind slab may break from your skis/board while traveling. These may still be large enough to knock you off your feet or surprise you in the wrong place. In addition stiff old wind slabs from last weeks wind event may pop once you are farther out onto the slab and can be tricky because of the supportable character. Be wary of hard over soft snow, hollow sounds and steep slopes with obvious deposition in the start zone. These wind slabs have the potential to be deeper and harder to manage. 

 Cracking along ridgeline on Sunburst yesterday

Sunburst with wind effect and old tracks 

 

Weather
Wed, December 7th, 2016

Yesterday was partly to mostly cloudy with no precipitation. Temperatures were in the high teens to low 20s. Winds were mostly light but there were some gusts into the high 20s early in the day. Last night temperatures stayed in the 20s and winds were light.

Today will be mostly cloudy with a chance of snow showers throughout the day and temperatures in the 20Fs. Winds will be light and easterly. Tonight will be similar with slightly cooler temperatures.  

Tomorrow the chance for snow showers and clouds decreases in the afternoon and the sun might shine for a bit. There is a chance of snow showers again on Friday and then clear skies and colder temperatures return for the weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  22 0    0 20  
Summit Lake (1400′)  19 0  0    4
Alyeska Mid (1700′)  22  0  0  10

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  18  NE 7   27  
Seattle Ridge (2400′)  20  ESE  5 18
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Riding Areas
Updated Wed, December 11th, 2019

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
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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