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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, January 6th, 2019 - 7:00AM
Expires
Mon, January 7th, 2019 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains  MODERATE  above 1,000′. Finding and triggering a slab avalanche 2-3′ thick is becoming less likely but still possible; most suspect areas are higher elevations that have seen prior wind effect. Second, glide cracks (brown cracks in the snow) are opening and avalanching during this cold snap. This is the time to avoid being under cracks. And as always, give cornices a wide berth, some may be teetering on the edge of breaking.

SUMMIT LAKE / JOHNSON PASS / LYNX DRAINAGE:  South of Turnagain Pass, keep in mind multiple buried weak layers exist in the middle and base of the snowpack. More potential for triggering a large slab avalanches exists in this zone.  

Sun, January 6th, 2019
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    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 time passes and more information is gathered, we are finding that being able to trigger a slab avalanche breaking 2-3′ deep is becoming less and less likely. Although this is a good trend, we can’t write this avalanche problem off just yet. The mountains have a way of humbling us and therefore, it will be prudent to keep in mind a buried layer of surface hoar may sit 2-3′ below the surface. Higher elevation zones that saw prior wind effect are most concerning for finding one of these isolated pockets.

This can be a spooky situation. We can stick to lower angle slopes or if we’re bent on the steep terrain, consider the consequences if part or all of the slope does release. Is there a terrain trap under us? Watch our partners and expose one person at a time. Again, the one known avalanche in this layer was on Wednesday, Jan. 2nd on Seattle Ridge, which was the day after the end of the New Year’s storms. Otherwise, snowpack tests and pits have shown the layer to be either not present or generally unreactive. 

 

              

The CNFAIC crew out in the God’s County area on the northern end of Seattle Ridge assessing the spatial variability in the Christmas buried surface hoar. Two pits at 1,500′ showed reactivity and propagation propensity, but many others did not. 

South of Turnagain – Lynx Creek/Johnson Pass/Summit Lake zone:  A poor snowpack structure exists in these areas. The buried surface hoar mentioned above exists as well as facet/crust combinations in the bottom of the snowpack. The New Year’s storm overloaded a variety of these weak layers as can be seen in photos from the avalanche activity throughout Summit LakeIf you’re headed this way, the pack becomes more complex – evaluate terrain exposure and the snowpack as you travel. Remember ‘whumpfing’ and recent avalanches are obvious clues of instability.

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to 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

The brown cracks easy to see in the Turnagain area are glide cracks. Take a good look at the photos below. The whole snowpack is slowly sliding down the mountainsides and can release into an avalanche at anytime. This is a completely unpredictable situation and one where a human does not play a role. Glide cracks are releasing now. Please don’t be caught in the wrong place at the wrong time and limit/avoid exposure under any crack you see. The most recent glide avalanche we know of was on the south face of Eddies where the glide debris covered fresh ski tracks

Cracks we know about are in all the hot spots on Turnagain: Lipps, Tincan, Eddies, Lynx Creek, Johnson Pass, Sunburst, Corn Biscuit, Magnum, Seattle Ridge.

 

Glide avalanche on south face of Eddies – take a close look as the bed surface (ground) could be mistaken for rocks. The debris in this photo covered recent ski tracks – likely released sometime 1/4 or early on 1/5. Photo: Alan Abel.

 

Glide cracks and an older portion that released (avalanched) Dec. 27/28 – note the small crack opening up on the upper left of photo. These could avalanche at any moment. Photo: Trip Kinney.

 

 

Glide crack under Tincan’s Hippy Bowl. These are now opening up at lower elevations. Photo: Mark Turner. 

Weather
Sun, January 6th, 2019

Yesterday:   Mostly clear skies were over the region. Ridgetop winds were light from a generally west direction (5-10mph). Temperatures remain cold and inverted; minus single digits in the parking lots and the low teens F along ridgelines.

Today:    Mostly clear skies will be over the area again today. Ridgetop winds are expected to remain light, 5-10mph, from the NW. Temperatures stay cold (-10 to 0F) at the lower elevations and in valley bottoms as an inversion remains. Ridgeline temperatures are only slightly warmer at 5-10F… burrr…

Tomorrow:    Sunny skies and cold temps are on tap to remain into the week. There is a chance for some clouds and snow flurries on Tuesday. Ridgetop winds at this point look to remain light from a NW direction.  

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6   0   0   58  
Summit Lake (1400′) -6 0   0   19  
Alyeska Mid (1700′) 7   0   0   46  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 11   W   5   16  
Seattle Ridge (2400′) 12   *N/A   *N/A     *N/A    
Observations
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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.