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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 25th, 2017 - 7:00AM
Expires
Sun, March 26th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is MODERATE  on all aspects and elevations today. Triggering a slab avalanche 1-2′ thick or loose snow avalanche is possible on slopes 35 degrees and steeper. Sunny skies and warming afternoon temperatures could make Southerly slopes more avalanche prone later in the day. Watch for changing conditions. Avoid travel on or under cornices and give glide cracks a wide berth.

Sunny Saturday with soft snow = Good travel habits are important! Expose only one person at a time on a slope, watch your partners closely, have an escape route planned in case the snow moves and pay attention to other parties in the same terrain.  

Summit Lake:  Read the Saturday  Summit Lake Summary HERE.  

Special Announcements

The deadline is fast approaching! Consider showing your support for public avalanche centers when applying for your 2017 PFD!!  Friends of the Chugach National Forest Avalanche Center is an  official  Pick. Click. Give. organization!

 

Sat, March 25th, 2017
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
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

Yesterday was the first day since last weekend’s storm that avalanches were not reported. It has been five days since the storm ended and the weak surface snow (near surface facets and surface hoar) from the March high pressure/drought was buried. Slab depths vary across the advisory zone due to the range of storm totals from 6″ to 2+ feet. Most of the avalanches that have occured have been small human triggered pockets and not well connected; a testament to the relatively cold weather this week keeping the new snow loose and mostly unconsolidated. The slabs that have released have been in places where the slab is more cohesive, either due to wind effect or warmth/settlement. On Thursday one of the avalanches that was observed was thought to have been a natural that occured later in the day from warming and direct sunshine. 

For today, with similar weather to the past few days, we can expect similar avalanche conditions. Triggering a slab avalanche is still possible. Things to keep in mind are:

  1. Southerly facing slopes receiving direct sunshine are suspect later in the day (these zones also have an old sun crust acting as a bed surface).
  2. Obviously wind loaded/pillowed slopes. If you find an old wind slab, it is likely sitting on weak faceted snow and may be triggered on steeper slopes.
  3. Remember, below last weekend’s new snow sits old weak faceted snow – quick hand pits can help assess bonding with this old layer that is 1-2′ below the surface.

Snow pit on Tincan Common. APU Snow Science Class

 

Additional Concern
  • Dry Loose
    Dry Loose
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.
More info at Avalanche.org

LOOSE SNOW AVALANCHES (SLUFFS):  Human triggered dry loose snow avalanches continue to be easily triggered on steep slopes without a sun or wind crust on the surface. Watch your sluff if headed to these steep lines with loose surface snow, they could be larger and run further than expected. Pay attention to Southerly slopes as the afternoon temperatures become warmer. We could start seeing more wet loose avalanches from direct sunshine; cold temperatures have keep these to a minimum lately. Look for roller balls as an indication of surface snow warming. 

CORNICES:  There has been a couple of cornice breaks after the storm and cornices are always worth giving a wide berth. Direct sunshine and warming can help to loosen them. 

GLIDE CRACKS:  Glide cracks continue to slowly ooze open on Seattle Ridge, Tincan’s Library, Lynx creek and other zones. Keep an eye out for them and limit time spent underneath.

Sluffing on Magnum observed on Wednesday. 

Weather
Sat, March 25th, 2017

Yesterday was sunny and clear with temperatures in the 20Fs in the valleys and teens at ridgetops. Winds were light and variable. Temperatures dipped into the single digits overnight and skies were mostly clear.

Today the sunshine will continue with a similar temperature pattern and winds will remain light. Clouds are forecasted to roll in this evening and there is a chance of snow overnight.  

Tomorrow will be mostly cloudy with a chance of snow showers and slightly warmer temperatures. According to the National Weather Service “Real change continues to be advertised by all models  early into next week and the bottom line is  that the pattern is now on the verge of change and the days of  cold and endless sun are going on a brief hiatus.”  The track of the low moving into the Gulf is still uncertain. Stay tuned!

  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15   0    0 63  
Summit Lake (1400′) 13 0    0 29  
Alyeska Mid (1700′)  20 0    0 58

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 11   W   6   10  
Seattle Ridge (2400′)  12 variable   4    11
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.