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Thu, February 4th, 2016 - 7:00AM
Fri, February 5th, 2016 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

Today the avalanche danger is HIGH in the Alpine (above 2500′) where natural avalanche activity is likely due to high winds and heavy precipitation.  A CONSIDERABLE danger exists at Treeline where natural glides avalanche and wind slabs +3′ thick are possible and could easily entrain wet snow below 1500′. Below treeline (1000′) a  MODERATE danger exists where an avalanche in steep channeled terrain could run into this elevation band.

South of Turnagian Pass, including Johnson Pass and Lynx Creek, a variety of weak layers persist within the snowpack. Today strong winds and precipitation will be adding stress to the snowpack and warrants extra caution in these areas. Click HERE for details about a large avalanche triggered in Groundhog Creek on Saturday in Lynx Creek area and for recent observations from Summit Lake click  HERE.  

Thu, February 4th, 2016
Above 2,500'
4 - High
Avalanche risk
3 - Considerable
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. Dangerous avalanche conditions. 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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Today is day two of a warm and wet storm that has dumped 1.5” of water (15-20” of new snow) in the upper elevations of Turnagain Pass. Rain was observed to 1000’ yesterday, but with rising temperatures rain will easily reach 1500’ today and maybe higher. Strong Easterly winds and another 12” of new snow (.9” of water) is expected today and will be adding stress to a variety of avalanche problems.   

Wind SlabsStormy conditions continue to make wind slabs our primary concern for the upper elevations. Triggering a wind slab +3’ thick is likely on wind loaded and cross loaded features. Below 3000’ these wind slabs are sitting on an old snow/crust combo and may propagate further than expected. Until more information is known about how this new snow is bonding to this interface give large open slopes like Magnum’s West face and the East Face of Seattle Ridge extra space today. 

Wet Snow: Wet snow is sitting on a slick crust in the mid elevation band. Rain to 1500’ will be lubricating this poor interface making wet avalanches possible in the mid elevation band. This hazard will be especially dangerous under big open slopes and in terrain traps like gullies or abrupt transitions where an avalanche from above could have high consequences. Keep slope angles under 35° and pay close attention to your runout zones. Natural activity is possible in steep channeled terrain and will likely entrain wet snow.

Cornices: Cornices will be unstable today and may release naturally. These features have been tender over the last week and now have the added stress of high winds and new snow. These backcountry bombs can easily trigger a a wind slab below and should be avoided.     


Below 3000′ a stout crust + old snow combo is sitting under under 2′ of storm snow. Click HERE for an observation from yesterday. 


Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
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.
More info at Avalanche.org

Warm temps, rain and wet snow continue to add weight and stress to glide cracks throughout Turnagain Pass. These unpredictable hazards are widespread in steep terrain between 1000’ to 2500’ and can release without warning. Today’s limited visibility will make it challenging to identify existing glides, and is an added reason to avoid being on or under steep terrain. 

Thu, February 4th, 2016

Since yesterday 1.2 € of water has been recorded; 14 € of new snow at the Center Ridge weather station. Northeast ridgetop winds have averaged in the 30’s with gusts in the 50’s.   Temperatures have been on the rise pushing rain as high as 1500′ early this morning.  Yesterday rain/snow line hovered around ~1000′ most of the day.

Today another 0.9 € of water is expected to fall, another 12 € in the alpine. Temperatures will remain warm with rain below 1500′.   Easterly ridgetop winds will remain moderate to strong throughout the afternoon.

Tonight temps look to be cooling slightly bringing rain/snow line back down to ~1000′. Easterly winds and precipitation will be decreasing this evening, but scattered showers are expected into tomorrow.  


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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   14    1.2 106  
Summit Lake (1400′) 33   1   .1   29  
Alyeska Mid (1700′) 33   6   1.06   75  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24   ENE   31    64
Seattle Ridge (2400′) 26   ~   ~   ~  
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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.