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ARCHIVED - Forecasts expire after 24 hours.
Tue, April 25th, 2017 - 7:00AM
Wed, April 26th, 2017 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is expected to remain at CONSIDERABLE for today and through Wednesday.  Light rainfall up to 2,500′ along with warm temperatures will continue to produce wet avalanches on all slopes above 1,000′. Several shallow wet loose and wet slabs were seen yesterday and similar conditions are expected for today. Additionally, human triggered wet slab and wet loose avalanches will be likely on steep slopes that have a wet, saturated and unsupportable snowpack.  There is a MODERATE avalanche danger below 1,000′ in snow-free avalanche paths where debris can run from an avalanche occurring above.  

Hiking on summer trails during the springtime warm-up (including the Byron Glacier trail, Crow Pass, etc).    Extra caution is advised for trails that cross under avalanche paths. Avalanches possible at the higher elevations could send debris over snow-free hiking trails.  

A CONSIDERABLE avalanche danger is expected for Wednesday. Temperatures are expected to increase Wednesday which will enhance the possibility for natural wet avalanches on all aspects above 1,000′. Please see the discussion below for more details.

Special Announcements
  • This is the final week the CNFAIC will issue avalanche forecasts.  These will be today, Thursday and Saturday morning. We will be closing up shop on April 30th.
  • Observations: We will continue to monitor and post observations all spring and summer – so please keep us, and the community, posted on any snow/avalanche information you may come across on your upcoming adventures!!
  • We have stopped issuing our Saturday Summit Summary for the 2016/17 season. Click  HERE  for our Springtime Avalanche tips.
Tue, April 25th, 2017
Above 2,500'
3 - Considerable
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
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Just as the unwritten rule states, after three consecutive warm nights in the mountains with no re-freeze at the ridgetop elevations, wet avalanches start running. Yesterday was the first of these days and in fact, several wet loose and shallow wet slab avalanches ran naturally. These occurred on all aspects, with North and West aspects seeing the majority of the activity at Turnagain PassWhat about today and tomorrow? Although stormy weather with slightly cooler temperatures have moved in, we can expect similar wet avalanche activity. 

This morning wet snow is falling above 2,000-2,500′ and rain below this. Only a few inches of snow is expected and this should stick well to the wet and warm old surface. That said, winds are blowing in the 20’s mph along ridgetops, which is enough to move the new snow into shallow wind slabs at the higher elevations where the snow is drier, such as 4,000′. Most of our terrain however is lower and wet snow issues will remain the main concern. 

As the snowpack continues to loose its strength with the springtime melt-down, several different wet avalanche concerns are present. Things to keep in mind if you are headed out: 

  1. Is the snowpack frozen or wet and soggy? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
  2. Are you punching through a shallow crust into wet soggy snow? A shallow re-freeze is still weak and could avalanche.
  3. Are you seeing recent avalanches?
  4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
  5. Buried weak layers in the pack can make a small avalanche or sluff larger by propagating across the slope and/or stepping down.
  6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

Wet loose and wet slab avalanches on the West face of Magnum, occurring Monday, April 24th

Wet loose avalanches in the North chutes of Tincan

Wet loose avalanches in the North chutes of Cornbiscuit



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

Similar to the wet issues above, glide avalanches are also occurring with the springtime melt-down. Glide cracks are opening up and releasing on many slopes in the region – steer clear of any slopes harboring glide cracks. Check out the photo below from the motorized up-track. This slope is notorious for producing glide avalanches. Additional glide avalanche activity is expected today and through the week.

Photo below: A comparison of the glide avalanches on Seattle Ridge during the past couple days (top photo from Saturday, April 22nd, bottom photo from yesterday, April 24th). The glide that released yesterday sent debris over a portion of the Turnagain Pass motorized up-track. 




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

Upper elevation Northerly aspects have now warmed to the degree the surface layer is wet and saturated. How deep the wet snow exists varies, but what this warming does is weaken the snowpack and increases the stress on underlying weak layers. There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6′ deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. As the upper elevation North, West and Easterly snowpack warms up, these weak layers could re-activate and large natural slabs are possible along with the increased chance for a person to trigger a slab. 

Tue, April 25th, 2017

Cloudy skies and light rainfall were over the region yesterday as a moist Southerly flow continued across Southcentral, AK. Around .1″ of rain was seen in general with higher amounts in the Portage area. Over the past 24-hours ridgetop winds have averaged 20-25mph from a generally East direction at Turnagain Pass. Temperatures climbed to the low 30’sF along ridgetops and near 50F at sea level before cooling off last night into the upper 20’s along ridgetops and near 40F at sea level.

Today, Tuesday, another wave of moisture is headed our way. We should see .1-.2″ of rain below 2,500′ and 1-3″ of wet snow above this. Ridgetop winds are expected to be in the 15-25mph range. Temperatures will hover in the upper 40’sF at sea level and the mid 30’sF along ridgelines.

For tomorrow, Wednesday, rainfall along with ridgetop winds should tapper off. Temperatures on the other hand are expected to increase a few degrees with cloud cover remaining over the area. There could be some patches of clearing sky on Wednesday before another wave of moisture moves in.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 40   Rain   0.1   56  
Summit Lake (1400′) 40   0   0   16  
Alyeska Mid (1700′) 38   1   0.09   51  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29   NE   18   45  
Seattle Ridge (2400′) No Data   SE   15   34  
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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.