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Sat, March 31st, 2018 - 7:00AM
Sun, April 1st, 2018 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger continues to be  MODERATE  above 1500′ in the periphery of the forecast zone, such as Girdwood Valley and South of Turnagain Pass. Triggering a hard slab avalanche 2-4 feet thick remains a possibility and may be triggered remotely.  A generally  LOW  danger exists in the core zone of Turnagain Pass where triggering this type of avalanche is trending toward unlikely.  Pay attention to afternoon warming and give cornices a wide berth.  

If daily warming and radiation break down a stout crust below 1000′ the danger could rise from LOW to MODERATE on Southerly aspects in the afternoon in this elevation band.  

If you are headed South of Turnagain Pass more snowpack info can be found in today’s  Summit snowpack and avalanche summary  

Special Announcements

SKOOKUM VALLEY closes to motorized use tomorrow, Sunday April 1st, due to National Forest Plan. Boundary extends East of the Railroad tracks from Luebner Lake (South) to private property boundary (North). The rest of the Placer River Valley remains open. Click HERE for a map and more details.

Sat, March 31st, 2018
Above 2,500'
2 - Moderate
Avalanche risk
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
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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.

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

It has been over two weeks since the last snowfall, 9 days since a strong wind event ended, and 8 days since the last human triggered avalanche. With little in the way of weather to contribute to avalanche danger the chances for triggering an avalanche are becoming unlikely. However if someone finds an unstable slope the size of the avalanche could be large and destructive. This scenario doesn’t fit neatly into the danger scale and we still recommend evaluating snow and terrain carefully and identifying features of concern.  Northern to Eastern aspects are the most suspect for harboring a generally thinner snowpack. This poor structure is the most pronounced in the periphery areas of Girdwood Valley and the South end of the Pass towards Johnson and Lynx Creek and Summit Lake. Terrain in the core Turnagain Pass zone is trending towards LOW danger, meaning triggering a slab avalanche is unlikely – but not out of the question. 

The slabs in questions are hard slabs 2-4′ thick. The weak layers in question were formed in January and are various layers of facets and buried surface hoar. Stability tests this week have been trending towards good stability in the heart of our forecast zone. The one exception being Girdwood where observers experienced a large collapse on Thursday near Goat Mountain. Without any notable weather changes to tip the balance we remain in a low probability, high consequence situation where multiple tracks could be present on a slope before someone finds a trigger point and the slope releases. These trigger points are often in thinner areas of the snowpack near rocks or in scoured areas along ridges. Evaluate the terrain for consequences before committing to a slope and practice safe travel habits to minimize exposure in avalanche terrain. 

If the sun shines in full force today be aware of warming later in the day on Southerly slopes. Especially steep southerly slopes with rocks that will help heat up the snow around them, aiding in possible wet avalanche activity. As we gear up for a weekend of sunny skies, keep the afternoon warming on your radar! Yesterday several ice climbers reported a stout crust breaking down and becoming unsupportable by 4pm in the afternoon on Southern aspects just below Treeline near Hope Wye.

Deep Persistent Slab is challenging to fit into the danger scale when stability is increasing due to their potential size and already low probability of triggering. 


A natural on a NE aspect of Frenchy Mountain, near the Hope Wye, was noticed yesterday and its unknown how recently this occurred.  Although this is just outside of our core advisory zone, it is a good example of a thin NE aspect that may still harbor unstable snow on the Southern end of Turngain Pass. 


Yesterday several groups of students in an avalanche class found poor structure on Pete’s South, Magnum, and Eddies but did not get any notable failure in their stability tests. 

Additional Concern
  • Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices are large in many places. As we head into warmer, sunnier weather remember this can help de-stabilize them. As always, give cornices plenty of space and limit exposure underneath them.

Sat, March 31st, 2018

Yesterday skis were clear and sunny most of the day. Daytime high temperatures near sea level reached the upper 30F’s and overnight dropped to low 20F’s.   Ridgetop temperatures were much cooler remaining in the teens to low 20F’s. Westerly ridge top winds were 5-10mph.   No precipitation recorded.  

Today clear and sunny weather is on tap. Daytime temperatures may reach the upper 30F’s near sea level and low 30F’s near ridge tops. Overnight lows will be in the low 20F’s to teens near ridge tops. Northwest winds may range from 5-15mph. No precipitation is expected.  

Tomorrow looks similar and clear skies are expected through Monday. Daily warming could increase into mid-30’s tomorrow afternoon in the upper elevations. Nighttime low temps are expected to drop into the low 20F’s again. Northwest ridge top winds may pick up to Moderate on Monday into Tuesday.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  28 0   0   76  
Summit Lake (1400′) 24   0   0   31  
Alyeska Mid (1700′)  28 0   0   71  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16   W   5   15  
Seattle Ridge (2400′) 22   NW   4   20  
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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.