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Wed, February 21st, 2018 - 7:00AM
Thu, February 22nd, 2018 - 7:00AM
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is  MODERATE  above 1,000′ on all aspects. Human triggered slab avalanches 1-2′ thick remain possible.  Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche.  

The Summit Lake area saw more avalanche activity last week. Take a look at the Summit Summary  HERE.  


Wed, February 21st, 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. 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
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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

Triggering a slab avalanche 1-2+ feet thick continues to be our main concern. There has been mostly quiet weather and lack of people triggering avalanches over the past week. However, in observations across the region the January 21st layer of buried surface hoar and a variety of other layers of weak snow continue to show signs of reactivity. Notably at lower elevations there are facets over melt-freeze crust that are also still showing triggering potential. Persistent slabs are becoming more difficult to trigger with time, but a large and unmanageable avalanche is still possible. Weak layers in the snowpack below your feet or snowmachine should not be forgotten.  Red flags may not be present before a slope releases and it may not be the first person on the slope that triggers the avalanche. The most likely place to find this avalanche problem are slopes that have not seen significant traffic this season. 

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could ‘wake up’ if you find the wrong spot above 3,000′ in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 

Lower elevation snowpit on Eddies showing more than one weak layer of snow present in the snowpack. 


Additional Concern
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Wind Slabs:  Watch for old wind slabs that could pop out on steep slopes. These hard slabs often break when you are out onto them. Steep rocky terrain where the slab is not supported from below is the most suspect. 

Cornices:  Avoid traveling under cornices and give them a wide berth on ridges, as they can break back further than expected.

Sunshine:  It’s that time of year when we need to pay attention to the sun. On calm days the sun can heat up Southerly aspects enough to melt surface snow. This heating can also cause a slab sitting on a weak layer to become more reactive. Keep this in mind if the sun is shining and you are enjoying Southerly aspects later in the day.



Wed, February 21st, 2018

Yesterday was mostly sunny above the valley fog. Temperatures at upper elevations climbed into the low 30Fs and due to the inversion stayed in the 20Fs in the valley bottoms. Winds were westerly 5-15 mph with gusts into the 20s.  

Today will be mostly cloudy with temperatures in the high 20Fs to mid 30Fs. Winds will be light and easterly. There are snow showers in the forecast for this evening with 1-3″ of snow possible.  

Tomorrow snow is likely in the morning. Due to warmer air there may be some “mixed precipitation.” Temperatures will be in the mid 20Fs to low 30Fs. Winds will be easterly in the morning and shift to the west in the afternoon. There is clearing in the forecast for Friday and then another shot of moisture and precipitation on tap for the weekend. From the NWS this morning:  The progressive nature of the pattern will continue  through next week, with front and lows rolling into the region  every 1-2 days.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27    0  0  63
Summit Lake (1400′) 22     0    0  24
Alyeska Mid (1700′)  23      0  0  55

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  27  W 8    23
Seattle Ridge (2400′)  28  W 9     25  
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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.