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Fri, January 11th, 2019 - 7:00AM
Sat, January 12th, 2019 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

A generally  LOW  avalanche danger exists across all elevations bands for the Turnagain area. Low danger does not mean no danger.  Watch for wind affected snow where an isolated wind slab may release on a steep terrain feature. Glide cracks are creeping open and may avalanche without warning. Limiting/avoiding exposure under them is prudent. Give cornices a wide berth and watch your sluff.

SUMMIT LAKE / JOHNSON PASS / LYNX DRAINAGE:  Keep in mind buried weak layers exist in the middle and base of the snowpack. More potential for triggering a large slab avalanche exists in this zone. Choose terrain wisely and please read the Additional Concerns below.  

Special Announcements

Check out our calendar  for upcoming avalanche classes and events in January! Lots of opportunities with all the avalanche education providers in the area.

Fri, January 11th, 2019
Above 2,500'
1 - Low
Avalanche risk
1 - Low
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
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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.

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

Yesterday a group found ‘touchy wind slabs’ on a Southeast aspect of Seattle Ridge near Bertha Creek Campground. These hard slabs were 3-10” thick, and formed on top of loose faceted snow and surface hoar that hundreds of people have been skiing and riding on this week. Moderate Northwest winds have channeled through some terrain in our forecast zone, but not all. Many folks have continued to get into steep terrain without incident  where snow conditions remain generally stable. These reactive wind slabs are an example of unstable snow that can be found on some terrain features. Today will be the last sunny day before a big weather pattern shift. If you’re headed into the mountains identify wind-affected snow that looks smooth or pillowed. Hard supportable snow that sounds drum-like should be suspect and could allow a person onto it before a slab releases.

Practice safe travel habits, such as exposing one person at a time, watching your partners and grouping up in safe zones. These are key ways to minimize risk. Ease into steep terrain and factor in the consequences should you encounter a wind slab or one of the following:

  • Glide avalanche:  
    • Identify glide cracks and avoid spending any time under these features. Glide cracks are opening and have avalanched within the last week. Glides are completely unpredictable and not human triggered.
  • Persistent Slab avalanche: 
    • Triggering a slab deeper in the snowpack is unlikely, but not out of the question in complex terrain. A layer of buried surface hoar 1-3′ below the surface has been mostly unreactive or hasn’t been found in most test pits over the last week.
  • Cornice fall: 
    • Remember cornices often break farther back from ridges than expected. Give them a wide berth.
  • Loose Snow Sluffs:
    • Be aware of fast moving surface snow in steep terrain. Sluffs are slowly becoming larger as the cold weather weakens surface layers.

Looking South from Center Ridge yesterday. The terrain in the Sun, SE shoulder of Seattle Ridge remains suspect for reactive wind slabs. This is a common area affected by NW wind direction. 


Loose snow surface conditions and glide cracks on a SW aspect of Sunburst yesterday. Close up of surface hoar, a possible weak layer lurking under isolated wind slabs. Photos by Kyle Van Peursem

Additional Concern
  • 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

South of Turnagain – Lynx Creek/Johnson Pass/Summit Lake zone:  A poor snowpack structure exists in these areas. The buried surface hoar that we have been talking about over the past week has been found as well as facet/crust combinations in the bottom of the snowpack. The last avalanche cycle was during the New Year’s storm, and overloaded a variety of these weak layers in Summit Lake. Cold weather this weak has been helping stability around the area, but localized NW winds this week may have added additional stress. Steep slopes without old debris below remain suspect. If you’re headed this way, the snowpack becomes more complex – evaluate terrain exposure and the snowpack as you travel.

Fri, January 11th, 2019

Yesterday: Skies were clear and sunny and temperatures in the alpine dropped to around zero F. Temperatures in the mid elevations remained in the single digits, but some areas like Portage Valley were closer to -10F. Ridgetop winds were light from the Northwest, 5-15mph. No precipitation occurred.

Today: Expect similar conditions, mostly sunny skies and sub zero F temperatures. Ridgetop winds are expected to remain light, but will shift from a SW direction to an Easterly direction in the evening. Cloud cover is also expected to move across our region this evening along with rising temperatures in anticipation of a pattern shift. Light snow showers are possible overnight.

Tomorrow: Low Pressure will be pushing the cold arctic air north as a series of storms track into our region. Temperatures will continue to rise through the weekend to above freezing temps in the lower elevations by Sunday. Easterly winds will build early Saturday morning and intensify by the evening. Expect precipitation to start out as snow, but rain is likely overnight in the lower elevations.

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 7   0   0   53  
Summit Lake (1400′) -4   0   0   22  
Alyeska Mid (1700′) 6   0   0   41  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 0   W   6   19  
Seattle Ridge (2400′) 7   *N/A   *N/A     *N/A    
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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.