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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 12th, 2018 - 7:00AM
Expires
Sat, January 13th, 2018 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is HIGH at all elevations above 1000′ due to a storm bringing new snow, strong winds and warm temperatures to our region. Natural and human triggered storm slabs 1-3′ deep will be likely today in avalanche terrain and may step down to an older more dangerous week layer. Travel is not recommended on slopes steeper than 30 degrees and in all runout zones.  

The avalanche danger is CONSIDERABLE below 1000′ where natural avalanches from above are possible in steep channeled terrain.  

**Portage and Whittier, outside of our advisory zone, are expected to receive double the amount of precipitation as Turnagain Pass. Avalanche activity in these zones may run to valley bottoms.    

Special Announcements

Our advisory page has changed!  Information on the changes can be found  HERE.  

*Tomorrow, January 13th, there is a  FREE avalanche rescue clinic at Hatcher Pass. Practice with your gear on your way to the backcountry – clinic runs from 11am – 1:30pm.  

Fri, January 12th, 2018
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.
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

Overnight a foot of new snow has fallen in the upper elevations of Turnagain Pass and Girdwood and another 10-20” of snow is expected today. This new snow combined with strong Easterly winds and warming temperatures will be forming unstable storm slabs and adding stress to preexisting weak layers within the snowpack. This new snow has fallen on surface hoar and near-surface facets and slabs are expected to be sensitive and easy to trigger. Below 2000’ these weak layers are sitting on a slick crust and could catch you by surprise in more protected areas and on small terrain features. Stormy weather today will be increasing the avalanche hazard, as slabs grown in size, and natural avalanches will become more likely as the day moves on.  Should you venture out today, stick it low angle slopes, less than 30 degrees and avoid being under the runout of larger slopes above. Shooting cracks and collapsing sounds “whumpfing” are expected and will be obvious signs the snow is unstable. This is a good day to ride in the flats and keep your terrain choices mellow. Don’t forget even small terrain feature can have high consequences. 

Shooting cracks observed yesterday during the beginning of the storm. 

 

 

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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

Rapid loading due to new snow and winds will be adding stress to existing week layers within the snowpack. We have been tracking a layer of buried surface hoar from the New Year’s holiday, which still is showing propagation potential in test pits above 2500’. Triggering a storm slab could step down to this layer producing a large to very large avalanche depending on the size of the slope. In addition, a Deep Persistent Slab problem remains a concern in the upper elevations above 3000’, and serves as one of the many reason to not go into the alpine today. In fact – today is a great day to stay on low angle terrain and practice your rescue skills. 

 

Several week layers exist within the snowpack, additional reasons to avoid travel in avalanche terrain. 

 

Weather
Fri, January 12th, 2018

Snow started falling yesterday morning and continued overnight with 0.7 € of Snow Water  Equivalent  (SWE) at Center Ridge Snotel and 0.62 € SWE at Alyeska Midway station. Unfortunately the Snotel site was not recording height of snow this morning, but Alyeska midway station recored 11 € since yesterday.   Easterly ridgetop winds averaged in the 30’s mph with gusts reaching the 60’s mph on Sunburst. Gusty valley winds were also observed along the road corridor at Turnagain Pass. Temps gradually increased overnight with sea level temps reaching the mid 36F’s this morning and transitioning to rain just above sea level.  

Today 0.8 € SWE, another 10-12 € of snow is expected during the day and double this amount midnight. Winds will continue to blow from East, 20-40mph and temperatures are expected to continue to warm with high’s in the upper 30F’s at sea level. Rain/snow line is likely to bump up to 500′ by this afternoon.  

Tomorrow more rain and snow and Easterly winds are on tap as another front moves into our region. Temperatures are expected to increase into the 40Fs at sea level and rain/snow line will continue to move up in elevation, possibly as high as 1500′ by Sunday.

*New snow was estimated at Center Ridge Snotel based on similar SWE (Water inches) at Alyeska midway station.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   *12   0.7   *54  
Summit Lake (1400′) 29   0   0   15  
Alyeska Mid (1700′) 28   11   0.62   45  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19   ENE   35   68  
Seattle Ridge (2400′) 23   SE   20   41  
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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.
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