Avalanche
This post first appeared on Powder Highway Backcountry, was written by Conor Hurley, and is reproduced with permission.
Avalanche Forecasting 101
Avalanche forecasting is a fundamental part of backcountry skiing and splitboarding. It is a skill every backcountry enthusiast should strive to develop. Avalanche forecasting involves understanding how weather, the snowpack, and terrain interact. Then, you add the human element to it. It’s really that simple.
Of course, the avalanche phenomenon is not that simple to forecast due to the spatial variability of the distribution of weak layers, the variability of the terrain on which the snowpack lies, and how local weather differs from valley to valley in the mountains. This article outlines the key components of avalanche forecasting and how to incorporate them into a daily operational plan. Of course, this avalanche forecast framework doesn’t replace the appropriate skills and knowledge required to travel in avalanche terrain. Read your public avalanche bulletins, get educated, and make conservative decisions.
The Human Element
Avalanche forecasting is further complicated by the human element at risk. We wouldn’t care about avalanches if we didn’t interact with them, but we do; thus, our daily avalanche forecasts need to consider the human element. That is why the avalanche danger scale discusses the likelihood of human-triggered avalanches.
The Building Blocks of an Avalanche Forecast
Certainty and Confidence
The interface of natural avalanche activity and the human factor is where certainty and confidence come into play. When a human element is at risk, we need elevated levels of certainty and confidence in our avalanche forecast to choose to expose ourselves to avalanche terrain.
During periods of high avalanche hazard, we can also have high levels of certainty. For example, there could be an omega block ridge of high pressure that persists for a couple of weeks, where a widespread surface condition such as surface hoar at tree line and below and facets in the alpine develop. Then a huge storm comes in and deposits over a meter of snow in a short period of time with lots of wind. In that case, forecasters will have high certainty and confidence that stability will be poor and the avalanche hazard will be high. In this case, it is possible to have high certainty and confidence, but a conservative operational plan is still needed.
Certainty relates to the forecaster’s confidence level in understanding the relationship between weather, the snowpack, and terrain. For example, if you spent the entire winter skiing the same planar slope every day and you paid attention to the weather and snowpack, you would have a really good idea of what layers were present in the snowpack, how deep they were buried, and how the weather was affecting them. Your level of certainty and confidence in their behavior would be quite high. However, if that same slope had gullies, micro changes in aspect, variations in pitch, thin to thick snowpack areas, and there was a deep, persistent weak layer, your level of certainty would be greatly reduced.
Ultimately, the less confidence and certainty you have in your avalanche forecast, the greater the margin of error you need to give yourself in your daily operational plan. A case where you probably hear forecasters talk most about low confidence and certainty is a Deep Persistent Slab. Often, the probability of triggering a deep, persistent slab is low, but the consequence of triggering it is high. Therefore, caution and conservative decision-making must be employed.
Here’s an article that elaborates on this subject: https://avalanche.ca/blogs/dps-management-and-mindset
Mindset
So, how do we apply certainty and confidence to real-world decision-making? That is where the mindset component of the avalanche forecasting process comes into play. Professionals use the mindset component to help guide their daily operations.
It gives us a means of ground-truthing our behavior in avalanche terrain. For example, if I am guiding a group on a basecamp trip in a remote zone I haven’t been in all year, my operational mindset for the first day will be “Assessment.” I will try to gather as much data as possible about the snowpack as I travel through the terrain. With an “assessment mode” mindset, I will choose terrain that gives me more options and make conservative decisions. I will look to confirm or disprove theories I had about the snowpack before I arrived.
If I gather evidence demonstrating “very good” snowpack stability and low avalanche hazard, my mindset will shift to “Stepping Out” over the ensuing days. If I observe instability and elevated avalanche hazards, my mindset will shift to “Stepping Back.”
We can quickly reflect on our morning avalanche forecast during our daily operations and reference whether our decisions and actions fall within the respective mindset. If not, we need to ask ourselves why and what evidence we have gathered to support that change in operational mindset.
The Avalanche Triangle
Weather
Weather is one-third of the avalanche phenomenon. It forms various surface forms that create instability within the snowpack. It also brings wind, which shapes and redistributes the snowpack, forming wind or storm slabs, cornices, or slopes.
Snowpack and Layers of Concern
The second component of the avalanche phenomenon is the snowpack, which is shaped by time, temperature, wind, sky conditions, precipitation, and vapor transport. It evolves throughout the winter and experiences periods of stability and instability.
Identifying the principal layers of concern daily, their likelihood of being triggered, their sensitivity to natural and human triggers, and the magnitude of an avalanche produced by the respective layer is an integral component of building an avalanche forecast.
Terrain
Terrain is the final third of the avalanche phenomenon; avalanches don’t happen without it.
Generally, slopes over 30 degrees are required for avalanches to occur. Furthermore, terrain complicates avalanche forecasting, as it creates spatial variability in the distribution of weak layers. On a macro-scale, terrain affects weather, wind, and precipitation values through orographic lift, catabatic winds, slope aspect, etc.
Developing an Avalanche Forecasting Process
In the Canadian guiding industry, we call it a morning workflow. It’s a framework for building an avalanche forecast and operational plan for the day.
- Weather is a good starting point. Check real-time data loggers and weather plots relevant to your forecasting zone. Then, move on to weather forecasting models. You want to come away from this step with a good picture of the overnight changes to the snowpack and what the weather will be like for your operational day. Here are some links for these resources:
https://arctosguides.com/backcountry-lodge-trips/telemetry-and-weather-data-loggers/
https://www.meteoblue.com/en/weather/forecast/multimodel/rogers-pass_canada_6127147
https://plan.navcanada.ca/gfa/
- Local Avalanche Bulletins and Mountain Information Network reading them is next on the list. This will give you an idea of what others have observed locally and what your local avalanche center is listing for avalanche problems, as well as their avalanche forecast. https://avalanche.ca/map
- List out your snowpack concerns and types of avalanches that could affect you. Listing them in order of priority is a good way to structure your list. After you identify your avalanche problems, rate their likelihood of being triggered, their sensitivity to natural and human triggers, and the magnitude of an avalanche produced by the respective layer. Make sure to identify where in the terrain you think they exist, as well as aspects, elevation, and terrain features.
This link has a great tutorial for this: https://avalanche.state.co.us/forecasts/tutorial/avalanche-problems
The CAA Observation Guidelines and Recording Standards is a great reference: https://cdn.ymaws.com/www.avalancheassociation.ca/resource/resmgr/standards_docs/ogrs2024web.pdf
Sensitivity to triggers Reference sheet: http://infoexhelp.avalancheassociation.ca/wiki/Sensitivity_to_triggers_definition_table
Likelihood Scale: https://www.avalancheassociation.ca/blogpost/1815963/352224/The-Likelihood-Scale-in-Avalanche-Forecasting?tag=likelihood
- Hazard Rating
Assign a hazard rating based on the previous information. https://avalanche.ca/glossary/terms/avalanche-danger-scale
- Rate your Confidence/ Certainty
Is it Low, Moderate, or High?
- Mindset:
Based on your avalanche forecast, set a strategic mindset for the day. This link outlines the types of mindsets and is a good read: https://arc.lib.montana.edu/snow-science/objects/ISSW14_paper_O9.02.pdf.
- Run List or Operational Plan:
Put together a plan for the day based on your avalanche forecast and strategic mindset. Your plan should reflect your forecast. Give yourself a number of options that align with your forecast.
Conclusion
That is the basic framework of avalanche forecasting. Try it out and use your avalanche forecast with your local avalanche bulletin. After you go skiing touring, take some time to reflect on your forecast and see what worked and what didn’t. The drive home can be a great time to debrief with your ski partners and make a plan for the following day.
