Technical information, news, research, and opinion on avalanches, snow safety, and winter backcountry travel.

Monday, November 23, 2009

Precision: Forecasting For Large, Medium, And Small Areas

Wish I knew what you were looking for, might have known what you would find—The Church

NOTE: Backcountry avalanche forecasting is composed of four interconnected elements: goal, people, awareness, and uncertainty. The size of the forecast area determines the precision of the forecast. It is more difficult to develop a forecast for a small area but the precision of the forecast is usually much higher than forecasts for large areas. Forecast precision is linked to awareness and uncertainty—maintaining awareness and managing uncertainty are central tools for helping people successfully align their beliefs about instability with reality ( which is the goal of backcountry avalanche forecasting ).

Introduction
Backcountry avalanche forecasting is concerned with the specific slopes where high-stakes decisions require more precise information than in available in the avalanche bulletin. Forecast precision is important because of its relationship to awareness and uncertainty.

For most people, the bulletin is available at the scale of an entire mountain range, and does not contain information about specific valleys or slopes. Therefore, information about specific valleys and slopes must be obtained from direct observations made in the field. Understanding how to prioritise your observations based on the size of the forecast area can greatly increase your backcountry avalanche forecasting skill. At the scale of an individual slope,variables such as slope angle, slope shape, and the snowpack on the slope ( and your desire to ski the slope ) are the primary concerns.

You must acquire this information in the field because the chaotic interaction between weather and rough mountain terrain causes complex changes in the existing snowpack and complex deposition patterns for new snow. Managing the resulting uncertainty, while maintaining an accurate sense of awareness about instability for a specific place and time, is the heart of backcountry avalanche forecasting.

Information Types And Size Of Forecast Area
Avalanche forecasting uses three types of observations: weather, snowpack, and terrain. The size of the forecast area determines how observations are prioritised. For regional and local forecasting, which consider large geographic areas, weather observations are the primary source of information, followed by snowpack observations, and finally terrain observations.

Backcountry avalanche forecasting is concerned with specific valleys or slopes. Here, terrain observations are the primary source of information, followed by snowpack observations, and finally, weather observations. To develop an accurate backcountry avalanche forecast for a single valley or slope, you need information relevant to the valley or the slope on which you plan to travel.

Table 1.1. Different scales of terrain with observations used in forecasting. For regional and local forecasts, a few very general terrain observations are used. This includes aspect and elevation band. For valley and slope forecasts, very specific terrain observations are used, including aspect, elevation band, shape, angle, and slope configuration. The priority of observations is reversed as the size of the forecast area decreases.
Forecast AreaRangeSizeObservation Priority
Regional1000 square kilometresLargeWeather, snowpack, terrain.
Local100 square kilometresMediumWeather, snowpack, terrain.
Valley10 square kilometresSmallTerrain, snowpack, weather.
Slope2-3 square kilometresTinyTerrain, snowpack, weather.

NOTE: Any observation that reveals direct information about snowpack instability, such as whumphing or cracking at the snow surface, automatically receives priority over any other observations. Revise your forecast immediately if you observe any absolute indicators of instability, or if you obtain such information from snowpack tests.

Scenario: Backcountry Avalanche Forecasting In The Cascades
A strong winter storm forms as a large mass of warm, moist air is forced over the Cascade Mountains. During the storm, office-based avalanche forecasters use meteorological data, along with knowledge of how air masses interact with mountain topography, to produce a forecast that is relevant for the Cascade Mountains in general. The bulletin may include information such as aspects where you might expect to find wind-loaded snow deposits, or other information about the snowpack that has been directly observed in some places. However, much of the snowpack data in the bulletin is derived from the weather observations before and after the storm.

After the storm, the bulletin rates the current avalanche danger as high above 4000 feet and considerable below. Excited by the prospect of fresh tracks, you and your friends discuss a trip to Snoqualmie Pass to ski the Phantom Trees backcountry ski run. The bulletin contains a set of generalisations that are accurate for the Cascade Mountains but may not apply directly to Alpental Valley, and will not contain any specific information on conditions near the Phantom Trees backcountry ski run. What is the appropriate course of action?

Table 1.2. Different forecasting data order for areas of decreasing size in the Cascade Mountains. Backcountry avalanche forecasting is only concerned with producing forecasts for valleys and slopes, not entire mountain ranges. However, information from wide-area forecasts may be very useful during the backcountry avalanche forecasting process.
Forecast AreaSizeType Of InformationSource Of Information
The CascadesLargeWeather, snowpack, terrain.Public Avalanche Bulletin
Snoqualmie Pass RegionMediumWeather, snowpack, terrainPublic Avalanche Bulletin
Alpental ValleySmallTerrain, snowpack, weather.Local Observations
Phantom TreesTinyTerrain, snowpack, weather.Local Observations

Figure 1.1. Regional. The Cascade Mountains in Washington State. Sometimes wide-area weather patterns create snowpack features, such as crusts, facets, or surface hoar, found across large areas of the Cascades. So what's the catch? A lot of information is missing. Little is known about the specific properties of the snowpack over most of the Cascades, and little is known about the specific properties of weather interaction with terrain during a given snow storm. While you can develop an accurate forecast of instability in general by observing the weather, you simply cannot create a precise forecast of snowpack instability for all the valleys and backcountry ski runs in an entire mountain range from weather data alone. Precise information on the existing snowpack and current snow deposition patterns is extremely important for backcountry avalanche forecasting. The bulletin does not contain precise information about the structure of the existing snowpack on specific slopes, nor about new snow deposition patterns on specific slopes. Existing snow structure and new snow deposition patterns are critical variables for avalanche formation.

Figure 1.2. Local. The mountains around Snoqualmie Pass. Even though this area is much smaller than the entire Cascade Mountains, the public avalanche bulletin still does not apply to these groups of mountains except in a general sense. In this area, certain aspects and elevation bands may conform to the pattern of instability discussed in the bulletin. As you travel through the area, your observations will help you develop the first version of your backcountry avalanche forecast for the day. Do you notice large amounts of new snow? Recent avalanches of any type? Is it raining? Is it snowing? Is the ambient air temperature warm or cool? What is the expected air temperature trend? Weather observations are the priority since you are still dealing with avalanches on a large scale, but snowpack observations may be useful as well. Terrain observations are of little use since you won't be skiing in most of this terrain. ( Always follow the golden rule: pay very close attention to any observation, such as cracking in the snow surface or recent avalanches, that reveals direct information about snowpack instability. )

Figure 1.3. Valley. Alpental Valley. A backcountry avalanche forecast is usually prepared for a single valley, however some elements may be relevant to other valleys nearby. The public avalanche bulletin does not contain information about instability in this valley because office-based forecasters do not have precise information on the interaction between the weather and the terrain during the storm. Without precise information, office-based forecasters only have a rough, general idea about how the interactions between the weather and the terrain have affected the snowpack here. Combining information from the bulletin with your own observations helps refine your backcountry avalanche forecast even further: once inside the valley you can begin to examine the terrain and snowpack to see the actual conditions created by the recent weather.

Figure 1.4. Slope. Phantom Trees backcountry ski run. A slope forecast applies to a specific backcountry ski run inside the valley. The public avalanche bulletin does not contain information about instability for this ski run because office-based forecasters do not know exactly which slopes have been loaded by wind, nor do they know the exact locations of weaknesses and whether or not these weaknesses have the right structure, strength, and energy to release avalanches. Therefore, you must combine information from the public avalanche bulletin with your own observations to determine whether or not the snowpack is unstable inside this specific backcountry ski run. For example, a quick visual observation of the east bowl below the summit of Mt. Snoqualmie will provide information on whether or not the slope has been loaded ( is a cornice present? ) and whether or not there have been recent avalanches. This observation might tell you whether or not a lot of snow has been blown off the upper section of Phantom Trees, and gives you an idea about what you might find on the upper half of the mountain. Could there be a transition zone between the lower and upper section of the run where the snowpack is thin and weak? Several observations are noted in this image—it should be obvious that the bulletin does not contain information with this level of precision. By this point, you should have some degree of awareness about instability. However, it is still important to measure your residual uncertainty and make decisions accordingly.

With respect to signs of instability, absolutes are rare but they do exist.Any observation that reveals direct information about instability, such as whumphing or cracking at the snow surface, automatically receives priority over any other observations. Revise your backcountry avalanche forecast immediately if you observe any absolute indicators of instability, or if you obtain such information from snowpack tests.

Building A Nowcast From Your Observations
When it's time to ski up or down, you need a nowcast, which is your belief about patterns of instability on the slope you plan to ascend or descend right now. As you combine observations, whether from the bulletin or your own, consider whether or not the observations point toward instability. The distribution of weaknesses and the energy required to release avalanches changes with the passage of time and location, so you may need several nowcasts. For route selection purposes, it's useful to have a nowcast prior to uphill travel.

Figure 1.5. Distribution of weaknesses could range from very rare to very frequent. What do your observations suggest?

Figure 1.6. Triggering energy required to release avalanches could range from high triggering energy to low triggering energy. What do your observations suggests?

On the day of this ski tour, from observations collected prior to travel, it is reasonable to conclude:

  • Observations of the snow surface above treeline show significant snow drifts.
  • Relatively low energy triggering energy is required for avalanche formation in wind-deposited snow.
  • Stability is poor on steep slopes above tree line.
  • Because of the consistent temperatures during the storm, there are fewer weaknesses below treeline and slightly higher triggering energy is required for avalanche formation.
  • Stability is good on gentler slopes below tree line and fair on steeper slopes below treeline.
  • This only applies to areas where the snowpack is sheltered from the wind.
  • There is a transitional region where stability is fair to poor on moderate and steep slopes at treeline.
  • Ski quality is best below treeline.

The mix of stability ratings illustrates a key concept from this discussion: even at the smallest scale, one size rarely fits all.

Conclusion
Your perception of instability is likely to be at its worst when snow quality is very good but instability is relatively difficult to find or trigger. Understanding forecasting procedure for geographic areas of various sizes helps you maintain awareness and manage uncertainty by teaching you how to effectively prioritise your observations.

Research by Bruce Jamieson ( which may be relevant only in British Columbia ) shows that the public avalanche bulletin for the Columbia Mountains tends to predict higher regional danger levels than you might actually find in the field. However, local danger can be much higher on specific terrain features. This is why it is very important to combine information from the public avalanche bulletin, which covers a large geographic area and does not account for specific terrain features, with information that matches the much smaller size of a backcountry avalanche forecast region.

At which location is your perception of instability poorest? Below treeline or above treeline? Where are you most likely to make a mistake?

Perception Of Instability

She loves me, she loves me not—Unknown

NOTE: Backcountry avalanche forecasting is composed of four interconnected elements: goal, people, awareness, and uncertainty. The elements of instability are linked to awareness and uncertainty—maintaining awareness and managing uncertainty are central tools for helping people successfully accomplish the goal of backcountry avalanche forecasting.

Introduction
The winter snowpack is stable most of the time, which is a state of existence referred to as conditional instability. This means it is possible to trigger avalanches under certain conditions, provided you discover a weakness and deliver enough energy to release an avalanche.

Figure 1.1. State of instability. Instability fluctuates between very stable and very unstable.
During conditional instability, weaknesses are not widespread, and the triggering energy is relatively high. Perception of instability is much poorer when the snowpack is mostly stable because it is very easy to become blind to instability. On the other hand, perception of instability is usually very good when instability is widespread and triggering energy is very low. Important questions are as follows:
  • What do I believe about the number of weaknesses and their locations?
  • What do I believe about the triggering energy required to release avalanches on these weaknesses?
  • Am I dealing with long-term weaknesses, short-term weaknesses, or some of each?
  • Am I at risk of making errors when weaknesses are rare?
  • Am I at risk of making errors when it may take a lot of triggering energy to release an avalanche?
To answer these questions, you have to start at the beginning, way back when your perception began to take shape.

The Origins Of Perception
This is a complicated subject, but it is important to realise that all of us have our own personal beliefs about the world around us. These ideas can influence our beliefs about snowpack instability and its consequences. Prior to a tour, you might review the public avalanche bulletin, or you might ask questions about local conditions on an Internet message board. You could also acquire information during the nightly weather report. Your perception of instability begins to take shape from the moment your brain begins to process relevant information. Similarly, taking an avalanche class may have a lifelong affect on perception of instability as a someone transitions from lack of awareness to awareness.

Your perception of instability is shaped whether or not you choose to manage the process. It's pretty easy to unconsciously form a perception of instability by reading the bulletin, talking to friends, and then making observations during a backcountry outing. However, it's much more useful to be consciously aware of what and how certain factors shape your perception of instability, and how this could affect your choices.

It's critical to remember that information of any kind can be helpful or harmful with respect to your beliefs about the presence and distribution of instability in the snowpack. This includes snowpack tests and weather reports and the presence of other parties. It is up to you to manage how this information affects your perception. Ideally, this information should help align your beliefs about instability with reality.

If your perception of instability is faulty, you will unknowingly expose yourself to hazards against which you will have little protection. If you can't assess your perception of instability, or if you feel your perception may have been compromised, then it's time to make conservative decisions.

Assessing Your Beliefs
Ask yourself the following questions:
  • How does the public avalanche bulletin affect my beliefs about instability?
  • How does the information I obtain from the Internet affect my beliefs about instability?
  • How does seeing tracks on the snow, or seeing other groups of skiers, affect my beliefs about instability?
  • How do weather observations affect my beliefs about instability?
  • How do the results of instability tests affect my beliefs about instability?
  • How does terrain selection reflect my beliefs about instability?
  • Am I aware of which elements shape my perception?
  • Am I aware of how my perception of instability affects my choices?
If you're interested in an quick exercise, evaluate a few memorable days from the last few seasons. If you can remember, write down your perceptions of instability on those days and look for patterns. Are your beliefs fairly uniform regardless of the public avalanche bulletin? Are your beliefs all over the map? Is it possible to place too much weight on the public avalanche bulletin and not enough on your own observations?

Are Your Beliefs Accurate?
Assess your beliefs about weaknesses and triggering energy to shape your perception of instability. This begins with your beliefs in general, and includes how the public avalanche bulletin influences your beliefs, and the effects of data sampling in the field.

Types Of Instability

Don't you, forget about me—Simple Minds

NOTE: Backcountry avalanche forecasting is composed of four interconnected elements: goal, people, awareness, and uncertainty. The type of instability is linked to awareness and uncertainty—maintaining awareness and managing uncertainty are central tools for helping people successfully accomplish the goal of backcountry avalanche forecasting.

Introduction
It's important to outline the two key classes of instability: temporary instability in new snow and persistent instability in old snow. Safe winter backcountry travel often involves dealing with both types of instability to some degree. Persistent instabilities are harder to trigger but much more difficult to manage. Temporary instabilities are much easier to trigger and easier to manage. Since it doesn't take very much snow to bury, injure, or kill a person, both types of instability can be equally dangerous.

Table 1.1. The two types of instability.
ClassDescription
Short-Term InstabilityGenerally found in new snow ( storm snow ). Instability expressed by loose snow avalanches and soft slab avalanches. Generally does not surprise professionals; definitely surprises recreationists. Instability at surface is easy to find. Large, new-snow slab avalanches may trigger secondary avalanches that involve long-term instability. Recency is critical factor; sensitivity to trigger is high. Hazard is obvious.
Long-Term InstabilityGenerally found in old snow. Instability expressed by wet or dry hard slab avalanches. Surprises professionals and recreationists alike. Instability far below surface is difficult to evaluate. Produces large primary avalanches. Sensitivity to trigger is unknown; recency is much less unimportant. Hazard is unclear.

Combinations Of Short-Term And Long-Term Instability
Absolutes are rare in chance-based activities such as backcountry avalanche forecasting. Even the type of instability is rarely a choice between one or the other. For the purposes of backcountry avalanche forecasting, instability is separated into weaknesses and triggers. The actual type and distribution of these weaknesses is usually a mix of long-term and short-term instabilities.

Figure 1.1. Combinations of long-term and short-term instability. The typical state of instability is often a blend of both, and largely defined by recent weather and the parameters of the snowpack.

Sunday, November 15, 2009

Elements Of Instability

There's gun in your hand and it's pointing at your head—Pet Shop Boys

NOTE: Backcountry avalanche forecasting is composed of four interconnected elements: goal, people, awareness, and uncertainty. The elements of instability are linked to awareness and uncertainty—maintaining awareness and managing uncertainty are central tools for helping people successfully accomplish the goal of backcountry avalanche forecasting.

Introduction

Forming an accurate perception of instability is the goal of backcountry avalanche forecasting. In simple terms, your perception of instability should match reality as closely as possible.

What exactly does instability mean? Let's answer this question with a question: what do you believe about weaknesses in the snowpack and the energy required to trigger avalanches?

Weaknesses & Triggers

From the perspective of backcountry avalanche forecasting, instability revolves around weaknesses and triggers. It is helpful to think about both of these elements on a scale because weaknesses may range from very rare to very frequent, and the triggering energy required to release avalanches may range from very low to very high.

Figure 1.1. Distribution of weaknesses could range from very rare to very frequent.

Figure 1.2. Triggering energy required to release avalanches could range from high triggering energy to low triggering energy.

Do you believe weaknesses are widespread and avalanches easily triggered? Or do you believe weaknesses are located near certain terrain features and difficult to trigger? Your beliefs about instability can refer to an entire season, a whole day, a specific hour, or a span of just a few minutes. Therefore, your beliefs about instability are not constant, and in fact, it is best practise to regularly update your beliefs about instability.

Tuesday, November 10, 2009

Elements Of Backcountry Avalanche Forecasting

Desire is the root of all suffering—the Buddha

NOTE: This post was updated on October 20th, 2010.

This discussion provides an intentionally brief outline of a skeletal framework for backcountry avalanche forecasting, along with some framing elements to help organise your thoughts. Remember, backcountry avalanche forecasting is just one technique out of a constellation of techniques that are useful for planning and traveling. For the purposes of this discussion, backcountry avalanche forecasting includes the decisions that are connected to the forecast.

The Elements Of Backcountry Avalanche Forecasting
Safe winter backcountry travel requires you to consider the current avalanche forecast during trip planning, and may require you to develop one or more on-site avalanche forecasts during the trip itself. Developing your own forecasts in the field is type of travel technique referred to as backcountry avalanche forecasting, and it is an essential element of safe route selection whether you're going up or coming down.

The following list combines several elements of avalanche forecasting as outlined by The Avalanche Handbook with a few thematic elements derived from some of my other work. The idea is to present backcountry avalanche forecasting in human-compatible terms using human elements that are highly related to decision-making in avalanche terrain. These elements are applicable before, during, and after a backcountry outing.
  • Goal. Align your perception of instability with reality.
  • People. Manage thoughts, actions, and beliefs that could affect the forecast.
  • Awareness. Maintain awareness of instability by observing terrain, snowpack, and weather.
  • Uncertainty. Acknowledge, identify, and reduce uncertainty to make safer decisions.
The elements of backcountry avalanche forecasting are framed around safety and provide tools that help you manage exposure and measure risk. The CAA defines risk as unacceptable if there is a significant chance of triggering a size 2 avalanche ( an avalanche large enough to bury, injure, or kill a person ).

Finally, before a brief explanation of each item, it is important to note that the elements of backcountry avalanche forecasting are interconnected. You cannot use any of these elements by themselves or errors will arise and lead to faulty or dangerous decisions.

Goal
The public avalanche bulletin provides good information about the distribution of instability across a large area, including information on aspects, specific snowpack concerns, and how changes in the weather might increase or decrease the amount of instability. Backcountry avalanche forecasting is not concerned with all the slopes in a mountain range, ski area, or highway corridor; backcountry avalanche forecasting is concerned only with forecasting instability for slopes that present a hazard during a backcountry outing. You cannot use a public avalanche bulletin to reach conclusions about instability on a specific slope because the spatial scale of the public avalanche bulletin is much larger than the spatial scale of a single slope. Therefore, to align your perception of instability with reality, you must combine the information from the public avalanche bulletin with accurate observations made at a specific time and place in the backcountry. In order to account for errors prior to decision-making, you must acknowledge that some degree of uncertainty exists, and you must integrate this uncertainty into your perception of instability.

People
Every human being has his or her own thoughts and beliefs that lead to actions. Positive qualities include priority, curiosity, honesty, humility, generosity, knowledge, and focus. Negative qualities include haste, disinterest, dishonesty, ego, greed, ignorance, and distraction. It is very important to maintain awareness of the self and of the group during any backcountry outing or these negative aspects will adversely affect the forecast. This includes outcomes such as not bothering develop a forecast in the first place, constructing a poor forecast from poor information, failing to realise that everyone is exhausted, or allowing fun and excitement to outshine awareness and uncertainty. Sometimes the best course of action is to suppress your personality and then proceed with a thoughtful evaluation of the human factors involved in the decision.

Awareness
Maintaining awareness first involves realising that awareness is important, which is followed by teaching yourself how to pay attention. The second part involves learning how to observe the terrain, snowpack, and weather to maintain awareness of instability and the likelihood of avalanches. This includes instability tests, snow surface observations, and weather observations. Data sampling has an extremely strong influence on your beliefs about the presence of instability and its consequences, and like almost everything else in snow safety, data sampling can work for or against you. Mistakes in data sampling such as poor technique, inability to interpret the results, or lack of thoroughness, will lead to errors and bad decisions. It is very important to be extremely honest with yourself about your weather observation, snowpack assessment, and terrain evaluation skills or you will fail to improve and you will remain unaware. If you believe that your ability to collect information has been comprised, or if you believe the information itself may be compromised, it's best practise to throw away the data and make very conservative decisions.

Uncertainty
Uncertainty is always present, but the amount of uncertainty is variable. High uncertainty is a sign that you lack the information—for whatever reason—required to make sound judgments about risk. This differs from normal uncertainty, which should not cause undue anxiety, nor lead to overly conservative decisions. When you're really not sure ( i.e. uncertainty is high ) then it's time to acquire more information or make conservative decisions. You must teach yourself to consciously acknowledge, identify, and reduce uncertainty if you wish to make safe decisions. Remember, if unaddressed, a highly uncertain mind is fertile ground for speculation, biases, and pseudo-scientific facts. ( Terrain selection is one of the best methods of managing uncertainty. ) Poor reactions to high uncertainty, including failure to acknowledge uncertainty, or failure to proactively manage uncertainty, are a direct cause of avalanche involvement in the backcountry.

Conclusion
This is a skeletal summary of backcountry avalanche forecasting. Being an exceptionally skilled backcountry avalanche forecaster may not be useful if you cannot read a map, use a compass, or if you possess poor first aid skills. This definition uses carefully selected terms to help shape and manage the learning process. Master as many planning and traveling techniques as possible.

Appendix
The three primary sources of uncertainty are as follows:
  • Variations in human perception and estimation.
  • The spatial and temporal variability of the snowpack.
  • Incremental changes to the snowpack across space and time.

The Strategies & Tactics Of Safe Winter Backcountry Travel

Winter backcountry travel is composed of strategies and tactics, mostly centered around planning and traveling. In many ways, the planning stage is a simulation of the trip you wish to undertake. This simulation provides chances for you to discover problems in advance and to evaluate whether or not your trip is realistic given the universal constraints of time, quality, and money.
  • Planning techniques include map reading, terrain evaluation, route selection, human resources, meal planning, equipment choices, and safety measures.
  • Traveling techniques include terrain evaluation, route finding, navigation, rope and anchor skills, forecasting, movement and spacing, skiing skills, aid/rescue, and making safe decisions.
Safe winter backcountry travel requires attention to both of these elements and requires that you truly understand how to correctly use these techniques to plan and execute a safe backcountry outing. Shortcuts and misapplication will cause invisible mistakes that can have serious consequences.

This winter I'm going to write a series of short articles that dig deeper into planning and traveling techniques that are essential to safe winter backcountry travel.

Sunday, November 1, 2009

For Beginners

Baby slow down, the end is not as fun as the start—U2

Always make conservative decisions when your uncertainty is high.

That's really all you need to know at the beginning.

3 Early Season Safety Notes

Each year there are numerous close calls, and sometimes a fatality or two, related to thin, early-season snowpacks. With this in mind, what can you do to avoid avalanche danger in the early season? Rather than discuss the terrain, weather, and snowpack, this post contains a few simple reminders for those of us who must transition back into "avalanche awareness mode" after a long, hot summer.
  1. Pay attention to early season avalanche danger.
  2. Assess your situational awareness skills.
  3. Plan your early season tours carefully.

Time to starting thinking about snow.