Wind Slab

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.

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas.

How they form

Snow begins to drift when wind speeds reach about 10 mph. The wind scours snow from the windward side of terrain features such as ridges, open bowls and gullies. The snow is broken into smaller fragments and deposited on the on the downwind, or lee, side of the terrain features. The deposited snow can form thick, cohesive slabs. The stronger the wind the harder the Wind Slab.

Where they are found

Wind Slabs form in specific areas depending on the wind speed and direction. They form on the lee aspects of ridgelines, cross-loaded gullies, or other terrain features. Areas around cliff bands and the lee side of krumholtz groves can also develop Wind Slabs. At stronger wind speeds, unusual loading/deposition patterns may occur. As wind speeds increase, the Wind Slabs may form further down slope than normally suspected, and may be found in small pockets in steep gullies or even down in the trees.

Wind Slab avalanche. Winds blew from right to left across the picture, so the area right of the trees was scoured and snow was deposited to the left.

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

Timing

Wind Slabs are most reactive during a wind event and the first day or two after it has ended. Wind Slabs can have a longer lifespan than Storm Slabs. During periods of very cold temperatures and extended wind events, Wind Slabs can persist for around a week. Wind slabs that form over a persistent weak layer like surface hoar, depth hoar, or near-surface facets may develop into Persistent Slabs.

Recognition

Look for convex pillows of wind-drifted snow on the lee side of ridges and other terrain features. The Wind Slab may have a chalky look and feel. Wind Slabs can be very hard, and may present a hollow drum like sound as you traverse across slope. Snowpack tests conducted in wind-loaded areas may reveal a Wind Slab problem in the upper few feet of the snowpack.

Treatment and Avoidance

Wind Slabs are common across Colorado. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind-scoured areas. Wind Slabs form in specific areas, so learning to recognize their characteristic shape and texture will help you avoid them. They usually stabilize in less than a week, so you can reduce your risk by waiting several days after a big loading event

Avalanche Essentials–Windslab

Persistent Slab

Release of a cohesive layer of soft to hard 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.

The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.

How they form

Persistent Slabs form when a persistent weak layer is buried by additional layers of snow. The problem persists after storm and wind slab instabilities have stabilized. The persistent weak layer can cycle through periods of sensitivity from reactive to nonreactive due to changes in weather conditions such as new precipitation, wind loading, strong solar radiation, and/or rapid changes in air temperature.

This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.

Where they are

The spatial distribution of Persistent Slabs is dictated by the distribution of the culprit weak layer. The weak layer distribution is dictated by the weather patterns responsible for its creation. Thus, Persistent Slab distribution can range from widespread across terrain to very specific terrain features. They can occur at all elevations and on all aspects. Persistent Slabs can be triggered remotely, and on low-angle to steep slopes. Consult the backcountry avalanche forecast to determine where in the terrain this problem exists.

A Persistent Slab avalanche that propagated over several terrain features.

Timing

Persistent Slabs can be a problem during any time of the snowy season. Anytime you have a slab resting over a reactive persistent weak layer, you have a Persistent Slab problem. This problem can develop during the fall and last well into the spring.

Recognition

Persistent Slabs can be distinguished from Storm and Wind Slabs by how the fracture lines fail in the terrain. Unlike storm instabilities, Persistent Slabs are commonly triggered remotely, from flat areas, and failures can propagate across terrain features like ridges, ribs, and gullies. It is possible to have a Persistent Slab problem that is susceptible to human triggering but not produce many spontaneous avalanches. The lack of avalanche activity does not always indicate the absence of a Persistent Slab problem. You can look for persistent weak layers in snow profiles, and perform snowpack tests to gauge sensitivity and distribution of a Persistent Slab problem. Consult the backcountry avalanche forecast to determine where in the terrain this problem exists.

Treatment and Avoidance

Persistent Slabs can be triggered by light loads and weeks after the last storm. They are commonly trigged remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Failures often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty. Intimate slope-scale knowledge and tracking of culprit persistent weak layers and avalanche activity over space and time will aid in assessing the severity and extent of this problem. The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices.

Avalanche Essentials–Persistent Slab

Storm Slab

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

How they form

Storm Slabs form when new snow consolidates over a weaker layer or interface. The weak point can be snow that fell early in the storm or just a poor bond with the old snow surface. Like a chain, it can just be the weakest part of a snow layer that formed in a single storm or prolonged snowy period. Storm Slabs commonly form during periods of light or no wind.

Where they are

Storm Slabs tend to form in sheltered areas where new snow falls with light winds. They can occur on any steep open slope, and are often found on several aspects at the same time.

Timing and Triggering

Storm Slabs tend to have a short life span. They are easiest to trigger during periods of heavy snow and typically stabilize within a day or two after the storm cycle has ended.

Recognition

Storm Slabs can be difficult to recognize since the surface snow is often soft and powdery. With enough cohesion in the new snow, these slabs can propagate shooting cracks and faint collapses at the interface of the new snow and old snow surface. Snowpack tests that load the snow from above (e.g. Compression Test) have limited utility since they often crush through storm slabs and buried weak layers, and do not identify the problem well. Tilt tests, ski cut results on small inconsequential slopes, or natural activity on indicator slopes are often the best clues that a Storm Slab problem exists.

A small Storm Slab triggered by a backcountry skier.

Treatment and Avoidance

Storm Slabs are most dangerous when they run into terrain traps such as timber, gullies, over cliffs, or areas difficult for a rider to escape off to the flank. Due to the nature of the soft, low-density slab, riders may not realize that a Storm Slab has failed until well after it is running. It is common to underestimate the extent of propagation with soft Storm Slabs, and resulting avalanches are often larger than expected. You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep avalanche terrain. They usually stabilize in less than a week, so you can reduce your risk by waiting several days after a big loading event.

Experienced riders can use slope cuts as a tool to help release a Storm Slab. Under most conditions, good planning will allow a group to recognize terrain traps as well as good escape routes prior to a triggered a Storm Slab. However, Storm Slabs, can trigger avalanches into deeper, old-snow layers. This scenario can lead to a much larger and more dangerous avalanche.

Avalanche Essentials–Storm Slabs

Spooky Moderate

01/19/2018

by Brian Lazar

The most basic tool for communicating the avalanche hazard is the avalanche danger rating. We have five ratings to choose from for each elevation band. The danger rating considers the likelihood of avalanches occurring and the potential size of the avalanche. This scale tries to take every possible avalanche situation and put it into one of five categories, but Mother Nature doesn’t always cooperate and conditions often don’t fit neatly into the prescribed boxes. When in doubt the forecasters use the travel advice to pick the danger rating for the day. This usually works well, but there are times when choosing a specific rating gets tricky. Now is one of those times.

Forecasters start using adjectives to qualify the danger rating when things get tricky. For example, when we have a low probability-high consequence Deep Persistent Slab avalanche threat, the term “scary Moderate” starts getting tossed around. It is not “scary moderate” right now, but the sensitivity of the weak layers and the number of remotely triggered avalanches is making the forecasters nervous. Internally we’ve been calling it “spooky Moderate”; there’s a high probability of triggering small to large (D1 to D2) avalanches, but only on specific slopes. On these specific slopes, the snowpack is very sensitive as we have seen lately in our growing list of human-triggered avalanches, but natural avalanches and avalanches larger than D2 are unlikely.

Here is a picture of a large skier-triggered avalanche in the Aspen zone on Jan 16th. Notice the wide propagation of this slide that broke on a persistent weak layer. Persistent Slab avalanches often break wider than Storm or Wind Slab avalanche, and in ways that can be surprising.

This situation doesn’t fit perfectly into either Moderate or Considerable. Looking at the whole picture, Moderate (Level 2) is the best fit for current conditions, but it is by no means safe. Each danger levels covers a spectrum, and we are much closer to Considerable (Level 3) than we are to Low (Level 1) danger.

So how can we safely enjoy the backcountry during these conditions?

Stay on top of current conditions by reading the forecast. The danger rating, text, and avalanche problem will describe the most dangerous slopes. The avalanche rose below depicts the number of all reported slab avalanches by aspect and elevation in Colorado from Jan. 9th (the start of our last loading event) through the 17th.

You can see that most avalanche activity is occurring on north through east facing slopes, with the apparent bullseye on northeast aspects. You can easily trigger an avalanche on these aspects, on slopes steeper than 35 degrees where there is a soft slab more than a foot thick. You can greatly reduce your risk by simply avoiding these slopes.

On other slopes, traditional travel advice for dealing with persistent weak layers is appropriate. Watch for cracking and collapsing, anticipate triggering avalanches remotely and from below, and give yourself a buffer around slopes greater than 30 degrees in areas where you experience obvious signs of instability.

Given the poor snowpack structure with reactive and well developed depth hoar, we probably won’t see Low (Level 1) at all elevations any time soon. It also won’t take much for avalanche danger to rise. New snowfall of 6 inches or more with just a little wind, and we’re likely to see more natural avalanche activity. At that point we could cross the line back to Considerable danger. A larger load of a foot or more in less than 24 hours, and we could see High (Level 4) danger.

The bottom line is that MODERATE avalanche danger (especially the flavor of Moderate we’ve been dealing with lately) doesn’t mean safe. It means you can trigger serious, even lethal slides unless you pay careful attention to slope angle and aspect. Keep this in mind as you are preparing for your day in the backcountry, and make sure to read the summary and/or discussion in the avalanche forecast. It could save your life or the life of your partner.

The Danger of Improving Stability

12/27/2016

by Brian Lazar and Ethan Greene

Santa delivered a lot of snow to Colorado in the past two weeks, just in time for Christmas. Have we been naughty or nice? Well riding conditions have been fabulous, but there have been some impressive avalanches.

The last storm brought significant snowfall and avalanche activity, but since then the snowpack has been getting stronger and we’ve seen fewer avalanches and less cracking and collapsing. Paradoxically, this does not mean things are necessarily safer for the backcountry traveler. The likelihood of triggering an avalanche is decreasing, but the size and consequences of avalanches that do release are steadily increasing. This trend has prompted discussions amongst our forecasters about whether or not we are moving into a new risk paradigm, and perhaps, a new avalanche problem: Deep Persistent Slab (DPS) avalanches.

DPS avalanches have many characteristics in common with Persistent Slab (PS) avalanches. Both break on persistent weak layers. You can trigger both remotely and from low-angle slopes. Both of these types of avalanches can fail in surprising ways, breaking across and around terrain features that would contain a Storm or Wind Slab avalanche. PS and DPS avalanches have a lot in common, but there are some very important differences that affect how we avoid them and manage our own personal risk.

DPS avalanches are low probability and high consequence events. The likelihood of triggering a PS avalanche and the size of that avalanche can vary over a wide range. DPS avalanches are a specific creature, very large in size and hard to trigger. We look for three things before we add it to our list of Avalanche Problems. Those three things are:

Avalanches will be stubborn to trigger, Unlikely or Possible on the Likelihood scale
Avalanches will be destructive, D3 or larger
Avalanches will break on deeply buried or basal weak layers

These criteria capture the low-probability/ high-consequence nature of DPS avalanches. A low Likelihood means there will be very few or no natural avalanches, human-triggered avalanches will be unlikely, and large explosive and cornice triggers will only produce some results (ADFAR2). A D3 (Very Large) avalanche could bury and destroy a car, damage a truck, destroy a wood frame house, or break a few trees. When the likelihood slider drops towards “Unlikely” and the size slider climbs to “Very Large or Historic”, we have a DPS avalanche problem (see image below).

DPS avalanches are especially scary because most people don’t have much experience dealing with them. It is hard to gain experience dealing with these beasts because we don’t see DPS avalanche cycles that often. In a typical year we could see over twenty cycles of Storm, Wind, and Persistent Slab avalanches, but we may only see one DPS avalanche cycle in five years. You could navigate through two Storm Slab avalanche cycles in a week of touring, but it could take you ten years to gain the same amount of experience with DPS avalanches. These avalanches are also very large and extremely dangerous. Most people that get caught in one get killed. This makes it very difficult to learn from a close call. Your first encounter with a DPS avalanche could very well be your last.

Over the last 15 years, almost all avalanche accidents in Colorado where more than one person died were the result of a DPS avalanche. In two seasons with pronounced DPS avalanche cycles (2008-09 and 2012-13), DPS avalanches accounted for more than 60% of the avalanche fatalities. In the figure below (covering two seasons: 2012-13 and 2013-14) you can see that avalanches involving persistent weak layers are particularly dangerous. DPS avalanches only accounted for 5% of the observed avalanches, but caused 42% of the fatalities. Sure sounds like low-probability/high-consequence, doesn’t it? You can read the whole study here.

In a year with DPS avalanches we can describe the forecast zones where they could happen and the aspect and elevation of the slopes that are most likely to produce one. This is the good news. The bad news is that if you have ten of those slopes, it is really hard to predict which one will produce a DPS avalanche. This is the low probability part. Remember the other half of the description is high consequence. Because DPS avalanches are so dangerous, the only safe way to manage your risk is by avoiding those suspect slopes. On a bad year, you might have to avoid those slopes for the rest of the season. This can be hard to do because people will test suspect slopes, and most will get away with it (they are low-probability events). And due to the nature of a DPS avalanche problem the danger is almost always MODERATE (Level 2) when this is our main avalanche problem, because these avalanches are hard to trigger. That combination -people testing slopes without immediate consequences and a MODERATE (Level 2) rating – doesn’t scream “dangerous” the way an avalanche warning does.

So where are we this year? In some places we can produce D3 avalanches, as demonstrated by the mid-December avalanche cycle. Between December 14 and 21, multiple D3 avalanches released in the Aspen, Gunnison, North San Juan, and Front Range zones. This includes both natural and human-triggered slides. Around half of these avalanches ran naturally during and shortly after the storm cycle. So while we met the size criteria, we weren’t at the point where we called these avalanches stubborn to trigger. Instead, we had Likely to Very Likely, and Large to Very Large PS avalanche problems. This resulted in avalanche warnings and HIGH (Level 4) danger.

The likelihood of triggering PS avalanches in these areas has since decreased, but some notable D3 avalanches released post storm. A narrow escape near Crested Butte, a very large avalanche triggered by a snowcat near Loveland Pass, and explosive triggered slides north of Berthoud Pass, and very large avalanche with an unknown trigger near Cameron Pass have us talking about if a potential DPS problem is in our future.

It is getting harder to trigger an avalanche that breaks into the weak snow near the ground in most of the forecast zones. So the Likelihood of triggering a Persistent Slab avalanche in decreasing. We have seen Very Large (D3) avalanches in the Aspen, Gunnison, North San Juan, and Front Range zones. Most of these zones have a deep enough snowpack to produce more Very Large (D3) avalanches. The Sawatch and Vail/Summit zones picked up less snow during the mid-December storms. Most of the avalanches in these zones have been large enough to kill you (D2), but not large enough to destroy a vehicle or timber structure (D3).We have a basal weak layer, the avalanches are getting harder to trigger, and in some zones they getting quite large. Although we have not started to warn people about DPS avalanches, some of the PS avalanches are getting larger and harder to trigger. The weather over the next couple of weeks will determine if we are just going through a scary period, or if we’ll move into a DPS cycle that lasts the rest of the season. For now, remember that we’ve seen some tricky conditions over the last few weeks and there is no indication they are over. Please read the forecast before you go out and keep in mind that this kind of Moderate (Level 2) danger includes some pretty big avalanches.

Stay safe out there and enjoy the snow! Happy New Year!

Click here to learn more about Avalanche Problems from the USFS National Avalanche Center.

Weather Stations – Measuring Precipitation

11/30/2016

By Nick Barlow

One of the most useful resources provided on the CAIC webpage is the weather stations page (Observations > Weather Stations). Here you will find a table of hourly and archived observations from a large network of weather stations throughout Colorado, sorted by forecast zone and elevation.

A screenshot of the CAIC Weather Stations Page

The several highlighted columns report different quantities of precipitation. For SNOTEL stations, up to seven different readings are given. Below is a description of these readings, the instruments that take them, and how the data can be useful for backcountry users.

Snow Water Equivalent (SWE)

SWE is the total amount of water contained in a fixed sample of snow. More simply, it is the resulting depth of water if the entire sample melted. In this context, “sample” could mean the entire seasonal snowpack (SWE), or just new snowfall over the past 24-hours from a single storm (SWE24). Seasonal SWE is particularly useful for long-term hydrological applications, such as forecasting water supply or seasonal runoff. For example, water managers use the data to determine how much water is stored in the mountain snowpack for the warmer months ahead. This is the primary function of the SNOTEL network, and the strategic placement of stations in important water basins throughout the United States. Yet SWE is also relevant for backcountry users.

The density of water varies only slightly with temperature. By contrast, snow density varies significantly from storm to storm. The SWE calculation is a way of standardizing snowfall for use in further applications. When we think about loading weak layers in the snowpack, calculating SWE can be of great value. The data can reveal the load added to the snowpack from an individual storm. By comparing SWE to snow depth, we can also discern whether the storm snow was dense and heavy vs. light and fluffy.

At SNOTEL stations, SWE is measured using snow pillows: large 3-meter x 3-meter bladders (steel and rubber) installed on the ground and filled with a volume of antifreeze. As snow accumulates on top of the pillow throughout the winter, instruments measure the increasing hydrostatic pressure upon the liquid. With that, the mass of the overlying snow is calculated. Knowing the density of water allows us to calculate SWE. A snow depth measurement allows us to calculate snow density.

Snow pillow and depth sensor

Measuring Snow Depth

Snow depth is perhaps the easiest quantity to measure, simply by using a ruler or avalanche probe. It is more complicated at remote weather stations with the automated measurement and logging of data.

At SNOTEL stations, an ultrasonic depth sensor mounted above the snow pillow measures the snow depth. The sensor sends a signal downward towards the ground and measures how long it takes the signal to bounce off the snow surface and return to the sensor. Knowing how fast the signal travels, a properly-calibrated sensor will give an accurate reading of snow depth. On the weather station page, there is a field for changes in depth over a 24-hour period (Sno24), in addition to the total depth of the snowpack (SnoHt).

The ultrasonic sensor is also useful for backcountry users. Most simply, it is the only tool at a SNOTEL station that can tell you how much new powder you’ll find on any given day. However, you can glean more, and more important information from a SNOTEL site.

For one, the total depth of the snowpack can be particularly useful. A shallow snowpack can promote changes in snow structure, and create persistent weak layers. This is important information to gather before traveling into the backcountry. On a shorter time-scale, the amount the snow depth increases in a single storm is a good estimate of how much snow is available for wind transport. We can also estimate the depth of new Storm Slab or Wind Slab avalanches, and at what depth we might find the old/new snow interface in our snow pits.

Measuring Liquid Precipitation

SNOTEL stations are equipped with a precipitation gauge to measure liquid for the entire water-year. During the warmer months, rain simply falls into the gauge. The gauge then measures and logs the data automatically. Snow also falls into the same gauge during the winter months. However, sub-freezing temperatures would make any kind of liquid measurement essentially impossible. To combat this effect, SNOTEL precipitation gauges are “charged” with a volume of propylene glycol, melting the snow on contact as it falls into the gauge. The gauges also contain mineral oil, designed to sit on top of the collected liquid and prevent evaporation over time. On the weather station page, data is in 1-hour (Pcp1), 24-hour (Pcp24), and since-midnight (PcpAc) format.

Liquid precipitation gauge

For backcountry users, liquid precipitation data can also be useful. Ideally, data from this gauge would match the calculated SWE data from the snow pillow and ultrasonic sensor. This is not always the case. It’s important to recognize the differences and primary functions of each piece of equipment. Data from the liquid gauge is used for seasonal purposes. The gauge keeps measuring precipitation long after the snow melts away from the snow pillow.

However, the data can be used in conjunction with the SWE and snow depth in order to provide a more well-rounded answer to what is going at the station. An example would be for rain-on-snow events.

Snow pillows may not always capture added SWE from rainfall, as some of the liquid may channel away from the pillow. In this case, the liquid gauge is the only piece of equipment that could tell us if rain-on-snow has occurred. A simultaneous temperature reading from the SNOTEL could also reinforce our suspicions.

Takeaway

Remember that automated SNOTEL stations exist in remote mountain locations. The stations use three different pieces of equipment to measure precipitation, and each piece has its own unique purpose for being there. Like any equipment, the gauges are prone to both random and systematic errors, and the data may not always be trustworthy.

A variety of issues can (and do) arise at SNOTEL stations. For this reason, they require continued maintenance and quality control of the data they output. This can be exceptionally difficult during the winter months, as access to many of the stations is difficult.

As backcountry users, we should analyze each piece of data individually before forming a conclusion about what has transpired. Compare the different forms of output (SWE, depth, melted liquid) and attempt to read between the lines.

Also, recognize the data is from a single point, and may not be representative of the entire area in which you’ll be traveling. Of all meteorological surface measurements, precipitation is by far the most spatially variable. You will likely find inconsistent snowfall results within different elevation bands and aspects as well. Study the data from other near-by stations; learn which stations typically receive more or less snowfall than others.

Most of all, be thankful the SNOTEL network exists. It is a wonderful tool to have at our disposal. These stations shed light into the dark and cold, providing us with vital information at just a mouse-click away.

Overview of precipitation quantities

Cornice Fall

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridge line areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.

How they form

Cornices develop whenever snow is available for transport and the wind is sufficiently strong to move the snow. The ideal wind speed for cornice development is 15 to 25 mph. Stronger wind speeds tend to move snow further down slope, which creates other hazards (see Wind Slab, Persistent Slab). Cornices can form quickly with favorable wind speeds and abundant available snow, typically following a recent storm. Multiple wind events over time generate large overhanging cornices comprised of numerous hard snow layers often interspersed with soft weak snow layers or hollow tunnels.

Where they form

Cornices form on the downwind (leeward) side of sharp terrain features. Ridges above treeline are the most common locations. Cornices also form downwind of vertical ridge lines and tops of couloirs, in a process referred to as cross-loading. The largest Cornices form over time in areas that receive persistent wind from a similar wind direction. A common example is an above treeline saddle that funnels persistent winds, resulting in a Cornice that increases in size through the winter season. In Colorado, high elevation winds typically blow from southwest through northwest; and hence, large Cornices are more likely to form on the easterly side of terrain features.

A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.

Timing and Triggering

Cornices develop in periods ranging anywhere from hours to all season. A brief wind event following storm snow quickly generates soft cornices on the lee of any terrain feature. Soft wind cornices are easy to trigger artificially. If they are not large, then they are often manageable by themselves. Soft Cornice Fall, however, can run long and fast while quickly entraining additional snow that results in a much larger and dangerous avalanche. A longer wind event, typically lasting at least a day, generates larger and harder Cornices. These stiff Cornices may appear supportive of a human, but they cannot be trusted. Additional weight, from more snow load or a human, can result in a crack that easily propagates resulting in a Cornice Fall. This can happen from a distance resulting in a remote release. Cornices can build to very large sizes through the winter. These large Cornice Falls are difficult to trigger, but if they do, the consequences can be deadly.

Recognition

Fortunately, Cornices are easy to see. Weather and terrain awareness are the best tools for recognizing potential cornice problems. When planning a backcountry trip, use topographic maps to learn where potentially hazardous cornices can form. Pay attention to weather observations during the past several days and wind forecasts to understand where Cornices are forming. While in the backcountry, look for cornice formation on the lee of terrain features. Look for local terrain-driven wind effects, which may generate Cornices in unexpected locations. Pay attention to unusual weather events. For example, winds from the east (often associated with a Front Range upslope storm) generate Cornices on westerly aspects.

Treatment and Avoidance

Cornices can never be trusted; and hence, avoiding them is necessary for safe backcountry travel. While moving along ridge lines stay well back from areas with cornice formation. Cornices often overhang the ridge edge and added weight can release the cornice, often from a remote distance. If necessary, use a probe pole to determine the existence of hard ground underneath the snow. Avoid areas underneath Cornices. Even small Cornice Fall can trigger a larger avalanche that runs far downhill. Large Cornice Fall can easily crush and kill a human. The spring season, or any period of significant temperature warm-up, are times to be particularly aware. Large Cornice Falls are most common during these weather regimes.

Avalanche Essentials–Cornice

Avalanche Problems

“Avalanche Problem:” A set of 4 factors (type, location, likelihood, size) whose
combination describes the avalanche hazard

Avalanche Character or Type – One of 9 potential avalanche descriptions
Location – Where the avalanche is most likely to exist in the terrain, shown with an Aspect/Elevation diagram
Likelihood – The chance of triggering an avalanche
Size – The destructive potential of the expected avalanche

Types of Avalanche Problems

Loose Dry

Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose-dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose-dry avalanches can trigger slab avalanches that break into deeper snow layers.

Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.

Storm Slab

Wind Slab

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas.

Persistent Slab

Deep Persistent Slab

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply buried over time.

Deep Persistent Slabs are destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.

Loose Wet

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

Wet Slab

Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very destructive.

Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty.

Cornice Fall

Glide

Release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

Predicting the release of Glide Avalanches is very challenging. Because Glide Avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide Avalanches.

December Summary

01/15/2020

by Mike Cooperstein

The year ended with average to above average snowfall for the month of December across Colorado. Five storms during the month pushed the Snow Water Equivalent (SWE) to over 100% of the long-term median across all of Colorado’s river basins. The Southern Mountains received the most snowfall in December with areas around Wolf Creek Pass picking up almost 90 inches of new snow in the month of December alone. The new snow and periods of wind created a stiff slab over a weak layer of depth hoar near the ground and we started to see large natural and human-triggered avalanches breaking at the ground. The CAIC recorded 547 avalanches in December. Eighty-three of those avalanches were human triggered. The CAIC recorded sixteen riders that were caught in avalanches. Tragically, one of those avalanches resulted in a fatal avalanche accident. This was the first person killed in an avalanche in Colorado during the 2019-2020 season.

Five storms in the month of December 2019 brought us to above average snow and water for the season. This figure shows the basin wide percent of normal (percent of median from 1981 to 2010) snow water equivalent (SWE) across Colorado at the beginning of January.
December began with a few days of high-pressure, clear skies, and dry conditions. The next two weeks were a stormy period across Colorado with three storms hitting almost back to back to back from December 3 to December 16. Many areas in the Northern Mountains received 30 inches of snowfall in those 13 days. Breckenridge Ski Area received 43 inches of snowfall in the 3 days period from December 13 through December 16. Favored areas in the Central Mountains received around 2 feet of snowfall from December 3 to December 8 and then another 2 feet of snowfall from December 14 to December 16. Areas in the Southern Mountains received almost 40 inches of new snow as well in those 13 days with Wolf Creek Pass getting hit with 20 inches of snow in a 12-hour period on the night of December 16.
All of the new snow spurred a widespread avalanche cycle. Two hundred and ninety-five natural and fifty-five human triggered avalanches, large enough to kill or injure a person were reported to the CAIC in the first 16 days of the month.

	Natural Avalanches	Human-Triggered Avalanches
Northern Mountains	44	26
Central Mountains	191	16
Southern Mountains	60	13

This table shows the distribution of natural and human triggered avalanches large enough to kill or injure a person (D2 or larger) across Colorado from December 1 to December 16, 2019.
On December 8, a backcountry skier was caught, buried, and unfortunately killed by one of these large human-triggered avalanches. The accident occured on the Diamond Peaks in the Cameron Pass area of the Front Range zone. Many of these large avalanches were remotely triggered, which illustrated unstable the the threat from our Persistent Slab avalanche problem. Despite all of the new snow, the snowpack remained relatively thin across most of the state and most of these avalanches broke at the ground.

On December 1, 2019, a snowmobiler remotely triggered this avalanche in the Rollins Pass area in the Front Range zone. Observers reported cracking and collapsing and many remotely-triggered avalanches to the CAIC in the first few weeks of December.

A skier triggered this avalanche on Berthoud Pass, in the Front Range zone, on December 11, 2019.

This photo shows a remotely-triggered avalanche in the Vail and Summit County zone on December 12, 2019.

From December 17 until about December 23 a period of high pressure brought dry conditions with clear skies and unseasonably warm temperatures. Temperatures rose well above freezing in many areas. This built sun crusts on southerly-facing slopes and left weak, faceted crystals on the snow surface on north and east-facing slopes. These would become the weak layers for avalanches toward the end of the month. Riders continued to trigger avalanches that broke at the ground during this prolonged dry spell.

A snowmobiler remotely triggered this avalanche in the Never Summer Range, Front Range zone, on December 17, 2019. He was farther away than where this picture was taken when he triggered the avalanche.

A snowboarder unintentionally triggered this large avalanche in the Loveland Pass area on the border of the Front Range and Vail and Summit County zones on December 19, 2019.
Just before Christmas another storm moved over Colorado. On December 25 and 26 areas in the Southern and Central Mountains as well as the Vail and Summit County zone accumulated 12 to 16 inches of new snow. The Steamboat and Flat Tops zone and Front Range zone picked up 3 to 8 inches of snow. This snow fell on a weak snow surface in many areas. We continued to receive reports of large natural avalanches over Christmas; however, we were seeing many fewer avalanches break at the ground and many more avalanches break at the interface between the new and old snow.

A natural avalanche in the Wemuniche Wilderness in the South San Juan zone, December 26, 2019.
The final snow storm of the decade occurred from December 27 to December 29. Snowfall favored the Southern Mountains with up to 20 inches near Wolf Creek Pass and diminishing totals as you headed north. There was still some avalanche activity breaking near the ground, but most avalanches released in storm or wind-drifted snow. Avalanches continued to break on these mid-pack weak layers for some time to come. In the deeper snowpack areas forecasters were becoming less concerned about the deeper buried weak layers. In the thin snowpack areas these basal weak layers continued to plague us every time we got big storms. We finished December the same way as we started, with clear skies and cold temperatures.

October and November Summary

12/14/2019

The 2019-2020 season began with storms in the second week of October. The month closed with several more storms continuing on and off through the end of the month. Observers reported “excellent for October ” conditions. SNOTEL stations in the Northern and Central Mountains reported far more than typical amounts of precipitation, but “more than normal” in October still translated to rather thin snow cover with just a couple inches of snow-water equivalent on the ground. The CAIC recorded six small natural avalanches in the Northern and Central Mountains. A foot or less of snow fell in the Southern Mountains, enough to offer a glimpse of winter but not much snowy recreational opportunities.

First reported natural avalanche of the 2019-20 season. This soft slab avalanche released on a northeast-facing slope on Independence Pass around October 24 after receiving around a foot of snow in the previous week.

November began with almost three weeks of dry, mild weather. The snow that lasted through the dry spell on high-elevation north and east-facing slopes faceted into well developed depth hoar. This became the poor foundation upon which we would build the rest of the season’s snowpack. Thin crusts formed on sunny slopes that did not melt back to bare ground, and widespread surface hoar formed on the snowpack surface. Snowpack characteristics were similar statewide, other than more melting in the San Juan Mountains, and some isolated drifts of dense snow in addition to the depth hoar and thin crusts in the Northern Mountains.

Snowfall starting November 20 brought an end to the dry weather, and a corresponding uptick in avalanche activity across the state. Most avalanches ran on higher-elevation north and east-facing slopes and most broke into the depth hoar. With a shallow snowpack most avalanches were small, but the pattern was a sign of things to come. A series of storms would close out the month starting just prior to Thanksgiving. The snowpack failed this second test and we saw another avalanche cycle. We also started to see some variations across the regions.

This is an example of a shooting crack from the Aspen zone on November 22, 2019. Obvious signs of instability like these were widespread around the state when snowfall returned around November 20, ending our November dry spell.

In the Southern Mountains observers found shooting cracks, collapses, and a natural avalanche cycle that occurred the day after Thanksgiving. That prompted the first Avalanche Warning of the season on November 29. On November 30, two snowshoers triggered and were caught in an avalanche east of Red Mountain Pass.

This avalanche was remotely triggered from flat terrain on Red Mountain Pass on the last day of November. Avalanches like these gave us a good indication of how December would unfold when we got more loading events.

Snowfall from storms around Thanksgiving Day overloaded portions of the Central Mountains. The result was a cycle of small to large natural and human-triggered avalanches in the Gunnison and Aspen zones. The month ended with Considerable (Level 3 of 5) danger ratings and backcountry forecasts discussing the potential for people to trigger large avalanches near and above treeline on north through east aspects, especially around terrain features with wind-drifted snow.

In the Northern Mountains, a strong upslope storm developed just before Thanksgiving Day. A backcountry skier was caught and carried in a small avalanche while skinning uphill in Jones Pass on November 22. A backcountry skier was buried with just an arm above the snow near Searle Pass on November 28. A swift companion rescue prevented a tragic outcome. As snow continued to accumulate, avalanche size increased with a few large avalanches reported on November 29 and 30.

This small avalanche buried a person with only one arm sticking out of the snow on Thanksgiving Day. The other two people in the group quickly rescued the victim. The storms around Thanksgiving Day caused avalanche danger to rise and a corresponding increase in avalanche activity.

We ended the month on the way to better coverage, but with poor snowpack structure and weak layers ranging from depth hoar, to crust-facet combinations, to buried surface hoar. We were primed for more avalanche activity as soon as we got our next loading event.

Mr. Magoos, Puckerface, and Developing Expert Intuition in Avalanche Terrain

03/25/2014

Blase Reardon

On January 17th, 2014, a pair of riders triggered a large avalanche on a steep, near-treeline slope in the backcountry behind Snowmass Ski Resort. The slope had previously been nicknamed “Mr. Magoo’s” after a ski patroller who sometimes acted like the near-sighted cartoon character. The riders escaped unhurt, despite an ugly terrain trap below. An hour later, the resort’s snow safety director watched a solo skier turn down the same slope and trigger a second slide adjacent to the first. He met the solo skier as he returned to the resort and asked him whether he’d seen the first slideâ€”or the larger natural avalanche just up the drainage at the same aspect and elevation. The solo skier replied, “It’s okay; I have skied Silverton and I skied the path a couple of years ago.”

The slope where the January 17th incidents occurred is steeper than 35 degrees and faces southeast. On that day, it was blanketed with a foot-thick slab formed by a recent storm and subsequent cross-loading; the slab sat on a thin, persistent weak layer. It was a slope that closely fit a pattern of recent avalanche activity and that was highlighted in the CAIC forecast as the kind of slope where people were most likely to trigger slides. With the danger rated as Considerable, skiing that slope on that day was a risky proposition, especially alone and with a fresh slide visible.

The solo skier didn’t answer the question posed to him – did he see the other slide and, implicitly, was he concerned about avalanche danger on the slope? Indeed, he seemed to answer a different question altogether, one centered on skiing rather than avalanche conditions. Perhaps standing at the top of Mr. Magoo’s he asked himself, “Can I ski a slope like this?” And his answer seems to have been “Yes, because I’ve skied slopes this steep before. I’ve even skied this slope before.”

According to Nobel-prize winner Daniel Kahneman, substitution like this is a nearly automatic cognitive response to complex, irregular environments. Our brains produce what Kahneman calls “off-the-shelf answers” to difficult problems by answering simpler, more familiar questions. It’s a sub-conscious process, and it provides solutions that leave us feeling very confident in our assessments and choices. Assessing the risk of triggering a slide on a steep slope covered with new snow is a complex task, fraught with uncertainty. Faced with that, our brains quickly default to questions with simpler answers, like “Can I ski this slope without falling?” or “Will the skiing be as good as it looks?”

Marketing provides numerous everyday examples of this pernicious tendency. When faced with a question like “Is this the best pair of skis for me to buy?” we often answer a question more like “Do I like this brand of skis?” or “Do I like the graphics?” In situations like these, substitution often provides adequate answers, because the alternatives aren’t that different and the consequences of not answering the initial question aren’t severe. And substitution has the advantages of saving us mental energy and time. Once we’ve substituted a simple, seemingly coherent answer to a complex question, we can confidently summon numerous arguments supporting our choice without recognizing the substitution.

That leads us back to Mr. Magoo, the cartoon character referenced in the slope’s nickname. Mr. Magoo stubbornly refuses to recognize his near-sightedness. He doesn’t have to, because situations always work out for him. Magoo mistakes an airport for a movie theater, takes a seat on a departing planeâ€””It’s like I can feel the plane taking off!”â€”wanders around on the wings, unknowingly leads the police to a bank robber, and when the plane lands, tells the flight attendant he really enjoyed the film. The tension in the Mr. Magoo cartoons derives from seeing how lucky the character can get yet be oblivious to the dangers he’s facing, thanks to his near-sightedness . They’re funny because we know his luck will never run out.

We can all be Mr. Magoos in the backcountry. When nothing bad happens, it’s easy to finish a day of skiing or riding in avalanche terrain feeling confident we made good choices. So it’s easy to take the wrong lessons from our experiences. We’re sure we really liked the movie, unaware of how close we came to falling off the wing. The three riders involved on the slides on January 17th might easily conclude that they judged conditions correctly. More correctly even than the forecast, which called slopes like Magoo’s dangerous. None of them were hurt. The answer of “Yes, I can ski this” seemed to work, so the solo skier might be more likely to rely on it the next time he’s faced with a slope where the stability is questionable.

The winter backcountry is no cartoon, however. Substituting an easy question for the relevant one can kill our friends, our loved ones, or us. Our luck can run out. Or we may not get lucky at all. It’s what Kahneman and others have termed a “wicked environment”â€”an environment in which a lack of regular, reliable feedback allows us to develop habits and patterns based on faulty correlations, or luck.

So, what’s the alternative, given our brain’s hardwired proclivity for substitution and the wicked nature of the backcountry? How do we keep from being Mr. Magoo?

The avalanche on Magoo’s

In previous section of this article, I noted that the winter backcountry is an instance of what Nobel-Prize winning researcher Daniel Kahneman and others describe as a “wicked environment” for developing expertise. In part, that’s because expertise in the backcountry is a collection of skills. We have to master the individual elementsâ€”technical skiing and riding skills, route-finding, and stability assessment among themâ€”while simultaneously learning which items in the set to prioritize and apply in a given situation. It’s also because in the winter backcountry, we don’t get much immediate, consistent feedback on our decisions and actions. We rarely know how close we are to triggering a slope, so it’s easy to develop habits and patterns based on faulty correlations, or luck.

A real-world example of the rarity of immediate feedback in avalanche terrain surfaced a few years ago, in a video posted on YouTube that’s since been pulled. It showed a skier finishing a run on Puckerface, a steep slope near Jackson Hole Mountain Resort. The soundtrack includes lots of whooping. Then a title card appears, reading “Second Run. 10 minutes later.” A snowboarder starts down the same face, and makes a hard first turn. The entire slope fractures several feet deep, and slides. The snowboarder claws into the bed surface and stops. The camera shakes and jerks, accompanied by lots of cursing. The snowboarder walks away on the ridge. The video shows the slide a second time, in slow motion.

Let’s put ourselves in the boots of the first rider on Puckerface on January 2, 2012. We choose to ride the Â slope for some reasonâ€”maybe a well-considered assessment of stability, maybe by substituting a question that’s easier to answer, like whether there’s enough sun on the face for good video. When it doesn’t slide, we conclude our rationale was correct. Given enough similar experiences, we could start to feel very confident in our skills. But the slide triggered by the second rider reveals a more accurate conclusion: we got lucky. And instead of developing skills, we might just be getting lucky, a lot.

Puckerface, just after the 2014 fatal avalanche. Photo courtesy Alex Do.

The image above also shows Puckerface on an early-winter day, this time nearly two years later, on Dec. 26, 2013. On this day, a rider wasn’t so fortunate; he was killed in the slide visible in the image. That’s the potential penalty for substitution, inadvertently relying on luck, or just plain making a mistake. Each day in avalanche terrain, each run or route we chose, is unique and novel; we have incomplete or ambiguous data, we get one chance, and the cost for choosing badly can be fatal.

An alternative to relying on luck is expert intuitionâ€”distinguishing familiar cues in a new situation and choosing an appropriate response. As Kahneman notes, “Expert intuition strikes us as magical, but it is not…[It] is nothing more and nothing less than recognition.” It’s Mr. Magoo with eyeglasses, a prescription that lets him recognize an airplane instead of confusing it for a movie theater. In his classic essay “The Ascending Spiral”, pioneering snow scientist Ed LaChapelle echoes that point; intuition “is not some sort of extra-sensory perception.” He describes it as a “lifetime accumulation” of observations about snow, avalanches and weather. That doesn’t just happen, because the backcountry is a wicked environment. We help develop it by adopting simple habits that, over time, make the backcountry environment more regular and expand the base of stored cues necessary for expert recognition.

Below are examples of practicesÂ that can improve the quality of our observations, our communication, and the feedback for our decisions.

It’s all about the up: Mostâ€”at least two thirdsâ€”of our time in the backcountry is spent going up. It’s our best opportunity for observing and communicating. It’s also when most miscommunications and mistakes occur. Set a low-angle, meanderthal skin track that takes advantage of the terrain to investigate different aspects and slope angles, and that allows relaxed discussions of your observations without having to stop. Steep skin tracks make it hard to see much beyond your ski tips, and even if you do notice something important, it’s hard to communicate it when you’re anaerobic. If you’re breaking trail and can’t hear the group behind you talking, your track is too steep for easy observations and communication.

Give it a rest: Take breaks at decision points. Fiddling with your clothes or gear randomly just slows you down yet provides little information about snow conditions or route choices. Stopping to drink, eat and layer up when you’re faced with a decision is productive; it allows you to look around when you’re comfortable and talk about what you see. More often than not, you’ll pick up nuances in the terrain that you didn’t see while moving and out of breathâ€”as will your partners. And you’ll make better decisions when your brain isn’t starved for oxygen or nutrition. Pace your group so you’re moving steadily and don’t feel rushed when you stop at decision points.
You are not the Captain now: Encourage feedback within your group. You’re looking for ideas that can save your ass, not aiming for agreement. It helps to rely on questions rather than declarations. “Does that side of the slope look wind-loaded?” instead of “Most of the slope isn’t wind-loaded.” Listen for contrarian opinions rather than trying to silence a squeaky wheel. Acknowledge that anyone in the group has veto power.

Write it down: Keep a field notebook or submit observations to your local avalanche center after each backcountry trip. It’s a sure way to notice and remember details about snow and weather conditions.. Summarizing them for a field report forces you to make sense of what you observed, to sort what’s most important from what’s irrelevant. And it gives you something besides dim memories when you’re checking impressions of past events.
Debrief: When we talk about a day in the backcountry immediately afterwards, we often focus on the highlightsâ€”the great run, the funny fall, the beautiful light or snow. You provide otherwise unavailable feedback on your decisions by including an opportunity to talk about how you did things and whether those actions put you at risk. Guides often do this formally, in afternoon meetings in which they can identify when they were most at risk during the day. A friend’s more informal approach, is to ask, “Well, did we get it done, or did we get away with it?” Find a way to expand your end-of-day conversation to more than high fives. If something nags at you a day or a week later, talk with your partners so everyone understands and learns from the experience.

Find a mentor: Years ago, I spent a day traversing a high peak in the Wasatch with a mentor when the avalanche danger was high.Â It was a lesson in micro-route-finding. Near the end of the day, when it seemed we’d mostly passed the hazards, I took a few extra turns on a small slope I now recognize as a terrain trap. I looked up to see my mentor giving me a look that said, “That. Was. Dumb.” That look still floats into my consciousness when I encounter similar slopes. Though the look clearly communicated stupidity of my move, it was much more forgiving feedback than triggering the slope. Or another like it, because without that mentorship I might have gone much longer without learning to take small slopes seriously. You learn from (and with) a mentor in an iterative process, the goal of which is your becoming equally skilled and knowledgeable, perhaps more so, than your mentor. This relationship is different than that with a guide, who may pass on some useful tips but who is a leader.

Others with extensive expertise in the backcountry can offer up other practices like these, which may work better for them or better period. The point is less the specific habits than making an effort to maximize the quality of our decisions and the feedback we get for them, so we have the best chances of seeing our Mr. Magoo-like close calls and learning from them, without the too-painful learning that comes if our luck runs out.Â Time in the backcountry with that kind of reflection is what leads to the lifetime of accumulation and instant recognition that Kahneman and LaChapelle identify as expertise.