'Is It a NO Go?' When to Dig
One of the most common misconceptions of new students in the avalanche world is that there is a sure-fire way to determine is a slope is safe to ski or not. Many have heard about digging snow pits to look at and test snow structure and think that this must be their silver-bullet to success. In reality it is this myopic mindset that we perpetually beat back as avalanche course instructors, as digging in the snow is just one tool in sorting a much larger puzzle of uncertainty.
Photo: Deliberating a run in the Chugach Mountains, Alaska...
Undoubtedly, decision-making is one of the most common stumbling points for backcountry travelers. It is very hard to separate ones desires from what one sees without emotionally driven bias. Time and time again avalanche accidents occur with a majority of information screaming a resounding, ‘NO,’ at a group and, experienced or not, the group finds a way to justify their decision because of how bad they want to find contrary information.
Aside from straight misinterpretation of data, such as anticipating snow at one elevation or aspect to behave similarly to another, perhaps the largest issue with snow pits, and looking at snow in general, is spatial variability. When snow stacks up on a slope wind helps level it clean to what appears to be a flawless virgin white sheet. In reality the snow sub-surface isn't so consistent. One large reason is that mountainsides are not uniform; a pile of rocks, a tree or a group of buried ski tracks could all be buried at various locations, all with their own effect on the snow, with no indication of their presence from the surface. The consequence is a variance in data if looking in the snow and the potential to mislead oneself.
So if we can’t rely on snow pits, then what good are they? And how can we get better and more reliable data? Again, a snow pit is a tool; it is one window into the snowpack and one data point. The more snow we look at, the more reference we are left with longer-term, and the more likely we are to understand its behavior. Day to day the same idea applies; more pits (data points) are more valuable than fewer. With a bit of experience combining ones own snowpack data with other weather and avalanche observations, regional forecasts and history should help dictate a reasonable current local forecast.
After stating all this, invariably, I get asked, “Well, then how often do you dig?” As with many answers in the avalanche world, I answer, “It depends.” First I consider why I should look at the snow and that answer should help me answer to what detail I want to analyze it.
Regardless of what problems lay deep in the snowpack or not I find myself looking perpetually in the snow surface for the presence of a slab. Lacking any buffer to the elements above, surface snow is the quickest to change and consequently often the most sensitive area of the snowpack. Also, the weight of a skier is more likely to affect weak layers the closer they are to the surface as snow dissipates force over distance. Quick tests and constant awareness of how snow feels under ones feet should be the base for every backcountry traveller’s situational awareness.
In the case where I am concerned about a particular more deeply buried snowpack layer, then things are a little trickier as to whether I dig down to it to have a look or not. First I try to consider; if I do decide dig, will what I see change my plan or not. In itself this question has the potential to be a dangerous proposition. Never should we use a snow pit to justify skiing something; in contrast, we should only use them to disprove our original forecast. If we obey this rule, which mind you, can be a challenge, we will leave ourselves with better odds.
When there is a profound layer of instability documented in the snowpack my forecast is usually easy and I don’t necessarily need to dig to it aside from a case where I am looking around from an inquisitive, scientific point of view (unrelated to my decision making process). When there is a lot of hazard my day to day is simple, play slope angles, follow a careful route and avoid avalanche terrain altogether. I try to remind myself that messing with the problems at hand are not worth my time and I will have fun in other ways. I know there is a time to ski committing terrain and a time not to. Some slopes have only a few weeks a season, on average, to justify the risk of entering, so I try to consider if the day I am out is one of those days or not. Having a broad viewpoint of a current situation can be invaluable in crunch time.
The hardest time to forecast is determining when a persistent weak layer in the snowpack is no longer an issue. If living here in the Wasatch, like me, this is an easier task than if one is in an isolated range. The sheer amount of information available here through the Utah Avalanche Center is astonishing. Knowing if recent avalanches have occurred or not is hugely relevant to developing ones own forecast. There aren’t any hard and fast rules but when activity appears dormant give it a little more time, then if things still look good start by moving into favorable terrain first; terrain with the least exposure to hazards. Pick terrain that appears the most in condition with the strongest snowpack you can think of. Work into terrain with baby steps, dig along the way and leave a viable out if data comes as a surprise. In the case of forecasting in a remote area without much outside information available the increased degree of uncertainty should be further reflected in the decisions made.
Snow pits are one of many avalanche-forecasting tools. We must look at snow to have a greater understanding of it but we must not use pits as tools to directly and exclusively justify our decisions. There is no means for a hard and fast ‘yes’ to our decisions made in the avalanche world but a snow pit can give a resounding ‘no, today is not the day.’