Spring can be a challenging time for avalanche conditions. Dramatic swings in weather and snow conditions are possible. As we’ve seen in the past month, we can move from mid-winter problems to wet snow problems within 24 hrs. Understanding avalanche problems can help us plan for successful days in the backcountry. You can read more about avalanche problems here.
We have a decent understanding and tests for dry avalanche problems. We know that propagations within a weak layer can travel horizontally under a slab, delaminating it from the bed surface in dry snow environments. If the slope’s steepness is enough to overcome the friction between the delaminated slab and bed surface, we get an avalanche. This is why the extended column test is such a good test; it gives us an idea of the propagation likelihood.
Wet problems have less understood mechanics and predictability. Standardized tests also become ineffective. As snow warms up, it loses cohesion, and water is introduced into the snowpack. The weight of the water can cause the release of slab avalanches on lingering and dormant weak layers. Rollerballs (pinwheels) indicate water in the snowpack and signal that the snowpack is losing cohesion. Wet loose avalanches are the first to occur. We can get wet slab avalanches with continued warmth and water in the snowpack. The rate of thaw that results in a wet slab avalanche is variable and unpredictable.
We know that the snowpack is stable when it is refrozen, and stability decreases as it thaws. With repeated daily freeze and thaw, called the diurnal cycle, the snowpack gets more dense and stable. With this pattern, instabilities become isolated to the upper snowpack that melts daily. This changes when we receive new snow that delivers a new load or have multiple nights with above-freezing temperatures that allow the snowpack to thaw to the ground and move moisture into underlying weak layers. Rain will also quickly destabilize the snowpack.
When the snow is wet, we can’t use tests for stability assessments, we must rely on observations to make decisions. This method lends itself to all avalanche problems, often simplifying the decision-making process.
Trask Baughman, an educator with the West Central Montana Avalanche Foundation (WCMAF) explains:
With the conclusion of the 21-22 avalanche forecast season, you will have to gather and observe all necessary data to plan your adventures and make on slope go or no-go decisions. Bruce Tremper, the author of Staying Alive in Avalanche Terrain, writes, “good habits are what will save your life”. Having easy to use tools will help build those good habits and aid with decisions in the complex, dynamic mountain environment. All backcountry users, regardless of experience, can use rule-based decision-making.
A powerful tool is ALPTRUTh, a mnemonic to help memorize and remember red flags and key terrain features. To utilize this tool, you note the factors and add them up. ALPTRUTh can be incorporated in a pre-trip checklist or a final check before committing to a slope. When 3 or 4 clues are present, extra caution and careful terrain management are needed (93% of accidents in North America have 3 or more factors present). If you have 5 or more factors present, it is recommended you push pause and carefully find an alternative path.
Avalanches, in the last 48 hours?
- Using resources like the Missoula Backcountry Facebook page and the WCMAC public observations page is an excellent place to find this information when planning your tour. When in the field, if you see avalanches on similar aspects and elevations that you want to ski, nature is screaming danger.
Loading, by snow, wind, or rain in the last 48 hours?
- Snow doesn’t like rapid changes; it takes time for it to settle and bond. Your pre-tour ritual should include looking at weather data for the last few days.
Path. Are you skiing an avalanche path?
- The “Path” in ALPTRUTh is for easily recognizable avalanche terrain. When choosing to ski avalanche terrain, it is essential to make sure no other factors are present and to use best travel practices like skiing one at a time.
Terrain Traps. Are there any terrain traps?
- Imagine the consequence of being caught? Any terrain features like gullies, trees, and cliffs will significantly increase the severity of being caught, even by a small loose wet slide.
Rating considerable or higher hazard on the current avalanche bulletin?
- Without an avalanche bulletin, assume the danger rating is Considerable. Only with careful consideration over days without significant weather change and no other red flags being present would I drop the danger rating to Moderate. Often in a spring diurnal cycle, the danger starts at low in the morning and rises throughout the day.
Unstable Snow. Has there been any collapsing, cracking, or rollerballs?
- Like recent avalanches, collapsing and cracking are clear signs of avalanche potential. Careful decision-making and terrain choices are recommended.
Thaw Instability. Is the temperature rising?
- When temperatures rise above freezing, the snowpack’s cohesion quickly falls apart, leading to thaw instability. Keeping an eye on the time of day and rising temperatures is the name of the game in the spring. Looking at weather data to see if it is freezing at night will help give you a go or no-go decision before leaving your house.
In my assessment continuum, I rely on observing red flags and weather trends listed in ALPTRUTh first and using data from snow pits last. If ALPTRUTh is indicating dangerous conditions then pits and stability tests are unnecessary. Additionally, stability tests do not reliably predict wet problems, and you should never use a single pit to make decisions when choosing to ski a slope. A quick hand pit can be helpful when investigating how saturated the snow surface is. Skiing a test slope is also a great way to gather information on surface conditions. When I decide that it is safe to ski avalanche terrain, I slowly step into more committing terrain in a systematic approach.
Roger Atkins’ strategic mindset is a great tool. More can be read here. We can simplify the decision-making process by deciding what sort of terrain we are willing to step into and what terrain to avoid, before entering the backcountry. For instance, if we decide that avalanches are possible in terrain over 35º, and we will stay out of that terrain, it removes quite a bit of the assessment process. If we decide to stick to terrain under 30º, it can eliminate almost all of the assessment process as less than 2% of all avalanches occur under 30º.
The public observations page is a great asset to learn about conditions, but it is only effective if observations are being submitted. It may be more important than ever this time of year. Don’t feel obligated to submit complex observations; anything is helpful, and pictures speak a thousand words. Pertinent negatives are also helpful; let people know if you didn’t see any red flags and found stable conditions.
Useful online resources:
- The NOAA backcountry forecast page has a number of useful links, including local SNOTEL sites.
- The NOAA home page also has good info; check out the discussion for more detailed weather information.
- Montana MDT has Cams at Lolo, Lost Trail, and other roads, giving a visual of weather conditions.
- Snow-forecast.com Has good weather maps that show snowfall, freezing level, cloud cover, wind, etc.
Ski and ride safe. See you next year!