Mother Nature’s Hoar
Although we are all anxious to get out and embrace winter with our new snowmobiles, it would be wise if we pay close attention to the weather and more specifically this past week of clear skies and frigid temperatures.
While most of us merely bundled up and watched the weather forecasts for the next storm front, we may have missed an important signal from Mother Nature—conditions have been optimum the creation of depth hoar.
Now, some of you may ask what this has to do with snowmobiling. Well, depth hoar is the main culprit behind most avalanche fatalities. It represents that weak layer of snow that tends to persist throughout the season just waiting for something to put enough pressure on it to break away and create slab slides.
Basically, this is how it forms. Early snow tends to provide an insulation factor for the ground. When cold temperatures freeze the surface of the snow, a hoar layer begins to grow, being maintained by moisture that is protected by the insulation of snow over the earth. This hoar has ample strength to sustain pressure from above, such as additional snow weight, but is very vulnerable to side pressure. And once it breaks away, it serves as ice beads that facilitate the sliding of heavy slabs of snow.
So all of this cold dry weather has just made our future base level a death trap for the next few months.
Depending on how Mother Nature distributes its snow and cold temperatures for the rest of the winter will determine how safe the high elevations will be. But for a while, snowmobilers need to be on their guard, particularly on west and south facing slopes and near ridgelines where wind tends to keep snow levels close to the surface.
Although we often equate avalanche danger to deep snow, in reality it is a thin snowpack and cold temperatures that create the most dangerous conditions. A thick snowpack can actually do more good in the long run to eliminate depth hoar … but that’s in the long run. The next deep snowfall might be the deadliest. So pay attention to the weather.
SnoWest Newsletter - December 8, 2011