Snowpack stability and the upcoming winter

Early season snowfall seems so harmless at first. Cold and sparkling white, it ignites the energy and imagination of skiers who have patiently waited through the summer months for a chance to slide on snow once more. The season’s first snowfall is exhilarating and magical, but unless it is quickly followed by more of the same, it sits on the ground and festers away. By the time it is buried beneath a midwinter snowpack, it is no longer a source of joy, but a weak layer waiting for a trigger to start an avalanche. And then it draws blood.

Right now is the ideal time to begin studying while there is snow in the surrounding mountains. As the saying goes, “today’s snowfall is tomorrow’s weak layer.” With colder air in the forecast and a shallow snow depth in most mountain ranges around southwestern Montana, the importance of studying the current snowpack is doubly so. Cold air and shallow snow depth is a recipe for weak, faceted snow on the ground. When the snowpack is shallow, cold air causes a strong temperature gradient to form in the snowpack, since the ground temperature is still close to freezing. Consequently, the snow is weakened and becomes faceted. Once this weak snow is buried, it becomes a persistent weak layer that can linger late into the winter. These weak layers on the ground are some of the deadliest and most difficult avalanche hazards to manage, and can bring steep backcountry skiing to a halt.

The snowpack was meager in most of the mountains I surveyed this past week. I observed below normal snow depths in the Bridger and Gallatin mountain ranges, as well as the mountains around Big Sky. There is minimal snow at the lower elevations in these locations, but there is some up higher. That snow will become a problem layer if there isn’t significant snowfall to bury it before colder temperatures set in. The mountains surrounding Cooke City had slightly more snow at lower elevations and significantly more snow up higher compared to the rest of southwest Montana, but that’s not saying much. The mountains surrounding Cooke City may fair better in terms of stability, in relation to the rest of the region, since the snowpack in Cooke City is currently deeper.

       

Whatever happens, the groundwork is laid for active avalanche cycles in the coming months. A similar pattern was set up the past two winters, with some snowfall and cold temperatures early in the season, but the second half of the past two winters was remarkably warm. Those warm temperatures largely healed the weak layers in the snowpack before any massive avalanches were triggered. We might not get that luxury this winter. The pattern that is shaping up for December, and potentially the rest of winter, could be significantly colder than what has been seen in recent years.  In such a scenario, weak layers in the snowpack may take longer to heal, and the snow in the mountains today could be a killer come February.