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Each morning of the ski season, the Ski Patrol is engaged in ongoing avalanche risk assessments. Of the multiple daily chores, one stands out for its precision, tradition, and importance: The Standard Weather Observation. Weather is a key factor in predicting avalanches as it is a constant modifier of the snow pack. Events such as wind, sun, snow, rain, freezing temperatures, and thaws influence and create layers of snow with different characteristics. How those layers strengthen or weaken over time is dependent on past, present and future weather events. Observations are made at standard times and at the same plot each day. Weather recordings have strict standards that are set by The National Research Council of Canada, and the Canadian Avalanche Association. Great care is taken to be sure that all observation guidelines are followed with precision.
The Main Study Plot beneath the Great Bear Chair is home to several instruments. Perhaps the oldest, most interesting, and precise is the precipitation gauge. Built by the Belfort Scientific Company in 1976, this universal recording precipitation gauge determines how much snow or rain has fallen over a specific time interval. A circular horizontal opening in the top of the unit catches snow, where a scale mechanism converts the weight of that snow into a water equivalent measured in millimeters of water. This is shown by the curvilinear trace from an inked pen on a rectangular chart paper. A spring-powered clock rotates a vertical cylinder on an 8-day cycle. Each week the chart paper is changed and the clock wound. This instrument is accurate to 0.2mm of water equivalent, and the clock mechanism accurate to 14 minutes over 8 days.
Why convert snow to water equivalent? Through a few simple equations the observer can calculate the density of the new snow layer. This again is a key factor in determining avalanche hazard for that given day, as well as the avalanche control strategies that will be required. In general, a dense layer over top of a less dense layer is a recipe for slab avalanches. The greater amount of weight added to the snowpack, the greater the stresses added to the underlying snow structure, and thus the greater the potential for avalanches. The “mill count” also can give an indication of the potential magnitude of an avalanche within the new snow layer. Perfect “Champaign” blower powder has a density of 40 kg/m3. Solid ice has a density of 900 kg/m3. In Fernie it is common to find new snow with a density between 75 kg/m3 and 125 kg/m3.
Even with innovative technologies, observation tools new and old, and weather forecasting products, predicting weather events remains a constant challenge. Since it is still extremely difficult to pinpoint the weather, it is also extremely difficult to pinpoint exactly when a natural avalanche may happen. The ski patrol would like to remind all backcountry users that there are still persistent weak layers lingering in the local snowpack. Some skier-triggered avalanches have been reported recently. Know before you go, stay safe, and have fun!
Visit www.skifernie.com for more information on the conditions, events, and news at Fernie Alpine Resort.