Friday, February 5, 2016

Avalanche fortune-telling, aka how we decide when to close passes for prevention work

Barbara LaBoe

How are you at predicting the future?

Avalanche Control Specialist John Stimberis checks weather
forecasts and computer models regularly to measure avalanche risk.
That’s the ultimate job description of our Avalanche Control crews, who work throughout the winter and early spring keeping our passes clear and the traveling public safe.

They’re tasked with both anticipating and preventing natural avalanches that could cover highways and bury vehicles.  They don’t peer into crystal balls, but they do use a variety of tools – including explosives –  to keep one step ahead of the snow.

By definition, avalanche control work means closing passes while snow slides are triggered and then the roadway is cleared. We know that’s disruptive to travelers and, when possible, we schedule the work for non-peak hours. Sometimes, though, conditions and the safety of motorists and our crews working the passes don’t allow for delays.

So, how do we decide when to conduct avalanche control work?

The short answer is whenever we feel the risk of a natural avalanche on the roadway is too high.

Stimberis uses a bucket to sample snow, measuring the water
content to determine the density of the snowpack.
The longer answer is that it’s a complicated alchemy of science, weather forecasts, historical data, traffic volumes, maintenance equipment availability and just general “snow sense” that our highly skilled crews calculate every day.

Our avalanche crews start with the science, including detailed weather forecasts, computer models and historical slide information. Snow pack information, temperatures, wind speed, wind direction precipitation and snow levels are all tracked to see which – if any – are increasing that day’s avalanche risk.

Next, they move on to the snow.

Snow consistency is studied and measured for water content and density. The snow’s temperature is taken and large blocks of snow are examined for any evidence of shears – or weak spots within the snow pack that could break loose and act as a sliding layer to bring snow down the mountain.

The final step is that little something extra that comes with experience – a sort of fortune telling for the snow. Using the models, data and a healthy dose of their own knowledge of the particular area, crews determine what the snow is expected to do in next 12 hours. Our crews are often ski patrol veterans, which can be valuable experience when it comes to evaluating snowpack and predicting next moves.

Stimberis shears off blocks of snow while measuring
a snowpack’s stability.
At times, some of their conclusions may seem counterintuitive to motorists. It doesn’t have to be snowing, for example, for the avalanche risk to increase. Roads may look bare and wet, but heavy rainfall puts extra weight on the snowpack that can trigger an avalanche. Warming temperatures – or even several hours of sun during a clear day – can also increase avalanche risks even during seemingly “perfect” pass driving conditions.

Can we prevent every avalanche? No. Nothing involving Mother Nature is ever 100 percent controllable.

But forecasting avalanche danger helps reduce the risk to motorists and our maintenance crews as well as decreasing the amount of snow available if a natural slide was to occur.

And, even though they can be frustrating, that’s the goal of every avalanche control closure: Reducing risks and keeping motorists safe.

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