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Today’s Storm is Tomorrows Avalanche Problem

As the seasons change and we begin shifting gears to winter, the temperature drops and storms begin to line up. On October 25th, we received our first snow fall with a trace to one inch of snow in the Ogden mountains.

On November 8th, the Ben Lomond Peak weather station reported thirteen inches with another rider storm passing through on November 11th resulting in an additional six inches. With snow beginning to accumulate, it is a sure bet that "today's storm is tomorrow's avalanche problem.” 

Over the years, I have developed a keen eye on the places I ski regularly. I often visit these areas in the Summer and Fall noting terrain features, bed surfaces, and past signs of avalanches. These observations have often helped me form strong opinions on where and how I choose to ski. 

I have created quite the archive of terrain photographs noting defined avalanche paths and areas with poor bed surfaces such as rock slabs or grass. I have even gone as far as to note these features on tools and apps like Gaia, Google Earth, or Cal Topo. As I later reference these tools to plan routes during the ski season, these notes act as reminders of what lurks beneath. 

During the season, as new storms arise, it is critical to note where old snow from these fall storms will likely persist. Typically, we look to upper elevations on shaded and sheltered aspects as being notorious for holding old snow plagued with persistent avalanche problems. These problems often linger in our Utah snowpack remaining well into the season with the potential to give rise to deep persistent slab avalanches.

Deep Persistent Slab

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply buried over time. Deep Persistent Slabs are destructive and deadly events that can take months to stabilize. You can trigger them from far down in the avalanche path and even after dozens of tracks have crossed the slope. As noted above, this problem is “particularly difficult to forecast for and manage." Old rotten snow from early storm cycles is often the culprit of persistent grain types like depth hoar or facets. When the season’s snow begins to build upon this weak foundation, the avalanche potential is significant and concerning. Deep persistent slabs have a destructive and deadly potential that can take months to stabilize. Taking note of where you have identified early season snow that could become old, rotten and eventually buried, and then avoiding these areas until time and evidence confidently ensure they are no longer a threat, might just save your life.

Daniel Turner Technical Director, Ogden Avalanche

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