Stubborn and persistent. This might sound like a lot of people you know. Right now, this is how our snowpack is shaping up for parts of Colorado. It's certainly not unusual to have this happen, but the fact that one of the main layers of concern is Surface Hoar, it's slightly uncommon. The CAIC is reporting widespread layers in Steamboat zone and Vail area, and we've noted some at Cameron Pass in the past couple weeks.
In addition, the natural avalanche cycle has decreased, leaving us with a post-storm, wind-deposited layer that's stubborn. However, if an avalanche starts on the surface hoar layer, it has a good chance of being big.
What is Surface Hoar? It's a weak, typically feathery layer of snow grains that grow on cold, clear, humid periods in the winter and create an extremely weak layer under new snow once they are buried.
I love to ski in British Columbia, where they live with surface hoar on a yearly basis. In fact, surface hoar is the biggest avalanche killer of all the weak layers in the snowpack. In the Columbias you have the perfect storm of cold weather (even at low elevations), relatively low wind speeds, and tons of humidity available from the enormous lakes along the Columbia River.
In Colorado we don't see widespread surface hoar on a yearly basis. Every few years an weather pattern exists that produces this grain type, we see a cycle of avalanches, and then we forget about it again for a while. We don't have the regular occurrence of long fracture lines that cross ridges and contour around entire valleys.
For Cameron Pass, I've most regularly seen surface hoar in the Seven Utes drainage - it tends to hold more humidity than other areas around the pass and allow for growth of the notorious layer. One morning I was able to poke around a very recent, large avalanche that literally encompassed the entire valley.
Large avalanche in Seven Utes drainage, encircled entire upper valley
There has been some great information published, even in the States, about surface hoar, mostly out of Montana, in the industry periodical.
How do you manage a ski tour in areas with surface hoar? You sprinkle extra caution on your tour plans, understanding that it can slide at lower angles, remotely across slopes, and wider than average. You look, listen and feel for obvious signs of instability - and you don't play the "it won't happen to me" game.
Join us for a Level 1 (AIARE 1) avalanche course to learn more about how to plan for a tour during a season like this and others with persistent weak layers. If you tour in Colorado, you need to learn about persistent weak layers, even when they are stubborn (like your last roommate!).