Feature: Careful What You Wish For, Looking At October Snow
By Griffin Post | October 5th, 2011
In this file photo, surface hoar forms on top of an early-season snowpack on Teton Pass in Wyoming.
October 5, 2011
— Griffin Post
I don’t want it to snow. The statement is nothing short of sacrilegious for skiers, but it’s true. As hyped up as people get around this time of year, snow this early can cause serious problems down the road in terms of the snowpack quality. Why? It all comes down to the fact that the earlier it snows, the more likely the development of persistent weak layers becomes. While I was generally familiar with this principal, I enlisted the help of Bridger-Teton National Forest Avalanche Center Director Bob Comey and Teton Gravity Research’s lead guide Kent Scheler to get a better grip on the downside of October snow.
As I found out, problems with early-season snow stem from two areas: the creation of depth hoar and the development of a hard crust that will eventually be buried deep in the snow pack.
First, the depth hoar.
The earlier it snows, the more probable depth hoar formation becomes. These conditions exist due to the generally thin nature of early-season snowpack — less than 3 feet — and the likelihood of cold snaps.
“If a thin pack is proceeded by a cold trend, there is less insulation to shield base layers from extreme temperature difference [gradient] that exist at the warm earth-cold air interface,” Scheler said. “Depth hoar forms at the base of the snowpack due to the upward movement of water vapor resulting from the extreme temperature gradient in this zone,” he said.
The longer a thin snowpack is on the ground — uninsulated by more snow — the more likely depth hoar will form.
The second scenario has to do with the development of a hard crust that can form after a prolonged dry period following the first snowfall. This hard crust creates a surface for weak layers to form on (i.e. surface hoar) that subsequently become buried deep in the snowpack.
Surface hoar crystals.
“The worst case is that you get a hard crust, some light density snow and a prolonged cold period, resulting in a persistent weak layer,” Comey said.
Once again, the likelihood of this scenario developing is proportionate to the length of time the early season snowpack is on the ground.
So, is October snow the end of the world? No, not at all. It really all depends on what happens next. Despite these weak layers, if the “next storm system can come in super warm and heal it,” the snowpack will stabilize, Comey said. However, if the storm “Comes in slow and backs off, you may never get rid of [the weak layer],” Comey said. “What’s dangerous about [this scenario] is that you don’t know what’s dangerous — it’s really hard to manage.”
What’s the ideal snowpack formation then?
“It starts snowing November 1 and keeps snowing a little everyday without any clear, cold nights that could create surface hoar or extended dry periods,” Comey said.
These conditions would help prevent both the formation of depth hoar and a hard crust for weak layers to from on.
It’s not that early-season snow is the end of the world, it’s just that the longer the snowpack is on the ground, the more susceptible it is to the above weather conditions, that could result in persistent weak layers. The development of these weak layers isn’t a guarantee, but it is something to keep in mind before you do a snow dance this October. More important than anything, when it does snow, pay attention to weather patterns afterward, as the formation of these weak layers is by no means limited to the timing of the snowfall.
In this post: Griffin Post Location: Wyoming Teton Pass MT Keywords: Ski Snowboard Feature Stories Backcountry Features Backcountry News Travel