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  • Writer's pictureJustin Ibarra

Fall for Thought

Updated: Oct 2, 2019

Touring through the changing leaves.

The nights are getting cold, the leaves are changing into yellow and orange, and pumpkin beers make their appearance again as the short-lived Colorado Summer passes by and another Fall season makes its arrival. For us snow enthusiasts this can only mean one thing.. Winter is almost here!

Powtown USA

We have seen our first couple of snow dustings in the high country already and some areas in the West have had inches to feet fall to the ground. Now while this does amplify the stoke that sliding on snow is near, this is also a great time to remember why and how these early season snow storms can wreak havoc on our winter snowpack.

New slide path on Peak 1 from last years historic avalanche cycle.Photo by Greg Hansen

Here in Colorado we have what you call a traditional “Continental Snowpack”. Cold, dry, and shallow. When we start to receive these early season snow storms they are typically followed by long cold and dry spells before the next snow storm cycle comes through. Under this scenario if it doesn’t melt then we will start to see the snow crystals break down into what we call Facets, or sugar snow. This sugary, un-bonded snow will then continue to grow into an advanced stage of facets called Depth Hoar. This is bad news bears because when we do then start to get into winter and receive accumulating amounts of snow it will be resting on those sugary Facets, causing a weak layer at the bottom of the snowpack. As you can imagine this could cause an avalanche to encompass the entire snowpack. Perfect example is last season’s historic avalanche cycles, a big player being the early season snow that we received that then became the seasons sleeping dragon.

Depth Hoar Crystal

So why do these lulls between storms cause the snow to facet? One of the main reasons why is due to what is called a Large Temperature Gradient, or a big change in the snow temperature over distance within the snowpack. How cold is the air, how warm is the ground, and how deep is the snowpack? When you have a shallow snowpack, cold Fall air temperatures in Colorado, and a warm Earth, you have a big change in snow temp within the shallow snowpack and a Large Temperature Gradient. In a perfect world whenever it starts to snow we want the floodgates to just open up lending to a deeper snowpack and more distance for the snow temperature to chance producing a Small Temperature Gradient. Mother nature likes gradual change and not drastic.

You can notice here the Depth Hoar layer near the base of the snowpack. The darker color is due to there being more air space between the snow grains.

Another big player that we typically see with these early season storms is what melts and what doesn’t between the lulls. Due to the fall equinox the sun will start to stay more South in the sky. This will usually then cause the Southerly aspects to almost completely melt out if long enough time between storms. Along with that most SW-W aspects will melt and depending on the temperatures, radiation, and again the amount of time between the storms SE-E will typically see a good amount of melting as well. Now the North side of the compass rose will stay cold and won’t see as much sun. This is a huge player in why Northerly aspects tend to be more dangerous here.

We basically just want to see one of two scenarios to play out. 1.) We don’t start to get snow until end Oct/November and then the floodgates open! 2.) We get some early season snow but not a significant amount and it gets the chance to all melt away. Or I guess we could add a third scenario, it starts snowing early season and it doesn’t stop!!

Fall… the perfect time to start going through your gear and making sure you fix your broken binding from last season, wax up the fleet, start brushing up on your avalanche skills again by reading books and blogs, get out and exercise, do some climbing or biking or hiking, get out and enjoy the colors, watch some ski porn, be patient, and stay STOKED for the season ahead because it will be here before we know it!

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