The absolute best riding of the year without a doubt is the spring corn snow. Corn snow is the most sublime experience you will find. Better than powder, corn snow is termed ‘hero snow’ to many. Corn snow is carvable, flawless, and perfect — it is like Christmas morning or a first kiss. Some of us use every tool in the arsenal to calculate when and where corn snow will be found, others just know from experience — and like a farmer going to harvest; we appear year after year to the same favorite areas on perfect cue to the season.
This year has been unique though as we had unusual winter snowpack conditions in to May. Typically the corn snow begins in early May and goes through the middle to end of June. It is in this same season that the snow consolidates enabling us to get the high altitude lines. Make no mistake though, consolidation and corn snow have nothing to do with one another.
I will simplify this for this for the sake of quick understanding. Most professionals categorize snow in two forms, wet snow, and dry snow. The avalanche conditions of both are completely different processes. Dry snow avalanches are caused by overloading the weak layers, while wet snow avalanches are caused by the decreasing strength of layers. This is an important distinction to finding ripe corn snow, and again – overly simplified.
Corn snow occurs under a special combination of environmental conditions. Temperature and sun angle cause the melt-freeze cycle that produces corn snow. The snow surface has to go through repeated freezing and thawing cycle to bond snow crystals which in turn generate larger granular snow pellets, roughly 2-3mm in size. Tiny amounts of water percolate between these granules through the surface of the snow. It is important to note; consolidation does not cause these granules.
These free floating granules with water between on the top surface of the snow offer perfect corn snow. There is a fine line though. Once this water between granules percolates to the ground surface the snowpack looses it’s bonding strength. This can quickly and dramatically change the snowpack from perfect to dangerous in a matter of hours or even minutes. What was a perfect supporting layer is now a recipe for the dangerous wet slide avalanche conditions.
Corn snow needs a constant repeated freeze-thaw cycle to form. Unlike powder, each day the cycle repeats itself. It generally only takes a few hours below 32F degrees for the snowpack to firm up in to a frozen granular. Once night time temps begin to creep in to the 34F-38F range (depending on the depth of the snowpack since the thermal mass plays a part too) corn snow will not appear the next day. When I see this gradient in temperature, I will not bother with steeper aspects. In Colorado, generally speaking from my own experience 38F seems to be the upper limit.
Temperature and sunlight play a huge part in the formation of corn snow. After a freeze the night prior, it becomes all about timing the next day. Corn will be unmistakable. A dry, slightly lubricated granular snow. The corn will occur briefly when the overnight crust softens, to the point where it gets velvety and breaks into mostly-dry “grain clusters”. Once the sun angle and temperature warm the granules and percolation begins, the snow enters the wet granular stage, better known as slush. On steep aspect terrain this can also turn to a dangerous condition.
Often times, early in the corn snow season you can find lines for most of the day with a little preplanning and an early start. As the season moves forward and the sun angle increases in to June, the window of corn snow decreases and gets tricky to properly time. Once a snowpack as a whole is isothermal (meaning the same temperature throughout the snowpack), the window decreases as well.
I have many tools I use in pre-planning to determine in advance areas that I will ride in. I usually try to estimate a time window in terrain. Sometimes these are cutoff times where I will turn back at a certain point. Hunting perfect corn snow for the most part comes with experience that is honed each year. There are however a few cool tools that you can use for route planning, and I will go over a few of these. While the process and tools of route planning look time consuming – this actually takes me less than 15 minutes the night prior. Some of these same tools I use to plan routes in avalanche terrain as well.
I have to say it here so that it is crystal clear; I would advise anyone that frequents the backcountry to take a Level One avalanche course PRIOR to venturing out. In no way are the methods that I am about to illustrate related to travel in avalanche terrain. These are simply methods to use in pre-planning to find awesome corn snow. Route planning in avalanche terrain is an entirely different set of circumstances and resources that should be used separately from this.
As I mentioned earlier; finding corn snow and hitting it right has a lot to do with temperature and sun angle. Therefore, in route planning one needs to determine what time that window is going to take place and work backwards to determine an appropriate time to leave the trailhead. The first thing to look at is pinpoint forecast. This will give you an idea of the night time and day time temperature of a given location. It’s a good method to keep an eye on this for a few days prior.
I personally use National Weather Service NOAA for a point forecast. To get a pinpoint area, first type in a location that is close (for instance a zip code). In the example below I am using a point forecast for Mt Audubon, a thirteen thousand foot peak with amazing descents in Indian Peaks Wilderness. I will use the map box to mouse in the exact area on the topo map as shown below. The green grid square will indicate the point forecast within the map.
Once you have the point coordinates set on the map, you can scroll down to Hourly Weather Forecast Graph. This area will show you the temperature trend which is valuable information determining the temperature gradient in the given area. There is also other information such as windspeed, precip, and one of my favorites; thunder. If you have never been above treeline during lightning / thunder my advice; don’t do it. In the graph below you can see a perfect temperature cycle for corn snow. Freezing temps at night, and thawing temps in the morning. Perfect conditions for a corn harvest!
Another fantastic tool is the Google Earth Sun Angle. This can give a rough idea of where the will hit on the intended route. I set the date and time in the parameters which will then show roughly which areas the sun will hit and approx for how long. Often times this can give you a solid idea of areas that might be sheltered with less sun exposure for a return trip.
In the example below I have highlighted the planned descent in a white outline. This Google Earth image was taken during the late summer and does not show the snow in the planned couloir. I start with the sunrise sun angle around 6am. Notice as I increase the time the couloir stays in a shaded area until around 8:30. This gives an idea that this line will receive less sun than areas around it, which is good news. It also tells me that the clock starts ticking around 9am, and that I will probably have until 10:30 to make this descent.
Another great tool is transforming a Caltopo overlay in to Google Earth. This overlay, imported to a specific area as a KMZ file will show slope angle in color band. In the example to the left, again I use Mt Audubon. Yellow indicates less than 10-20 degrees, orange 20-30, red 30-40, purple 40+. My concern would be areas over 30 degrees that get high sun exposure on the return trip out of this basin. If I notice any terrain traps, I may note those on the map I carry.
These are just a few of the tools I personally use to find corn snow and plan routes. For avalanche safety you will want to read and understand the avalanche forecasts, and have a good idea of how to travel in avalanche terrain. During the spring months you will also want to keep in mind that dry snow avalanches, and their potential paths may be different from wet snow (spring) avalanches. My own words of caution are to be off of steep aspects if you get more than a few inches of thaw happening. Again, a slope can change from stable to unstable in a matter of minutes when a warming trend occurs.
Another factor we have all had to deal with in the past few years is the dust layer. Depending on the snowpack, the dust layer can prevent bonding and in some cases it prevents percolation from occurring in the freeze-thaw cycles. Instead of a deep penetrating cycle, this instead happens above the dust layer which can cause weakness and slides at the dust layer. This can also cause anomalies to occur that run full depth with poorly formed snow granule clusters.
May and June are the best months in Colorado for backcountry steep aspect lines. We live in an amazing place where we can ride a few thousand vertical feet of corn snow in the morning, and at the base, be in a t-shirt and shorts having a beer in the green grass. I hope everyone is able to find some amazing corn snow this spring!