Snow performance under sun and shade

For decades, I’ve been wondering how we can explain that, when alpine skiing in Utah during spring season, on days that are relatively warm (close to 50 F), the snow exposed to the sun becomes incredibly slow, but as soon as we traverses a shaded area, the acceleration is not just noticeable, it's impressive. This in comparison to similar dates and conditions in the Alps? 

As I just ran again into these conditions, I deepened my search and found a few more things. Do you really want to know what these are? Just read on… Sun angle and intensity seems to be the main reason. In central Rocky Mountain ski resorts like here, in Park City, Utah, the higher altitude and dryer air, compared to the Alps this means that the sun's rays are more intense, especially in the spring when the sun angle is higher. Latitude (lower in the Rockies 40 vs 46 degrees North in the Alps) also exacerbates that effect. 

There’s also less atmospheric filtering, as the drier Utah air allows more direct sunlight to reach the snow surface. In the Alps, there's often more humidity and cloud cover, which filters a great deal of the sun's energy. Utah's spring days often see large temperature swings. The sun heats the snow surface quickly, causing it to become wet and slushy. At night, or in shaded areas, the temperature drops, and the wet snow refreezes. 

This creates a very "sticky" snow surface in the sun. Snow moisture content, as I have claimed in the past, is very low in Utah. A drier snow-pack, while fantastic in the winter, means that when spring melt occurs, the snow suddenly turns very wet, heavy and sticky. That’s drastically different in the Alps, where the snow higher moisture keeps gliding okay and more consistently during spring time. Utah snow, when it melts, tends to hold onto water more than the wetter Alpine snow. 

This wetness creates a suction effect, slowing skis down considerably and creating that huge difference with skiing in the Alps. Apparently, a strong sun can also create a "sun crust" on the snow surface, which can be very slow when it's soft and sticky, but I’m not quite convinced. What I should do is wax for these warm and wet conditions, but that’s a whole different subject! 

One thing for certain is that “corn snow” in the central Rockies is never very good and doesn’t compare well with its Alpine equivalent! Then of course, there are the real conditions we all experience, like when skiing shaded areas where the snow remains colder and drier, or refrozen, retaining its faster glide. The slope orientation also plays a critical role in timing the process and that’s when savvy skiers know how to “follow the sun” during spring skiing. In summary, an intense sun on dry air, and rapid melt-freeze cycles in Colorado or Utah spring create unique snow conditions that can slow things to a crawl under sunny areas and dramatically faster in shaded sections. The Alps, with their higher moisture content and less intense sun, tend to have a more consistent snow behavior, even in the spring. 

As you can read, nothing new under an intense sun!