When winter arrives in earnest, snow covers the mountainside, and skiers and snowboarders rush to resorts around the country. There are a few things that top snow sport enthusiasts’ wish lists: a cozy lodge, short lift lines, and lots of runs covered in corduroy, that iconic pattern of parallel ridges in the snow that make for a delightful surface to ski on. But these textures carved into all your favorite ski runs don’t happen by magic—though they do happen overnight. There’s plenty more science and engineering that goes into maintaining a run that skiers of all abilities can’t wait to carve than meets the eye. And no one knows that better than Brian Dubuque, snow surface manager at Snowbasin, one of Utah’s top resorts. He’s responsible–in concert with an orchestra of skilled groomers–for keeping the mountain in ideal skiing condition all winter long. And that all starts with grooming. Grooming: defined Grooming is the practice of using machinery to maintain and shape ski hills. It has one main purpose: to process snow, whether it’s natural or manmade, and create a crisp, fresh surface for visitors to ride down. At major resorts, it’s done via a small army of skilled operators who drive a fleet of snowcats, large pieces of machinery with wide, tank-like tracks that dig into the snow, carve it up, move it around, and maintain slopes. Yes, regular grooming hours are at night when slopes are empty. At Snowbasin specifically, groomers work in shifts, combing out snow in snowcats with a dizzying number of toggles and switches from about 4:00 pm to 9:00 am. Their job: To put snow back where it needs to go, which involves driving up and down slopes, smoothing surfaces and creating perfect corduroy stripes in the snow. Doing so across an entire resort requires lots of communication. That’s Dubuque’s main job. He communicates with the resort’s snow-making department about where they need more snow and where they don’t, and works with a team of groomers, sometimes from a snowcat himself, to dictate which of the resort’s 60 runs get priority and if there are any special projects that need attention from night to night. Like digging out lift terminals after a storm, pulling snow around to smooth out the lift unloading area, or flattening areas around snow-making devices. But mostly, groomers spend hours smoothing slopes for tomorrow’s visitors and laying down corduroy. What’s the deal with corduroy, anyway? It’s an important job, as the simple pattern plays a surprisingly important role. Not only does it create an attractive slope, but it provides a more stable surface for turning and gliding on skis or boards. That’s because, in part, the increased surface area of the pattern versus a flat landscape means there’s also an increased rate of evaporation of water from the snow. This leads to stiffer peaks and valleys in the snow, which results in more easily navigable terrain that’s a pleasure to ski for beginners and experts alike. This type of surface and snow density offers better control, excellent turning conditions, and the ability to build up plenty of speed. It functions to smooth uneven surfaces, too. “If you didn’t [groom] there would just be a mountain full of moguls,” Dubuque says, which very few people, including himself, find enjoyable. Indeed, what most snow sports enthusiasts want is a run that’s packed into ridges, a little crispy, predictable and processed in order to enjoy easier turns and fewer holes or bumps, which can be unpleasant at best and dangerous at worst. Carving corduroy also prevents snow from going rotten, Dubuque explains, which describes snow with a consistency like sand or sugar. It’s a texture that results from snow with too much moisture, which can happen if you neglect to groom an area at all, and few prefer it as the consistency can slow borders down and inhibit maneuverability. But it’s not just the experience that matters; it’s the health and longevity of the run itself, too. The corduroy grooming pattern makes for more robust and resilient trails, which means those skiing mid-day will have a tolerably similar experience to those first in line at the lift. Plus it helps keep the run in ideal shape all season long. The snow’s the thing How and when grooming takes place depends heavily on the weather forecast. While Dubuque’s team may be able to tackle all of Snowbasin’s 60 runs in a night if there’s little to no fresh snow, if Mother Nature decides to dump a few inches, plans change quickly. “It all depends on the intensity of the storm,” Dubuque explains. That, and what his crew can get done in the time they have available between shutting the lifts down in the evening and opening them in the morning. The best case scenario is a storm that provides two to four inches of fresh powder, Dubuque says. “We call that hero snow because it makes every [snowcat] operator look like they’ve been doing it for years.” Plus, it provides a beautiful surface to ski on. If there’s more snow, however, say six inches or more, the snowcats can start sliding on steeper slopes as the tracks get packed with snow and lose traction. In that case, a winch cat is sometimes called for, a type of snowcat that can be anchored to the top of the run, which provides the extra leverage necessary for the machine to get up a hill without issue. But another option Dubuque sometimes opts for, and one powder hounds love, is to simply leave some runs untouched so they’re coated in the light, fluffy, dry snow Utah is known for and advanced skiers and borders crave. This approach is practically required on nights when the snow never stops, when groomers can’t do much with it until it abates. The consistency of the snow plays a role, too. Heavy, wet snow, which Dubuque refers to as mashed potato snow or styrofoam snow depending on the consistency, creates unique challenges. It can bind up in the machinery’s tiller and leave streaks in the usually picture perfect pattern. It’s more challenging for groomers and requires—even more than usual—that they constantly adjust tiller speed and depth to create a good skiing surface.  “It’s not just set it and forget it; you’re always fiddling with something,” Dubuque explains. Which is why this winter, if you’re shredding immaculately groomed slopes free of moguls and rotten snow, don’t forget to raise a glass to the groomers who are hard at work while you’re dreaming of powder days and bluebird skies. The post The science of ski grooming appeared first on Popular Science.