How Hidden Valley turns green slopes into a winter wonderland


EUREKA, Mo. – St. Louis winters bring a mix of temperatures and conditions. At Hidden Valley, there are certain ingredients necessary to turn their green slopes into a winter wonderland. 

“Air, water, and mother nature’s help of temperature…and really the combination of all of that is what makes snow,” said Brandon Swartz, General Manager at Hidden Valley Ski Reso. 

Snowmaking is a science and includes another key factor, relative humidity. 

“The tool that we really look at as snowmakers is that wet-bulb temperature. So the combination of relative humidity and temperature,” Swartz explained. 

The wet-bulb temperature is the lowest temperature that can be obtained by evaporating water into the air at a constant pressure. Basically, the lower the relative humidity is, the colder the wet bulb temperature will be from the actual air temperature. 

“Once we get 32 degrees, lower humidity, we’ll be able to hit that sweet spot and get going,” he said. 

That sweet spot is a wet-bulb temperature of 27 degrees. In snowmaking, the colder and drier, the better. 

“Once we start getting around that mid-teens it really, the system just takes off and we can really open the guns fully open and make a lot of snow in a short period of time,” Swartz said. 

Hidden valley is equipped with 110 fan guns and once the proper ingredients are in place snowmaking begins with high-pressure air and water from two on-site reservoirs. 

Operating at around 450 psi, 10 times greater than the pressure out of your garden hose, air and water are mixed together at a volumetric rate of 6600 gallons per minute. That’s enough water to fill a typical backyard pool in 4 minutes or get Hidden Valley ready to ski in less than a week 

“The fan guns actually propel a mist of water out. We have a nucleator in the middle which actually nucleates water particles and then that water particle and the nucleated particle come together and that’s what creates the snow,” Swartz said. “So it shoots it up into the air. Thanks to evaporative cooling it wicks away that moisture and as it falls to the ground it starts to cool and that’s what creates snow.” 

If the forecast agrees, snow-making will commence any time after Thanksgiving, so how do the staff decide when it’s “go time”? 

“I pour over the weather forecasts and really just do as much as I can in my beginner meteorology sense to just really look and see what we can do. And as soon as we start to see those trends of where we see multiple cool nights. We get out there we get the system all ready to go. We start staffing to bring everybody on and we’ll wait for those temperatures,” he said.  

Early season it may take 5 to 7 nights of marginal but decent snowmaking temperatures to get that two-foot base down.  

Pumping a lot of snow out over smaller areas of terrain. 

“We really try to condense our snowmaking to our primary terrain phases to open up as soon as we can with that base and then you’ll see us to start to expand our terrain after that. And that’s going to help to also ensure that once you get that January warm-up, things like that, we’re able to stay open through that and we’re not having to completely start from scratch,” he said. 

And there are a few benefits to denser, man-made snow in Missouri. It’s a lot wetter than natural snow so it tends to be a bit more resilient to the rain, wind, and temperature. 

They strategically place piles around the mountain to help when the snow does some melting. 

“We try to disrupt the piles as little as possible. We really like to try to keep it as piled up and it kind of acts as its own refrigerator and it’ll help to keep the snow from melting too excessively during rain spells, warm-ups, and things like that,” said Swartz. 

So as soon as those nighttime temperatures fall know that Hidden Valley will be ready to start pumping out that snow. 

“We’re a business. Our business is snow and we’re going to take advantage of every chance and effort that we can to get that snow down. We want to be open as soon as possible and get everybody out here to enjoy it,” Swartz said. 

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