When it comes to making snow at Howelsen Hill, it's all about the physics.
The weather of the past five days closely resembles the pattern that brings ideal snow-making conditions to the Yampa Valley in mid-November -- cold starry nights. But Jeff Nelson, ski complex and rodeo supervisor for the city of Steamboat Springs, said overnight lows in the 20s and unusually high humidity in downtown Steamboat have thwarted his crew's efforts to crank out the man-made white stuff.
"Our fire-up temperature is 25 degrees, and we didn't start making snow until 6 a.m. (Tuesday morning)," Nelson said. "The problem we've had is high humidity. The humidity last night was 97 percent. It's kind of strange."
The ideal range for snowmaking in Steamboat is 10 to 15 degrees. But temperature isn't the only critical atmospheric factor for snow-makers.
Instead, they look at a measurement commonly called "wet bulb temperature," which is a measurement of temperature and humidity.
Man-made snow is produced when tiny water droplets are sprayed into the air. They must freeze before they hit the ground and to do that, they must dissipate heat at a rapid rate. The higher the humidity, the less capacity the air has to absorb heat from the water droplets.
The humidity in downtown Steamboat is sure to drop when a good cold snap begins to form a layer of ice on the Yampa River, Nelson said. At the same time, the ground will freeze and stop releasing moisture into the air.
Nelson's crews produced some large white "whales" of man-made snow last week when the overnight temperature got down to 9 degrees one night. But they haven't accomplished much since, he said.
One of the largest existing piles of snow is in the rodeo arena, which will be transformed into the start and finish area for a world Cup B Nordic combined competition scheduled for Dec. 10 to 12. No snow has been made on the nearby ski jumps, but Nelson said the snow-making guns soon would be turned on the jumps.
Construction on the K-68 jump, which is being readied for a summer jumping surface, was shut down Monday, Nelson said. Equipment and temporary roads are being removed so the ski jump can be readied for this winter's training and competitions.
Howelsen Hill has greater snow-making capacity this year, but making snow when temperatures are in the 20s is merely practice for the real thing, Nelson said.
What he really wants is overnight lows in the teens and dry air.
"When the temperature is between 10 and 15 degrees, you can watch (the snow piles) grow by the minute," Nelson said. "If we get four days of 15-degree nights, we'll be there."