More than cold air: Ski resorts rely on this number for snowmaking

Ski resorts need more than cold air to make snow: wet-bulb temperature, which combines air temperature and humidity, has to drop to roughly 26 to 28 degrees. That's why resorts from Colorado to Utah to Arizona can hit early opening dates with barely any natural snow. Here's how dry air and humid air change the snowmaking equation as opening dates are announced.

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