A lot of people assume that once it gets to be 32ºF or below you can make snow. This is not always the case. Snowmaking goes by the wetbulb temperature, which is the outside air temperature with the humidity level factored in. There are times when you can make snow above freezing and then there are times when you cannot even make snow when it is below freezing! Sometimes the humidity level plays the biggest role when it comes to making snow.
Generally speaking you can start making snow with a high pressure snowmaker when you get a wetbulb temperature of 27ºF or less. A garden hose snowmaker generally needs a wetbulb temperature of 28ºF or less before it can start making snow. When you have low humidity (50%) or below it is not uncommon to be able to make snow at 29ºF or even 30ºF with one of our snowmakers. However when the humidity is really high you might have problems making snow, even when the outside air temperature is in the mid to low 20's.
Snowmaking is all about heat transfer. This means taking the warm molecules out of the water you are trying to freeze into snow. When the humidity is high, it is difficult to transfer the heat from the water. Think about it like this. You feel much more comfortable on a 100ºF day with 10% humidity than on a 100ºF day with 100% humidity. Why? Because on the day with 10% humidity your body heat transfers a lot better compared to when the humidity is 100%.
While you might get a wetbulb temperature cold enough to technically make snow, you might not be able to if the humidity is too high. For example last night we tried to make snow when it was 27.4ºF and 93% humidity. While the wetbulb temperature said we should be able to make snow, all we were able to do is produce ice on the ground because the high humidity didn't allow for enough heat transfer to occur in the water to allow it to fully freeze into snow.
Early season snowmaking runs or trying to make snow in an area that is generally warm has it's own complications of warm water temperatures and ground that is not completely frozen. Add high humidity to the mix and it can be even harder to make snow. Another misconception is that if it is snowing outside, it is cold enough to make snow. This is generally not the case because the humidity will likely be very high while it is snowing, especially if the temperature is hoovering around freezing.
Many people ask if they can make snow indoors and the answer is no unless you can regulate the humidity level. The reason being running the snowmaker in an enclosed area will increase the humidity level quickly. This is because all the heat you are removing from the water will have nowhere to escape to since it is trapped in an enclosed area. Once the humidity gets too high, you won't be able to make snow.
http://www.snowstormsnowmaking.com
