Evaporative Cooling

Evaporative cooling is where the humidity in the air is lower than 100% and precipitation or a humid mass moves into it. The result is the temperature drops towards the dew point and the dew point goes up. This can be seen on soundings as the middle line between temperature and dew point.

In winter, this can help snow to fall to the ground, mainly by the mid and/or lower levels being dry before a storm, and temperatures in the 30s or 40s. When the storm moves in, the air moistens and evaporative cooling takes place, sending the temperatures below freezing, allowing snowfall.