It's also an easy way to get a rough estimate of the bottom of the clouds: 400' above the ground for every 1degC of difference between the temperature and the d

It's also an easy way to get a rough estimate of the bottom of the clouds: 400' above the ground for every 1degC of difference between the temperature and the dew point. This is useful for a couple of things, including whether or not you can legally take off or land when flying under visual flight rules.