Two years ago I did a post called Ice and Frost about water freezing overnight outside in winter when the temperature was below zero degrees. This morning there was a bit of frost outside but the weather report said the temperature only got down to about two degrees here. We were wondering how it was possible to be frosty because water freezes at zero and below.
I searched on the Internet for some help and found two useful sites, the NZ Meteorological Service site and a British Gardening site. I found the gardening site easier to read but the two sites explained that the temperature we hear on the weather reports is taken at about waist height on an adult and is the air temperature, not the ground temperature. At night when the sky is clear the ground temperature gets colder than the air, but on cloudy nights it doesn’t. So because last night was clear the ground got cold enough to go below zero even though the air temperature didn’t.