dry air can get colder at night much easier than moister air (where the condensation to dew releases heat ) 
given the right condition: no wind, clear skies and dry cold air to start off with, you can get a frost alright 8O
dry air can get colder at night much easier than moister air (where the condensation to dew releases heat )
given the right condition: no wind, clear skies and dry cold air to start off with, you can get a frost alright 8O