On Sun, 18 Nov 2012 19:36:50 +0000, stuart noble wrote:

Last night the temperature in my area was supposed not to drop below 3
degs yet there was a hard frost on cars this morning. Does this mean
the temperature fell further than the Met Office thought, or is there
some other explanation?

There is a difference between an air frost (air temperature) and a ground
frost (the temperature of surfaces).

Weather forecasts quote air temperature.

--
Cheers
Dave.