Temperature inversion is a reversal of the normal behavior of temperature in the troposphere, in which a layer of cool air at the surface is overlain by a layer of warmer air. (Under normal conditions, temperature usually decreases with height).
Ideal conditions for temperature inversion-
Long nights, so that the outgoing radiation is greater than the incoming radiation.
Clear skies, which allow unobstructed escape of radiation.
Calm and stable air, so that there is no vertical mixing at lower levels.