Temperature inversion is a reversal of the normal distribution of temperature near the ground, in which a layer of colder air is overlain by a layer of warmer air. Whereas normally air temperature usually decreases as you go higher.
There are four types: ground, turbulence, subsidence, and frontal, but in the case of large areas contained by mountains in southern New Zealand they’re a bit of of pain in May to July each winter, when they form due to a high pressure system sitting over the country.
Some winters such conditions can last for up to two weeks and when this occurs the easist solution is to drive part way up a ski area road. In the Wanaka area this comes down to either Treble Cone, The Snow Farm or Cardrona.
Looking across the Cardrona Valley from the Snow Farm access road in early July 2017