Crossover 3 : The point at which the relative humidity is less than, or equal to, the ambient air temperature. May be used as an indicator of extreme burning conditions
The Canadian Interagency Forest Fire Centre (CIFFC), Glossary of Forest Fire Management Terms, Manitoba, Canada 2003. http://bcwildfire.ca/mediaroom/Backgrounders/2003_ Fire_Glossary.pdf, (For Fr - Canad) {474}