Downslope winds occur over slopes which are cooled. Downslope wind occur where air in contact with sloping ground is colder that air at the same level away from the slope. Downslope winds are nocturnal phenomena as there is surface cooling. The change in wind form upslope to downslope can change wildland fire behavior from active to less active during the transition period.
Source: MetEd. 2011. MetEd Education and Training pages. Accessed 23 November 2011. https://www.meted.ucar.edu/