Q: What is the term for the rapid descent of cold, dense air down a mountain slope, often resulting in warmer, drier conditions on the windward side?

Arab Weather - The term given to the rapid descent of cold, dense air down a mountain slope, leading to warmer, drier conditions on the windward side, is downslope winds or Foehn winds.

These winds occur when moist air is forced to rise over mountains, where it condenses and falls as rain or snow on the windward side (the wet side). The dry, warm air then descends on the other side of the mountains, causing a rise in temperature and a drop in humidity.