That's exactly what it is Jackone: Foehn (or Föhn) effect: mechanisms which give rise to a warm, dry wind on the leeward side of mountains or significant hills. Broadly, there are two: (i) the 'subsidence' type where air at & just above the hill/mountain crest descends by lee-wave action, becoming even drier & warmer than when it started out; (ii) all air in a moist airstream on the upstream side of the hill/mountain rises, leading to cloud/precipitation formation, thence lowering the humidity content, this air then descending/warming adiabatically on the leeside. Taken from a good glossary of weather terms at: http://homepage.ntlworld.com/booty.weather/FAQ/AF.htm