Understand, weather: the short term condition of the atmosphere. Lifting air masses cool adiabatically (by expansion) to reach the dew-point temperature. Four principal lifting mechanisms operate in the atmosphere: Atmospheric lifting mechanisms produce adiabatic cooling and condensation: convective lifting: stimulated by local surface heating, convergent lifting: air flows towards an area of low pressure, orographic lifting: air forced over a barrier such as mountain range. Distinctive windward from bodies of water, leeward conditions from land battle. Effects on precipitation patters as seen in coastal bc, lots of ran: frontal lifting: along the leading edges of contrasting air masses. A larger body of air w/ similar temps. Two types commonly influence weather in e. north america. Air masses affecting north america: ca, cp, mt mt: maritime tropical. Gulf air, rich w/ moisture cp: continental polar. Originates in siberia/high arctic; bitter colder, dryer than cp. Lake effect where cp air obtains moisture, heat as it travels over great lakes.