Types of precipitation by lifting mechanism

Precipitation forms when moist air is lifted, cools and condenses. Based on the lifting mechanism there are three types.

1. Convective precipitation

Heated ground warms the air above it; the warm, light, moist air rises, cools and condenses into cumulus clouds. It gives short, intense, local showers and thunderstorms, common in the tropics and in Nepal's pre-monsoon season.

2. Orographic precipitation

Moist air is forced to rise over a mountain barrier, cools and condenses. The windward side gets heavy rain and the leeward side lies in the rain shadow. The southern slopes of the Himalaya (for example Lumle-Pokhara, with heavy rainfall) are a good example.

3. Cyclonic precipitation

Caused by the movement of air masses towards a low-pressure area. Two kinds:

• Frontal: a warm air mass rides over a cold one (warm front, gentle, long rain) or a cold front pushes under warm air (steep, short, heavy rain).
• Non-frontal (tropical cyclone / monsoon depression): air converges into a low-pressure centre and rises. The monsoon is of this kind.

 Convective       Orographic         Cyclonic (front)
    ^ ^ ^          clouds /|           warm ///  cold
   (cloud)        wind-> / | rain      -------\---
  hot ground     ______/   |_____      ground