Weather Patterns

High-pressure system – large body of circulating air with high pressure at its center and lower pressure outside the system; brings sunshine and good weather Low-pressure system – large body of circulating air with low pressure at its center and higher pressure outside the system; brings clouds and precipitation

Air mass – large bodies of air that have uniform temperature, humidity and pressure Air masses are classified by temperature and moisture – those formed over water are called maritime, those formed over land are called continental; warm masses are tropical and cold are polar

In the continental United States, air masses are commonly moved by prevailing westerlies and jet streams.

Colliding air masses can form four types of fronts: (illustrate with definition) cold fronts – cold air moves under warm air forcing warm air up warm front – move slowly and bring warm, humid air stationary front – forms when a cold mass meets a warm mass but neither have enough force to move the other occluded front – warm air mass is caught between two cold air masses

Illustration of fronts:

Storm – violent disturbance in the atmosphere called severe weather thunderstorms – small storm accompanied by thunder and lightning formed from large cumulonimbus clouds tornado – rapidly, whirling, funnel-shaped cloud that reaches down from a storm cloud and touches the Earth’s surface formed when thunderstorm updrafts begin to rotate

Storm cont. hurricane – intense tropical storm with winds exceeding 119 km/hr formed over warm ocean water as a low-pressure area blizzard – violent winter storm characterized by freezing temperatures, strong winds and blowing snow