Weather Patterns Chapter 5 lesson 2

Pressure Systems There are 2 types of pressure systems: High-pressure system – A large body of circulating air with high pressure at its center and lower pressure outside (air sinks in the center) Low-pressure system – A large body of circulating air with low pressure at its center and higher pressure outside (air rises at center)

Air Masses Air masses – Large bodies of air with distinct temperature and moisture characteristics. They form when a large high pressure system lingers over an area for several days. 5 types of air masses: Continental air masses – form over land Maritime masses – form over water Tropical air masses – form in warm equatorial regions Polar air masses – form over cold regions Arctic and Antarctic air masses – for near the 2 poles (coldest regions)

Air Masses

Fronts Front – a boundary between 2 air masses. 4 types of fronts: Cold front – cold air mass moves towards a warmer air mass Warm front – lighter, warmer air moves towards the cooler, heavier air. Stationary front – when the boundary between 2 air masses stalls (stays in that place for several days) Occluded front – when a fast-moving cold front catches up to a slow-moving warm front

Fronts

Severe Weather Examples: Tornadoes, Drought, Hurricanes, Floods, Sinkholes, Wildfires, Blizzards, Thunderstorms Thunderstorms – Warm air rises due to a low-pressure system. 3 stages Cumulus stage (cloud formations and updrafts, then downdrafts form) Mature stage (heavy winds, rain, and lightning) Dissipation stage (storm ceases)

Tornadoes A violent, whirling column of air in contact with the ground. Form when thunderstorms updraft begin to rotate Tornado Alley – place in central United States that experience most tornadoes

Hurricanes Intense tropical storm with winds exceeding 200km/h