Recurring Weather

– drought– heat wave– cold wave– wind-chill factor

Objectives• Describe recurring weather patterns and the

problems they create.

• Identify atmospheric events that cause recurring weather patterns.

Vocabulary

Floods• Floods can occur when weather patterns

cause even mild storms to persist over the same area.

• Northern California Sacramento River Flood

Malibu Landslides caused by Flooding and runoff…

Drought

• Droughts are extended periods of well-below-normal rainfall.

1. shifts in global wind patterns

2. allow large high-pressure systems to persist for weeks or months

3. over continental areas.

– Heat waves, which are extended periods of above-normal temperatures, can be formed by the same high-pressure systems that cause droughts.

HEAT WAVES

-high-pressure system blocks cooler air masses from moving into the area, so there is little relief from the heat.

– As the air under a large high-pressure system sinks, it warms by compression and causes above-normal temperatures.

Heat Wave Dangers!!!– If the air is

humid, it slows the rate of evaporation, which diminishes the body’s ability to regulate internal temperature.

Cold Waves• A cold wave is an extended period of

below-normal temperatures.

•Winter high-pressure systems are much more influenced by the jet stream than are summer systems and therefore rarely linger

over one area.

• Several polar high-pressure systems can follow the same path and subject the same areas to bout after bout of numbing cold.

Wind-chill factor

• measured by the wind-chill index

• estimates the heat loss from human skin caused by the combination of cold air and wind.

Section Assessment

1. What is the primary cause of a drought?

Recurring Weather

Droughts are usually the result of shifts in global wind patterns that allow high-pressure systems to persist for weeks or months over continental areas.

Section Assessment2. What would the heat index be if the air temperature is

90ºF with a 60 percent relative humidity?

Recurring Weather

The heat index would be 100ºF.

Section AssessmentRecurring Weather

3. Which type of air masses are usually responsible for cold waves?

Cold waves are caused by air masses of continental polar or arctic origin.