Ch 21 Understanding Weather Water in the Air Water in the Air Air Masses and Fronts Air Masses and Fronts Severe Weather Severe Weather

Water in the Air The Water Cycle The Water Cycle Evaporation Evaporation Condensation Condensation Precipitation Precipitation Runoff Runoff

Water in the Air Humidity- the amount of water vapor in the air Humidity- the amount of water vapor in the air

Water in the Air Dew point- the temperature to which air must cool to become saturated. Dew point- the temperature to which air must cool to become saturated. Saturated- when air holds all the water vapor it can at a given temperature Saturated- when air holds all the water vapor it can at a given temperature

Clouds Cumulus- puffy white clouds with flat bottoms Cumulus- puffy white clouds with flat bottoms Stratus- clouds that form in layers Stratus- clouds that form in layers Cirrus- feathery, wispy white clouds at high altitudes Cirrus- feathery, wispy white clouds at high altitudes

Air Masses and Fronts Cold Front- a fast-moving cold air mass moves under less dense warm air, pushing it upwards Cold Front- a fast-moving cold air mass moves under less dense warm air, pushing it upwards Results in thunderstorms, cooler weather Results in thunderstorms, cooler weather

Air Masses and Fronts Warm Front- warm, less dense air moves over the cold, denser air, bringing drizzly rain and then clear warm weather Warm Front- warm, less dense air moves over the cold, denser air, bringing drizzly rain and then clear warm weather

Air Masses and Fronts Occluded Front- a warm air mass is caught between two colder masses, resulting in cool temperatures and lots of precipitation Occluded Front- a warm air mass is caught between two colder masses, resulting in cool temperatures and lots of precipitation

Air Masses and Fronts Stationary Front- cold and warm air masses meet but do not have the force to create storms Stationary Front- cold and warm air masses meet but do not have the force to create storms

Severe Weather Thunderstorms- heavy rainstorms with strong winds, lightning and thunder Thunderstorms- heavy rainstorms with strong winds, lightning and thunder Lightning- an electric discharge that takes place between a positively charged area and a negatively charged area Lightning- an electric discharge that takes place between a positively charged area and a negatively charged area Thunder- the sound caused by the rapid expansion of air along the lightning strike Thunder- the sound caused by the rapid expansion of air along the lightning strike

Severe Weather Tornado- a small, spinning column of air that has high wind speed and touches the ground Tornado- a small, spinning column of air that has high wind speed and touches the ground Hurricane- a large, spinning tropical weather system with wind speeds of at least 119 km/hr Hurricane- a large, spinning tropical weather system with wind speeds of at least 119 km/hr

Severe Weather How does a tornado form? How does a tornado form? Wind moving in two different directions causes a layer of air in the middle to spin like a roll of toilet paper. It works it’s way to the bottom of the cloud and eventually to the ground. Wind moving in two different directions causes a layer of air in the middle to spin like a roll of toilet paper. It works it’s way to the bottom of the cloud and eventually to the ground.

Severe Weather How does a Hurricane form? How does a Hurricane form? It’s a group of thunderstorms that form over the oceans. Wind that travels in different directions causes it to spin. Energy is gathered from warm waters. It’s a group of thunderstorms that form over the oceans. Wind that travels in different directions causes it to spin. Energy is gathered from warm waters.

Severe Weather A weather forecast is a prediction of weather conditions over the next 3-5 days. A weather forecast is a prediction of weather conditions over the next 3-5 days. A meteorologist is a person that observes and collects data on atmospheric conditions. A meteorologist is a person that observes and collects data on atmospheric conditions.

Forecasting Weather Meteorologists use a barometer to measure air pressure and an anemometer to measure wind speed. Meteorologists use a barometer to measure air pressure and an anemometer to measure wind speed. Weather balloons carry radio transmitters that send measurements to the weather stations Weather balloons carry radio transmitters that send measurements to the weather stations