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Understanding weather Chapter 7 Notes. Water in the Air Weather is the condition of the atmosphere at a certain time and place. Weather is the condition.

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Presentation on theme: "Understanding weather Chapter 7 Notes. Water in the Air Weather is the condition of the atmosphere at a certain time and place. Weather is the condition."— Presentation transcript:

1 Understanding weather Chapter 7 Notes

2 Water in the Air Weather is the condition of the atmosphere at a certain time and place. Weather is the condition of the atmosphere at a certain time and place. The condition is affected by the amount of water in the air. The condition is affected by the amount of water in the air.

3 The Water Cycle Water is constantly being recycled through the water cycle. Water is constantly being recycled through the water cycle.

4 Humidity As water evaporates from lakes oceans and plants it becomes water vapor. As water evaporates from lakes oceans and plants it becomes water vapor. The amount of water vapor in the air is called humidity. The amount of water vapor in the air is called humidity. As the temperature increases, the amount of water vapor the air can hold increases.

5 Relative Humidity Relative Humidity is the amount of water vapor in the air compared with the maximum amount of water vapor that the air can hold at a certain temperature Relative Humidity is the amount of water vapor in the air compared with the maximum amount of water vapor that the air can hold at a certain temperature

6 Factors that affect Relative Humidity Amount of Water Vapor The more water vapor in the air the higher the relative humidity. The more water vapor in the air the higher the relative humidity. The water vapor drops the relative humidity drops. The water vapor drops the relative humidity drops. Temperature The relative humidity decreases as the temperature rises and increases as the temperature drops The relative humidity decreases as the temperature rises and increases as the temperature drops

7 Measuring Relative Humidity A psychrometer is an instrument that is used to measure relative humidity. A psychrometer is an instrument that is used to measure relative humidity. –It consists of two thermometers: one wet bulb thermometer and one dry bulb thermometer. –The difference in the temperature readings between the two thermometers indicates the amount of humidity.

8 Measuring Relative Humidity

9 Condensation Condensation: the process by which a gas, such as water vapor, becomes a liquid. Condensation: the process by which a gas, such as water vapor, becomes a liquid. Condensation occurs when saturated air (air full of humidity) cools. Condensation occurs when saturated air (air full of humidity) cools.

10 Dew Point Dew point: the temperature at which a gas condenses into a liquid. Dew point: the temperature at which a gas condenses into a liquid. Air is saturated at dew point Air is saturated at dew point

11 Clouds A cloud is a collection of millions of tiny water droplets or ice crystals. A cloud is a collection of millions of tiny water droplets or ice crystals. Clouds form as warm air rises and cools Clouds form as warm air rises and cools

12 Clouds

13 Cumulus Clouds Puffy, white clouds that tend to have flat bottoms Puffy, white clouds that tend to have flat bottoms Form when warm air rises Form when warm air rises Indicate fair weather Indicate fair weather When they get larger they produce thunderstorms – cumulonimbus clouds When they get larger they produce thunderstorms – cumulonimbus clouds Clouds with nimbus or nimbo will produce precipitation Clouds with nimbus or nimbo will produce precipitation

14 Stratus Clouds Stratus Clouds form in layers Stratus Clouds form in layers Cover large areas and often block out the sun Cover large areas and often block out the sun Caused by a gentle lifting of a large body of air. Caused by a gentle lifting of a large body of air. Nimbostratus clouds are dark stratus clouds that produce continuous rain. Nimbostratus clouds are dark stratus clouds that produce continuous rain. Fog is a stratus cloud found near the ground. Fog is a stratus cloud found near the ground.

15 Cirrus Clouds Cirrus Clouds are thin feathery white clouds found at high altitudes Cirrus Clouds are thin feathery white clouds found at high altitudes Cirrus clouds form when the wind is strong Cirrus clouds form when the wind is strong They can indicate a change in weather. They can indicate a change in weather.

16 Clouds and Altitude Clouds are classified by the altitude that they form Clouds are classified by the altitude that they form

17 Cloud Classification Low clouds – have no prefix – –Ex. Cumulus, Stratus Middle clouds – Have the prefix alto – –Ex. Altocumulus, Altostratus High clouds – Have the prefix Cirro – –Ex. Cirrostratus, Cirrus

18 Precipitation Precipitation is water in solid or liquid form that falls from the air to the Earth Precipitation is water in solid or liquid form that falls from the air to the Earth There are four major forms There are four major forms –Rain –Snow –Sleet –Hail

19 Rain The most common form of precipitation. The most common form of precipitation. Rain is produced when the water droplets become a certain size. Rain is produced when the water droplets become a certain size.

20 Sleet and Snow Sleet forms when rain falls through a layer of freezing air. Sleet forms when rain falls through a layer of freezing air. Snow forms when temperatures are so cold that water vapor changes directly to a solid. Snow forms when temperatures are so cold that water vapor changes directly to a solid.

21 Hail Hail are balls or lumps of ice that fall from clouds. Hail are balls or lumps of ice that fall from clouds. Hail forms in cumulonimbus clouds due to updrafts freezing the water droplets. Hail forms in cumulonimbus clouds due to updrafts freezing the water droplets.

22 Air Masses and Fronts Changes in weather are caused by the movement and interaction of air masses. Changes in weather are caused by the movement and interaction of air masses. An air mass is a large body of air where temperature and moisture content are similar throughout. An air mass is a large body of air where temperature and moisture content are similar throughout.

23 Air Masses Air Masses are characterized by their moisture content and temperature which is determined by the area over which the air mass forms (Source Region) Air Masses are characterized by their moisture content and temperature which is determined by the area over which the air mass forms (Source Region)

24 Types of air masses Maritime (m) Forms over water; wet Continental ( c ) Forms over land; dry Polar ( P) Forms over polar regions; cold Tropical (T) develops over the tropics: warm

25 Cold Air Masses Cold air masses are responsible for bringing extremely cold winters. Cold air masses are responsible for bringing extremely cold winters.

26 Warm Air Masses Warm air masses bring warm air weather systems into the United States. Warm air masses bring warm air weather systems into the United States. This brings milder temperatures This brings milder temperatures This can also bring severe weather during the summer months. This can also bring severe weather during the summer months.

27 Fronts Front: the boundary between air masses of different densities and usually different temperatures Front: the boundary between air masses of different densities and usually different temperatures Four kinds of fronts Four kinds of fronts –Cold front –Warm front –Occluded front –Stationary front

28 Cold Fronts A cold front forms where cold air moves under warm air A cold front forms where cold air moves under warm air Move quickly and bring thunderstorms, heavy rain, or snow Move quickly and bring thunderstorms, heavy rain, or snow Cooler weather follows a cold front Cooler weather follows a cold front

29 Warm Fronts A warm front forms where warm air moves over colder denser air A warm front forms where warm air moves over colder denser air Warm air replaces cold air Warm air replaces cold air Bring drizzly rain Bring drizzly rain Followed by clear and warm weather Followed by clear and warm weather

30 Occluded Front An occluded front forms when a warm air mass is caught between two colder air masses An occluded front forms when a warm air mass is caught between two colder air masses This produces cold temperatures and large amounts of rain and snow. This produces cold temperatures and large amounts of rain and snow.

31 Stationary Fronts Stationary fronts form when a cold air mass meets a warm air mass Stationary fronts form when a cold air mass meets a warm air mass Brings many days of cloudy wet weather. Brings many days of cloudy wet weather.

32 Air Pressure and Weather Areas that have lower pressure than the surrounding areas do are called Cyclones. Areas that have lower pressure than the surrounding areas do are called Cyclones. These areas the air masses come together and rise These areas the air masses come together and rise

33 Air Pressure and Weather Areas that have high pressure are called anticyclones. Areas that have high pressure are called anticyclones. Anticyclones are areas where the air moves apart and sinks Anticyclones are areas where the air moves apart and sinks

34 Air Pressure and Weather By keeping track of the cyclones and anticyclones, meteorologists can predict the weather. By keeping track of the cyclones and anticyclones, meteorologists can predict the weather. Cyclones cause stormy weather Cyclones cause stormy weather Anticyclones bring dry clear weather Anticyclones bring dry clear weather

35 Severe Weather Thunderstorms Thunderstorms Tornadoes Tornadoes Hurricanes Hurricanes Severe weather safety Severe weather safety

36 Thunderstorms Thunderstorms are small intense weather systems that produce strong winds, heavy rain, lightning, and thunder. Thunderstorms are small intense weather systems that produce strong winds, heavy rain, lightning, and thunder. Two atmospheric conditions are needed to produce a thunderstorm: Two atmospheric conditions are needed to produce a thunderstorm: –Warm and moist air near the Earths surface –Unstable atmosphere

37 Thunderstorms Cumulonimbus Clouds

38 Lightning Lightning is an electric discharge that occurs between a positively charged area and a negatively charged area. Lightning is an electric discharge that occurs between a positively charged area and a negatively charged area. Can occur Can occur –Between two clouds –Between Earth and a cloud –Between two parts of the same cloud

39 Lightning When lightning strikes, energy is released. When lightning strikes, energy is released. Energy is transferred to the air. Energy is transferred to the air. Thunder is the sound that results from the rapid expansion of air along the lightning strikes. Thunder is the sound that results from the rapid expansion of air along the lightning strikes.

40 Severe Thunderstorms Can produce: Can produce: –High winds –Hail –Flash floods –Tornadoes –Lightning that causes forest fires and burning down homes

41 Tornadoes Tornadoes occur in 1% of all thunderstorms. Tornadoes occur in 1% of all thunderstorms. A tornado is a small spinning column of air that has high wind speeds and low central pressure and that touches the ground. A tornado is a small spinning column of air that has high wind speeds and low central pressure and that touches the ground. It starts as a funnel cloud that pokes through a cumulonimbus cloud. It starts as a funnel cloud that pokes through a cumulonimbus cloud.

42 Tornadoes

43 Tornadoes 75% of the worlds tornadoes occur in the United States. 75% of the worlds tornadoes occur in the United States. Occur in spring and early summer Occur in spring and early summer They average 120-180 km/h wind speed They average 120-180 km/h wind speed

44 Tornado Pictures

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46

47 Hurricanes Hurricanes are large rotating tropical weather systems that have wind speed of at least 120km/h Hurricanes are large rotating tropical weather systems that have wind speed of at least 120km/h They are the most powerful storms on Earth. They are the most powerful storms on Earth. Pacific Ocean hurricanes are called: typhoons Pacific Ocean hurricanes are called: typhoons Indian Ocean hurricanes are called: cyclones Indian Ocean hurricanes are called: cyclones

48 Hurricane Hurricanes happen over warm tropical oceans. Hurricanes happen over warm tropical oceans. Hurricanes vary in size from 160 to 1500 km in diameter and can travel for thousands of kilometers. Hurricanes vary in size from 160 to 1500 km in diameter and can travel for thousands of kilometers.

49 How Hurricanes form Begins as a group of thunderstorms moving over tropical ocean waters Begins as a group of thunderstorms moving over tropical ocean waters Winds traveling in different directions cause the storm to spin Winds traveling in different directions cause the storm to spin It gets its fuel from the contact with the warm ocean waters It gets its fuel from the contact with the warm ocean waters The hurricane continues to grow as long as it is over the moist warm source. The hurricane continues to grow as long as it is over the moist warm source.

50 Hurricane

51 Hurricane Damage Very destructive Very destructive Average wind speed is 120-150 km/h Average wind speed is 120-150 km/h Can knock down trees and destroy buildings Can knock down trees and destroy buildings Flooding is the most destructive part.( storm surge). Flooding is the most destructive part.( storm surge).

52 Weather Safety Thunderstorm Safety Lightning is attracted to tall objects Lightning is attracted to tall objects Crouch down in open areas Crouch down in open areas Stay away from water Stay away from water Tornado Safety Weather forecast: watch and warning system Weather forecast: watch and warning system Watch- tornado may happen Watch- tornado may happen Warning- tornado has been spotted Warning- tornado has been spotted Find shelter: basement or cellar Find shelter: basement or cellar

53 Weather Safety

54 Flood Safety Weather forecast: watches and warning system Weather forecast: watches and warning system Find a high place Find a high place Always stay out of flood waters Always stay out of flood waters Hurricane Safety Watch weather updates Watch weather updates Evacuate the area Evacuate the area Have a disaster supply kit available with food and water Have a disaster supply kit available with food and water Board up windows with plywood Board up windows with plywood Stay indoors during the storm Stay indoors during the storm

55 Weather Safety

56 Forecasting the Weather A weather forecast is a prediction of weather conditions over the next 3 to 5 days A weather forecast is a prediction of weather conditions over the next 3 to 5 days A meteorologist is a person who observes and collects data on atmospheric conditions to make weather predictions A meteorologist is a person who observes and collects data on atmospheric conditions to make weather predictions

57 Weather-Forecasting Technology High in the sky High in the sky –Weather balloons Measure weather conditions as high as 30 km above Earth Measure weather conditions as high as 30 km above Earth Measures temperature, air pressure, and relative humidity Measures temperature, air pressure, and relative humidity Meteorologists can also measure wind speed and direction by tracking the weather balloons. Meteorologists can also measure wind speed and direction by tracking the weather balloons.

58 Weather-Forecasting Technology

59 Measuring Air Temperature and Pressure Measuring Air Temperature and Pressure –Thermometer: a tool used to measure air temperature –Barometer: an instrument used to measure air pressure The mercury inside a barometer rises as the air pressure increases The mercury inside a barometer rises as the air pressure increases

60 Weather-Forecasting Technology Measuring Wind Direction Measuring Wind Direction –Can be measured by using a windsock or wind vane Windsock: is a cone shaped cloth bag open at both ends Windsock: is a cone shaped cloth bag open at both ends Wind vane: is shaped like an arrow with a large tail and is attached to a pole Wind vane: is shaped like an arrow with a large tail and is attached to a pole

61 Weather-Forecasting Technology Measuring wind speed Measuring wind speed –Anemometer: an instrument used to measure wind speed Consists of four cups connected by spokes to a pole Consists of four cups connected by spokes to a pole The cups move The cups move The motion sends an electric current that measures the wind speed The motion sends an electric current that measures the wind speed

62 Weather-Forecasting Technology

63 Radar and Satellites Radar and Satellites –Radar is used to find the location movement and amount of precipitation –Doppler Radar systems on the weather station –Weather Satellites provide the Earth images of weather systems you see on TV weather reports

64 Weather-Forecasting Technology

65 Weather Maps National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) use information from about 1000 weather stations in the US National Weather Service (NWS) and National Oceanic and Atmospheric Administration (NOAA) use information from about 1000 weather stations in the US This is information from one weather station. This is information from one weather station.

66 Reading Weather Maps


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