8.10 Weather Patterns

8.10 Weather PatternsObjectives:Identify two types of pressure systems.Identify and describe what causes weather patterns.Explain why it is useful to understand weather patterns.Why is it important to understand how severe weather forms?Vocabulary: high-pressure system, low-pressure system, air mass, front, tornado, hurricane, blizzard.1Pressure SystemsCool air masses have high pressure, or more weight.Because, molecules are closer together.Warm air masses have low pressure.Because, molecules are further apart.

What is air pressure?2A high-pressure system is a large body of circulating air with high pressure at its center and lower pressure outside of the system.Dense air sinks, bringing clear skies and fair weather.

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Low-pressure system is a large body of circulating air with low pressure at its center and higher pressure outside of the system.Air inside system rises and coolsWater vapor condenses forming clouds and sometimes precipitation.

4Pressure SystemsHigh-Pressure SystemAir spirals away

Air sinks at center

Clear skies and fair weatherLow-Pressure SystemAir spirals to center

Air rises at center

Clouds and sometimes precipitationForms as a result of pressure differencesCompare and contrast two types of pressure systems.Explain why clouds do not form in a high-pressure system.5Air MassesLarge bodies of air that have uniform temperature, humidity, and pressure are called air masses.Forms when air mass stays over an area for several days.System takes on the temperature and moisture characteristics of the surface below it.Can extend over large areas, e.g. 1000 km.Have you ever noticed that weather sometimes stays the same for several days?6

Air Mass Classification7Air Mass Classification (continued)Classified by temperature and moisture characteristics.Those that form over land are referred to as continental.Over oceans, maritime.Equatorial regions, tropicalCold regions, polarNear the poles, arctic or antarctic.

If an air mass forms over land, what type of air mass is it?Where is the source of continental polar air?What words would you use to describe an air mass that formed over land near the equator?8FrontsWeather front is boundary between two air masses.Collisions between air masses causes changes inTemperatureHumidityCloud typesWindPrecipitationThese changes can be severe.Types of fronts: cold front, warm front, stationary front, and occluded front.What is a weather front?How do fronts form?Why do you think weather changes along fronts?9

Which air mass is denser: a cold air mass or a warm air mass? EXPLAIN your answer.What type of air masses might make up the cold air mass in an cold front? (see Air Mass Classification)What happens when colder air runs in to warmer air?What happens to the warmer air?What causes warm fronts to form?What types of weather is associated with warm fronts?What type of air masses might make up the air in a warm front? (see Air Mass Classification)10Cold FrontWarm FrontCold air pushes under warm air.Warm air rises, vapor condenses forming clouds.Temperatures drop as much as 10 oCWind gusty and changes directionShowers and thunderstorms along front, some severe.Warm, less dense air moves toward and above cold air mass.Vapor in warm air condenses creating a wide blanket of clouds.Warmer temperatures and change in wind direction.Steady rain or snow for several hours, even days.11

12Stationary FrontOccluded FrontWhen an approaching front stalls with warm air on one side and cold on the other.Cloudy skies and light rain.Can last several daysCold fronts move faster than warm fronts.Forms when cold front catches warm front.Usually brings precipitation.What happens when the boundary between two air masses stalls?How do occluded fronts differ from other kinds of fronts?13Severe WeatherThunderstorms

Severe weather can cause major damage, injuries and death. Types of severe weather include thunderstorms, tornadoes, hurricanes, and blizzards.14Thunderstorms (continued)Warm temperatures, moisture, and rising air from a low-pressure system.Three stages:Cumulus stage: warm air and moisture rise forming cumulonimbus clouds, 10 km high.Mature stage: continued lifting of warm, moist air with downdrafts of colder air. Heavy winds, rain and lightning.Dissipation stage: up drafts stop, winds die down, lightning stops, and precipitation weakens.What are the three stages of a thunderstorm?How are thunderstorms and low-pressure systems related?During which stage of a thunderstorm would you expect to see the most lightning? Why?15Tornadoes

16Tornadoes (continued)A violent whirling column of air in contact with the ground.Several hundred meters to 1500 m in diameter.Whirling winds can reach more than 400 km/h (250 mi/h).Form when thunderstorm updrafts begin to rotate.Most frequent in central U.S., from NE to TX, where cold air from Canada collides with warm moist air from the Gulf of Mexico.How do tornadoes form?Tornadoes are associated with which type of front?Why do you think it is important for scientists to learn about how tornadoes form?

Classifying TornadoesDr. Ted Fujita developed a method for classifying tornadoes based on the damage they cause.F0 causes light damageF1 through F4, moderate to devastating damage including tearing off roof, throwing vehicles and derailing trains.F5, incredible damage including demolishing concrete and steel buildings and pulling the bark off trees.17Hurricanes

18Hurricanes (continued)Intense tropical storms with winds exceeding 119 km/h (75 mi/h), and average 480 km in diameter (150 thousand times bigger than a tornado).Formation is described on previous slide.Damage caused by strong winds and flooding.Looses strength when moving over land or colder water.Called typhoon in Asia, and cyclone in Australia.How can hurricanes cause floods?Infer how ocean temperature would affect the formation and strength of a hurricane.Compare and contrast hurricanes and tornadoes.19Winter Storms

How does freezing rain form?Why is it important to be inside during blizzard conditions?20Winter Storms (continued)Snow and ice can be dangerous.Ice storms can coat trees, ground and buildings with ice.Blizzard is a violent winter storm characterized by freezing temperatures, strong winds, and blowing snow.Hazards:Reduced visibilityFrostbiteHypothermiaSevere Weather SafetyU.S. Weather Service issues watches and warningsA watch means that severe weather is possible.A warning means that severe weather is already occurring.Know how to protect yourself during dangerous weather.