1. Weather Patterns

2. Air masses ✦ A huge body of air that has similar temperature, humidity, and air pressure at any given height is called an air mass

3. The 4 major types of air masses that affect the weather in the United States are: ✦ 1. Maritime Tropical- forms over the ocean, near the equator, warm moist air. ✦ 2. Maritime Polar- forms over the Pacific Ocean and North Atlantic. Brings fog to California. Cold, moist air.

4. ✦ 3. Continental Tropical- forms over land in Mexico, brings dry, hot air. ✦ 4. Continental Polar- forms over land in Northern Canada, brings cold, dry air.

5. How do air masses move? ✦ Prevailing Westerlies: Major wind belts of US, push air masses west to east ✦ Jet Streams: Bands of high-speed winds that blow west to east ✦ Fronts- boundary where air masses meet, Storms and changealbe weather usually develops here

6. Fronts ✦ When 2 air masses that have different properties meet, they do not mix readily. Instead a boundary called a front forms. There are 4 different types of fronts.

7. 1.Cold Front: A cold air mass that replaces a warm air mass 1.If there is a lot of water vapor: snow or rain may fall 2.Move quickly, causing abrupt weather changes sometimes thunderstorms 3.After: comes cold, dry air and clear skies, low temperatures

8. Fronts ✦ 2. Warm Front: Warm air mass replaces a cold air mass ✦ Warm air moves over the cold air, if the warm air is humid: precipitation falls ✦ May last several days

9. 3.Occluded Front: A warm air mass is caught btwn. Two cold air masses. 3.The cooler air masses push the warm air upward. 4.The temperature near the ground becomes cooler 4. Stationary Front: Warm air mass meets a cold air mass and no movement occurs. Rain may fall for several days.

10. Diagram of a cold front

11. Cyclones ✦ A swirling center of low air pressure ✦ Play a major part in the weather ✦ Cyclones and decreasing air pressure are associated with clouds, wind, and precipitation

12. Anticyclones ✦ High pressure centers of dry air ✦ Usually called highs (H) on the weather map ✦ The descending air in an anticyclone generally causes dry, clear weather

13. Storms A storm is a violent disturbance in the atmosphere. When 2 different fronts collide, rainstorms or snowstorms form. When a warm front moves in and meets a cold front, heavy nimbostratus clouds produce heavy rain or snowfall. Thunderstorms are heavy rainstorms accompanied by thunder and lightning.

14. Lightning is a sudden discharge or spark of electricity between two clouds or between a cloud and the ground. This spark forms because areas in the clouds build up with positive and negative charges. Thunder is the sudden expansion of the air when lightning strikes.

15. Thunderstorm damage ✦ May cause floods ✦ Lightning may cause damage on trees or cause electrocution

16. Thunderstorm Safety ✦ Stay indoors ✦ Avoid touching telephones, anything with electricity ✦ If traveling stay in the car ✦ Stay out of reach of lightning ✦ Avoid bodies of water

17. Tornadoes ✦ A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface.

18. Tornadoes ✦ Tornadoes can form in any situation that produces severe weather ✦ They most commonly form in thick cumulonimbus clouds- (thunderstorm clouds)

19. Tornadoes ✦ Tornadoes occur more often in US than in any other country ✦ Weather patterns on the Great Plains result in a “tornado alley”

20. Tornadoes ✦ Tornado safety- The safest place to be is a storm-shelter or a well- built basement

21. Hurricanes ✦ A hurricane is a tropical cyclone that has winds of 119 km ph

22. Hurricanes ✦ It begins over warm ocean water as a low pressure area, or tropical disturbance. If it grows in strength it becomes a tropical storm which then may develop into a hurricane ✦ It draws it’s energy from warm, humid air ✦ At the center is a ring of clouds “the eye”

23. Hurricanes ✦ They usually last a week or more, gradually losing strength ✦ Hurricane damage ✦ The result is a storm surge- a dome of water that sweeps across the coast where the hurricane lands

24. Hurricane Safety ✦ It is best to evacuate- move away temporarily ✦ If you hear a hurricane warning and are told to evacuate, leave immediately

25. Winter Storms ✦ Most precipitation begins in clouds as snow. If the air is freezing all the way to the ground, precipitation falls as snow ✦ Buffalo and Rochester get about 3 meters of snow every winter ✦ If you are caught in a snowstorm find shelter from the wind

26. Predicting Weather ✦ Meterologists- scientists who study the causes of weather and try to predict it ✦ Use maps, charts, and computers to analyze weather data and prepare forecasts

27. Predicting Weather ✦ Most weather info comes from the National Weather Service ✦ They use ballons, satellites, radars, and surface instruments

28. Predicting Weather ✦ Weather ballons- carry instruments into the tropo and lower stratosphere. The instruments measure temp, air pressure and humidity

29. Predicting Weather ✦ Satellites: orbit Earth, taking pictures of clouds, storms and snow cover ✦ Collect data on temp, humidity, solar radiation, wind speed, wind direction

30. Weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather.

31. A THERMOMETER measures the air temperature. Most thermometers are closed glass tubes containing liquids such as alcohol or mercury. When air around the tube heats the liquid, the liquid expands and moves up the tube. A scale then shows what the actual temperature is. A BAROMETER measures air pressure. It tells you whether or not the pressure is rising or falling. A rising barometer means sunny and dry conditions, while a falling barometer means stormy and wet conditions. An Italian scientist named Torricelli built the first barometer in 1643.

32. A SLING PSYCHROMETER measures relative humidity, using the cooling effect of evaporation. Two thermometers are used in a sling psychrometer. Wet the cloth of one of the thermometers and swing the psychrometer around a few times. Water evaporates from the cloth, causing the temperatures on that thermometer to be lower the the other. A RAIN GAUGE measures the amount of rain that has fallen over a specific time period. A WIND VANE is an instrument that determines the direction from which the wind is blowing. An ANEMOMETER measures wind speed. The cups catch the wind, turning a dial attached to the instrument. The dial shows the wind speed.