Understanding Weather Patterns and Air Masses

1. CHP. 17 WEATHER PATTERNS

2. AIR MASSES • A large body of air (thousands of miles) • Changes in weather are caused by movements of air masses • As an air mass moves away, temp & humidity change.

4. Classification • Air masses are named from the area where they come from. • Classified according to : temperature & moisture content.

5. Tropical- HOT air mass formed in tropics • Polar- COLD air mass formed near poles • Maritime- air mass formed over oceans, WET • Continental- air mass formed over land, DRY

6. TYPES OF AIR MASSES • MARITIMETROPICAL • MARITIMEPOLAR • CONTINENTAL POLAR • CONTINENTAL TROPICAL

7. MARITIME TROPICAL Warm, humid air mass formed over ocean near equator. Summer = hot humid weather Winter = heavy rain/snowfall

8. MARITIME POLAR Cool, humid air masses formed over ocean near poles Summer = cool temps, fog, rain Winter = snow, coldtemps

9. CONTINENTAL TROPICAL • Hot, dry air masses formed mostly in the summer over drylands of SW & N Mexico.

10. CONTINENTAL POLAR Large, cold air mass formed over land in Canada & Alaska. Winter- extremely cold, dry air. Summer- cold, dry airtemps

11. HOW AIR MASSES MOVE • Prevailing Westerlies push air masses west to east. • Jet Stream- blow west to east • Fronts- boundaries between air masses, changeable weather & storms develop along fronts.

12. Types of Fronts • Colliding air masses can form 4 types of fronts: 1. Cold fronts 2. Warm fronts 3. Stationary fronts 4. Occluded fronts

13. COLD FRONT • forms when a cold air mass meets & pushes under a warm air mass. • Warm air cools, clouds form, & heavy rain. (thunderstorms). • cool weather

14. Cold Front

15. WARM FRONT • Forms when a warm air mass moves over a cold air mass. • Rain showers then hot, humid weather.

16. Stationary Front • Warm air mass meets a cold air mass & no movement occurs. Produces rain & clouds.

17. Occluded Front • When a warm air mass is caught between 2 colder air masses. Warm air cut off. • Produces clouds, rain/snow.

18. CYCLONES • A center of low air pressure, winds spiral inward. • As air rises in a cyclone, the air cools forming clouds & precipitation.

19. ANTICYCLONES • High pressure areas of dry air where winds spiral outward. (clockwise) • Descending air in an anticyclone causes dry, clear weather.

20. Sec. 2 STORMS

21. STORM • A violent disturbance in the atmosphere

22. THUNDERSTORMS • A small storm often accompanied with heavy precipitation & thunder & lightning. • Form in large cumulonimbus clouds called thunderheads.

23. T-Storm Formation • On hot, humid days, warm air rises rapidly, & cools forming cumulonimbus clouds. • This movement of air creates updraft & downdraft winds.

24. LIGHTNING Areas of (+)/(-) charges build up in storm clouds. It is a sudden discharge of electricity between 2 clouds or the cloud and the ground. Electric energy is released.

25. Light travels faster than sound. Lightning heats air. Heated air expands rapidly which results in sound waves (thunder).

26. T-Storm Damage • Heavy rains which can lead to floods. • Lightning, Hail, & winds can cause damage.

27. Tornado • Whirling, funnel shaped cloud that reaches down from a storm cloud to touch earth’s surface. • Warmth & Moisture feed it • Season: late spring/early summer

28. FORMATION • Warm, humid air meets cold, dry air. A squall line of thunderstorms develop which can develop into a tornado. • Warm air rises rapidly & begins to rotate. The cloud will then start to descend to earth in a funnel.

29. Tornado Alley- Mid-West US • This is where the conditions are the best- warm, humid air from Mexico mixes with cold, dry air from Canada.

30. Tornadoes occur most frequently in the US • Damage comes from strong winds & flying debris.

31. FUJITA SCALE • Tornadoes are ranked on the Fujita Scale (by the amount of damage they cause.) • F0 light damage to F5 extreme damage. • F4 F5 tornadoes account for only 1% of all tornadoes.

32. HURRICANES • A tropical cyclone that has winds of 119kmh or higher. • Forms in the Atlantic, Pacific, & Indian Oceans. In western Pacific- typhoons.

33. HURRICANE FORMATION • It begins over warm ocean water as a low-pressure area (tropical disturbance). • It grows from a disturbance to a tropical storm and maybe to a hurricane.

34. It draws energy from warm, humid air at ocean’s surface. • Warm air rises to form clouds, more air is drawn into the system. • Storms bands, high winds, & heavy rains spiral around a center.

35. Cool, dry air sinks into the center (eye) of the hurricane. • Hurricanes last longer than other storms- usually a week or longer.

37. Winter Storms • Year round, most precipitation begins in the clouds as snow.

38. Lake-Effect Snow • Cold, dry air moves across warmer water picking up water vapor & heat from the water. Once the air reaches the other side of the lake, air condenses & falls as snow.

39. In New York, Buffalo & Rochester are 2 of the snowiest cities in the US because of Lake-Effect Snow.

40. Snowstorm Safety • Find shelter from the wind. • It can be dangerous because high winds/snow limit your vision so you can get lost easily & you can lose a lot of body heat out in the cold.

41. Section 3 Predicting the Weather

42. Meteorologists • Scientists who study the causes of weather & try to predict it. • Meteorologists use maps, charts, & computers to analyze weather & prepare weather forecasts.

43. ISOTHERMS • Lines joining places that have the same temps.

44. ISOBARS • Lines joining areas with the same air pressure.

45. TECHNOLOGY • Has improved the accuracy of weather forecasts. • Weather balloons carry instruments into the troposphere & stratosphere to measure temp., air pressure, & humidity.

46. Weather Satellites- orbit earth in the thermosphere, cameras make images of the earth’s surface, clouds, & storms which get sent to meteorologists to analyze.

47. Computer Forecasts- gathers weather data from a large area then the computer works through thousands of calculations using equations from weather models to make forecasts for 12, 24, & 36 hours. Each one builds on the previous forecasts.