1. Air Mass, Wind, and Weather Systems Sixth Grade GPS Earth Science Pam Myers

2. Quick Review What causes wind? Answer: UNEVEN HEATING OF THE EARTH BY THE SUN.

3. Air Masses A large body of air that has nearly the same temperature, humidity & air pressure throughout They have similar properties as the part of the earth’s surface over which they form

4. Why are Air Masses important? They can cover an area of thousands of square kilometers. are responsible for day to day weather changes. Move/change – so does weather in area over area over which it moves.

5. x Less Dense Rises Up holds more moisture More Dense Sinks Down holds less moisture

6. Which Way Do The Winds Blow? From ___________ pressure to _____ pressure. high low Do you know what instrument we use to measure air pressure? A Barometer

7. Quick Review Is hot air high pressure or low pressure? Answer: LOW PRESSURE means it rises, and it holds more moisture than cold air

8. WEATHER SYSTEMS

9. Front? What is a Front? boundary between two air masses of –different density –moisture –temperature Four types of fronts; can you name them?? _____________, ______________ _____________, and __________________ _____________, and __________________ Warm front Cold front Occluded frontStationary front

10. Precipitation Along a Cold Front lifting the warm moist air ahead of it

11. Precipitation Along a Warm Front warm moist air overriding colder air

12. Quick Review Is cold air high pressure or low pressure? Answer: HIGH PRESSURE means it sinks, and it holds less moisture than cold air

14. Cool, dry Air mass … …butts against an equally strong mass of warm, humid air. Stationary front Warm Air Cool Air Battle for control ends with no winners; front moves little.

15. #1 Cold Front #2 Warm Front #4 Occluded Front #3 Stationary Front

16. Quick Review Which type of air rises? Which one sinks? Answer: HOT AIR ( LOW PRESSURE ) rises, and cold air (high pressure) sinks.

17. What information do you need to know to forecast weather??  Temperature  Winds  Air pressure  Humidity  Precipitation

18. Rain F ROZEN PRECIPITATION MELTS AND REACHES THE GROUND AS RAIN. Freezing Rain F ROZEN PRECIPITATION MELTS IN WARM AIR. R AIN FALLS AND FREEZES ON COLD SURFACE Sleet F ROZEN PRECIPITATION MELTS IN SHALLOW WARM AIR. T HEN REFREEZES BEFORE REACHING THE GROUND. Snow P RECIPITATION FALLS THROUGH COLD AIR AND REACHES THE SURFACE.

19. So What is a Hailstone?  begins as frozen raindrop or ice crystal –Travels through different levels of storm cloud –Strong warm air updrafts & cool air downdrafts –move frozen particles up & down

20. So What is a Hailstone?  encounters different forms of moisture  layers of frozen ice particles accumulate on surface  The resulting hailstone has a layered structure http://www.classzone.com/books /earth_science/terc/content/visu alizations/es1805/es1805page0 1.cfm?chapter_no=visualization http://www.classzone.com/books /earth_science/terc/content/visu alizations/es1805/es1805page0 1.cfm?chapter_no=visualization

21. Quick Review What about cold air? Is it high pressure or low pressure? Answer: HIGH PRESSURE means HIGH density, HIGH pressure, it sinks, and it does not hold much moisture

22. Do you know the scientific name for a weather forecaster?

23. A Meteorologist  measure temperature, air pressure, winds, humidity, and precipitation.  Tools Doppler radar, satellites, instruments attached to balloons  gather information from Earth’s upper atmosphere and the surface

24. A weather map shows surface- pressure systems, air masses, fronts (G REEN - SHADED AREA REPRESENTS PRECIPITATION ) isobars (millibars): SOLID GRAY LINES. L ARGE ARROWS IN COLOR SHOW AIR FLOW. (G REEN - SHADED AREA REPRESENTS PRECIPITATION.) Isotherms : SIMILAR TO ISOBARS, EXCEPT THEY SHOW TEMPERATURE (N OT S HOWN HERE )

25. References  Glencoe Science  http://www.nhc.noaa.gov/aboutsshs.shtml http://www.nhc.noaa.gov/aboutsshs.shtml  http://www.spc.noaa.gov/faq/tornado/f-scale.html http://www.spc.noaa.gov/faq/tornado/f-scale.html