1. Air Masses and Fronts:How are they related to storms? S.C. Standard 6-4.4

2. AIR MASSES • Huge bodies of air • Formed over water or land in tropical or polar regions • The prevailing westerlies generally push air masses from west to east.

3. Air masses (cont.) • Tropical air masses- warm air masses with low air pressure • Polar air masses- cold air masses with high air pressure

4. Air masses (cont.) • Whether an air mass is humid or dry depends on whether it forms over water or land • Water - humid • Land – dry

5. Air Masses (cont.) • 4 types: 1-Maritime tropical warm, humid air masses that form over oceans near the tropics 2-Maritime polar cold, humid air masses that form over icy cold North Pacific and North Atlantic oceans

6. Air masses (cont.) 3- Continental tropical hot, dry air masses that form only in summer over dry areas in Southwest and northern Mexico 4- Continental polar cold, dry air masses that form over central and northern Canada and Alaska

7. FRONTS • As air masses move and collide with each other, fronts are formed at the boundaries between the air masses

8. 4 Types of Fronts: 1- Cold front A rapidly moving cold air mass runs into a slowly moving warm air mass. The dense cold air slides under the lighter warm air. The warm air is pushed upward and causes a cold front. • Causes sudden changes in weather and severe storms

9. 4 Types of Fronts: (cont.) 2. Warm Fronts  a moving warm air mass collides with a slowly moving cold air mass. The warm air moves over the cold air . • Clouds, fog and rain also accompany warm fronts, sometimes may bring storms.

10. 4 Types of Fronts: (cont.) 3. Stationary Front when warm and cold air masses meet, but neither is stronger than the other a “standoff” occurs known as a stationary front • May bring days of clouds and precipitation

11. 4 Types of Fronts: (cont.) 4. Occluded Front a warm air mass is caught between two cooler air masses. The denser cool air masses move underneath the less dense warm air mass and push upward. The two cool air masses meet in the middle and may mix. • Weather may turn cloudy and rainy or snowy

12. PRESSURE SYSTEMS • High/Low Pressure Systems are created by warm air rising and cool air sinking combined with the spinning of Earth that causes rotation of air masses

13. PRESSURE SYSTEMS (cont.) • 2 Types • HIGH usually signals fair weather with winds that circulate around the system in a clockwise direction • LOW counterclockwise circulating winds that often result in rainy and/or stormy weather conditions

14. STORMS! • Occur when pressure differences cause rapid air movement • Thunderstorms • Tornado • Hurricane

15. Thunderstorms • A storm with thunder, lightning, heavy rains and strong winds • Usually forms along a cold front but can form within an air mass • Forms within large cumulonimbus clouds

16. Tornado • Rapidly whirling, funnel shaped cloud that reaches down from a storm cloud • Area of low pressure • Strong winds • Likely to form within the frontal regions where strong thunderstorms are also present

17. Hurricane • Low pressure tropical storm that forms over water • “eye” of the storm Winds that are spinning in a circular pattern around the center of the storm • Lower the air pressure at the center, the faster the winds blow toward the center of the storm

18. Weather Instruments: Thermometer- measures temperature Hygrometer/Psychrometer- measure relative humidity Barometer- Measures air pressure Rain Gauge- measures amount of precipitation Anemometer- measures wind speed Wind vane- direction of wind

19. COPY THE CAUSE AND EFFECT CHART INTO YOUR NOTES. Complete as you watch the storms video.