1. Weather Patterns

2. Air masses Changes in the weather are caused by movements of large bodies of air called air masses. Air masses usually cover thousands of square kilometers. The properties of an air mass are nearly the same throughout the 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.  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.  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. 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.

6. 1.Cold Front: A cold air mass that replaces a warm air mass (draw the blue one here-#1) 2. Warm Front: Warm air mass replaces a cold air mass (draw the red one here-#2) 1.Cold Front: A cold air mass that replaces a warm air mass (draw the blue one here-#1) 2. Warm Front: Warm air mass replaces a cold air mass (draw the red one here-#2)

7. 3.Occluded Front: Cold front overtakes a warm front. (draw the purple one here-#4) 4. Stationary Front: Warm air mass meets a cold air mass and no movement occurs. Rain may fall for several days. (draw the red & blue one here- #3) 3.Occluded Front: Cold front overtakes a warm front. (draw the purple one here-#4) 4. Stationary Front: Warm air mass meets a cold air mass and no movement occurs. Rain may fall for several days. (draw the red & blue one here- #3)

8. Diagram of a cold front

9. 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.

10. 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.

11. A hurricane is a powerful cyclone (A low pressure area containing rising warm air) that forms over tropical oceans. Hurricanes that form over the Pacific Ocean are called typhoons. In a hurricane, there is a calm center called the eye of the hurricane.

12. A tornado is a whirling funnel shaped cloud that can be incredibly destructive. The air pressure at the bottom of a cumulonimbus funnel cloud is very low. When this low pressure area touches the ground, the tornado acts as a vacuum. Scientists are not sure how tornados form. Tornadoes are very common in the Great Plains of the United States. This area is referred to as Tornado Alley.

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