Weather Patterns Chapter 15-2

I. Changes in Weather A. Air Masses 1. An air mass is … … a large body of air that has the same … a large body of air that has the same properties as the surface it develops over. properties as the surface it develops over. 2. For example … a. Dry air mass over land Moist air mass over water Moist air mass over water b. Warm air mass over the tropics Cold air mass over the poles Cold air mass over the poles 3. Daily weather is due to … … movement of air masses. … movement of air masses.

B. Pressure Systems 1. Three things that determine atmospheric pressure are … pressure are … -Temperature -Temperature -Density -Density -The amount of water vapor 2. High pressure is the result of … Descending (Sinking) Air Descending (Sinking) Air 3. High pressure brings good weather because … Sinking air makes it difficult for air to rise Sinking air makes it difficult for air to rise and clouds to form. and clouds to form.

C. Fronts 1. Low pressure systems form … … along the boundaries of air masses. … along the boundaries of air masses. 2. A Front is … … the boundary between two different air masses. … the boundary between two different air masses. 3. You would expect to see … storms and precipitation storms and precipitation as a front passes overhead. as a front passes overhead. 4. Air movement as fronts collide 5. The winds rotate counterclockwise as a result of … the coriolis effect. the coriolis effect.

D. Four types of fronts 1. Warm Front a. A Warm front occurs when … a. A Warm front occurs when … … less dense, warm air slides over a departing … less dense, warm air slides over a departing cold air mass. cold air mass. b. The precipitation associated with a warm front … b. The precipitation associated with a warm front … … would be a wide band of precipitation. … would be a wide band of precipitation. c. The clouds you would expected to see would be c. The clouds you would expected to see would be …cirrus. …cirrus.

2. Cold Front a. In a cold front … a. In a cold front … … a colder air mass pushes under a warm air … a colder air mass pushes under a warm air mass and forces warm air up on a steep mass and forces warm air up on a steep curve. curve. b. A cold front produces … b. A cold front produces … … a narrow band of violent storms. … a narrow band of violent storms. c. The type of clouds it produces would be … c. The type of clouds it produces would be … … cumulus and cumulonimbus. … cumulus and cumulonimbus.

3. Occluded Front a. An occluded front results from … a. An occluded front results from … … two cool air masses crashing together … two cool air masses crashing together and forcing warm air between them to rise. and forcing warm air between them to rise. b. You would expect to see … b. You would expect to see … … strong winds and heavy precipitation. … strong winds and heavy precipitation.

4. Stationary Front a. A stationary front occurs when … a. A stationary front occurs when … … pressure differences cause warm and cold … pressure differences cause warm and cold fronts to stop moving. fronts to stop moving. b. In a stationary front you expect to see … b. In a stationary front you expect to see … … light winds and wide spread precipitation … light winds and wide spread precipitation across the frontal region. across the frontal region.