Weather PatternsWeather PatternsChapter 15-2Chapter 15-2

I. Changes in WeatherI. Changes in WeatherA. Air MassesA. Air Masses

1. An air mass is …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 properties as the surface it develops over.over.

2. For example …2. For example …a. Dry air mass over landa. Dry air mass over land Moist air mass over waterMoist air mass over waterb. Warm air mass over the tropicsb. Warm air mass over the tropics Cold air mass over the polesCold air mass over the poles

3. Daily weather is due to …3. Daily weather is due to … … … movement of air masses.movement of air masses.

B. Pressure SystemsB. Pressure Systems

1. Three things that determine atmospheric 1. Three things that determine atmospheric

pressure are …pressure are …

--TemperatureTemperature

-Density-Density

-The amount of water vapor-The amount of water vapor

2. High pressure is the result of …2. High pressure is the result of …

Descending (Sinking) AirDescending (Sinking) Air

3. High pressure brings good weather 3. High pressure brings good weather because …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. FrontsC. Fronts1. Low pressure systems form …1. Low pressure systems form … … … along the boundaries of air massesalong the boundaries of air masses..2. A Front is …2. A Front is … … … the boundary between two different air the boundary between two different air

massesmasses..3. You would expect to see …3. You would expect to see … storms and precipitationstorms and precipitation

as a front passes overhead.as a front passes overhead.4. Air movement as fronts collide4. Air movement as fronts collide

5. The winds rotate counterclockwise as a result 5. The winds rotate counterclockwise as a result of …of … the coriolis effect.the coriolis effect.

D. Four types of frontsD. Four types of fronts

1. Warm Front1. Warm Front

a. A Warm front occurs when …a. A Warm front occurs when …

… … less dense, warm air slides over a less dense, warm air slides over a departing departing

cold air mass.cold air mass.

b. The precipitation associated with a b. The precipitation associated with a warm front …warm front …

… … would be a wide band of would be a wide band of precipitation.precipitation.

c. The clouds you would expected to see c. The clouds you would expected to see would be would be

……cirrus.cirrus.

2. Cold Front2. Cold Front

a. In a cold front …a. In a cold front …

… … a colder air mass pushes under a a colder air mass pushes under a warm air 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 Front3. Occluded Front

a. An occluded front results from …a. An occluded front results from …

… … two cool air masses crashing two cool air masses crashing togethertogether

and forcing warm air between them to and forcing warm air between them to rise.rise.

b. You would expect to see …b. You would expect to see …

… … strong winds and heavy strong winds and heavy precipitation.precipitation.

4. Stationary Front4. Stationary Front

a. A stationary front occurs when …a. A stationary front occurs when …

… … pressure differences cause warm pressure differences cause warm and cold 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 light winds and wide spread precipitationprecipitation

across the frontal region.across the frontal region.