Changing Weather

1. Changing Weather From: Ck-12.org Foundation Earth Science Chapter 16 By: Robert Smith

2. weather in a location often depends on what type of air mass is over the location • A key factor is whether the spot is beneath a front, the meeting place of two air masses • characteristics of the air masses and their interactions determine whether the weather over an area is constant, or whether there are rapid changes

3. Air Mass • air mass is a batch of air that has nearly the same temperature and humidity • air mass acquires characteristics above an area of land or water known as its source region • air mass that sits over a region for several days, or longer, it picks up the distinct temperature and humidity

4. Air Mass Formation • Air masses form over a large area • Air masses form primarily in high pressure zones, most commonly in polar and tropical regions • Temperate zones are ordinarily too unstable for air masses to form • air masses move across temperate zones so the middle latitudes are prone to having interesting weather

5. cPk • symbol cPk is an air mass with a continental polar source region that is colder than the region it is now moving over

6. Air Mass Movement • Air masses are slowly pushed along by high-level winds • temperature and humidity of a particular location depends partly on the characteristics of the air mass that sits over it • cold air masses tend to flow toward the equator and warm air masses tend to flow toward the poles

7. Fronts • Two air masses meet at a front • the two air masses have different densities and do not easily mix • One air mass is lifted above the other, creating a low pressure zone • If the lifted air is moist, there will be condensation and precipitation. • Winds are common

8. Four Types of Fronts • stationary front the air masses do not move • may bring days of rain, drizzle, and fog • Winds usually blow parallel to the front, but in opposite directions

9. Cold Fronts • a cold air mass takes the place of a warm air mass, there is a cold front • squall line is a line of severe thunderstorms that forms along a cold front. Behind the front is the cold air mass

10. Cold fronts vary by season • spring and summer: The air is unstable so thunderstorms or tornadoes may form. • spring: If the temperature gradient is high, strong winds blow. • autumn: Strong rains fall over a large area. • winter: The cold air mass is likely to have formed in the frigid arctic so there are frigid temperatures and heavy snows.

11. Warm Front • a warm air mass slides over a cold air mass

12. Occluded Front • occluded front usually forms around a low pressure system • starts when a cold front catches up to a warm front • air masses, in order from front to back, are cold, warm, and then cold again • If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion

13. Images of Weather