2. Air Masses & Weather Fronts Ms. Cervera

3. Bellringer # 4 1. How do yesterday’s observations relate to air masses? 2. What would happen if a warm air mass ran into a cold air mass? Today you need: Bellringer sheet Blank paper Pencil WEATHER PATTERNS WORKSHEET Lab worksheet

4. Today’s Objectives Students will be able to…  Classify the four major air masses that affect weather in the United States by their characteristics  Distinguish between and air mass and a front  Describe how a weather front forms

5. Pressure Systems  A high-pressure system is a large body of circulating air with high pressure at its center and lower pressure outside of the system.high-pressure system A low-pressure system is a large body of circulating air with low pressure at its center and higher pressure outside of the system.low-pressure system

6. Stop & Think Why do clouds usually form in the center of a low-pressure system?

7. Air Masses  Air masses are large bodies of air with distinct temperature and moisture characteristics.  An air mass forms when a large high pressure system lingers over an area for several days.  As a high pressure system comes in contact with Earth, the air in the system takes on the temperature and moisture characteristics of the surface below it.

8. Air Masses  Air masses are classified by their temperature and moisture characteristics. If an air mass forms over land, what type of air mass is it? What words would you use to describe an air mass that formed over land near the equator?

9. Air Masses  Five main air masses impact climate across North America.  Continental air masses form over land.  Maritime masses form over water.

10. Air Masses  Five main air masses impact climate across North America.  Tropical air masses form in the warm equatorial regions.  Polar air masses form over cold regions.  Arctic and Antarctic air masses form near the poles, over the coldest regions of the globe.

11. Describe how a continental polar air mass can change to a maritime polar air mass.

12. Stop & Think What drives weather patterns?

13. Fronts  A weather front is a boundary between two air masses.  Changes in temperature, humidity, clouds, wind, and precipitation are common at fronts.

14. Fronts  When a colder air mass moves toward a warmer air mass, a cold front forms.  A warm front forms when lighter, warmer air moves toward colder, heavier air

15. Fronts (cont.)  When the boundary between two air masses stalls, the front is called a stationary front.  When a fast-moving cold front catches up with a slow-moving warm front, an occluded or blocked front forms.

16. Exit Ticket Imagine this: A warm front is approaching Tallahassee. It is one day away. What would you expect to observe regarding weather? True or false: A front that forms when a warm air mass meets a cold air mass is an occluded front. When cirrus clouds form close to the ground, the result is ground fog.