Air Masses

What You Need


Note: Even though students will need online access for the activities, they also will need hard copies to write out their answers and or take notes.

Air Masses


To develop an understanding of air masses and the role they play in weather and climate.


This lesson is based on a module developed by the University of Illinois WW2010 project. It introduces air masses that commonly influence the weather in the United States, characteristics of these air masses, and how to identify air masses on weather maps.

By the time they leave high school, it is important that students understand that the earth has a variety of climatic patterns, which consist of different conditions of temperature, precipitation, humidity, wind, air pressure, and other atmospheric phenomena. They should realize that the sun—in the form of solar radiation—is the basic energy source for heating the land, ocean, and air. Layers of different temperatures in the air and oceans result from the transfer of this heat energy, causing winds and ocean currents to vary as they carry heat energy between warm and cool regions. The cycling of water in and out of the atmosphere also plays an important part in determining climatic patterns—evaporating from the surface, rising and cooling, condensing into clouds and then into snow or rain, and falling again to the surface, where it collects in rivers, lakes, and porous layers of rock. It is worth emphasizing that there are also large areas on the earth's surface covered by thick ice (such as Antarctica). This thick ice interacts with the atmosphere and oceans in affecting worldwide variations in climate. In addition, students should realize that the earth's climates continue to change and that even minor changes of atmosphere or ocean temperature, if sustained long enough, can have widespread effects on climate. (Science for All Americans, pp. 42-44.)

By the end of middle school, students should understand that climates have sometimes changed abruptly in the past as a result of volcanic eruptions or impacts of huge rocks from space. They also should understand that water evaporates from the surface of the earth, rises and cools, condenses into rain or snow, and falls again to the surface. This cycling of water in and out of the atmosphere is a significant aspect of the weather patterns on earth. Finally, they also should understand that thermal energy carried by ocean currents has a strong influence on climates around the world. Areas near oceans tend to have more moderate temperatures than they would if they were farther inland but at the same latitude because water in the oceans can hold a large amount of thermal energy. (Benchmarks for Science Literacy, p. 70.) In the course of this lesson (which should take one 90-minute class period), you may wish to test or reinforce these earlier learning goals with your students.

Ideas in this lesson are also related to concepts found in these Common Core State Standards:

  • CCSS.ELA-Literacy.RST.9-10.4 Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant togrades 9–10 texts and topics.
  • CCSS.ELA-Literacy.RST.9-10.5 Analyze the structure of the relationships among concepts in a text, including relationships among key terms (e.g., force, friction, reaction force, energy).
  • CCSS.ELA-Literacy.RST.9-10.7 Translate quantitative or technical information expressed in words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g., in an equation) into words.
  • CCSS.ELA-Literacy.RST.11-12.4 Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant togrades 11–12 texts and topics.


To entice students and check their present knowledge and understanding of air masses and weather in general, begin the lesson by asking orientation questions like these:

  • How often do you watch the weather on TV? Why?
  • What kinds of weather or weather conditions are there?
  • Can you name situations in which weather has impacted your life or affected your plans? Explain.
  • What kinds of elements, things, or conditions influence the weather?
  • Why is the study of weather important? Offer examples.
  • Why do people in general pay little attention to the weather? Do you think this is a good idea? Why or why not?

(Accept all answers, but ask students to offer explanations to support their views.)

If students do not mention "air masses" in the course of this discussion, you may ask them the following as a way to begin to focus them on the key learning goal and the online activities ahead:

  • What can you tell me about air masses? Do you know what they are?

(Accept all answers, but ask students to offer explanations to support their views.)

Have students take notes and make a list of things that influence the weather. In the course of this warm-up discussion, they may or may not mention air masses. This will enable you to get an idea of what students may already know about air masses before they begin the central activity of the lesson.


Continue the lesson by handing out to students the Air Masses Scaffolding Activity, which is a WW2010 online classroom activity guide that introduces and teaches "characteristics of air masses that commonly influence weather in the U.S. and how to identify them on weather maps."

In total, there are four steps or activities that students will perform. Have them work in pairs or small groups. Then discuss their results as you go to help students reach a complete understanding of the concepts taught in the lesson.

Have students read the Introduction and discuss with them what air masses are, what would be considered their "best source regions" and why, and how air masses change as they move out of these source regions. It is important that they understand these basic concepts before moving forward.

Characteristics of Air Masses (Activity 1)

Using your Air Masses Scaffolding Activity teacher guide as a visual of the resource, direct students to read from their handouts the Characteristics of Air Masses activity. This way, they won't waste time looking online for answers to the questions below.

After previewing the map and chart of this first air mass activity, have them guess at the answers for the characteristics for Air Mass #1 and Air Mass #2.

Ask students:

  • What type of air mass is Air Mass #1? Air Mass #2? Why?
  • What do you think is the source region for Air Mass #1? Air Mass #2?
  • What do you think is the relative temperature for the two?
  • What do you think is the wind direction for the two?
  • What do you think is the moisture content for the two?

(Accept all reasonable answers. Encourage students to elaborate on their views.)

When students are finished speculating on these key characteristics, have them use their Air Masses student esheet to go to Air Mass #1 and Air Mass #2 to check their answers. Then discuss with them briefly any similarities or differences they found. Have them take notes as they proceed.

Use WW2010's teacher guide for this and the other discussion activities in this lesson. NOTE: It is recommended that you wait until students finish the activities below before you share the correct graphic outlines with the class.

Find the Air Masses (Activities 2-4)

Now students should use their esheet to go to and read the information and directions for activity #2 online. Encourage them to follow the deeper pages into the site so they can learn about reading temperatures, surface observations, and the example to see how to find and draw an outline of the air masses (which is the goal of activity #2).

Before students will be able to effectively map out the tropical and polar air masses using temperature, they will need to understand how to read the symbols on the Interpreting Surface Observation Symbols page. It is recommended that the class as a whole goes through the charts, sections, and deeper pages covering: Temperature, Weather Symbol, Dew Point Temperature, Cloud Cover, Sea Level Pressure, and Wind Barb. Ask questions as you go and, before they begin, use the map graphic to check their understanding of the material. Here's a sample question:

  • By reading the symbols on the map, what can you tell me about the weather in Denver, Colorado?
      (The temperature is 22 degrees F. The dew point temperature is low at 18 degrees. There is 25% cloud cover or scattered clouds. The wind is going southeast at 5 knots or 5.75 miles an hour.)

Once you feel that each group has a working understanding, give them time to figure out and draw blue lines and red lines outlining the polar and tropical air masses on their hard copy maps.

When ready to go on, students should use their esheet again to go to and read the directions and information for activity #3. Once again, walk them through the deeper site pages, if necessary, particularly the ones for tropical air mass and polar air mass, which offer sample map graphic outlines that take into account the surface observations or "additional information" students will need to complete this phase of the activity.

As directed, discuss with the class any differences students found between their first and second analyses. Encourage debate and have students support their views with evidence based on the temperatures and surface observations they have learned about. Once students are ready, show them the correct outlines from the Air Masses Scaffolding Activity teacher guide and discuss their successes, missteps, and reactions in general.


As a way to step back and think about what your students have learned, you may wish to ask these questions:

  • What are the characteristics of maritime tropical air masses? Where do they originate? How do they affect weather?
      (The characteristics are warm temperatures, rich in moisture. They originate over the warm waters of the tropics and Gulf of Mexico. The northward movement of tropical air masses transports warm moist air into the United States, increasing the chances of precipitation.)
  • What is a continental polar air mass? Where does it originate? How does it affect weather?
      (It is an air mass with cold temperatures and little moisture. It originates in snow-covered regions of northern Canada. It affects weather by turning it colder.)
  • In your own words, describe the role that air masses play in weather.
      (Answers may vary. Encourage students to offer explanations to support their views.)
  • What was the most challenging part of mapping out air masses?
      (Answers may vary. Encourage students to offer explanations to support their views.)
  • How, if any, has this lesson affected your view of weather?
      (Answers may vary. Encourage students to offer explanations to support their views.)


Pressure Differences Get the Wind Going, from USA Today Weather, will help students better understand this and other weather-based natural phenomena.

 Other related lessons and project ideas can be found in the WW2010 Project website.