Chapters 6, 7 and 8
Remember to read the assigned textbook chapters.
Chapter 8 Videos
Chapter 7 and Chapter 8 review
Chapter 8 — Air Masses
What Is an Air Mass?
An air mass is a large body of air, often 1,600 kilometers or more across and several kilometers thick, with relatively uniform temperature and moisture characteristics at a given altitude.
Air masses help control day-to-day weather in the middle latitudes. When one remains over an area, weather conditions can be relatively consistent. This is called air-mass weather.
An air mass develops over a source region: a broad, relatively uniform area where air remains long enough to acquire the temperature and moisture properties of the underlying surface.
Air Mass Classification
Air masses are named using two letters. The lowercase first letter tells you whether the source is over land or water. The uppercase second letter describes the source-region temperature.
Moisture
c — continental: land, generally dry
m — maritime: water, generally moist
Temperature
A — Arctic: extremely cold
P — Polar: cold or cool
T — Tropical: warm or hot
Know these air masses
| Code | Full name | Typical characteristics |
|---|---|---|
| cA | Continental Arctic | Extremely cold and dry |
| cP | Continental Polar | Cold, dry; often stable |
| cT | Continental Tropical | Hot and dry; may be unstable near the surface |
| mP | Maritime Polar | Cool to cold and moist |
| mT | Maritime Tropical | Warm and humid; can support thunderstorms |
Air Mass Source Regions
Source regions need a large, physically uniform surface and a period of relatively stagnant air so that the air can take on local temperature and moisture characteristics.
Cold, dry continental polar and Arctic air typically originate over high-latitude land. Maritime polar air forms over cooler oceans. Maritime tropical air originates over warm waters such as the Gulf of Mexico, Caribbean and western Atlantic. Continental tropical air forms over hot, dry land in northern Mexico and the southwestern United States.
Air Masses and the Weather We Experience
Air masses change as they move away from their source regions. Their temperature, moisture and stability can be modified by the surfaces they cross, topography and atmospheric motion.
Continental Polar and Arctic
Cold and dry air often brings chilly weather. When cold air crosses the warmer Great Lakes, it can pick up moisture and produce lake-effect snow.
Maritime Polar
Cool, moist air can contribute to cloudy, damp conditions. Atlantic maritime polar air may be involved in the development of nor'easters along the Northeast coast.
Maritime Tropical
Warm, humid air from the Gulf of Mexico, Caribbean or western Atlantic supplies moisture for showers and thunderstorms.
Continental Tropical
Hot, dry air from desert regions can contribute to extreme heat and low humidity.
Isohyets are lines on a map connecting places with equal precipitation amounts.
What to Know for Exam 3
Chapters 6, 7 and 8. Focus on pages 206–212 and Table 8.1 on page 208 for this chapter.
- Define an air mass and a source region.
- Explain the difference between continental (c) and maritime (m).
- Explain Arctic (A), Polar (P) and Tropical (T).
- Identify the full names and typical weather of cA, cP, cT, mP and mT.
- Determine whether an air mass reaching Long Island is likely to be warmer, colder, drier or more humid based on where it came from.
- Explain how cold or warm water modifies an air mass.
- Connect warm, humid air masses to possible thunderstorms and cold air crossing the Great Lakes to lake-effect snow.