Section 6.1 Air masses
NOAA Jetstream: https://www.weather.gov/jetstream/airmass
An air mass is a large body of air characterized by temperature and humidity, properties that are largely inherited from the air mass source region:
Humidity: continental or maritime
Temperature: arctic, polar, or tropical
These parameters can be combined to yield cP, mP, cT, mT, and cA air masses. Note that arctic air masses are always dry (there is no "mA" air mass), and are also very stable. These combinations are summarized in the following table:
| arctic | polar | tropical | |
| very cold | cold | warm | |
| continental | v cold, dry (cA) | cold, dry (cP) | hot, dry (cT) |
| marine | v cold, dry (cA) | cool, humid (mP) | warm, humid (mT) |
Air masses are not static and may undergo air mass modification as they travel (advect) over the surface, via heat/moisture exchange and/or lifting.
A prime example of modification is lake-effect snow, during which a cold air masses moves over (relatively) warmer water.