Air Masses- are immense bodies of air that have similar properties at a given altitude. Air masses take on the properties over which they form, of which there are two- temperature and moisture. The diagram above shows the air masses which impact the continental United States. Air masses are identified by a combination of two letters, the first letter is lower case the second letter is upper case.
- m - maritime, forms over water will contain moisture
- c - continental, forms over land will be drier.
- T - tropical, forms in warmer regions
- P - polar, forms in colder regions
- A - arctic, forms in very cold regions.
For example an air mass that forms over land in Canada would be labeled cP. The two air masses that have the greatest effect on the US are cP and mT.