Which two air masses most affect the weather of Eastern United States?

The two air masses that most affect the weather of the Eastern United States are the continental polar and maritime tropical air masses.

Continental polar air masses originate over the vast, cold land areas of Canada and the northern United States. They are typically cold and dry, and can bring freezing temperatures and snow to the Eastern United States, especially in the winter months.

Maritime tropical air masses develop over the warm waters of the Gulf of Mexico and the Atlantic Ocean. They are warm and humid, and can bring heavy rainfall and thunderstorms to the Eastern United States.