Fronts That Come in From the Ocean

Basics of a Front

• There are two primary types of meteorological fronts: warm fronts and cold fronts. These fronts represent the boundary between colliding air masses. When a cold air mass is replacing a warm air mass, a cold front is formed. When a warm air mass is replacing a cold air mass, a warm front is formed. Fronts represent the area where most clouds are formed and precipitation falls, due to the transition from one type of air mass to another.

Source of Ocean Fronts

• The locations where air masses are developed are called source regions. These regions are categorized by location and nature. In terms of location, areas above 60 degrees latitude are known as polar or arctic source regions, while areas within 25 degrees latitude of the equator are known as tropical source regions. If located over land, source regions are called continental source regions; if located over large bodies of water, they're called maritime source regions. The primary source for maritime polar cold fronts is the North Pacific and North Atlantic. The primary source for tropical maritime warm fronts is the subtropical Pacific Ocean, the Gulf of Mexico, the Caribbean and the subtropical Atlantic Ocean.

Maritime Cold Fronts

• Cold fronts associated with oceanic air masses are typically found in the northwestern and northeastern regions of the U.S. These cold fronts represent the boundaries of advancing cold, moist air. In the Northwest, these fronts deliver rain or snow, along with colder temperatures. As they cross the Rocky Mountains, their moisture is squeezed out and they enter the Plains as dry, cold air. In the Northeast, these cold fronts typically bring colder temperatures than their west coast sisters, but tend to be drier. Northwest cold fronts typically proceed across the country in a southeasterly direction, while Northeast cold fronts proceed in a southwesterly direction.

Maritime Warm Fronts

• Warm fronts associated with oceanic air masses typically move inland from one of three source regions: the subtropical Pacific Ocean, the Gulf of Mexico or the Caribbean. These warm fronts represent the boundaries of advancing warm, moist air. Warm fronts related to subtropical Pacific air masses rarely reach further inland than southern California. Warm fronts associated with the Gulf of Mexico are typically responsible for the severe spring weather in the Plains. This occurs as they move northward and collide with cold fronts moving eastward from the Rockies. Warm fronts associated with the Caribbean typically move up the east coast. These fronts can be associated with tropical storms and hurricanes.