Weather & Climate Chapter 11

air mass

A large body of air that has similar horizontal temperature and moisture characteristics.

source regions

Regions where air masses originate and acquire their properties of temperature and moisture.

continental polar

An air mass characterized by low temperatures and dry air. Not as cold as arctic air masses.

continental arctic air masses

An air mass characterized by extremely low temperatures and very dry air.

lake effect snows

Localized snowstorms that form on the downwind side of a lake. Such storms are common in late fall and early winter near the Great Lakes as cold, dry air picks up moisture and warmth from the unfrozen bodies of water.

maritime polar air mass

An air mass characterized by low temperatures and high humidity.

pacific air

Cool, moist air that originates over the Pacific Ocean, moves eastward, then descends the Rocky Mountains and moves over the plains as dry, stable, relatively cool air.

maritime tropical

An air mass characterized by high temperatures and high humidity.

atmospheric river (AR)

A region of upper-level flow that transports large amounts of moisture, typically from the tropics and subtropics into the midlatitudes.

continental tropical air masses

An air mass characterized by high temperatures and low humidity.

front

The transition zone between two distinct air masses.

stationary front

A front that is nearly stationary with winds blowing almost parallel and from opposite directions on each side of the front.

cold front

A transition zone where a cold air mass advances and replaces a warm air mass.

frontolysis

The weakening or dissipation of a front.

frontogenesis

The formation, strengthening, or regeneration of a front.

back door cold front

A cold front moving south or southwest along the Atlantic seaboard of the United States.

cold air damming

A shallow layer of cold air that is trapped between the Atlantic coast and the Appalachian Mountains.

warm front

A front that moves in such a way that warm air replaces cold air.

overrunning

A condition that occurs when air moves up and over another layer of air.

frontal inversion

A temperature inversion encountered upon ascending through a sloping front, usually a warm front.

Drylines

A boundary that separates warm, dry air from warm, moist air. It usually represents a zone of instability along which thunderstorms form.

occluded front

A complex frontal system that ideally forms when a cold front overtakes a warm front. When the air behind the front is colder than the air ahead of it, the front is called a cold occlusion. When the air behind the front is milder than the air ahead of it, it is called a warm occlusion.

cold type occlusion

A complex frontal system that ideally forms when a cold front overtakes a warm front. When the air behind the front is colder than the air ahead of it, the front is called a cold occlusion. When the air behind the front is milder than the air ahead of it, it is called a warm occlusion.

warm type occlusion

A complex frontal system that ideally forms when a cold front overtakes a warm front. When the air behind the front is colder than the air ahead of it, the front is called a cold occlusion. When the air behind the front is milder than the air ahead of it, it is called a warm occlusion.

upper air front

A front that is present aloft but usually does not extend down to the ground. Also called an upper front and an upper-tropospheric front.

source regions for air masses

Regions where air masses originate and acquire their properties of temperature and moisture.

continental polar air mass

An air mass characterized by low temperatures and dry air. Not as cold as arctic air masses.

continental arctic air mass

An air mass characterized by extremely low temperatures and very dry air.

maritime tropical air mass

An air mass characterized by high temperatures and high humidity.

continental tropical air mass

An air mass characterized by high temperatures and low humidity.

occluded front occlusion

A complex frontal system that ideally forms when a cold front overtakes a warm front. When the air behind the front is colder than the air ahead of it, the front is called a cold occlusion. When the air behind the front is milder than the air ahead of it, it is called a warm occlusion.