A front is a weather system that is the boundary separating two different types of air. One type of air is usually denser than the other, with different temperatures and different levels of humidity. This clashing of air types causes weather: rain, snow, cold days, hot days, and windy days.
Two major types of fronts are cold fronts and warm fronts.
Cold fronts often come with thunderstorms or other types of extreme weather. They usually move from west to east. Cold fronts move faster than warm fronts because cold air is denser, meaning there are more molecules of material in cold air than in warm air.
Strong, powerful cold fronts often take over warm air that might be nearly motionless in the atmosphere. Cold, dense air squeezes its way through the warmer, less-dense air, and lifts the warm air. Because air is lifted instead of being pressed down, the movement of a cold front through a warm front is usually called a low-pressure system. Low-pressure systems often cause severe rainfall or thunderstorms.
Warm fronts usually show up on the tail end of precipitation and fog. As they overtake cold air masses, warm fronts move slowly, usually from north to south. Because warm fronts aren't as dense or powerful as cold fronts, they bring more moderate and long-lasting weather patterns. Warm fronts are often associated with high-pressure systems, where warm air is pressed close to the ground. High-pressure systems usually indicate calm, clear weather.
Fronts on Weather Maps
On weather maps, cold fronts are illustrated by blue lines with sharp "teeth" pointing in the direction of the wind. Warm fronts are illustrated by red lines with rounded bumps pointing in the direction of the wind.
Term Part of Speech Definition Encyclopedic Entry air mass Noun
a large volume of air that is mostly consistent, horizontally, in temperature and humidity.
Encyclopedic Entry: air mass atmosphere Noun
layers of gases surrounding a planet or other celestial body.
Encyclopedic Entry: atmosphere boundary Noun
line separating geographical areas.
Encyclopedic Entry: boundary cold front Noun
interaction between two air masses, where the cool, dense mass is replacing the warm one.
having parts or molecules that are packed closely together.
clouds at ground level.
Encyclopedic Entry: fog front Noun
boundary between air masses of different temperatures and humidities.
Encyclopedic Entry: front high-pressure system Noun
weather pattern characterized by high air pressure, usually as a result of cooling. High-pressure systems are usually associated with clear weather.
amount of water vapor in the air.
Encyclopedic Entry: humidity indicate Verb
to display or show.
low-pressure system Noun
weather pattern characterized by low air pressure, usually as a result of warming. Low-pressure systems are often associated with storms.
smallest physical unit of a substance, consisting of two or more atoms linked together.
all forms in which water falls to Earth from the atmosphere.
Encyclopedic Entry: precipitation rain Noun
Encyclopedic Entry: rain rainfall Noun
amount of precipitation that falls in a specific area during a specific time.
precipitation made of ice crystals.
degree of hotness or coldness measured by a thermometer with a numerical scale.
Encyclopedic Entry: temperature thunderstorm Noun
cloud that produces thunder and lightning, often accompanied by heavy rains.
warm front Noun
mass of warm air that replaces a mass of cold air.
state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.
Encyclopedic Entry: weather weather system Noun
movement of warm or cold air.