Air Masses and Fronts What is an Air

Air Masses and Fronts

What is an Air Mass? • A large body of air that has similar temperature, humidity, and pressure

Four Main Types Continental Polar Continental Tropical Maritime Polar Maritime Tropical

Continental Air Masses • Continental air masses form over land • Continental Polar – Cool, dry air mass that forms over land • Continental Tropical – Warm, dry air mass that forms over land

Maritime Air Masses • Maritime Air Masses form over Oceans • Maritime Polar – Cool, humid air masses that form over oceans • Maritime Tropical – Warm, humid air masses that form over oceans

How Air Masses Affect Weather Air masses move along jet streams When the jet stream moves south, it will often bring cooler and drier air to the south

Fronts • Fronts are boundaries between air masses • They are indicated by red, blue, or purple lines on a weather map • Fronts indicate a change in weather

The Four Main Types of Fronts Warm Front Cold Front Stationary Front Occluded Front

Warm Fronts • The boundary where a warm air mass is replacing a cold air mass • Air behind the warm front is usually warmer and more humid than the air it is replacing

Warm Fronts cont. • Warm fronts are indicated by a red line with red half-circles on one side of it

Weather Associated with Warm Fronts • A warm front brings gentle rain or light snow, followed by warmer, milder weather • Warm fronts can also favor the formation of light and fluffy clouds

Cold Fronts • The boundary where a cold air mass is replacing a warm air mass • Bring cooler, and drier air than the air ahead of it

Cold Fronts Cont. • Cold fronts are indicated on a weather map by a blue line with triangles

Weather associated with cold fronts • Cold fronts will bring drastically cooler temperatures • They can favor unstable atmospheric conditions • This leads to heavy rain, snow, and likely strong thunderstorms and strong winds

Stationary Fronts • Stationary fronts are the boundaries between two air masses in which neither air mass is strong enough to replace the other

Stationary Fronts cont. • Stationary Fronts are indicated on a weather map by a blue and red line with half circles and triangles • Kind of a mix of a warm and a cold front

Stationary Fronts and Weather • Because stationary fronts indicate two air masses that are not strong enough to move one another, the weather associated with a stationary front typically sticks around for many days • Many days of light rain or snow • If the front sticks around long enough, it may produce small thunderstorms

Occluded Fronts • Occluded fronts form when a cold front begins to overtake a warm front – The cold front moves faster than a warm front ahead of it

Occluded Fronts cont. • Occluded fronts are indicated on a weather map by a purple line with purple triangles and half circles

Weather and Occluded Fronts • In an occluded front, the cold air mass will eventually take over the warm air mass, lifting the warm air up further into the atmosphere • As cooler air starts to overtake the warmer air, light rain or snow may start to fall

How do Fronts Move? • You can always tell the direction a front is moving by looking at the arrows or half circles on the frontal line • The front always moves in the direction that the triangles or half circles are pointing towards