Aim: What is a front?

•Fronts are boundaries that separate air masses of different densities.•One air mass is always warmer and often contains more moisture than the other.

•Types of fronts•Cold front•Warm front•Stationary front•Occluded front

– Fronts (Cold) A cold front represents a zone where cold, dry, stable polar air is replacing warm, moist, conditionally unstable subtropical air.

Understanding Fronts

Cold Front

– At the cold front, the cold, dense air wedges under the warm air, forcing the warm air upward.

– Behind the front the air cools quickly (Freezing level dips as it crosses the front).

– Winds shift.– Leading edge of the

front is steep. Vertical rise to horizontal distance is 1:50

Warm FrontA warm front is the opposite of

a cold front.In this case, warm air displacing

cold air.The front is drawn as a solid red

line with semicircles pointing in the direction of the movement of the warm front.

The direction of movement is determined from the weather conditions.

In this case the warm is less dense than the air it is displacing so it rides up over the top of the dome of cold air.

This makes the ascent of the air much slower compared to a cold front

Warm Front

• Fronts (Warm)

Understanding the Weather

• Fronts

– Cold front is rapidly approaching the slower moving warm front.

The occluded front

• Fronts (Cold Occlusion)

• The cold front now overtakes the warm front.

Understanding the Weather

• Fronts (Cold Occlusion)

• Cold front now under rides and lifts the warm front and the warm air mass off the ground.

Cold Occluded Front

• Fronts (Warm Occlusion)

– When the cold front catches up to and overtakes the warm front, the lighter air behind the cold front is unable to lift the colder heavier air off the ground.

Warm Occluded Front