Special Fronts

Stationary Fronts

• In certain cases, then airflow on both sides of a front is neither toward the cold air mass nor toward the warm air mass, but almost parallel to the line of the front.

• The surface position of the front does not move, or it moves slowly.

• This condition is called a stationary front.

Stationary Fronts

• On a weather map, stationary fronts are shown with blue triangular points on one side of the line and red semi-circles on the other side of the line.

• Because overrunning usually occurs along stationary fronts, gentle to moderate precipitation is likely.

• Stationary fronts may remain over an area for several days.

• Flooding may be possibe.

Stationary Front

Stationary Front

Occluded Fronts

• The fourth type of front is called the occluded front.

• Here, a rapidly moving cold front overtakes a warm front.

• As the cold air wedges the warm air upwards, a new front forms between the advancing cold air and the air over which the warm front is gliding.

Occluded Fronts

• The weather in an occluded front is usually complex.

• Most precipitation is associated with the warm air being forced aloft.

• When conditions are suitable, the front that is formed is capable of producing precipitation on its own.

Occluded Fronts

• Because a cold front produces roughly the same amount of lifting as a warm front but over a shorter distance, the precipitation intensity is greater, but of shorter duration.

Occluded Fronts

• There are both cold-type and warm-type occluded fronts.

• For the cold-type, the air behind the cold front is colder than the cool air it is overtaking.

• This is the most common type of cold front east of the Rocky Mountains.

• For the warm-type, the air behind the advancing cold front is warmer than the air it is overtaking.

• These occur most frequently along the Pacific coast.

Occluded Front

Occluded Front