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.
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.