This document discusses different types of fronts: 1) Stationary fronts occur when airflow on both sides of a front is parallel to the line of the front, causing it to remain stationary or move slowly. They are shown on weather maps with blue triangles and red semicircles and can cause gentle to moderate precipitation over several days. 2) Occluded fronts occur when a cold front overtakes a warm front, forcing the warm air upwards and creating a new front. They produce complex weather and precipitation as the warm air is lifted, and can generate rain on their own under suitable conditions. 3) There are cold-type and warm-type occluded fronts depending on whether the air behind the advancing cold front is col

1. Special Fronts

2. 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.

3. 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.

4. Stationary Front

5. Stationary Front

6. 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.

7. 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.

8. 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.

9. 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.

10. Occluded Front

11. Occluded Front