Occluded Fronts

Often, a cold front will travel faster than a warm front and will eventually catch up and overtake the warm front. The boundary created is called an occluded front or an occlusion. Here, the layer of warm air is lifted above both layers of cold air. Preceding the occluded front would be showers typical of a warm front. But as the front gets closer, more stormy-like conditions may prevail.

Meteorologists differentiate between two types of occluded fronts:

1. cold-type occluded fronts ("cold occlusion"): the air behind the front is colder than the air in front of it
2. warm-type occluded fronts ("warm occlusion"): the air behind the front is warmer than the air in front of it

Weather Element	Before passing	While passing	After passing
Winds	East, southest, or south	Variable	West or northwest
Temperature	Cold type: cold or cool Warm type: cold	Cold type: dropping Warm type: rising	Cold type: colder Warm type: milder
Pressure	Usually falling	Low point	Usually rising
Clouds	In this order: cirrus, cirrostratus, altostratus, nimbostratus	Nimbostratus, sometimes towering cumulus and cumulonimbus	Nimbostratus, altostratus, or scattered cumulostratus
Precipitation	Light, moderate, or heavy precipitation	Light, moderate, or heavy continuous precipitation or showers	Light to moderate precipitation followed by general clearing
Visibility	Poor in precipitation	Poor in precipitation	Improving
Dew point	Steady	Usually slight drop, especially if cold-occluded	Slight drop, although may rise a bit if warm-occluded