Cold occlusions occur when a faster
moving cold front overtakes a slower warm front. When the cold air forces
the warm air upward, this is a cold occlusion. (the cold air might also
ride up over the warm air). A cold occlusion is nothing more than
a warm front aloft. If the air behind the occlusion is colder than
the air ahead of the warm front, then it is a cold occlusion.
Surface temperatures are fairly cool ahead of the front
and drop to much colder after the front passes. Since cold air holds less
moisture than warm air, surface dew points will fall. Visibility and weather are usually poor before and during passage, but improve after passage.
Pressures fall ahead of the front. Pressures reach the lowest point during
passage of the front and rise after passage. Surface winds can be gusty.
Winds are usually from the south to southeast before passage and rotate
clockwise to the west - northwest after passage (veering winds).