Climatological concepts

17/09/2020

A front is defined as the boundary of separation between two air masses of different characteristics, mainly temperature and density.

Air masses normally move cold fronts from NW to SE and SW to NE on warm fronts. They can be classified into four groups that I will detail below.
 

Cold front

A cold front is defined when the cold air mass pushes the warm air mass that is less dense, forcing it to rise and causing the formation of vertical development type clouds. The speed with which it moves is approximately 20 kts and can cause storms, strong winds and snowfall.


Warm front

On the warm front, it happens that the warm air mass displaces the cold air mass ahead. At the same time that the warm mass pushes, it also slides over the cold one, creating stratiform clouds. The speed with which it moves is somewhat lower than on the cold front, about 15 kts on average.


Occluded forehead

An occlusion forms when a rapidly advancing cold front meets a slower advancing warm front. The cold front wedges under the warm one, forcing it to rise above it. There are two types of occluded fronts:

- Cold Occluded Front - occurs when the air behind the cold front is colder than the air in front of the warm front. The associated weather is similar to that of the cold front, with development of storms and abundant rainfall.

- Warm occluded front - occurs when the air behind the cold front is warmer than the cold air in front of the warm front. The associated time is similar to that of the warm front, and will depend on the degree of atmospheric instability.


Stationary fronts

Stationary front is called the border between two air masses that do not present any type of displacement. This type of front, if it lasts for several days, ends up disappearing and, if one of the two air masses begins to displace the other, it will become a cold or warm front, depending on the mass of air that pushes the other. The development of different types of cloudiness and precipitation will depend on the stability of the air masses. If stable, stratiform clouds will form with light rain. If, on the other hand, it is unstable with strong convective movements, it is more likely that cumulus or cumulonimbus clouds will form.