These are very common weather engines in the middle latitudes. Their dynamic is defined by the interaction of masses of air at different temperatures.

On this page you will find:

1. A video with Tomàs Molina with a basic description of cold and warm fronts.
2. A video synopsis with the basic concepts in further detail.

1. The fronts

2. Video synopsis

At the middle latitudes, fronts are a fairly common occurrence, which can lead to those inhabiting these latitudes to believe that they are the only engines powering the weather, however that is not the case. More often the weather engines are orography, convection and convergence and divergence, rather than frontal systems.

Fronts occur when masses of air at different temperatures clash.

Cold air is more dense and warm air is less dense and so when warm air meets cold it moves on top of it. This creates a boundary between the two.

The cold front is drawn using a blue line with blue triangles. This corresponds to the location of the boundary separating these masses of air at surface level. However, the frontal boundary is not the same higher up.

The warm front is drawn using a red line with red semicircles. It is also drawn where the boundary between the two masses of air is positioned at surface level. However, higher up that boundary varies considerably more than for a cold front, as it bends, and high up it can be very big indeed. Warm fronts can be very large and the cloud associated with them is far more extensive than the cloud found with cold fronts.

Cloud associated with fronts

The cloud that comes with warm fronts is stratified: Cirrus (Ci) high up and then, lower down: Cirrostratus (Cs) and Altostratus (As) and Nimbostratus (Ns). The latter can bring with it steady but light precipitation.

The mass of moving cold air generates an almost vertical wall opposite the warm air. The warm air rises vertically which is why the cloud associated with a cold front is Cumulonimbus (Cb), bringing showers and storms.

Wind direction

Another defining feature of fronts is the variation in wind direction.

The wind ahead and behind the front will shift.

With the cold front that shift is marked: ahead of the front, the wind is westerly or somewhat southwesterly. After the front the wind shifts northwest.

With the warm front the differences in the direction of the wind aren't as notable, especially in latitudes below 50º. Generally the winds will shift from the southwest to the west as the front passes.

At latitudes below 40º, warm fronts are very blurry as they pass and are difficult to verify.