WEATHER FRONTS
HOW often have you heard a weather forecaster say a cold front will push southeast across the UK today?
I will try to explain in simple terms what frontal systems are and the weather conditions they bring.
Fronts are usually associated with low pressure and they often but not always bring precipitation with them.
However, whether rain or any other precipitation for that matter falls, depends on whether the front is decaying or intensifying. There are three types of front, warm, cold and occluded and each marks the boundaries between different air masses that are moved around the globe by the wind. A weather front is unusually several hundred miles long and extends vertically up into the troposphere.
Warm fronts are marked on weather maps, also known as synoptic or pressure charts, by red semicircles along a red or black line. These show warmer air moving in behind the front as its name suggest. Normally several hours of rain can be expected at and behind the front, but ahead of it, the rain band can be two or three hundred miles wide. The heaviest rain will be along the front itself.
Cold fronts are seen on weather charts as blue triangles along a blue or black line and these represent the arrival of a cooler air mass pushing in and also a change of wind direction towards the north. Often, violent winds can accompany the clearance of a cold front and even thundery activity. Usually there is a short period of rain or showers. In winter precipitation can include rain or snow. The cold air that follows the front is usually very unstable and further showers may follow.
Occlusions are a mixture of the town frontal types where the cold front catches up with the warm front and are shown on weather maps as such with both red semicircles and blue triangles. Precipitation is likely to fall along the frontal zone.