Download Low pressure systems A low pressure system or

Low pressure systems A low pressure system or depression is an area of low pressure which has formed due to the air being heated and expanding, making it less dense and causing to rise. This causes a lack of air and the low pressure area is formed. Weather that is typical of low pressure is very unsettled – characteristically, rain, wind and cloud tend to be associated with low pressure. High pressure systems A high pressure system contains cool and fair air and often can cause light winds and sunny conditions, although not always. Coming from the south, these conditions should occur, but if the system comes from the north then it will usually bring cold weather in the winter months. Because the UK gets most of its weather from the south west, high pressure is usually indicative of good weather. Cold front A cold front is where a mass of cool air replaces a mass of warmer air at the surface. It is denser than warm air so it is displaced upwards. Along the front, there can be thunderstorms or showers assuming that there is enough moisture in the air. Warm Front A warm front is a mass of warm air replacing a mass of cooler air at the surface of the Earth. A warm front can be preceded by rain, but once the front hits then it can become foggy. After it has passed it will clear up and temperature will increase. Occluded front An occluded front is a mixture of a warm and a cold front. A cold front travels faster than a warm front and so can catch it up. Because it is denser, it can push the warm front up off the ground. A wide variety of weather can be found at an occluded front, with thunderstorms possible assuming there is enough moisture in the air. However in general occluded fronts bring drier air and cooler temperatures.