Download Low Pressure Systems A low pressure system or a

Low Pressure Systems A low pressure system or a depression is an area of low pressure air where the air is rising. In Britain the depressions usually moves from west to east. The Coriolis effect stops air moving in a straight line, this means winds move in a spiral, inwards and upwards in the case of a low pressure system. They can also be known as cyclones. Cyclones bring with them cloudy conditions windy weather, rain and snow and changeable weather. This system develops when warm and moist air rises from the surface of the Earth. As the warm humid air moves upwards it cools and clouds are formed. In low pressure systems the air spirals inwards towards the earth causing the windy conditions. The low pressure systems that affect England are normally formed out in the Atlantic. High Pressure Systems High Pressure systems or anticyclones are regions of high pressure or sinking air. They bring with them good fair weather. They also tend to cover a much greater area than low pressure systems. They are formed by a large mass of descending air which as it sinks warms up. This causes the humidity to decrease and causes water droplets in the air to evaporate and cause dry weather. Cold Fronts A cold front is represented by blue triangles on a blue line on a surface map. It is very different to a warm front. The cold front has a mass of cold air behind it and is pushing warm air in front off it. Usually accompanied by cloud and rain along the front of this. The air masses on either side are greatly contrasting and the pressure will increase. On a cold front the wind direction is usually north west ‐ west with cumulus clouds forming along the front of it. Warm Fronts This is represented by a red line with red semi circles on it. This front has a mass of warm air behind it and a mass of cool air ahead of it. Since warm air is slightly less dense it rise above the cool air slightly. The warm front will bring at first light precipitation but then usually warm weather afterwards. Occluded Fronts Occluded fronts can form in many different ways but it is when the cold and warm fronts coincide. This creates a front that doesn’t have a very large difference in temperatures between the two sides of the front. Usually accompanied by a small band of rain and then clear weather. Wind will come from the north west once it has past.