Finlands Variable Weather 

Around the world situated weather stations, satellites and radars give us information about the weather. According to this information, computers make predictions of the weather, and meteorologists examine the predictions reliability. Weather forecasts are usually made for a few days, at most for five days. The forecasts are important first of all for peasants and tourists, but also air, marine and overland traffics continuously need specific weather reports and forecasts. Weather forecasts always use the concepts high pressure and low pressure. When the air rises up, low pressure is formed on the ground. Then when the air go down, it forms high pressure. From the high-pressure area the air moves as wind towards the centre of the low pressure. At time of high pressure the sun is shining and during low pressure it is raining. Above the North Atlantic, the cold air masses from Polar Regions and the warm air masses brought by the south-western winds from the southern Atlantic collapse. This line of two different air masses is called the Polar Front. When the air masses collapse, their temperature and humidity differences tend to even out. At the line of the air masses the fast-moving warm air pushes as a flap to the area of the cold air. The heavy cold air tends to go down towards the earths surface and the light warm air upwards. They form wave movements and whirlwinds, which develop to cyclones. After their birth the cyclones move towards east and north-east at the speed of 30-60 km/h. Cyclones are hundreds of kilometres wide and they move thousands of kilometres in a couple of day so they affect a large area. Cyclones cause the unstable weather that is typical for Finland. The meeting places of the air masses are rainy. When the warm air spreads to the cold air area, a warm line is formed. When the air rises up, it cools down and the humidity it contains becomes tense, to a widespread rain. Behind the warm-air flap, in the cold line, the cold air pushes under the warm air and raises it strongly up. In this area there is hard wind and showers, at summertime often thunderstorms. The cold line is not wide and it goes by fast, after that the weather is clear. Between the warm line and the cold line there is usually clear and warm. The cold line finally reaches the warm line, then a occlusion line is born. In it the warm air has risen up and the humidity becomes tense and it rains. When the low pressure fulfils, the rain stops, the air pressure rises and the temperature differences get smaller.