Dew point temperatureĭew point temperature is plotted to the nearest whole degree Celsius, i.e. Weather systems and fronts Relationship between isobars and windįig 4: Relationship between isobars and wind speed[/captioĪir temperature is plotted to the nearest whole degree Celsius, i.e. Isobars are lines joining places with equal mean sea-level pressures (MSLP).įig 3: Identification of weather systems, isobars and front Drizzle in warm sectors or showers in cold air occur fairly randomly, but occasionally, lines of more organised precipitation can develop. However, precipitation is not confined to fronts. They also happen to be where there is significant precipitation. The direction in which the symbols point is the direction in which the front is moving.įronts describe thermal characteristics. ![]() On a synoptic chart an occluded front appears as a purple line with a combination of triangles and semi-circles. Occlusions form when the cold front of a depression catches up with the warm front, lifting the warm air between the fronts into a narrow wedge above the surface. The direction in which the semi-circles point is the direction in which the front is moving. On a synoptic chart a warm front appears as a red line with semi-circles. The direction in which the triangles point is the direction in which the front is moving.Ī warm front marks the leading edge of an advancing warm air mass. On a synoptic chart a cold front appear as a blue line with triangles. Cold FrontĪ cold front marks the leading edge of an advancing cold air mass. Three types of front were identified which depend on the relative movement of the air masses. ![]() ![]() Since the air masses could be considered as being in conflict with each other, the term ‘front’ was used to describe the boundary between them. During the 1920s, a group of Scandinavian meteorologists, known collectively as the Bergen School, developed the concept of representing the atmosphere in terms of air masses. Fig 2: A depression FrontsĮarly weather charts consisted simply of station plots and isobars, with the weather being written as comments, like ‘Rain, heavy at times’. Winds blow in an anticlockwise direction around depressions in the northern hemisphere, this is reversed in the southern hemisphere. Fig 1: An anticyclone Low pressure or depressionsĭepressions are areas of low pressure, usually with a well-defined centre, and are associated with unsettled weather. Winds blow in a clockwise direction around anticyclones in the northern hemisphere, this is reversed in the southern hemisphere. Weather systemsĪnticyclones are areas of high pressure, whose centres are often less well defined than depressions, and are associated with quiet, settled weather. These are drawn to highlight the areas of most significant weather, but that does not mean that there is nothing of significance elsewhere on the chart. Other features on a weather chart are fronts and troughs. These features are best shown by charts of atmospheric pressure, which consist of isobars (lines of equal pressure) drawn around depressions (or lows) and anticyclones (or highs). Weather charts consist of curved lines drawn on a geographical map in such a way as to indicate weather features. Understanding station plots on a weather map
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