The yellow lines on the map have a very important place onthe map. They are called isobars, joining together places with the same meansea level air pressure. At some points on the isobars, the air pressure ismeasured by hectoPascals. When the isobars enclose an area of high airpressure, this is called a High, marked on the weathermap by an ‘H’.
Theseareas are normally characterized with good and warm weather. Similarly, theisobars also enclose areas of low air pressure, marked by an ‘L’. The areas oflow air pressure have normally stormy, cloudy weather. Isobars tell us a lotabout the general wind flow, but not very many details.The blue lines with triangles attached represent a coldfront. It indicates the leading edge of a colder air-mass. The cold air pushesin underneath the warmer air in front of them, forcing the warmer air upwards.
This creates clouds and rain, and the temperature drops.The red lines with semicircles attached indicate a warmfront. It is the edge of an invasion ofwarm air into colder air. The semicircles point to where the air is moving,rising over a zone of cooler air, making a cloud bank, which often bringssteady rain. In this front, the wind changes direction, pressure steadies, andtemperature rises.The small amount of purple semicircles and trianglesindicate an occluded front. Occluded fronts happen when a cold front overtakesa warm front.
All the warm air is trapped above where it cools, making heavycloud and rain. The air temperature does not change very much and wind eases.And the last front in this weather map is the stationaryfront. This is represented by interchanging blue triangles and red semicircles.A stationary front forms when two air-masses lose its impetus for movement. Asa result, neither air-mass makes much progress, causing little change intemperature, pressure, and rain fall.
The orange lines indicate a trough. This happens whenisobars make a sharp bend around a Low and create an area where it bends.Troughs usually have weather similar to low pressure areas and fronts.The different colours in the map seem to represent thetemperature in Celsius degrees. The legend of this particular map is partlycovered by isobars and so it is difficult to see everything that it represents.For example, if this was the scenario, the areas with light blue would be about5 degrees Celsius.