The sea level air pressure. At some points on

The yellow lines on the map have a very important place on
the map. They are called isobars, joining together places with the same mean
sea level air pressure. At some points on the isobars, the air pressure is
measured by hectoPascals. When the isobars enclose an area of high air
pressure, this is called a High, marked on the weathermap by an ‘H’. These
areas are normally characterized with good and warm weather. Similarly, the
isobars also enclose areas of low air pressure, marked by an ‘L’. The areas of
low air pressure have normally stormy, cloudy weather. Isobars tell us a lot
about the general wind flow, but not very many details.

The blue lines with triangles attached represent a cold
front. It indicates the leading edge of a colder air-mass. The cold air pushes
in underneath the warmer air in front of them, forcing the warmer air upwards.
This creates clouds and rain, and the temperature drops.

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The red lines with semicircles attached indicate a warm
front.  It is the edge of an invasion of
warm 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 brings
steady rain. In this front, the wind changes direction, pressure steadies, and
temperature rises.

The small amount of purple semicircles and triangles
indicate an occluded front. Occluded fronts happen when a cold front overtakes
a warm front. All the warm air is trapped above where it cools, making heavy
cloud and rain. The air temperature does not change very much and wind eases.

And the last front in this weather map is the stationary
front. This is represented by interchanging blue triangles and red semicircles.
A stationary front forms when two air-masses lose its impetus for movement. As
a result, neither air-mass makes much progress, causing little change in
temperature, pressure, and rain fall.

The orange lines indicate a trough. This happens when
isobars 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 the
temperature in Celsius degrees. The legend of this particular map is partly
covered 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 about
5 degrees Celsius.