Weather maps also known as the synoptic chart, are an example of an isoline map.
Isoline maps are made up of lines that join points of equal value. Contour lines
drawn on a topographic map are another example of an isoline map. Weather maps
use lines called isobars plus other symbols to join together lines of equal
air pressure. Today most meteorologists use the
hectopascal for measuring atmospheric pressure. Many weather reports to the
public use of millibar. One hectopascal equals one millibar. On these
American weather maps the isobars are drawn at intervals of four millibars.
1,013 millibars is the average sea level air pressure. Therefore areas with an air
pressure of over 1,013 millibars are considered to be areas of high pressure,
and areas with an air pressure below 1,013 millibars are considered to be
areas of low pressure. On a weather map areas of high pressure or anticyclones
are identified by a letter H. These areas are associated with clear skies and
little wind. Areas of low pressure or depressions are usually identified by
the letter L and are associated with rain, clouds and high winds. High pressure
systems have enclosed isobars which increase in pressure towards their
center. Low pressure systems on the other hand contain isobars which decrease in
pressure towards the center. When isobars make a sharp bend around a low
this Bend area is called a trough. One of the main symbols employed on a weather
map is called the front. A front represents the boundary between two air
masses and appears on the weather map as a line with triangles or semi circles
attached. At the front of two masses there is stormy weather.
There are four types of front most commonly seen on weather maps. A cold
front is the boundary where a cold air mass pushes underneath the warm air mass forcing
the warm air mass upwards which forms clouds and rain. A cold front is
represented by a blue line with the triangles pointing towards the direction
of movement. A warm front is the boundary where a moving warm air mass as you're placing
a cold air mass. A warm front is represented as a red line with semi circles pointing
towards the direction of movement. Warm fronts move more slowly than cold fronts
because it is harder for warm air to push against the denser cold air. As the
warm air rises above the cold air, water vapor condenses forming high clouds.
Light precipitation can fall on areas as the warm front passes. A stationary front
is the boundary between two air masses which are not moving. Neither mass is
strong enough to move the other, therefore a stationary front can be
pushing back and forth over a given area for days. A stationary front is
represented as an alternating warm and cold front symbols. An occluded front is
a composite of two frontal systems that merge as a result of occlusion. Cold
fronts generally move faster than warm fronts, therefore the cold front will
overtake a warm front and force it aloft. An occluded front is represented as a
purple line with triangles and semi circles. Weather maps also show wind
conditions. Wind is the movement of air. Wind moves from high pressure areas
towards low-pressure areas. Winds do not travel in a straight line due to the
Coriolis effect. This effect is created by her rotation of the earth. The
Coriolis effect deflects wind to the left in the southern hemisphere and to the
right in the northern hemisphere. Thus in the southern hemisphere wind flows
clockwise around low-pressure systems and anti-clockwise in high-pressure
systems. In the northern hemisphere when clothes anti-clockwise around low
pressure systems and clockwise around high pressure systems. Generally wind
flows towards the center of low pressure systems and away from high pressure
systems. When isobars are close to giver wind is strong. When isobars are far
apart wind is weak. Now it is time for you to go and read some weather maps and
see if you can interpret them.