Isobars are lines of constant pressure. Drawing the isobars reveals features (eg highs, lows, ridges and troughs) which help us understand the weather.
When trying to draw isobars, remember the following
– You are trying to draw the isobars of pressure for the values below the
– The symbols on the map give the observed pressure and wind speed and
direction. Remember that the wind is blowing from the tail of the arrow
to the centre. The bars on the tail of the arrow tell you the wind speed:
– The wind blows almost parallel to the isobars (they are usually blow
slightly more towards the centre of the low pressure area). If you stand
with your back to the wind in the northern hemisphere the pressure is
lower on your left than on your right.
– Isobars tend to be parallel to each other, don’t wiggle and never cross.
– The closer the isobars are to each other, the stronger the wind. You can
use the bars on the tail of the weather station symbol to give you the
Beaufort force of the wind. Look at the scale at the top of the map (this is
called the ‘geostrophic scale’). The distance from the left hand edge of
the scale to the force at the symbol gives you the spacing between 2mbar
isobars at that point.