the weather map or synoptic chart as us meteorologists call them you see them on
the news in the paper and in our videos but do you know what all the lines and symbols mean
you can tell a lot about the current weather just from looking at the features on a map
so let me take you through the basics now the white lines on a chart these are called isobars
and they're lines of constant or equal atmospheric pressure and you'll see these on a weather map no
matter where you are in the world they give us an indication of the airflow around weather features
and you can also interpret the wind strength from isobars with the general rule being that where the
isobars are the tightest most squeezed together that's where the wind will be the strongest and
whether the furthest apart or the slackest that's where the wind will be the lightest
now it's time to look at the H's and the L's and these are also to do with pressure they
Mark areas of local pressure extremes so if we look at the H for example that's indicating
an area of high pressure much like the peak of a mountain no matter which way you moved
away from the h the pressure is going to drop and in the southern hemisphere the wind flows
anti-clockwise around a high pressure system an interesting point is that the air in the center
of a high pressure system is sinking and that tends to lead to more settled weather conditions
lows on the other hand are like the bottom of a valley they're the local minimums of atmospheric
pressure and in the southern hemisphere the wind flows clockwise around a low pressure system and
in the center of the low the air is rising so lows on the map are normally associated with clouds wet
and Stormy Weather and you can also see that the isobars are quite close together around and low
so this is also indicating an area of windy conditions now it's time to talk about fronts
now fronts are the lines and shapes that you see on the weather map and they indicate a boundary
between two different air masses so we'll start by looking at the cold front the blue line with the
triangles now these indicate an area of where cold air is moving in and pushing warm air upwards so
we tend to expect to see a blanket of cloud along the Leading Edge of a front which can produce
fairly consistent rain and as a front passes over you you'll notice a change in wind direction and
also temperature and in summer there can be quite a sharp drop in temperature behind a cold front
now the red lines and semi-circles over here are indicating a warm front now a warm front is where
warmer air will replace cooler air and just like a cold front there can be quite a marked temperature
change when a warm front moves through but typically less dramatic than what we would
see with a cold front and we do see these less frequently around Australia than we do cold fronts
now there's other types of fronts too stationary and occluded fronts and if
you'd like to know more about these check out the blog linked in our video description
we also see dashed lines like this one over here now this is an area called a trough it's an area
of relatively low atmospheric pressure compared to its immediate surroundings and like cold fronts
troughs are separating two different air masses usually moist air on one side and drier air on the
other and as the trough moves towards the moist air it causes the air to lift and so we see cloud
and showers and thunderstorms often developing on a trough now another type of trough that we see
in the Australian region is the monsoon trough shown by this dot dashed line now a monsoon is
a seasonal wind pattern and it typically brings heavy rain and it moves in the seasons with the
seasons so over our winter months we see the monsoon trough move to the north of the equator
far away from Australia but in the summer it will shift back into the Southern Hemisphere and bring
a return of the wet season to Northern Australia so there you have it the basics of a synoptic
chart or weather map a meteorologist road map to understanding and predicting what weather we
might experience you can find synoptic charts and other maps and forecasts on the bureau's website