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Weather forecasting

5 questions with Luke Johnston from the Bureau of Meterology

We spend our summer checking the BOM site, but the weather and forecasts often remain a bit of a mystery to us so we’ve asked Luke Johnston, Senior Meteorologist with the Bureau of Meteorology, Tasmania a few questions we have all probably pondered at some time.

How do you predict the weather?

We look at as many observations as we can to see what is happening right now and what will happen in the very near future. From there we rely on a whole range of computer models to determine the evolution of the weather systems we are seeing right now. The trouble is that they rarely get it right, and so as weather forecasters, we try to add as much of our expertise and experience as we can to come up with what we deem to be the most likely scenario going forward into the week ahead.

To gain an understanding of what is happening right now we use a network of observation sites on the ground throughout the country, combined with radar and satellite imagery, even by looking out the window to see how much the leaves are moving on the trees in some cases! As an example, we are able to use these tools to track the timing of an approaching cold front; we then use our knowledge of meteorology to forecast how that front will behave when it reaches Tasmania, aided by a suite of computer model data for guidance.

Can a layperson predict the weather?

With enough experience at forecasting at a particular location and building a knowledge of how weather systems affect our weather locally, I think that a layperson can certainly predict the weather on a broad scale. For example, will it rain or be sunny, cold or hot, etc. Simply observing the clouds, anyone can start to recognise patterns and types that are linked to certain weather and conditions.

Why do the forecasts not match reality on occasion?

There are many uncertainties that occur when forecasting the weather. Timing of weather systems can delay or speed up the arrival of expected weather, they can weaken/strengthen ahead of arriving, which affects the intensity of the weather.

Sometimes a cold front that is expected to cross Tasmania in four days from now can end up passing to the south by the time we get to that day. This could be due to a high pressure system to the north that is slightly stronger than originally expected and as a consequence a forecast of rain in four days' time can turn into a partly cloudy but otherwise fine day. There are many ingredients that go into the weather, and by altering one or two ingredients by a miniscule amount, you can quite easily end up with completely different weather at a particular location. For example, thunderstorms move though an area and it is likely that they'll move over Strahan. However the temperature at ground level is just half a degree colder than expected, and the storms end up moving 20 km to the south where the temperature is slightly warmer and storms were not expected.

What do you think of the weather apps and is there one you would recommend?

The BOM weather app is very good for providing up to date information and forecasts for your location based on the forecasts from meteorologists, rather than model data.

What do you need to do to become a meteorologist?

Maths and physics degrees at University level. The Bureau of Meteorology have an intake once a year and it involves completing a Graduate Diploma of Meteorology at our Training Centre located in Melbourne. Information about this course can be found here