Building your 'weather' skills

This section starts with suggestions about how you might build a profile of your local climate from your own experience (and that of other weather observers) to complement the official climate statistics.

We indicate key weather and climate sources such as the Bureau of Meteorology's web site, and newspaper weather pages.

There are examples and analyses of common weather map sequences, and some related exercises to assist your understanding of weather processes.

We conclude with some final suggestions and a brief checklist on making your own forecast.

Know your local climate
Weather is the daily variation within the long-term records and experience which we call climate.

Each region has its own distinctive climate. Weather characteristics may change gradually across a region until they merge into those of adjacent areas. While the official weather of a region is measured at one place, 'local' weather for people living elsewhere may differ noticeably, particularly with changes in topography.

Melbourne is a good example. Although rain often falls when cold fronts sweep in from the south-west, there is also significant rain from prevailing north-westerly winds. Before reaching Melbourne these north-westerlies cross the central highlands, which create uplift and force clouds to rise. The resultant cooling, and consequent rain there, leads to a rain 'shadow' which extends from the lee of the highlands towards Melbourne's outer western suburbs.

To the east of Melbourne, clouds coming from both the south-west and the north-west are uplifted by the Dandenong Ranges, causing increased rain. There is therefore quite a gradient in average annual rainfall from Melbourne's western suburbs to those in the outer east. Melbourne's official annual average rainfall, measured in the city, is close to 600mm, compared to less than 500mm in the outer west and nearly 800 mm in the foothills of the Dandenongs.

Temperature is also modified by topography, vegetation, and structures. Solar radiation on bare soil is absorbed at a minutely thin surface layer, causing very high daytime surface temperatures and considerable heating of the air layers near the surface.

In contrast, with very tall vegetation, like forests, the radiation is absorbed 'in depth' down through the canopy, resulting in much less heating of the air in any given layer. In Melbourne, for instance, a thermometer at the height of a meteorological screen experiences hotter daytime temperatures over the grassy plains on which the western suburbs are built, compared to one in the treed and forested suburbs in the outer east and the Dandenongs. Higher elevations also have some cooling effect.

Night-time temperatures tell a different story. Any large city soaks up and stores daytime solar radiation, because of the high heat capacity of dark bitumen roads and solid high-rise buildings. This heat, slowly released during the night, keeps the city minimum temperatures higher than those in the surrounding open countryside causing the 'heat island' effect.

Central Melbourne has less than three frosts per year, far lower than the number recorded in the outer suburbs.

(below) The 'heat island' effect: a snapshot of a winter's night, showing how temperatures varied greatly from central Melbourne to outer suburbs and open land.

Another interesting local effect is seen in Melbourne's south-eastern bayside suburbs from Mordialloc to Chelsea. On calm nights, cooled air from the foothills of the Dandenongs drains towards Port Phillip Bay across the flat open landscape.

Much of this cold air is dammed behind the coastal railway embankment between Mordialloc and Chelsea.

The CSIRO Division of Atmospheric Research, built immediately inland of the embankment, consistently reported lower minimum temperatures than any other Melbourne suburb when serving as an official meteorological observing station.

From your experience, or the comments of other weather observers, you will build a profile of local weather to complement the broad scale official forecasts. If you're living by the water, this might include an understanding of the timing and duration or sea breezes or fog. People living near hills may be familiar with local phenomena like Adelaide's gully winds.