Features of a weather map Using a weather map Warnings

The weather map that appears in our newspapers or on T.V. is the result of surface weather readings taken all around Australia. Upper atmosphere information is gathered from weather balloons and satellite information. Like a huge jig-saw puzzle, the weather map brings together temperature, wind direction and strength, air pressure, rain and storm information into one easy to read illustration.

Features of a weather map
Typically, a weather map is made of a series of high and low pressure zones interlaced with warm or cold fronts. These high and low pressure zones are simply called highs and lows. Sometimes two lows are joined by a region of low pressure known as a trough.

The lines on the map are called isobars and join places of equal air pressure. At sea level, the average air pressure is 1010hPa with highs typically up to 1030hPa and lows down to 990hPa.

Wind speed and direction indicators show the direction and strength of local winds. The arrow points in the direction of the wind movement and the number of strokes on the tail indicates the strength of the wind. Rain is shown by hatching.

A very good explanation of words used in forecasting by the Bureau of Meteorology can be found at: Weather Words - Bureau of Meteorology

Using a weather map
Wind direction and speed can be quickly found by a close inspection of the relative positions of the highs and lows and the closeness of the isobars between them. The wind will blow from high pressure to low pressure, but will also be affected by the rotation of the Earth. In the Southern Hemisphere, winds move around high pressure systems in the anti-clockwise direction and low pressure systems in the clockwise direction.

Cold and warm fronts are typically felt as sharp changes in temperature created by changes in wind direction. Fronts lie between high and low pressure zones and mark the boundary between circling winds. Cold fronts usually bring rain as moist warm air from a high mixes with colder air from a low.

The weather systems typically move from the west in Southern Australia, so look towards Western Australia and South Australia for an indication of the weather to come over the next few days to a week in Victoria.

Warnings
The Bureau of Meteorology issues the warnings with forecasts. Explanations of the terms used in Bureau warnings are given at: Bureau of Meteorology - Storm Warnings

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