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The
Weather forecast
The provision of weather forecasts is one of the basic tasks of Australia's
national weather service - the Bureau of Meteorology. Every day, the
efforts of many of its 1600 staff are directed towards the preparation
and dissemination of the 3000 forecasts that are issued for the general
public and a wide range of 'special users' whose activities are dependent
on the weather. To prepare a forecast of tomorrow's weather, a meteorologist
must first obtain a detailed picture of present weather conditions in
the area for which the forecast is being prepared. This involves the
cooperation of many people both within and outside the Bureau of Meteorology,
and covers a wide range of activities - communications, observations,
analysis, prediction, and dissemination - all of which are
essential components of the weather forecast service.
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Observations
Basic weather data are obtained from more than 60 Bureau-staffed observing
stations around Australia, on offshore islands, and in the Antarctic.
Every three hours instrument readings are made of temperature, air pressure,
humidity, wind speed and direction, and rainfall, and visual observations
are made of cloud cover and visibility. In addition to the 'surface'
observations, winds in the upper atmosphere are measured every six hours
by a balloon tracked by radar. Once or twice a day the temperature and
humidity at different levels of the atmosphere are obtained by balloon-borne
instruments to an altitude of 25 kilometres. The Bureau also has a network
of more than 400 part-time observers who provide surface observations
up to seven times a day. Other sources of observations include meteorological
satellites, automatic weather stations, drifting ocean buoys, ships
and aircraft.
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Analysing
the data
The raw weather data are transmitted direct into computers in the Bureau's
Regional Forecasting Centres in each capital city and the National Meteorological
and Oceanographic Centre in Melbourne. Analyses of the Australian region
and the whole of the southern hemisphere are prepared by computer in the
National Meteorological and Oceanographic Centre.
The
new SX-6 computer
How
the computer is used
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Prognostic
charts
Prognostic charts (what the weather chart is expected to look like in
24 or 36 hours time) are produced by computer in the National Meteorological
and Oceanographic Centre. The future weather chart is calculated by
solving complex mathematical equations, and larger and faster computers
enable more complex equations to be solved and more elements to be taken
into account.
Preparing
the forecast
Using analyses and
prognoses produced locally and received by facsimile, a statement of
the weather expected over the next one to four days is prepared in the
Regional Forecasting Centre. There are however many factors to be taken
into account, such as topography, proximity to the sea, time of day,
time of year, and the forecaster's personal experience. (The forecast
has to be written with one eye on the clock, as deadlines have to be
met for the media, airline flights and many other users of daily weather
information).
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Dissemination
Public weather forecasts for the general community are issued for States,
districts, cities and provincial centres, and for coastal waters, bays
and harbours. Special user forecasts are issued to aviation, shipping,
agricultural interests, to public utilities such as power authorities,
and to fire fighting and other emergency services.
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