Seasonal Climate Outlook Rainfall Archive

Frequently Asked Questions

Mixed Autumn rainfall outlook - Bureau of Meteorology, National Climate Centre, Seasonal Rainfall Outlook

Three-month Seasonal Climate Outlook Statement
Rainfall probabilities for Autumn 2003
Issued 18th February 2003

Mixed Autumn rainfall outlook

The latest seasonal rainfall outlook from the Bureau’s National Climate Centre shows a mixed pattern of odds for the autumn season.

The chances of ABOVE median rainfall for the March to May period are 60 to 70% in north Queensland, central WA and parts of northern and eastern SA. So with climate patterns like the current, about 7 seasons out of 10 are expected to be wetter than average in these areas, whilst about 3 out of 10 are drier. The statistical outlook scheme is moderately reliable in north Queensland and central WA for autumn, but has little skill in SA.

In contrast, the chances of above median rainfall in southwest WA between 30 and 40%, meaning BELOW median falls have a 60 to 70% chance of occurring and the outlook scheme has low to moderate reliability in this area.

The overall pattern of probabilities has resulted from a sharp rise in Indian Ocean temperatures, and the current but weakening El Niño pattern of above average Pacific Ocean temperatures. In fact in terms of just the ocean data, the El Niño is close to being finished. Furthermore, the SOI is showing a clear rising trend. Whilst a regeneration of El Niño cannot be ruled out entirely, this is much less likely than either neutral or La Niña conditions. For more detail see the El Niño Wrap-Up.

The heavy rain that has occurred over Queensland so far this month is consistent with what the National Climate Centre has been saying for some months now; that is, the most likely time for a switch in Australia’s rainfall patterns was between January and March. However, in terms of an end to the drought there are several points to note:

  • (a) it may take several months of sustained above average falls in some areas to effectively end the drought;
  • (b) the breakdown will not occur uniformly across all drought affected areas;
  • (c) some El Niño indicators (eg SOI, trade winds) may continue to fluctuate in and out of neutral values after the change in Australian rainfall patterns.

Background Information:

  • The Outlook probabilities are based on recent Indian and Pacific Ocean temperatures. The Pacific Ocean cooled in January and the Indian Ocean warmed.
  • The Australian impacts of 23 El Niño events since 1900 are summarized on the Bureau's web site.
  • January’s value of the Southern Oscillation Index (SOI) was –2, a rise of 9 points from the –11 in December. The approximate SOI for the 30 days ending 15th February was –5.
  • This outlook represents a summary, more detail is available from the contact people or from SILO.
  • Important: Probability outlooks should not be used as if they were categorical forecasts. More on probabilities is contained in the booklet "The Seasonal Climate Outlook - What it is and how to use it", available from the National Climate Centre.

More information on this outlook is available from 9:00am to 5:30pm (EDT) Monday to Friday by contacting the following climate meteorologists in the National Climate Centre:

Grant Beard on (03) 9669 4527
David Jones on (03) 9669 4085
Blair Trewin on (03) 9669 4603
Janita Pahalad on (03) 9669 4859


Archive of previous Seasonal Climate Rainfall Outlooks

Archive of previous Seasonal Climate Temperature Outlooks

January 2003 rainfall in historical perspective

November 2002 to January 2003 rainfall in historical perspective

probability of exceeding median seasonal rainfall
Click on the map for full resolution.

Information on tropical cyclones


Information on tropical cyclones
The tropical cyclone season around northern Australia extends from November to May. The average number of cyclones per season is 9.4 (mean from 1949/50 season to 1993/94 season), with a standard deviation of 3.4. Cyclone activity in this region is related to the El Niño-Southern Oscillation phenomenon, with fewer than normal cyclones during El Niño episodes, and slightly more during La Niña episodes. Below is a map showing the extreme bounds of the Australian Tropical Cyclone Region (Australia's area of responsibilty).

australian tropical cyclone region

Frequently Asked Questions

A:General statements about the probability or risk of wetter or drier than average weather over a three-month period. The outlooks are based on the statistics of chance (the odds) taken from rainfall and sea surface temperature records. They are not, however, categorical predictions about future rainfall, and they are not about rainfall within individual months of the three-month outlook period.

A:Being above or below the median rainfall, average maximum temperature, or average minimum temperature for the three-month period.
The median is a useful measure of "normal" rainfall. In the long term, rainfall is above median in one half of years, and below median in the other half.
For example, from July to September at Mackay in Queensland, one-half of 3-month rainfall totals have been below 80mm, and one-half have been above. If rainfall was above 80mm in that period it would be "wetter than average" or above median. Over the long haul there is a 50% chance of this occurring. In terms of odds this is even money.
Note that the average maximum temperature is the average of all the daily highest temperatures for the period.
Similarly, the average minimum temperature is the average of all the daily lowest temperatures for the period

A: In the places and seasons where the outlooks are most skilful, the eventual outcome (above or below median) is correctly given the higher chance about 70 to 80% of the time. In the least skilful areas, the outlooks perform no better than random chance or guessing. The rainfall outlooks perform best in eastern and northern Australia between July and January, but are less useful in autumn and in the west of the continent. The skill at predicting seasonal maximum temperature peaks in early winter and drops off marginally during the second half of the year. The lowest point in skill occurs in early autumn. The skill at predicting seasonal minimum temperature peaks in late autumn and again in mid-spring. There are also two distinct periods when the skill is lowest - namely late summer and mid-winter. However, it must always be remembered that the outlooks are statements of chance or risk. For example, if you were told there was a 50:50 chance of a horse winning a race but it ran second, the original assessment of a 50:50 chance could still have been correct.

A: Very unlikely. There is a certain level of natural variability in the climate which is chaotic and unpredictable. This is particularly the case with rainfall. For example, rainfall in a season can be significantly above average in one region, and significantly below average less than 50km away.

A: As another tool in risk management and decision making. The benefits accrue from long-term use, say over 10 years. At any given time, the probabilities may seem inaccurate, but taken over several years, the advantages of taking account of the risks will outweigh the disadvantages. For more information on the use of probabilities, farmers could contact their local departments of agriculture or primary industry.

Definitions and Explanations....

THE SOUTHERN OSCILLATION INDEX (SOI) is calculated using the barometric pressure difference between Tahiti and Darwin.

The SOI is one indicator of the stage of El Niño or La Niña events in the tropical Pacific Ocean. It is best considered in conjunction with sea-surface temperatures, which form the basis of the outlooks.

A strongly negative SOI (below -10) is characteristic of El Niño, which is often associated with below average rainfall over eastern Australia, and a weaker than normal monsoon in the north.

A strongly positive SOI (above +10) is characteristic of La Niña, which is often associated with above average rainfall over parts of tropical and eastern Australia, and an earlier than normal start to the northern monsoon season.

El Niño & La Niña

El Niño translates from Spanish as "the boy-child", and refers to the extensive warming of the central and eastern Pacific Ocean.

La Niña translates from Spanish as "the girl-child", and refers to the extensive cooling of the central and eastern Pacific Ocean. The term has recently become the conventional label for the opposite of El Niño.

See for more on SOI and El Niño.