Long Paddock

Commentary on rainfall probabilities based on phases of the SOI

Previous commentary

Seasonal climate outlook message for February to April 2018

Commentary on rainfall probabilities based on 'phases' of the SOI

The monthly value of the Southern Oscillation Index (SOI) was -2.6 for December and +8.9 for January. According to the SOI Phase system, the SOI is in a ‘Rapidly Rising’ phase.

A map showing the probability of exceeding median rainfall for the next three-month period (February to April) is now available. This map is based on previous years from 1900 to 1998 which, like 2017, had a ‘Rapidly Rising’ phase of the SOI for January (i.e. 1901, 1902, 1920, 1930, 1931, 1935, 1937, 1940, 1953, 1954, 1963, 1967, 1968, 1977, 1980, 1982, 1986 and 1996). This map indicates a 40 to 60 per cent (near-normal) probability of above-median rainfall for much of Queensland.

When using a climate outlook it should be remembered that the probability, or per cent chance, of something occurring is just that – a probability. For example, if there is a 70 per cent probability of exceeding median rainfall, then there is also a 30 per cent probability of below-median rainfall. It does not mean that rainfall will be 70 per cent more than the median.

Users should note that the SOI in summer has low reliability as an indicator of rainfall for the autumn season. Furthermore, while climate outlook schemes cannot provide outlooks with absolute certainty, users who follow a skilful scheme should benefit from doing so in the long-term. Thus, users should consider the historical track record of any scheme, and such information is becoming increasingly available.

The Department of Environment and Science (DES) provides outlooks for the summer period (November to March). The outlooks for summer rainfall are based on conditions leading up to summer, including the state of the El Niño–Southern Oscillation (ENSO) phenomenon and factors which alter the impact of ENSO on Queensland rainfall (i.e. the more slowly changing extra-tropical sea-surface temperature (SST) pattern in the Pacific Ocean). The DES Monthly Climate Statement for February 2018 is now available.

Last updated 18 March 2011

Seasonal climate outlook