Seasonal Climate Outlook Message for May to August 2014

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

The monthly value of the Southern Oscillation Index (SOI) rose from -12.0 in March to +6.4 in April. According to the SOI Phase system, the SOI is in a ‘Rapidly Rising’ phase.

Based on previous years when the SOI has been in a ‘Rapidly Rising’ phase at the end of April, the probability of above-median rainfall for the next three-month period (May to July) is above 50 per cent for much of Queensland.  However confidence is low, given the autumn predictability gap and currently warmer than average central Pacific sea surface temperatures.

Previous years with a ‘Rapidly Rising’ SOI phase at the end of April include 1904, 1916, 1918, 1919, 1933, 1934, 1936, 1938, 1943, 1948, 1954, 1961, 1984, 1985, 1989, 1990, 1999, 2009 and 2010. The rainfall probabilities stated above are based on the 1900 to 1998 period and do not include 1999, 2009 and 2010.

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 above-median rainfall, then there is also a 30 per cent chance 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 is less reliable 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.

Further seasonal climate outlook information for Queensland is available in the monthly climate statement produced by the Department of Science, Information Technology, Innovation and the Arts and at www.bom.gov.au.