Monthly Climate Statement for April 2016

The Department of Science, Information Technology and Innovation’s (DSITI’s) seasonal outlooks for the Queensland summer are based on the state of the El Niño–Southern Oscillation (ENSO) phenomenon prior to summer, and on 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 Science Division of DSITI considers that, for most of Queensland, the probability of exceeding median rainfall for summer (November to March 2016/17) is currently slightly higher than normal.  This view is based on an analysis of the March extra-tropical Pacific Ocean sea surface temperature (SST) pattern. Read More (PDF, 367K, last updated 12:03PM, 18 April 2016)*

Currently:

• As at 13 April, the 30-day average SOI value remains negative (-8.6). The monthly value of the SOI was -6.3 in March, compared to -19.1 in February and -21.8 in January. The three-month (January to March) average was -15.7.

• The monthly SST anomaly in the Niño 3.4 region of the equatorial Pacific Ocean was +1.7 ºC in March, compared to +2.4 ºC in February and +2.6 ºC in January. As at 9 April, the weekly Niño 3.4 region SST anomaly was +1.3 ºC.

• The Bureau of Meteorology (ENSO Wrap Up, 12 April), notes that the current El Niño (which remains at weak to moderate levels) is likely to have ended by mid-2016.

• Only a few (less than 10 per cent) international global climate models indicate continued El Niño conditions beyond mid-2016.

• ENSO development is least predictable at this time of year and this period known as the ‘autumn predictability gap’.

• Eighty-six per cent of Queensland has been drought declared since 1 November under state government processes.

• Summer (November to March 2015/16) rainfall was above-median in many north-western and far-western parts of Queensland. Elsewhere, areas of above-median summer rainfall tended to be patchy.

The El Niño - Southern Oscillation (ENSO)

At this time of year (known as the ‘autumn predictability gap’), the ENSO pattern tends to change very rapidly. Although the change in the ENSO pattern over autumn may provide a guide as to the likely development of El Niño or La Niña events, it is not until late autumn (May) that the prevailing ENSO pattern (as measured by indices such as the SOI or central equatorial Pacific Ocean SST anomalies) begins to provide a useful basis for seasonal forecasting (i.e. for providing rainfall outlooks for winter, spring or summer). However, it is useful to monitor the change in ENSO indices over this time of year as a guide as to whether an El Niño or La Niña pattern may develop. Global climate models also provide a more formal means of assessing this likelihood.

Summer rainfall outlook (Nov-Mar 2016/17)

DSITI scientists have shown that extra-tropical SST anomalies, when measured in specific regions of the Pacific Ocean in March each year, provide a useful basis for long-lead forecasting of summer (November to March) rainfall in Queensland.  The accuracy of this outlook increases as the evolving ENSO-related SST pattern is also taken into account from May through to October. This understanding has been incorporated in an experimental system known as SPOTA-1 (Seasonal Pacific Ocean Temperature Analysis version 1), which has been operationally evaluated by DSITI scientists for over a decade.

As at 1 April 2016, DSITI’s initial long-lead outlook for summer (November to March 2016/17) indicates a slightly higher than normal probability of exceeding median rainfall for most of Queensland. This outlook indicates that warmer than normal extra-tropical SSTs currently east of Australia may have a favourable influence on Queensland summer rainfall.

In summary, it should be noted that:

• The current long-lead summer rainfall outlook is based solely on extra-tropical Pacific Ocean SST anomalies.

• While the current El Niño is likely to have ended by mid-2016, outlooks for ENSO development are least predictable at this time of year – a period known as the ‘autumn predictability gap’.

• Users should also be aware that seasonal outlooks are probabilistic, rather than deterministic, in nature. For example, if an outlook is described as having a 50 to 70 per cent probability of below median rainfall, there is also a 30 to 50 per cent probability of above median rainfall.  Although outcomes with a high probability may be more likely, it does not mean that less probable events will not occur in any given year.

Updates to the summer rainfall outlook will be reported in future Monthly Climate Statements.

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