Monthly Climate Statement for April 2012

The Queensland Climate Change Centre of Excellence (the Centre) considers that the probability of above- or below-median rainfall for the next three-month period (April to June) is normal (40-60 per cent) for most of Queensland. This outlook is based on the currently near-neutral state of the El Niño-Southern Oscillation (ENSO) phenomenon. At this stage, the sea-surface temperature pattern in the extra-tropical Pacific indicates a higher than normal probability of above-median rainfall for the coming summer (November to March). Read more (PDF, 206K, last updated 09:29AM, 20 April 2012)* 

The Centre’s understanding is based on the current and projected state of the ENSO phenomenon and on factors which alter the impact of ENSO on Queensland rainfall (e.g. the Pacific Decadal Oscillation (PDO)). La Niña conditions coupled with a cool PDO, as experienced over the 2011/12 summer, tend to be associated with above-average summer rainfall and enhanced tropical cyclone activity in the Coral Sea. While most of Australia, including much of Queensland, experienced a wetter than average summer, no tropical cyclones made landfall in Queensland. Although small, the risk of a tropical cyclone making land fall in Queensland remains a possibility during the remaining month (April) of the cyclone season.

The Bureau of Meteorology (BoM) have stated that the 2011/12 La Niña event has ended and that ENSO neutral conditions will persist into our winter (‘ENSO Wrap-Up’ (PDF)* March 27 and April 10). A neutral SOI at this time of year means that rainfall probabilities for the next three-month period are no different than long-term climatology (i.e. there is no forecast skill in a neutral SOI at this time of year).

As at 1 April 2012, the Centre notes that:

• the SOI, a key atmospheric measure of ENSO, fell substantially from high values in December (+23.0) and January (+9.6), to near-average values in February (+0.8) and March (+2.3)
• observed sea-surface temperatures in the key Niño 3.4 and Niño 4 regions warmed over February and March and are currently near-normal
• the recent breakdown of the La Niña pattern is consistent with a historical tendency for ENSO events (i.e. La Niña or El Niño events) to break down over autumn
• the likely continuation of ENSO-neutral conditions over the coming autumn and early winter months is supported by most global climate models.

The Centre reaffirms previous advice that, at this time of year (known as the ‘Autumn predictability gap’), ENSO indices are least reliable for seasonal forecasting. The Centre will closely monitor the SOI and sea-surface temperatures in coming months when ENSO conditions tend to ‘lock in’ and become a more reliable indicator of rainfall for the season ahead.

Rainfall outlook

There are various approaches used to provide rainfall outlooks. These approaches tend to differ in terms of the components of the climate system that are considered and, for this reason, each approach may convey a different outlook, particularly for specific locations.

The Centre produces two statistical climate risk assessment schemes. They are:

• the experimental SPOTA-1 scheme, which integrates sea-surface temperature information, including indices of ENSO and the PDO
• the SOI phase scheme, which relies solely on the SOI, an atmospheric measure of ENSO.

The Centre's experimental SPOTA-1 scheme provides long-lead probabilities of summer (November to March) rainfall for Queensland from mid-April through to mid-November each year. In April 2011 and from June through November 2011, the SPOTA-1 scheme indicated a high probability of above-median summer rainfall. The summer of 2011/12 was wet over much of Queensland, with rainfall exceeding the long-term median for at least two thirds of the state.

An initial outlook, for the upcoming 2012/13 summer, based on the experimental SPOTA-1 scheme is now available and indicates a higher than normal probability of above-median rainfall for much of Queensland. This outlook is based on an index of March sea-surface temperature anomalies in both the South-West Pacific and the North Pacific which, in part, reflect the current ‘cool’ state of the PDO. This outlook will be modified when the SPOTA-1 scheme takes into account a monthly ENSO index from June through to November this year.                                                    

The Centre's SOI phase scheme provides probabilities of rainfall for the coming three-month season based on SOI values over the previous two months. The SOI phase scheme currently indicates that the probability of above- or below- median rainfall for the next three-month period (April to June) is near-normal (50 per cent) for most of Queensland. This analysis is based on the SOI having remained consistently near zero from February to March as discussed further in the Centre's Australia's Variable Rainfall poster (PDF, 9.3M, last updated 03:09PM, 29 July 2016)*, or the Centre's archive of historical rainfall maps).

The Centre understands that each of the above schemes may have their own particular following. Although such schemes cannot provide outlooks with absolute certainty, users of the information who follow a skilful scheme should benefit from doing so in the long-term. Users should consider the historical track record of any scheme, and such historical information is becoming increasingly available.

The Centre's Long Paddock website provides the historical archive of SPOTA-1 reports and past commentaries on the SOI phase scheme. Users should also consider the wide range of information available each month describing the current state of the ocean/climate system, for example the 'ENSO Wrap-Up' (PDF)*.

For more information, please visit LongPaddock Monthly Climate Statement or contact QCCCE@climatechange.qld.gov.au

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