Another La Niña forming: a tale of two years
National map of probability of exceeding median rainfall
While there are signs of a La Niña event re-developing in late 2011, indicators suggest it will be considerably weaker than the event of late 2010 and early 2011.
The strong La Niña of 2010 started around July, far earlier than the event presently forming. As a result, the July–September period in 2010 was the wettest on record for Australia.
In contrast, it rained significantly less during the same months this year, recording marginally below median rainfall when averaged over the continent. Although the spring of 2011 is vastly different to that of 2010, some rainfall records have been set: the wettest October day on record was experienced at Cairns Airport on 19 October 2011.
In 2010–11, several climate indicators strongly favoured widespread heavy rains over eastern and northern Australia, including Queensland. However, this is not the case for all indicators in 2011–12.
While climatologists are confident that widespread rainfall will be above average over southern Queensland, New South Wales and the Northern Territory, they have less confidence that November 2011–January 2012 rainfall will be as extreme as during the same period in 2010–11. That said, some locations may experience comparable or greater rainfall associated with local conditions, such as the increased chance of tropical cyclones crossing the coast which comes with any La Niña wet season in northern Australia.
Water storages continue to be replenished with the total storage levels in all states either near or greater than 2010 levels. Perth's combined storage levels are about the same as last year and have increased from below 18% to near 30% in the past three months.
Australia's combined storage levels are at least the highest since the early 2000s, while those in the Murray–Darling Basin are at their highest since the early 1990s. Lake Eildon in Victoria has reached 100% and is spilling for first time since 1996.