The Bureau of Meteorology has declared a La Nina pattern is officially under way, signalling we could be in for a wet spring and summer.
La Nina is a phase of the El Nino Southern Oscillation (ENSO), which describes ocean and atmospheric circulations over the Pacific Ocean.
During a La Nina phase, Australia’s northern waters are warm with increased convection.
This allows more moisture to be lifted into the air than normal, typically resulting in increased rain for eastern and northern Australia – but, historically, the south-east misses out.
That moisture can lead to cooler daytime temperatures, the BOM’s head of climate operations Andrew Watkins said.
“We tend to have more cloud and a bit more moisture around to evaporate to keep the air a bit cooler,” he said.
“Conversely at night, when you’ve got the cloud acting like a lid trapping in that heat, it can be a bit warmer.”
But every La Nina is different.
Will we get a repeat of 2011?
The last major La Nina events were in the summers of 2010-11 and 2011-12. They resulted in 2010 to 2012 being Australia’s wettest two-year period on record.
Flooding was widespread and devastating.
In early 2011, large parts of south-east Queensland were under water; the Lockyer Valley was hit by a cascade of water coming off the Toowoomba range and Brisbane saw its worst flooding since 1974.