LONG range forecasting for many years has utilised the fact that certain patterns appear and reappear.
Events such as El Ninos and La Ninas occur regularly but their sequence and persistence can vary.
El Nino events appear to be slightly more common in that it has previously two such events have occurred close to each other interspersed by a period of a neutral pattern but two such La Nina events have never occurred. That said, we are now entering unchartered waters because of global warming.
This is especially the warming of the Earth’s oceans – their current temperatures indicate that the oceans of the world are now holding more energy because of their higher temperatures than at any time in the previous century (and probably longer if data were available).
What this means for weather forecasting is that one important tool – looking for analogous years (years previously when patterns were similar to those expected) – is useless because they do not exist. For example, at the moment the major El Nino event of last summer has passed and we now have a neutral pattern over the Pacific bordering on a La Nina.
There is nothing unusual about this – but at the same time sea surface temperatures around most of continental Australia and the adjacent eastern Indian Ocean are all above normal.
Southern Ocean temperatures (not as readily available) appear to be such that they are helping the southern ocean lows to stay a little further north than normal for summer.
This reduces rainfall potential – the other features enhance it – as a result the confidence level of any long tern assessment is lower than usual. That said, there is a reasonable level of confidence that 2017 in NSW will not be drought year.
Rainfall is favoured to average out near to or slightly up on normal overall with extended periods of stable weather. Temperatures are favoured to average out one to three degrees above the 20th century norms. So overall, there are optimistic signs – I hope 2017 is good for all of us.
