THE BUREAU of Meteorology (BOM) has slightly scaled back its optimism for a wet winter in its monthly temperature and rainfall outlook but much of Australia still has very healthy odds in favour of above median rainfall for the upcoming three months.
Andrew Watkins, head of long term forecasts at the BOM said while there had been a slight tempering of expectations conditions were still generally favourable for above average rainfall.
"The scenarios we have in both the Pacific and the Indian Oceans are not classic La Nias or Indian Ocean Dipole (IOD) negatives that correlate with wetter conditions but they are both more likely to see more rain rather than less," Dr Watkins said.
He said areas that had benefited from good autumn rain had been the beneficiaries of moisture feeding in from a patch of warm water in the Indian Ocean off the Western Australian coast.
"It is not where you would see warm water in a more classic IOD negative but it has seen moisture bands created."
"We don't have the classic patterns like a year like 2016 where we saw signs of an IOD early and it formed as predicted but the conditions are still promising for rain over winter."
Dr Watkins said nearly all of the parched Murray Darling Basin (MDB) was on track for wetter than average conditions.
Across the MDB the odds range from a 60 per cent chance of exceeding median rainfall up to over 80pc in parts of far western NSW and eastern South Australia.
Interestingly, Dr Watkins said the odds were less favourable in areas traditionally among Australia's wettest, to the east and south of the Great Dividing Range, Tasmania and south-west Western Australia.
This is because conditions are not favouring the rain fronts coming up from the south that provide the bulk of these regions' rainfall through winter.
And in the case of the south-east and Tasmania Dr Watkins said the mountains would provide somewhat of a rain shadow effect.
"A lot of the rain is coming from the west, rather than the south-west, which is slightly unusual, and some could be blocked by the ranges," he said.
Dr Watkins said visually it looked as if northern Australia would suffer a dry spell, but said this was largely symbolic.
"The northern dry season has officially began and rainfall totals in that part of the world are very low anyway so it does not take much to skew the averages, it will not be a concern for people up there that it is going to be dry over winter, that is normally the case."
Dr Watkins said while things augured well for farmers looking for rain, they would have to be patient.
"There is not likely to be much on the horizon for at least the first week of June."
He said a positive Southern Annular Mode at present would inhibit rain forming in southern regions over the next week to ten days.
Dr Watkins said while the headlines had been on the drought breaking over much of the MDB this year there were still places that had not done so well.
"South-east Queensland has been dry, the rain has focused on NSW and Victoria rather than pushing north into Queensland."
Dr Watkins said the warm water in the Indian Ocean off north-western WA often occurred after a strong Indian Ocean positive event like last year.
"Some years - particularly after a positive event we see a trigger for a little less water coming up from the south, so the water off north-west WA tends to get warmer meaning more evaporation and more rainfall."
The story Odds decline marginally but still good chance of wet winter first appeared on Farm Online.