A wet start to 2020 means root zone soil moisture for this time of year is above average for most of Victoria except for parts of the southwest and East Gippsland.
Looking ahead, the previously wet outlook for May is now more neutral, with roughly equal chances of a wetter or drier than average month for most of the State. The average rainfall for May ranges from around 15 mm in the northwest up to a bit over 100 mm at a few elevated sites and exposed parts of the south coast.
While the chance of above average rainfall in May has eased, the three-month outlook for May to July still shows above average rainfall is likely for northern Victoria. Similarly, above average rainfall is likely during winter (June to August) for the northern half of the State.
In winter, the far northwest of Victoria typically receives around 60 mm of rain for the season while much of southern Victoria and the elevated northeast gets more than 200 mm. In parts of the Alps and exposed parts of the south coast the average rainfall for winter is over 400 mm.
Nights are likely to be warmer than average during May to July across Victoria. At the same time, days are likely to be warmer than average in the east but elsewhere there is no strong push towards higher or lower than average maximum temperatures.
So, what is driving the wet outlook for winter over most of Australia, including parts of Victoria? There are a few factors at play. Warmer than average waters in the eastern Indian Ocean are expected to provide moisture to weather systems as they sweep across the country, increasing the likelihood of rainfall with fronts and troughs this winter.
Looking further into winter, the climate computer models are showing us that a negative Indian Ocean Dipole could develop, and that typically brings above average winter-spring rainfall to much of southern Australia. However, caution should be exercised as the accuracy of forecasting the Indian Ocean Dipole is low during autumn.
In the Pacific, most models suggest the El Niño–Southern Oscillation is likely to stay neutral through winter. However, there is a possibility of La Niña developing in late winter or early spring. La Niña often means above average winter–spring rainfall for eastern, central and northern parts of the country.