SSF April to October outlook
The SSF is indicating less than 40% chance of exceeding median rainfall for April to October. The most probable decile map is indicating decile 2-3 rainfall most likely. Skill is 50 to 100 percent consistent.
Past success of the SSF for April to October indicates: that the outlook was correct in Esperance for the years 2013 and then 2015 until 2018. In the northern agricultural area (Northampton to Chittering) April to October of 2013, 2016 and 2017 was corectly indicated by the SSF. In the southern (Wagin to Ravensthorpe) agricultural area, 2016 until 2018 were correctly indicated by the SSF. In the central (Toodyay to Lake Grace) agricultural area, the SSF had success in 2016 and 2017.
March rainfall was above average in the Great Southern, but below average to average elsewhere in the SWLD.March maximum temperatures were generally average to above average and minimum temperatures were average to above average. The past two to three decades have seen a decline in autumn rainfall for southern Australia.
The rainfall to date decile map for 1 January to 3 April 2019 shows some of the grainbelt has received less rainfall (decile 4 and below) than usual based on historical rainfall for the years 1975-2018.
In March, the atmospheric pressure was slightly above normal over the SWLD, reducing rainfall across parts of southern Australia.
The Indian Ocean sea surface temperatures off the western WA coastline have been slightly cooler than average. The April to June SST forecast by the Bureau of Meteorology indicate that SST will be slightly warmer, but not warm enough to influence moisture flowing into Western Australia.
The Southern Annular Mode (SAM), also known as the Antarctic Oscillation (AAO), describes the north–south movement of the westerly wind belt that circles Antarctica, dominating the middle to higher latitudes of the southern hemisphere. For the last two weeks SAM has been positive. The Bureau model ACCESS is indicating SAM to remain positive until June. In a positive SAM event, the belt of strong westerly winds contracts towards Antarctica. This results in weaker than normal westerly winds and higher pressures over southern Australia, restricting the penetration of cold fronts inland and therefore less rainfall.
The Indian Ocean Dipole (IOD) is currently neutral and forecast to remain neutral through autumn. The Bureau's ENSO Outlook is currently at El Niño ALERT. This means the chance of El Niño developing in 2019 has increased to approximately 70%, around triple the normal likelihood. However, the Bureau's model suggests that any El Niño is likely to be weak and short-lived, and is unlikely to have a significant effect on the rainfall patterns for April to June. For further information, see the Bureau of Meteorology’s ENSO Wrap Up.
The table below gives a summary of past month and three-month southwest Western Australia (SWWA) climate conditions, and can indicate what is likely to occur in the near future if climate conditions follow the current pattern.
|Climate Indicator||Past month||Past 3 months|
|SWWA Rainfall||Mixed||Average to below average|
|SWWA Mean Temperature||Average to above average||Average to above average|
|SWWA atmospheric pressure||Slightly Above Normal||Above Normal|
|Indian Ocean Sea surface temperature||Cooler||Cooler|
|El Niño/Southern Oscillation (ENSO)||Neutral||Neutral|
|Indian Ocean Dipole (IOD)||Neutral||Neutral|
|Southern Annular Mode (SAM)||Positive||Positive|