With the development of an east coast low or at least a trough of low pressure, a rain event is expected in many parts of northern and eastern NSW and southern Queensland for the start of May.
Such occurrences are appearing about once per month with extended periods of stable weather in between. However, they are likely to be sufficient to generate enough moisture to keep rainfall totals at least close to average throughout winter.
The main problem for some could be associated with the fact that such set-ups generate quite variable rainfalls with some areas missing out and therefore it is possible that missing out on one such event could create some moisture deficiencies lasting a couple of months.
Overall, in the east and NE of NSW and south of Queensland there remains about a 70 per cent chance that rainfall between now and the end of the year will exceed normal. It is likely that Victoria and southern NSW will miss significant rainfall for much of May with the Southern Annular Mode (SAM) remaining mostly positive. There may be a shift in this pattern in June and during the rest of winter.
Although the oscillation between El Nino and La Nina events produce reduced rainfall and excessive rainfall respectively, the influence of these major climate drivers can vary significantly in combination with other events. The demise of the recent El Nino event has meant we will end autumn and enter winter in a neutral pattern. Most international models still predict to development of a La Nina by spring. Because the longer-term models are less reliable in autumn than at other times, this prediction must be taken with a degree of caution. However, there appears to be little chance of another El Nino returning in the foreseeable futures so there is some optimism in the long-term rainfall outlook.
The situation with the Indian Ocean remains unclear. Most models now favour a period of positive Indian Ocean Dipole (IOD). Remember a positive IOD reduces rainfall potential in SE Australia. They also indicate the IOD will be back to neutral by late winter and possibly negative by early spring when the Pacific La Nina is favoured to form as well. Consequently, the outlook for spring rains is fairly good at this stage.
Overall, temperatures are favoured to remain above average for the rest of the year. That said, the situation is conducive for occasional but potentially significant cold outbreaks in the SE states but such events will be brief, so most days will see above average temperatures.
