The climate pattern this year is totally different from the same period last year. In 1998, we witnessed the breakdown of the El Nino pattern. This produced widespread rain through cropping districts of NSW and Queensland but also increased the chances of getting late frosts in Western Australia and southern NSW. In northern NSW and southern Queensland that sort of pattern actually reduced frost risk.
In winter of 1999 we see a slight weakening of the La Nina pattern that emerged in late 1998. Sea-surface temperatures remain reasonably cool in the eastern and central Pacific Ocean and remain warm in the eastern Indian Ocean. The SOI has followed a 'sawtooth' pattern over the autumn months. The mean position sub-tropical ridge (high-pressure belt) has recently started to shift further north from its position over Victoria and southern South Australia — a position it has occupied for the past couple of years.
What does all this mean for winter-spring 1999?
The rainfall probability values for winter, based on the SOI patterns or 'phases' of late autumn 1999 show the chances of receiving above-median rain are about 30-40 per cent for most of NSW, parts of southern Queensland, parts of Victoria, South Australia and southern Tasmania for the core winter months (areas shaded yellow on the map).
However, a closer look at the whole rainfall 'distribution' for most locations shows that the chances of getting smaller falls are still quite good — close to 'normal'. Indeed, as the sub-tropical ridge moves further north this should alleviate some of the problems associated with very low rainfall felt over areas of Victoria and southern NSW over recent years.
In other regions of Australia (those regions shaded blue or grey), the chances of getting above-median rainfall during winter are still reasonably high (e.g. Central Highlands of Queensland). Furthermore, the La Nina pattern has a high chance of regaining strength over spring and summer 1999, which suggests a reasonable chance of wetter conditions for many areas of northern and eastern Australia later this year.
The chances of getting later frosts than normal are slightly increased over northern New South Wales and central Queensland this year.