Climatic indicators across the Pacific Ocean have been significant recently with developments having a major influence on our weather so far during 2022. However, as we approach winter, the influences of the Indian Ocean and Southern Ocean become more important.
Unfortunately, the Indian Ocean patterns have remained highly unpredictable since the record positive Indian Ocean Dipole event of 2019, which was a significant factor contributing to the extreme drought conditions for much of that year. In recent times, we have seen IOD forecasts switch from positive to negative multiple times over a short period of time (one to two months). However, this appears to be slowly changing in that the model forecasts for a negative IOD event developing are stronger than they have been for some time. In addition, there has been longer persistence and agreement of model forecasts during the past four to six weeks, which is bringing increased confidence of a negative IOD event for winter.
A Pacific Ocean La Nina and negative IOD in the India Ocean last occurred together in 2010-11. Both patterns exert their influence during different times of the year. Negative IOD events typically favour rainfall during the cooler months while La Nina events favour rainfall during the warmer months. However, the two events can certainly work together to increase rainfall outside of their respective seasons, but normally the main impacts are follow-on impacts (i.e. a wetter winter could lay the groundwork for flooding in a wetter summer). We have just had a wet summer and autumn in many parts of eastern Australia and regardless of this, above average rainfall is favoured to continue through the winter months across NSW, with a general increase in easterly winds helping to bring a higher incidence of showers to the NSW east coast, while the moisture streaming across from the northwest due to the expected increased potential of northwest cloud bands will help bring a higher potential for rainfall across inland areas of NSW.
In addition, higher levels of moisture result in decreased frost potential over winter. This doesn't mean frost won't occur or there'll be no cold mornings - just a decreased number of these cold mornings. Maximum temperatures typically remain closer to average but these patterns also encourage the occasional burst of extremely cold weather as colder air masses to push up for a few days at a time from the Southern Ocean to assist in below average maximum temperatures, often bringing highland snow briefly to low levels.
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