Weather pattern shifts in favour of rainfall

Rain finally arriving in NSW | Weather In Focus

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Widespread totals of 20 to 40 millimetres are likely across the eastern half of NSW between now and the middle of next week

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SHOWERS and thunderstorms will affect fire and drought affected areas of NSW during the next several days.

A near-stationary low pressure trough being fed by moisture-laden easterly winds will produce a multi-day spell of showers and thunderstorms during the coming week.

While this type of weather pattern is typical during summer, it's the most widespread rain and storm event we have seen in eastern Australia so far this season.

The focus of the heaviest falls will shift around a bit from day to day, although widespread totals of 20 to 40 millimetres are likely across the eastern half of NSW between now and the middle of next week.

Some places will pick up 50mm to 100mm during this time and isolated totals over 100mm a good chance.

This week's seemingly abrupt change in weather, from exceptionally warm and dry conditions in December to widespread rain and storms in January, follows the breakdown of two dominant climate drivers that influenced Australia's weather patterns towards the end of 2019.

The first driver was the strongest positive Indian Ocean Dipole (IOD) event in at least 20 years.

A positive IOD refers to a pattern of sea surface temperatures across the tropical Indian Ocean that causes below-average rain and above-average temperatures in parts of Australia between winter and early summer.

Last year's positive IOD pattern persisted from late-May until the end of December.

The other dominant climate driver in 2019 was a negative Southern Annular Mode (SAM) episode, which persisted from mid-October to late December.

Negative SAM occurs when the belt of westerly winds surrounding Antarctica shifts further north than usual. When a negative SAM occurs in spring and summer, westerly winds increase over Australia's eastern states, promoting unusually warm and dry weather and elevated fire danger.

NSW registered its warmest and driest year on record during 2019. By December, 100 percent of the state was affected by drought.

While the impending rain won't break this drought, it will help extinguish some of the fires that are still burning across the state.

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