Rain to come as cold front 'pulls cord' on unusually dry October
A rainy end has been forecast for the end of an unusually dry October, with a cold front due to bring rain to Sydney from Saturday and into next week.
After a number of overcast days with just the occasional sprinkle, a cold front travelling across NSW will "pull the cord" on moisture in the atmosphere, leading to days of consistent rain in Sydney and possible heavy falls in the state's south.
Sunday and Monday are likely to be the wettest days in Sydney, with daily falls of up to 20 millimetres forecast.
"So far, Sydney has received just under 10 millimetres of rainfall for the month, whereas the average for October is 77 millimetres," Bureau of Meteorology forecaster Alex Majchrowski said.
The chance of a thunderstorm is highest on Friday, when the rain will begin in the evening, and Saturday.
The rain comes after the Bureau of Meteorology officially declared a La Nina last month, a weather cycle associated with wetter than average conditions and mild minimum temperatures in south-eastern Australia.
"You can't attribute [the La Nina] to just one weather event, [but] you can see it as priming weather events along the eastern coast," Mr Majchrowski said.
"We've got a lot of moisture being fed in by weather systems at the moment, and then on Saturday we've got a cold front coming through the state from the west that is going to drive underneath and help lift the moisture."
Mr Majchrowski compared the process to starting a lawnmower: "With the moisture, you're priming the lawnmower, then when the cold front comes you are pulling the cord."
It will be a muggy day on Saturday, with highs of 29 degrees forecast. The temperature will drop significantly on Sunday to a maximum of just 19 degrees before settling in the early-to-mid 20s for the week.
Although this week's Sydney rain is expected to be the heaviest in recent weeks, much heavier falls are forecast in southern parts of the state.
Rainfall in the western Snowy Mountains and western ACT regions could total up to 80 millimetres on Saturday. It is possible a warning for heavy rainfall will be issued by the bureau on Friday.
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Mary Ward is a reporter at The Sydney Morning Herald.