Warmer temps, but is it a false start to spring?
BALMY nights and the hint of rain - it sounds like a delightful spring is in store for Clarence Valley residents, but we might still have a few cold nights ahead of us before winter is done.
The Bureau of Meteorology said parts of NSW will experience windy, cold conditions later this week, with temperatures over the weekend dropping by as much as 4-8 degrees below average and wind speeds reaching up to 35km/h.
Significant snowfall is expected across the Alps this week and is also forecast to fall at low levels along the NSW ranges on the weekend, including parts of the Northern Tablelands.
By Saturday, temperatures in Grafton will drop by up to six degrees from Wednesday's maximum of 25C, with daytime temperatures of 19C forecast. Overnight temperatures will drop from a minimum of 10C last night to 4C on Monday morning.
Likewise, Coffs Harbour's daytime maximum will drop from 24C recorded on Wednesday to 18C on Saturday, and overnight minimum from 11C to 7C.
Daytime temperatures in Yamba will drop from 25C on Wednesday to 19C on Monday, with minimum overnight temperatures dropping from 14C last night to 8C on Monday.
In longer range forecasts, BoM said above average rainfall was expected across much of the country, including the Clarence Valley, from September to November.
Little rainfall was expected to fall on the Clarence Valley over the next eight days and it may be September before decent widespread rain falls.
"We're seeing a greater than 80 per cent chance that spring is going to be wetter than average for the eastern two thirds of the country," BOM senior climatologist Robyn Duell said.
"The ocean in the central Pacific is cooling and at that same time the ocean is warming to the north of Australia. This means there is a chance that La Nina may develop in the coming months.
"For Australia La Nina is typically associated with wetter than normal springs in the eastern half of the country, with an increased chance of widespread flooding as well."
Ms Duell said warmer temperatures in the Indian Ocean near northern Australia could be the sign of a developing negative Indian Ocean dipole (IOD), which also points to potentially wetter conditions for Australia.
Cooler than average days are likely across most of NSW and southern Queensland in spring, but the nights are expected to be warmer than average.
"Day time temperatures are likely to be cooler than average where that chance of rainfall is high," Ms Duell said.
"At night time though that extra cloud acts as a blanket, so this combined with those warmer oceans means nights are likely to be warmer than average over most of Australia this spring."
BoM raised its El Nino-Southern Oscillation Outlook to La Nina ALERT status, meaning the chance of a La Nina occurring this year has increased to 70 per cent, roughly three times the normal likelihood.
BoM's manager of Climate Operations, Dr Andrew Watkins, said La Nina typically results in above-average winter-spring rainfall for Australia, particularly across eastern, central and northern regions.
"It typically also brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north," Dr Watkins said.
"The cooling of surface temperatures in the tropical Pacific Ocean and an increase in the strength of the Pacific trade winds indicates the chance of La Nina has risen. When these two changes occur at the same time, at this time of year, we see a greatly increased chance of a La Nina forming and persisting through spring.
"Climate models suggest that further ocean cooling and intensification of trade winds may occur over the coming months, which has triggered the bureau to shift from a La Nina Watch, issued on June 26, to a La Nina Alert."
The last significant La Nina event was in 2010-11, which was Australia's wettest two-year period on record beating the previous record from the La Nina years of 1973-74. The last time the Pacific Ocean approached La Nina conditions was in late 2017, but thresholds were only briefly exceeded.