One of the coldest June days in recorded history looks like it is about to be set in the Northern Territory in the middle of the dry season.
The Top End's typically hot and sunny middle months have been disrupted by dark clouds and rain over the past couple of days, in what the Bureau of Meteorology is describing as "quite unusual".
An out-of-place cloud band and south-easterly winds are combining to produce cold temperatures across the Territory.
The reading on Friday, from a Katherine weather station at the Tindal RAAF Base, could be the second-coldest June day on record, with the BOM forecasting a high of 19 degrees.
Other than a chilly 17 degree day in 1986, temperatures below 20 degrees have never been recorded at that station.
To make matters even more unusual, 2mm of rain was recorded in the Katherine region overnight, and 18mm was recorded in Tennant Creek.
Warnings issued
On Monday, the BOM issued a cold weather warning to farmers and producers in the Katherine, Tennant Creek, Mount Isa and Longreach area.
"Temperatures are expected to be 8 to 14 degrees below average for this time of year and could see 15-30mm of unseasonal rainfall over a few days with isolated heavier falls," it said.
"Producers should note that, the rapid change in temperature could cause stress to livestock."
How long will it last?
Billy Lynch, a senior meteorologist at the BOM, says an upper-level trough hovering over northern Western Australia is tapping into tropical moisture across Indonesia and the Timor Sea, and spreading across the Northern Territory in the form of a cloud band.
"Cloud bands through Central Australia, this time of year are pretty common," Mr Lynch said.
"But cloud bands getting up into the Top End? Uncommon.
From Saturday, the cloud band is expected to start weakening and move eastwards into Queensland, but not before bringing an unexpected bout of rain.
South of Katherine, through the Carpentaria and the northern Barkly district, the BOM is forecasting 15 to 30 millimetres of rain, if not more, this week.
It's welcome news for residents in the region following significant rainfall deficiencies.
For Katherine itself, it's not unusual to get rainfall at this time of year.
In any given June, it averages point six of a millimetre and two millimetres in July, but this week the forecast is as much as 30 millimetres.
"It would definitely be unusual to get that sort of rainfall at this time of year," Mr Lynch said.
In Darwin, depending on how the cloud band develops, Thursday could be quite a wet day, with as much as 10 to 20 millimetres predicted.
Cold weather ramifications
Veterinarian Campbell Costello said the short, cold snap could go as far as stressing cows so much that birth rates could be reduced.
"[There is a] sort of tipping point where the environmental stresses — in this case cold — reach a point. The cow starts having to dig into her energy reserves more and they can lose weight or become immunocompromised," he said.
Mr Costello said cattle may require more food intake in cold weather "just to keep warm and keep the furnaces stoked", especially with added stresses like mustering or trucking.
The unseasonal weather could also have impacts on pasture quality and quantity for cattle producers, according to Dr Robyn Cowley, a senior rangelands scientist with the NT Department of Industry.
"If you have perennial Mitchell grasses, they won't be negatively affected by this rainfall event, but you wouldn't really expect much pasture growth because they respond to warm season rain," she said.
"If you have annual pastures like Flinders grass, then potentially you could lose the bulk of your pasture … they can spoil with this out of season rainfall and become unpalatable and unavailable to livestock."
Editor's note 29/06/2022: This story has been amended to correct an error. A previous version indicated the coldest day being reported on was in July, rather than June.
