As predicted by the MetSwift analogues, December 2020 didn’t follow the typical moderate La Niña pattern for New South Wales. In fact, it was even drier than anticipated, raising bushfire concerns for the opening third of 2021.
This lack of a La Niña pattern was also observed widely across the rest of Australia. Only the warmth in Queensland and wetness in eastern Victoria really fit what would be expected based on that driving force alone.
The observed pattern doesn’t match well with the response to any of the main climate drivers for Australia. Instead, we must look at something shorter-term and far less predictable: Tropical cyclones. The northwest of the country was affected by three tropical lows in December 2020, a high count.
These systems dumped an exceptional amount of rainfall as they meandered over land and slowly dissipated. Meanwhile, the environment around was modified in favour of drier conditions, most notably in the southwest corner, around Perth.
Building Bushfire Concern for New South Wales & Western Victoria
After the dry start to summer, residents of both south-eastern and south-western Australia are hoping that January can dampen the bushfire risk.
Analysis of historical years suggests that a typical moderate La Niña pattern is undesirable, being drier than average for both regions. This was evident in the seasonal probability guidance when examining the early signals for the summer back in August 2020.
January Could Turn Things Around
The MetSwift analogues suggest that other factors will override the La Niña forcing, resulting in wetter month instead, albeit only near-average away from Victoria.
As of writing this, rainfall in the first half of January is looking near-average for most places within the two regions.
There is, however, some suggestion of a wetter trend toward mid-month. It’s also looking hotter than usual in both New South Wales and the southwest of the country for at least a few days starting this Friday. These are atypical conditions for January in a moderate La Niña. It raises hopes that a strong bushfire season will be avoided for these regions.
Still Some Fears for February in the Southeast
As detailed in the mid-December blog, the MetSwift analogues suggest a hotter and drier than average February 2021 for much of Victoria and New South Wales. This being largely due to the La Niña establishing a bit more control for the last month of summer.
This is not without precedent – the atmospheric response to a La Niña event sometimes takes many months to fully establish. In fact, it’s been known to peak while the La Niña pattern in the ocean is fading away, which could well be what we see in 2021.
Such an outcome would raise the bushfire risk for Feb-Mar 2021. Just how high will depend on how January plays out. Hopefully, January will see the advertised relaxation of the La Niña forcing, enabling above-normal rainfall for at least a couple of weeks.
James Peacock MSc
Head Meteorologist at MetSwift
Cover Photo by Unknown Author is licensed under CC BY-SA