THE CLIMATE KELPIE BLOG: What’s predicted in December?

Posted by BCG on 2nd December 2021

The El Niño-Southern Oscillation (ENSO) officially reached La Niña thresholds in late November with most models indicating that this event will persist until late summer. A La Niña typically increases the chances of ‘Above Average’ rainfall in eastern Australia.

The negative Indian Ocean Dipole (-IOD) is near its end and when neutral it will have little influence on Australia’s climate.

Our shorter-term climate driver, the Southern Annular Mode (SAM) has generally been positive for several weeks and is forecast to remain this way for much of December. A positive SAM during summer typically brings ‘Above Average’ rainfall to eastern parts of Australia, except western Tasmania. 

The Madden-Julian Oscillation (MJO) is currently over the Maritime continent and is weak to moderate in strength. Models are however forecasting it to strengthen in the coming weeks. If the MJO strengthens it would also contribute towards increasing the chances of ‘Above Average’ rainfall across north-east Australia in early to mid-December.

The overall outlook for December to February is therefore for likely rainfall to be ‘Above Average’ for eastern parts of Australia. In terms of temperatures, both maximums and minimums are likely to be ‘Above Average’ for most of Australia except for south-eastern Western Australia and south-western South Australia where equal chances of ‘Above’ or ‘Below Average’ minimum temperatures are likely.

Rainfall Roundup

In November, rainfall was ‘Above Average’ for much of Australia with some places even recording totals that were three times higher than usual (Fig. 1). Notable exceptions included western and northern parts of Tasmania, south west Victoria and across into south east South Australia as well as south west Western Australia and a few small areas in northern Australia where rainfall was ‘Below Average’ (Fig. 1). 

During Spring, most parts of Australia received ‘Above Average’ rainfall with the majority of this falling in October and November (Fig. 2). Following a similar pattern to November rainfall totals, some places did however record ’Below Average’ rainfall including south west Victoria and into south east South Australia as well as some southern and northern parts of Western Australia (Fig. 2).

Figure 1. Rainfall deciles for November 2021.
Figure 2. Rainfall deciles for September 2021 to November 2021.

Rainfall Forecast

The BoM’s ACCESS model predicts that rainfall in December is likely to be ‘Below Average’ across western and central parts of Australia as well as south west Tasmania (Fig. 3). Rainfall has an increased chance of being ‘Above Average’ in eastern Australia with the remainder of the country likely to have equal chances of rainfall being ‘Above’ or ‘Below Average’ (Fig. 3). For the three-month forecast, December to February, rainfall is likely to follow a similar pattern to December but with less area of western and central Australia likely to receive ‘Below Average’ rainfall.

At this time of year accuracy for the three-month forecast is moderate to high for most of Australia except for parts of central Australia where accuracy is low (Fig. 3). 

Figure 3. Australian rainfall outlook for December 2021 to February 2022.

Temperature Roundup

Maximum temperatures in November were ‘Below Average’ across most parts of Australia except for the northern region where ‘Above Average’ day temperatures have continued for another month (Fig. 6).

Minimum temperatures were also ‘Above Average’ across parts of northern Australia and along the east coast (Fig. 5). In contrast a large area in central and western Australia recorded ‘Below Average’ minimum temperatures.

Figure 4. Maximum temperature deciles for November 2021.
Figure 5. Minimum temperature deciles for November 2021.

Temperature Forecast

The BoM’s ACCESS model predicts that over the next three months maximum temperatures are likely to be ‘Above Average’ for much of Australia except for eastern New South Wales extending into Victoria which is likely to be ‘Below Average’ (Fig, 6). For areas in northern and southern Queensland, central New South Wales, eastern Victoria and southern parts of Western Australia and South Australia there are equal chances of maximum temperatures being ‘Above’ or ‘Below Average’ (Fig. 6).

For minimum temperatures, much of Australia is likely to be ‘Above Average’ for the next three months, except for south-east Western Australia and south-west South Australia where they have an equal chance of being ‘Above’ or ‘Below Average’ (Fig. 7).

At this time of year accuracy for the three-month maximum temperature forecast is moderate to high for much of Australia excluding southern parts of the Northern Territory where accuracy is low (Fig. 6). For minimum temperatures, accuracy is moderate to high for much of Australia but again excluding a small area in the central region of the Northern Territory where accuracy is low (Fig. 7). 

Figure 6. December 2021 to February 2022 maximum temperature outlook.
Figure 7. December 2021 to February 2022 minimum temperature outlook.

Climate and Water Outlook Videos

The Bureau of Meteorology releases regular outlook videos, covering all this information. Watch the most recent video below.

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