Weekly update - 1 October 2020

During the week ending 30 September 2020 low pressure systems and cold fronts moved over south-eastern Australia and troughs developed across parts of northern Australia and south-western Western Australia, bringing moderate rainfall to parts of Australia. Rainfall totals of between 10 and 50 millimetres were recorded across parts of southern New South Wales, central-eastern Queensland, south-eastern and central South Australia, the south-west and north-east of Western Australia, the north-west of the Northern Territory and much of Victoria and Tasmania. Rainfall in excess of 50 millimetres was recorded across isolated parts of eastern Victoria, the north-west of the Northern Territory and western Tasmania.

In Australia’s cropping regions, rainfall totals of between 5 and 25 millimetres were recorded across parts of southern New South Wales, far northern Queensland and Victoria. Rainfall totals of between 15 and 50 millimetres were recorded across most cropping regions in South Australia. Little to no rainfall was recorded across remaining cropping regions during the week ending 30 September 2020.

These substantial falls in South Australia and parts of New South Wales and Victoria are likely to support yield prospects, benefit pasture growth and boost soil moisture, particularly in South Australia.

Rainfall for the week ending 30 September 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 30/09/2020

Note: The rainfall analyses and associated maps utilise data contained in the Bureau of Meteorology climate database, the Australian Data Archive for Meteorology (ADAM). The analyses are initially produced automatically from real-time data with limited quality control. They are intended to provide a general overview of rainfall across Australia as quickly as possible after the observations are received. For further information go to http://www.bom.gov.au/climate/rainfall/

September 2020 rainfall was above average to well above average across large parts of northern, eastern and southern Australia, and below average across parts of south-western Australia and isolated parts of south-eastern Australia.

Across most cropping regions, September  2020 rainfall totals were generally average. Rainfall totals for the first two weeks of September were moderate and contained over limited cropping regions, mainly benefitting those in parts of Western Australia, north-eastern New South Wales, central Queensland and south-western Victoria. This was followed by significant rainfall across parts of eastern and southern cropping regions, particularly in New South Wales. This rainfall supported favourable yields and pasture growth, and provided a boost to soil moisture. In contrast, in regions that recorded below average rainfall during winter and have low soil reserves, particularly Western Australia, the low September rainfall totals are likely to be a concern for yield and pasture production as temperatures increase.

During the remainder of the month, moderate rainfall was recorded across cropping regions in parts of southern New South Wales and southern Victoria, much of South Australia and scattered parts of northern Queensland. In most parts of Victoria and South Australia that had generally recorded average or lower September rainfall, these falls provided a boost to soil moisture, and stabilised crop yield potential and pasture growth rates.

Rainfall percentiles for September 2020

Source: Bureau of Meteorology
Note: Rainfall for September 2020 is compared with rainfall recorded for that period during the historical record (1900 to present). For further information, go to http://www.bom.gov.au/jsp/awap/

Upper layer soil moisture in September  2020 was above average to extremely high for this time of year across large parts of northern Australia and parts of eastern and southern Australia, largely reflecting rainfall patterns during the month. Soil moisture was average across much of south-eastern and central Australia, with extremely low to well below average soil moisture in parts of south-western Australia. Upper layer soil moisture is important at the beginning of the summer cropping season since plant germination and establishment utilise this moisture.

Relative upper layer soil moisture was generally average for this time of year across cropping regions in New South Wales, Queensland, Victoria, South Australia and parts of Western Australia. Upper layer soil moisture was extremely low to well below average across cropping regions in parts of south-eastern Queensland, eastern Victoria and the east and north of the Western Australia wheat belt.

Modelled upper layer soil moisture for September 2020

Source: Bureau of Meteorology (Australian Water Resources Assessment Landscape model)
Note: This map shows the levels of modelled upper layer soil moisture (0 to 10 centimetres) during September 2020. This map shows how modelled soil conditions during September 2020 compare with September conditions modelled over the reference period (1911 to 2016). Dark blue areas on the maps were much wetter in September 2020 than during the reference period. The dark red areas were much drier than during the reference period. The bulk of plant roots occur in the top 20 centimetres of the soil profile. Soil moisture in the upper layer of the soil profile is therefore useful indicator of the availability of water, particularly for germinating seed.

Lower layer soil moisture for September  2020 was above average to extremely high for this time of year across large areas of central and south-eastern Australia and scattered parts of northern and western Australia. In contrast, it was extremely low to well below average across large parts of south-western Western Australia and scattered parts of southern, eastern and northern Australia.

In cropping regions, lower layer soil moisture was average to well above average for New South Wales and much of central and southern Queensland. Lower layer soil moisture was well below average to average in cropping regions across northern Queensland, Victoria and South Australia.

Relative lower layer soil moisture was extremely low to well below average for cropping regions across much of the Western Australia wheat belt. Production outcomes in cropping regions with below average or worse lower layer soil moisture, particularly south-western Victoria, western and central South Australia and the central Western Australia wheat belt, will be heavily reliant on further rainfall during spring.

Modelled lower layer soil moisture for September 2020

Source: Bureau of Meteorology (Australian Water Resources Assessment Landscape model)
Note: This map shows the levels of modelled lower layer soil moisture (10 to 100 centimetres) during September 2020. This map shows how modelled soil conditions during September 2020 compare with November conditions modelled over the reference period (1911 to 2016). Dark blue areas on the maps were much wetter in September 2020 than during the reference period. The dark red areas were much drier than during the reference period. The bulk of plant roots occur in the top 20 centimetres of the soil profile. The lower layer soil moisture is a larger, deeper store that is slower to respond to rainfall and tends to reflect accumulated rainfall events over longer time periods.

Cold fronts and troughs are expected to bring rainfall to parts of central, south-eastern and far northern Australia, with onshore flow expected to bring rainfall to parts of north-eastern Queensland and southern Western Australia. Rainfall totals of between 10 and 50 millimetres are forecast for much of Victoria, South Australia and Tasmania, and parts of southern New South Wales, the south and north-west of the Northern Territory and isolated parts of north-eastern Queensland and far southern Western Australia. Rainfall in excess of 50 millimetres is expected across western Tasmania.

In cropping regions, rainfall of between 10 and 50 millimetres is expected across Victoria, South Australia and parts of southern New South Wales. Little to no rainfall is expected across cropping regions in Queensland and Western Australia, and remaining cropping regions in New South Wales during the next eight days. These falls are likely to support favourable winter crop yields and boost soil moisture in south-eastern Australia during the final stages of winter crop development.

Total forecast rainfall (mm) for the period 8 September 2020 to 1 October 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 1/10/2020

Note: This rainfall forecast is produced from computer models. As the model outputs are not altered by weather forecasters, it is important to check local forecasts and warnings issued by the Bureau of Meteorology.

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