Weekly update - 9 July 2020

During the week ending 8 July 2020, a high-pressure system restricted the development of rain bearing systems over southern Australia. Rainfall totals of between 10 and 50 millimetres were recorded across parts of far south-eastern Australia, much of Tasmania and isolated parts of south-western Western Australia and eastern Queensland. Rainfall in excess of 50 millimetres was recorded across parts of western Tasmania.

In Australia’s cropping regions, rainfall totals of between 5 and 15 millimetres were recorded across parts of southern New South Wales, southern Victoria, southern South Australia and the southern regions of Western Australia. Across remaining cropping regions little to no rainfall was recorded during the week ending 8 July 2020.

Despite the low rainfall totals this week, most cropping regions have average to above average levels of root-zone soil moisture, with the exception of Western Australia, and parts of South Australia, Queensland and northern Victoria. Production outcomes in regions across southern Australia with low root-zone soil moisture will be heavily reliant on rainfall during the remainder of winter and early spring to support pasture growth and crop development.

Rainfall for the week ending 8 July 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 08/07/2020

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/

Following a generally favourable start to the winter cropping season in Australia, there is interest in how the remainder of winter and early spring may pan out. To gain some insight it is important to look at the major climate drivers—the Indian Ocean Dipole (IOD) and the El Nino Southern Oscillation (ENSO)—that influence winter and spring rainfall across southern Australia. If negative IOD or La Niña conditions were to eventuate as forecast by a range of international climate models, these key climate drivers would become the major influencing factor for late winter and spring rainfall across southern Australia.

For further information, go to http://www.bom.gov.au/climate/enso/

The El Niño–Southern Oscillation (ENSO) is currently neutral and likely to remain neutral through winter. It is expected that further cooling in the central and eastern tropical Pacific Ocean will occur and a La Niña-like pattern could emerge, potentially contributing to the above average late winter and spring rainfall outlook for parts of Australia.

Monthly sea surface temperature anomalies for NINO3.4 region

The Indian Ocean Dipole (IOD) is currently neutral and while the Bureau’s model suggests it is likely to remain neutral, half of the international models surveyed suggest a negative IOD could develop in late winter or spring. A negative IOD typically brings above average rainfall to southern Australia during winter and spring.

Monthly sea surface temperature anomalies for IOD region

The Southern Annular Mode (SAM) is currently neutral and expected to remain neutral for the next fortnight, having little influence on Australia’s climate. The SAM refers to the north-south shift of the band of rain-bearing westerly winds and weather systems in the Southern Ocean compared to the usual position. When SAM is neutral during winter, the top of this band of westerly winds is over southern Australia and the sub-tropical ridge, a belt of high-pressure systems, is over northern Australia. This allows for cold fronts and troughs to move over southern Australia, bringing normal winter rainfall.

Southern Annular Mode (SAM) daily index

The Bureau of Meteorology’s ENSO Outlook remains at La Niña WATCH. This means that while the El Niño-Southern Oscillation is currently neutral, the chance of a La Niña forming during the southern hemisphere spring has increased to around 50% - twice the normal likelihood.

The cooling trend in the tropical Pacific Ocean has eased during the past fortnight, however more than half the international climate models suggest the cooling will approach or exceed La Niña thresholds in spring.

Difference from average sea surface temperature observations 29 June to 5 July 2020

A La Niña WATCH is not a guarantee that a La Niña will occur; it is an indication that some of the typical precursors of an event are in place. The potential impact of a La Niña event on agricultural production across southern Australia decreases if the event forms during spring or summer, as it has a shorter time to strengthen and will persist for a shorter time before it decays in late summer.

These climate outlooks are generated by ACCESS–S (Australian Community Climate Earth-System Simulator–Seasonal). ACCESS–S is the Bureau of Meteorology's dynamical (physics-based) weather and climate model used for monthly, seasonal and longer-lead climate outlooks.

For further information, go to http://www.bom.gov.au/climate/ahead/about/

The latest rainfall outlook released by the Bureau of Meteorology suggests above average rainfall is likely for isolated parts of north-western Australia during July 2020, with below average rainfall likely across parts of south-eastern Australia and Western Australia. The rainfall outlook for July to September 2020 suggests that wetter than average conditions are likely for parts of eastern Australia and drier than average conditions are likely for parts of northern Western Australia. There are roughly equal chances of a wetter or drier than average three months across the remainder of Australia (Bureau of Meteorology ‘National Climate Outlook’, 2 July 2019).

Chance of exceeding the median rainfall July to September 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 18/07/2020

10 and 50 millimetres across south-eastern, south-western and far southern Australia. Rainfall totals in excess of 50 millimetres are likely across isolated parts of south-eastern Australia, far south-western Australia and much of Tasmania.

In cropping regions there is a 75% chance of rainfall totals between 10 and 25 millimetres across much of New South Wales, Victoria, South Australia and Western Australia. In Queensland there is a 75% chance of rainfall totals between 1 and 10 millimetres across southern growing regions for July 2020.

Rainfall totals that have a 75% chance of occurring July 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 02/07/2020

The outlook for July to September 2020 suggests that there is a 75% chance of rainfall totals between 50 and 200 millimetres across south-eastern, south-western, and far southern Australia. Rainfall totals in excess of 200 millimetres are likely across isolated parts of south-eastern and south-western Australia and northern and western Tasmania.

In many areas where soil moisture is close to average to above average for this time of year, there is a good chance of recording July to September rainfall totals sufficient to sustain crop and pasture production. In cropping regions, there is a 75% chance of receiving between 50 and 100 millimetres across most of New South Wales, Victoria, South Australia and Western Australia. Across cropping regions in Queensland there is a 75% chance of rainfall totals between 10 millimetres in the north and up to 50 millimetres for most remaining areas between July and September 2020.

Rainfall totals that have a 75% chance of occurring July to September 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 02/07/2020

The temperature outlook for July to September 2020 indicates that daytime and night-time temperatures are likely to be between 1°C to 2°C above the 1990-2012 average across parts of the northern half of Australia. Average (- 1°C to 1°C) daytime and night-time temperatures are likely for the remainder of the country (Bureau of Meteorology ‘National Climate Outlook’, 2 July 2020).

Predicted maximum temperature anomaly for July to September 2020

Predicted minimum temperature anomaly for July to September 2020

A low-pressure system over south-eastern Australia is expected to bring rainfall, thunderstorms and snow during the next eight days. Rainfall totals of between 10 and 50 millimetres are forecast for much of central and eastern New South Wales, south-eastern Queensland, eastern Victoria and south-western Western Australia. Falls in excess of 50 millimetres are forecast across parts of the New South Wales coastline.

In cropping regions, rainfall of between 10 and 50 millimetres is expected across much of New South Wales, central and southern Queensland, and parts of eastern Victoria and the west of Western Australia. Little to no rainfall is expected across remaining cropping regions during the next eight days.

Total forecast rainfall (mm) for the period 9 July 2020 to 16 July 2020

©Commonwealth of Australia 2020, Australian Bureau of Meteorology - Issued: 09/07/2020

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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