Seasonal rainfall update

Rainfall update 27 June 2018

The past week has seen lighter rainfall, mostly less than 5mm, for the bulk of the grainbelt until a significant cold front crossed the coast over 26/27 June. This has brought heaviest rain only over the south-west to 9am 27 June. Rain since 9am has been mostly 5-10mm over southern parts of the central grainbelt. The pattern of generally low rainfall has continued for the south coast.

Rainfall totals in the past week

Figure 1 Western Australian rainfall totals (in millimetres) for the week ending 27 June 2018 (source: Bureau of Meteorology, www.bom.gov.au/climate/)

For more information refer to the Bureau of Meteorology weekly rainfall table for the south-west.

Rainfall for the month to date

Western and south-western locations have received good rainfall to date and may achieve average rain for the month. Rainfall over the south-eastern grainbelt remains well below average to date. Gascoyne and Pilbara regions have had well above-average rainfall for the month to date, noting that this is a time of year when rainfall is usually low (Figure 2).

Figure 2 Western Australian rainfall totals (in millimetres) for 1–27 June 2018. (source: Bureau of Meteorology, www.bom.gov.au/climate/)

Monthly rain to date from DPIRD weather stations

Figure 3 Monthly rainfall to date (in millimetres), 1– 27 June 2018, from DPIRD weather stations in northern and central agricultural areas.

Figure 4 Monthly rainfall to date (in millimetres), 1–27 June 2018, from DPIRD weather stations in southern agricultural areas.

Seasonal rainfall to date

Much of the eastern grainbelt and south coast have had seasonal rainfall totals well below the median for the period to date (see Figure 6 in particular). The lower west coast and south-west are close to median to date and further rain over 26 and 27 June is likely to bring these regions close to average.

Figure 5 Seasonal rainfall in millimetres (mm) from 1 April to 25 June 2018 (data source: Patched Point Database).

Figure 6 Season rainfall to date as a percentage of the median from 1 April to 25 June 2018 (data source: Patched Point Database)

Soil moisture

The soil water maps this week do not include rain over 26/27 June, so are showing storage that is lower than current. Figure 7 shows the estimated root zone soil water storage from the Bureau of Meteorology landscape model, as relative storage for the time of the year. Low levels of soil water remain in the eastern and south-eastern grainbelt.

Figure 7 Estimated root zone soil moisture 26 June 2018, relative to expected levels at this time of year (source: Bureau of Meteorology's landscape water balance model, www.bom.gov.au/water/landscape/)

Figure 8 shows the estimated fallow soil water storage to 25 June 2018 from the DPIRD soil model. Rain since 25 has been mostly less than 5mm, so these regions are likely still to have relatively low levels of soil water storage.

Figure 8 Estimated plant available soil water in millimetres at 25 June 2018 (data source: Patched Point Database).

Rainfall forecast for the next week

The rain event over 26/27 June is likely to be the last system for the month. Rainfall forecast for the week ending 4 July 2018 includes the 27 June system and what appears to be a rain band interaction occurring over 1 and 2 July 2018. The latter system could bring significant rain throughout the grainbelt (Figure 9).

Figure 9 Bureau of Meteorology forecast rain in millimetres for 27 June to 4 July 2018 (source: www.bom.gov.au/jsp/watl/rainfall/pme.jsp).

The ECMWF model is predicting a similar spatial pattern of rainfall over the coming week. Total predicted rainfall from the ECMWF model for the next 10 days is shown in Figure 10.

Figure 10 Total predicted accumulated rainfall from the ECMWF for 26 June to 4 July 2018 (source: https://weather.us/model-charts/euro/western-australia).