Seasonal rainfall update

Rainfall update 4 July 2018

Rainfall over the past week has been good along the west coast from the south-west to Shark Bay and for much of the central grainbelt. While the south coast has picked up some useful falls, totals remain lower.

Rainfall totals in the past week

Map of Western Australia showing coloured areas of rainfall levels in millimetres
Figure 1 Western Australian rainfall totals (in millimetres) for the week ending 3 July 2018 (source: Bureau of Meteorology, www.bom.gov.au/climate/)

Rainfall for the month to date

The month has begun with good falls in the areas already indicated. The south coast and far north-east of the grainbelt have received mostly less than 10mm so far.

Map of Western Australia showing coloured areas of rainfall levels in millimetres
Figure 2 Western Australian rainfall totals (in millimetres) for 1-4 July 2018 (source: Bureau of Meteorology, www.bom.gov.au/climate/)

Monthly rain to date from DPIRD weather stations can be found at https://weather.agric.wa.gov.au/. Select Month to date from the drop-down menu.

Seasonal rainfall

June rainfall was near-average or below for most of the grainbelt and south-west (Figure 3). Rain from cloudbands ensured the Gascoyne and Pilbara were well above average.

Seasonal rainfall deciles (April to June) show a very dry the start to the growing season (Figure 4). Good rain in early July has advanced much of the northern grainbelt to be close to median rain to date (Figure 5). South-eastern parts of the grainbelt remain well below seasonal median rain to date.

Map of Western Australia showing coloured areas of rainfall decile ranks
Figure 3 Rainfall deciles for June 2018 (source: Bureau of Meteorology)

Map of Western Australia showing coloured areas of rainfall decile ranks
Figure 4 Rainfall deciles for April to June 2018 (source: Bureau of Meteorology)

Map of Western Australia showing coloured areas of rainfall levels in millimetres
Figure 5 Season rainfall to date as a percentage of the median from 1 April to 3 July 2018 (data source: Patched Point Database)

Soil moisture

Soil water storage has improved over northern and western parts of the grainbelt, as expected from the rainfall pattern in the past week. Figure 6 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 shows the estimated fallow soil water storage to 3 July 2018 from the DPIRD soil model. Rain since 27 June has been mostly less than 10mm, so north-eastern and southern parts of the grainbelt have low levels of soil water storage.

Map of Western Australia showing coloured areas of soil water storage relative to average
Figure 6 Estimated root zone soil moisture 3 July 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/)

Map of Western Australia showing coloured areas of soil water storage at 3 July 2018
Figure 7 Estimated plant available soil water in millimetres at 3 July 2018 (data source: Patched Point Database)

Rainfall forecast for the next week

Rainfall forecast for the week ending 11 July 2018 is likely to be lighter than for the start of the month. Although rain will occur over the grainbelt, totals appear to be less than 10mm (Figure 8).

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 9.

Map of Western Australia showing coloured areas of rainfall predicted in the next week
Figure 8 Bureau of Meteorology forecast rain in millimetres for 4-11 July 2018 (source: www.bom.gov.au/jsp/watl/rainfall/pme.jsp)

Map of forecast rain to 11 July 2018 from the ECMWF model
Figure 9 Total predicted accumulated rainfall from the ECMWF for 3-11 July 2018 (source: https://weather.us/model-charts/euro/western-australia)

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