Seasonal rainfall update

Rainfall update 24 July 2018

Rainfall for the month to date

Rainfall has continued through July, with good falls along the west coast and northern grainbelt. Much of this region has received 80% or more of average monthly rain. The south coast remains patchy, with higher rainfall only near the coast (Figure 1).

Map of WA showing rainfall in millimetres for 1  to 23 July 2018
Figure 1 Western Australian rainfall totals (in millimetres) for 1–24 July 2018 (source: Bureau of Meteorology, www.bom.gov.au/climate/)

Monthly rainfall to date is available from the DPIRD weather stations and radar page (select Month to Date from the drop-down menu).

Seasonal rainfall

Good rain in July has advanced much of the northern and central grainbelt to be close to median seasonal rain to date (Figure 2). South-eastern parts of the grainbelt remain well below normal seasonal rain to date, with much of the South Coast at decile 1.

Map of seasonal rainfall for 1 April to 23 July 2018 shown as decile ranking
Figure 2 Rainfall deciles from 1 April to 23 July 2018 (data source: Patched Point Database)

For graphs of rainfall at individual locations, see DPIRD’s Rainfall to date tool .

Soil moisture

Figure 3 shows relative root zone soil water storage to 23 July 2018 from the Bureau of Meteorology’s Landscape Water Balance model. Rain in July has improved soil water storage for much of the grainbelt; however southern parts of the grainbelt and south coast still have low levels of soil water storage for this time of year.

For soil water estimates at individual locations with and without crop water use, see DPIRD’s Soil water tool.

Map of relative soil water storage showing areas with average or low storage for this time of year
Figure 3 Estimated relative root zone soil water at 23 July 2018 from the Bureau of Meteorology’s Landscape Water Balance model

Potential yield

Potential crop yield is estimated using the French-Schultz relation, and uses seasonal rainfall from1 April to date. Rainfall for the rest of the growing season (to 30 September) is assumed to be decile 5. This model does not account for crop diseases or soil constraints.

Map of Western Australia showing coloured areas of predicted crop yield in tonnes per hectare at 23 July 2018
Figure 4 Potential crop yield based on seasonal rainfall to date, and assuming an average finish to the season

Rainfall forecast for the next two weeks

Rainfall forecast for the rest of July is likely to bring monthly rainfall to be near average over most of the grainbelt (Figure 5). Again, relatively small totals are forecast for the south coast.

Similar rainfall patterns are predicted by the US NCEP model for the start of August, as shown in Figure 6.

Map of forecast rain in millimetres to 31 July 2018 from Bureau of Meteorology model
Figure 5 Bureau of Meteorology forecast rain in millimetres for 24-31 July 2018 (source: www.bom.gov.au/jsp/watl/rainfall/pme.jsp)
Map showing predicted rainfall in millimetres for the next two weeks to 8 August 2018
Figure 6 Rainfall predicted for the next two weeks from the US NCEP model, to 8 August 2018 (source: http://wxmaps.org/pix/prec7)