Seasonal rainfall update

Rainfall update, 11 July 2018

Rainfall over the past week has been heaviest in the lower west and coastal parts of the south. Most of grainbelt has received less than 10mm for the week.

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 11 July 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

The month began with good falls along the west coast and northern grainbelt. The south coast and far north-east of the grainbelt have received mostly less than 25mm so far.

Map of monthly rainfall in millimetres for 1  to 11 July 2018
Figure 2 Western Australian rainfall totals (in millimetres) for 1– 11 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 early July has advanced much of the northern grainbelt to be close to median rain to date (Figure 3). South-eastern and eastern parts of the grainbelt remain well below seasonal median rain to date. See Figure 4 for examples from DPIRD’s rainfall to date tool.

Map of seasonal rainfall as a percentage of median rain for 1 April to 10 July 2018
Figure 3 Season rainfall to date as a percentage of the median from 1 April to 10 July 2018 (data source: Patched Point Database).

Graphs of rainfall to date compared with historical records
Figure 4. Rainfall for 1 April to 11 July at selected locations, showing rain to date and projections using historical rainfall. From DPIRD Rainfall to Date tool.

Soil moisture

Figure 5 shows the estimated fallow soil water storage to 10 July 2018 from the DPIRD soil model. Rain since 1 July has been mostly less than 25mm, so north-eastern and south parts of the grainbelt have low levels of soil water storage.

The Seasonal climate information page now shows soil water storage for each of the 10 soil types used in the model.

Map of soil water storage in millimetres at 10 July 2018
Figure 5 Estimated plant available soil water in millimetres at 10 July 2018 (data source: Patched Point Database).

Potential yield

Potential crop yield is estimated using the French-Schultz relation and uses seasonal rainfall from1 April to date. 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 potential crop yield
Fig 6 Potential crop yield based on seasonal rainfall to date, and assuming an average finish to the season.

Rainfall forecast for the next week

Rainfall forecast for the week ending 18 July 2018 is likely to be modest over the grainbelt; totals appear to be less than 10mm (Figure 7).

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 8.

Map of forecast rain to 18 July 2018 from Bureau of Meteorology model
Figure 7 Bureau of Meteorology forecast rain in millimetres for 11 to 18 July 2018 (source: www.bom.gov.au/jsp/watl/rainfall/pme.jsp).

Map or rainfall forecast in the week to 18 July from the ECMWF model
Figure 8 Total predicted accumulated rainfall from the ECMWF for 10 to 18 July 2018 (source: https://weather.us/model-charts/euro/western-australia).

In this Issue

Seasons