A major burst of rain across southern Western Australia has brought significant rainfall to farming districts, with some areas recording close to 100 millimetres over the weekend.

The weather system moved across the state's south after developing in northern Western Australia. The rainfall has produced mixed results for farmers, with some crops benefiting from the additional moisture while others have been damaged by the volume of rain.

In the Goldfields, Kalgoorlie-Boulder recorded around four times its usual September rainfall. Other locations across the southern part of the state received considerably higher totals, with some gauges recording almost 100 millimetres.

For farmers preparing for the grain harvest, the timing of the rainfall is particularly important. Some growers have welcomed the extra moisture because much of the state experienced a dry winter. Rain at this stage of the growing season can help crops that still need moisture before harvest.

However, heavy rainfall can also create problems when crops are close to being harvested. In one farming area, more than 70 millimetres was recorded at a property, with another nearby gauge recording about 94 millimetres.

The heavy rain caused some oats to lodge, meaning the plants have fallen over. Farmers may now need to adjust their harvesting methods, including swathing or using machinery capable of collecting crops close to the ground.

Wet paddocks are another concern. Machinery cannot easily operate in saturated fields, and farmers may need to delay haymaking and harvesting until conditions become drier.

Wet grain can also create problems during harvest and storage. Grain harvested with excessive moisture can be difficult to process and may spoil if it is not dried and stored correctly.

The rainfall has also filled tributaries and increased water levels in dams across parts of the South West Land Division. For some agricultural areas, this provides an important boost following a relatively dry winter.

The Bureau of Meteorology said the weather system responsible for the heaviest rainfall had largely moved away, with conditions expected to become drier later in the week. Some lighter to moderate rain was still expected around parts of the south coast on Monday and Tuesday.

The rainfall was not evenly distributed. Some farming districts received substantial falls while other areas only received small amounts. Farmers north of the main rain band were hoping for additional rainfall before harvest because their properties received much less than surrounding areas.

The contrasting conditions demonstrate how strongly agricultural outcomes can depend on the location and timing of rainfall. While excessive rain can damage crops that are ready for harvest, moderate rain can improve prospects for crops still developing.

With grain harvesting approaching across Western Australia, farmers will now be watching weather forecasts closely and waiting for fields to dry sufficiently for machinery to operate.