Heavy rain is forecast across much of Western Australia this morning as a strong cold front hits the coast.

The Weather Bureau says good falls of up to 20 millimetres are expected from Jurien Bay in the north to Walpole in the south.

The bureau's Neil Bennett says rain during the next two days will provide some relief for farmers as they continue to experience drier than normal conditions in the South West.

"It does look at the moment as if the front itself has enough energy behind it and holding itself together quite nicely on all the computer models to suggest that many parts of the agricultural districts will receive some rain," he said.

"We've had very little rainfall in that area over the last 12 months, we saw a particularly dry winter last year so we do need a lot of rain in that area, and as we go through into the winter months we're hoping to see more and more of these fronts."

The Water Corporation says the rain is unlikely to have a significant impact on the state's dams.

The corporation's Phil Kneebone says dam levels remain around 23 per cent.

"The catchments are still bone dry and the only water that will actually find it's way into the dams will be that which falls straight out of the sky onto them," he said.

"That situation will remain until we get steady, consistent soaking rain for about a month that will soften up our catchments and then if we get good rain after that, the water will skate off into the dams and then we'll see some action."