Valley becomes a white wonderland

The Ferguson Valley was transformed into a white wonderland on Sunday afternoon when the area was struck by a hail storm residents said sounded like a "war".

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Hitting at about 3pm, a slow-moving thunderstorm unexpectedly dumped a deluge of pea-sized hail on the picturesque valley for 15 minutes astonishing residents and tourists.

The Weather Bureau had forecast isolated showers and thunderstorms for the South West on Sunday.

Ferguson Valley resident Jan Gray said she had never experienced anything like the hail which had "decimated" her lavender farm.

"It was frightful -my husband Kevin and I were looking at each other thinking 'when is it going to stop?'," Mrs Gray said.

Weather Bureau Manager of Climate Services in WA Glenn Cook described the hail storm as a "significant" weather event.

Hail is generated by strong updrafts in thunderstorm cloud, which create unusually big rain drops that then freeze as they reach higher altitude.

When it is too heavy for the updrapht to hold, the hail falls and decreases in size as it melts on the way down to earth.

Mr Cook said a slow moving thunderstorm caused the localised deluge and allowed for a considerable fall.

"While not always dangerous, hail can cause significant damage to agriculture, so it is a significant event," Mr Cook said.

With hail still lying on the ground at Ferguson Hart Winery on Monday afternoon, owner Jan Hart said she had never seen anything like it in 18 years of living in the valley.

Mrs Hart said the severity of the storm meant their vineyard production would be affected next year.

"It sounded like a war - it was just full-on crashing," Mrs Hart said.

"We've lost a good 50 per cent of our crop and everybody in valley will have lost at least 50 per cent of their crop."