Perth and the southwest are set for another coolish day on Sunday after more of the same weather that delivered WA its coldest December day on Saturday for more than 50 years.

The maximum reached just 19 degrees, making it the coolest December day since 1961.

Stormy weather is expected in Perth later on Monday. Credit:Perth Weather Live - Facebook

A Bureau of Meteorology spokesman said light showers were expected on Sunday and they could carry through into Monday morning.

"The cooler weather is being caused by a low south of Albany along with southerly winds," he said.