Perth will experience a swing from warm to wet weather this week, with the city forecast to have its first 30°C of the season on Wednesday before rain sets in on Friday.

A high pressure system passing to the south of Western Australia during the first half of this week will cause warm air to flow towards the state’s west coast.

This injection of warm air will cause daily maximum temperatures to increase from around 24°C on Monday to 27°C on Tuesday and possibly reaching 30°C on Wednesday. If it does get this warm, Wednesday would be Perth’s first 30°C so far this spring and the city’s warmest day in five months.

After another warm day on Thursday, with a maximum around 27°C, Friday will be noticeably cooler in Perth and surrounding areas as a cold front causes cloud and rain to develop over the state’s west.

Current forecasts suggest Perth could see around 10-20 mm of rain as the front passes through on Friday, although totals may vary depending on the timing and strength of the front.

Image: Forecast accumulated rain this week. Most of the rain predicted here for the state’s southwest will fall on Friday into Saturday. Source: Weatherzone.

It will also be noticeably cooler behind the front, with maximum temperatures forecast to reach about 23°C on Friday and 20°C on Saturday.

Further inland, a separate low pressure trough will cause widespread showers and thunderstorms over WA between Monday and Wednesday this week. This thunderstorm activity will stretch from the Interior towards the Pilbara, Gascoyne and parts of the state’s west and south. Some of these storms are likely to become severe and there may even be a few storms around Perth, most likely on Wednesday.

Perth's temperature see-saw this week, with maximums ranging from 30°C on Wednesday to 20°C on Saturday, and the widespread thunderstorms are sure signs that spring is well underway in WA.