The first day of summer in Brisbane will feel a lot more like the first day of winter, with persistent heavy showers and a top temperature of just 20°C on the cards.

At the official weather station where records have been kept in Brisbane since 1999:

• Brisbane's average December maximum is 29.6°C
• Brisbane's average July maximum (the coldest month) is 21.9°C.

So the Queensland capital is staring at a first day of summer with a maximum temp lower than the average max temp of the coldest month of the year.

Why the chilly start to summer?

Thursday's cool temps will largely be caused by the widespread Queensland rain which we told you about on Monday.

A very slow-moving low pressure trough and one or two embedded low pressure systems is producing a prolonged spell of rain and storms over QLD which will last pretty much all week.

As the main low drifts slowly southeast in the Coral Sea in a trajectory roughly parallel with the Queensland coastline, its impact will begin to be felt in southeast Queensland.

Air rotating clockwise around the low will direct coolish southeasterlies towards Brisbane, which will also help keep temps down.

How much rain has fallen/will fall?

Brisbane can expect showery weather right through till next Monday, but the heaviest day of rain should be Thursday, Dec 1, with falls likely in the 20-40 mm range. The rain has just started to make its way into the northern fringe of the city as we write this story just before midday (local time) on Wednesday.

To 9 am this morning, heavy falls were experienced further north, especially in the Central Highlands and Coalfields forecast district.

• One of the highest official totals was in the coal mining town of Moranbah, with 119.4 mm to 9 am. That was the heaviest day of November rain in over 50 years, and the wettest day in any month for seven years.

Cricket fans can thank their lucky stars that Wednesday's first men's Test match between Australia and the West Indies is in Perth (where the outlook is for five days of dry weather) rather than Brisbane, where historically the first Test of the summer season has often been played.