Another trough is gearing up to drag heat over southeast Australia at the beginning of this week before much colder air surges in behind, dividing the week into definitely-not-suitable-for-Christmas-baking and the gingerbread-house-might-not-wilt parts.

Monday will be the warmest day for Adelaide and Melbourne, while Tuesday will be the hottest for Sydney and Canberra. Peak heat will struggle to reach southern coasts, sparing Adelaide and Melbourne from going much above 30°C. The heat will instead be most pronounced over the inland and east, including Sydney, where temperatures are forecast to be around 10 degrees above average on Tuesday, reaching the high thirties in the west and the mid-thirties on the coast. It'll also be humid, making it feel even hotter.

The NSW capital has had a record hot start to December and, since the start of spring, has tallied up five days over 35°C. That's the equal most September to December days above 35°C since 2015. A maximum above 35°C on Tuesday would make it the most for the spring to early summer period since 1957.  

Image: Animation showing forecast maximum temperatures and afternoon wind streamlines for southeast Australia Monday 18th to Thursday 21st December.  

The good news is that showers and thunderstorms will arrive Tuesday afternoon with the trough, bringing likely cooling even before the southerly winds surge in in the evening.  

The showers and storms will be a day earlier for Adelaide and Melbourne (Melbourne is more likely to just have showers), heralding the start of cooler period that will see maximum temperatures 5-6 degrees below average on Tuesday and Wednesday. Western Sydney and Canberra will deviate similarly below the average on Wednesday and Thursday.  

So, do your baking and rushing about late in the week.  

Image: Forecast maximum temperatures Monday to Thursday for Canberra, Adelaide, Melbourne, Sydney and Penrith.