BATTLE-weary firefighters may have another horror day ahead of them with temperatures to spike again later this week.

The Bureau of Meteorology has forecast 40C in some regional areas on Thursday, while Melbourne is set to cop a sweltering 39C.

Mildura and Horsham are forecast to hit 41C, while Wodonga and Shepparton are set to reach 40C.

State Control Centre spokesman David Harris urged Victorians to remain vigilant despite the current cool reprieve.

Bureau of Meteorology duty forecaster Stephen King said a cold front and light showers were forecast to whip through Victoria early Friday.

He said while the rain would have little effect on the big bake, an earlier wind change could complicate firefighting efforts.

He stressed the weather forecast was still uncertain.

Mr Harris said firefighting agencies had been buoyed by the cooler weather.

Mr Harris said emergency services would be well equipped if conditions flared up later in the week, despite Victorian firefighters still deployed in NSW and Tasmania.

Mr King said Thursday could be the first in a fresh wave of hot weather.

"We still have that really hot front over the middle of the continent. Early into the week we'll quite easily get another streak of hot days.

"In general terms, we're really still going to see some heatwave conditions whenever the winds go around to the north," he said.

The Bureau has signalled Victoria has entered its fifth month of a "dry spell", with conditions not forecast to ease much in the coming months.

Read more on the Herald Sun.