A cool change will sweep across the state this afternoon, but it is not expected to reach the Longwood fire grounds until late evening to early morning, and may not bring much relief.

Victoria is again expected to swelter through a day of catastrophic and extreme bushfire risk conditions. However, the cool change, once it arrives, could instead make things even more difficult and dangerous for firefighters.

Temperatures are expected to exceed 40 degrees across much of the state. In Longwood, where an uncontrolled fire has burnt through tens of thousands of hectares, the Bureau of Meteorology is predicting a maximum of 43 degrees. In Walwa, near where a second major blaze is burning out of control, a high of 44 degrees is expected.

Daniel Sherwin-Simpson, a meteorologist at the bureau, said that despite the drop in temperature, the cool change would not necessarily help firefighting efforts.

“In terms of the wind change, it can be a double-edged sword. Yes, it will lead to temperatures dropping, the humidity increasing – which generally reduces fire danger – but we still can see gusty winds with this wind change,” he said.

“It could actually increase the area that the fire starts burning immediately as that cool change moves through. It can rapidly increase the fuel load with the shifting direction.

“The cool change is, in fact, probably one of the more hazardous points in terms of fire dangers, particularly with active fires today, just because it’s such a rapidly changing thing, and it can catch people off guard. These fires of such significant size spread very, very rapidly.”

The change is expected to sweep across Melbourne between 6pm and 7pm, reaching the north and east of the state later tonight.

“It’s probably going to go through that Longwood fire at some point in the evening or very early morning on Saturday,” said Sherwin-Simpson.

“Anyone nearby should definitely listen to the CFA with their emergency warnings in those areas. Keep up to date with any other fire that starts in your area.”