A low pressure front will arrive over Finland this weekend, bringing stormy weather and rain.
Thursday will be warm and largely sunny, with the temperature rising to 30 degrees Celsius or more in the west and north.
But Yle meteorologist Matti Huutonen says this will change on Friday when a low pressure system arrives. The front will bring thunderstorms and showers to the south, as well as some parts of central Finland.
The Finnish Meteorological Institute (FMI) has issued a warning of heavy rain for most of the south-western part of the country on Friday
Slow-moving front could bring deluge
Huutonen says that several millimetres of rain could fall in many places, as storm clouds will be moving slowly.
"Thundershowers always present the possibility of a lot of rain. There will be huge differences between areas, however. Some places could get up to 50 millimetres of rain, while their neighbours get just two," he says.
He says the slow-moving front will mean there's a good chance of some impressive lightning flashes, too.
The system is forecast to stick around over the weekend, and on Saturday the rain is expected to reach even further into central Finland and to make inroads into south-western Lapland.
On Sunday, the thunderstorms will concentrate over eastern and northern parts of the country.
Huutonen says that there is also a good chance that some areas will receive hail.
"Thunder clouds can extend 10 to 15 kilometres up into the atmosphere, where temperatures can be extremely frigid. Air from the surface of the Earth rises up and the moisture condenses and forms hail," he explains.
Forest fire warnings still in effect
The summer of 2018 has been relatively rain-free in Finland, and conditions are very dry in several areas – especially the southwest.
The FMI's forest fire warning for the entire country holds on both Thursday and Friday, despite the projected rain. After the Friday storm, the warning will continue in western areas and Lapland.
"There's always a risk that a flash of lightning will start a forest fire that is not extinguished by the rain," says Yle's Huutonen.