Powerful electrical storms with heavy rain are expected across southern and central Finland this weekend. The heaviest rainfall was in Uusimaa on the south coast beginning around 6pm Saturday, as well as north of Turku.

The rain is being brought by a warm, humid air mass moving in from Poland and the Baltic states. The volatile mix may generate thundersqualls and even small tornadoes.

The highest risk for lightning is in western Finland on Saturday evening and in the east on Sunday.

Met Institute issues alerts

The forecast calls for cloudy but warm conditions through most of the country, with local showers or thunderstorms in the north, but drier in the far north.

Western Finland will get rain, sometimes accompanied by lightning. On Sunday showers and thunderstorms also predicted throughout the country except Lapland. Temperatures could climb to 27 degrees Celsius.

The Finnish Meteorological Institute warns of heavy downfalls of more than 20 millimetres an hour in the west with thundery gusts of more than 15 metres per second on Saturday in Western Finland and southern Lapland, and the next day in the east. There is also a warning of strong winds and thundersqualls on southern sea areas.

Bracing for outages

Power utilities are gearing up to respond in case of blackouts.

The nation's biggest energy company, Fortum, is warning customers of potential supply disruptions this weekend.

The utility has laid on four times as many employees as usual to fix faults as the band of storms hits.

The company is reminding customers to disconnect electrical appliances before any storms hit, particularly computers, modems and routers. Experts also recommend ensuring a store of batteries, candles, water and non-perishable food.

Mega-festival in the line of fire

The forecasts placed one of Finland's largest rock festivals, Ruisrock, in the crosshairs of the storm. The nation's oldest pop festival -- and the world's second-oldest after the Netherlands' Pinkpop -- is expected to draw some 60,000 people to Ruissalo, on the coast just outside of Turku. Saturday's headliner is the Finnish orchestral hard rock band Nightwish.