As the weather charts, also this forecasts provided by saakeskus.fi are based on data of the GFS model of the US National Oceanic and Atmospheric Administration / National Centers for Environmental Prediction.
Please keep in mind that computer models are not always precise and the further you go to the future, the more likely is a difference between the model and what really will happen.

Please note also that all date and time information are in Zulu-time which is UTC or GMT. For Finland please add 2 hours in winter and 3 hours in summer.