It is almost the end of March. At this time of the year, it is very common for the difference between the daily maximum and the nightly minimum to be quite large. The average daily maximum is slightly above freezing whereas the average nightly minimum is well below freezing. Because the 24 hour average is still clearly below freezing it is still winter meteorologically speaking. Only when the daily (24 h) average rises above freezing and stays there for a week, is the winter considered to have ended.
http://ilmatieteenlaitos.fi/saa/lahti?forecast=long
It seems that the 24 h average will climb above freezing only a week from now but who knows whether it will stay there. I would stay away from lake ice after Easter. Snowmelt during the day create small vertical channels in the ice compromising its load carrying capacity.