Impossible to predict. I bet helsinki will be well organised if there is snow. So that you know the other day I was stuck on Tarmac in plane at Manchester for over 2 h when there was virtually no snow but very little de-icing provision- everyone had to wait their turn for the de-icer team to come over.
However I imagine there are a dozen days at year where Manchester is severely affected by weather, and it's finnair's problem to sort out, assuming the journey is all one one ticket. Unlike the charter flight I was on the flight will be full of people hoping for connections to Asia, I would have thought,