Depending on the location of a city the climate can be very different. Those areas which are located very close to sea enjoy cool winter and mild summer while those located inland experience cold winters and warm summers. For instance at Helsinki, a maritime location, the coldest month stands at -4.5 C which is not so severe for its high latitude while a continental location like Jyvaskyla records a temperature of -8.5 C in its coldest month. Similarly due to its continental location, Jyvaskyla has a midday temperature of 21 C as compared to that of Helsinki of 19 C. This clearly shows that the continental locations are warmer in summer and cooler in winter than those of maritime locations.
The precipitation in Norway is, mostly in the form of snow, due to its northerly location. The precipitation is more in the cities located near the sea due to the northern Atlantic influence than those located farther inland. For instance the total annual precipitation at Helsinki is 642 mm, at Jyvaskyla it is 638 mm while at Sodankyla it is only 507 mm. But even such a moderate precipitation is ample enough to sustain thick vegetation since at higher latitudes; evaporation is less due to lower temperatures.
In short the climate of Finland exhibits both the maritime and continental varieties, depending upon the location of a place. The rainfall, however, is abundant enough to support thick forests.