More seriously, Finland lies between the Gulf stream and Siberia. The same can be said of the other Nordic countries, but Finland is a bit closer to Siberia. Thus the weather can be quite mild, or really cold.

The Finnish army traditionally doesn't mind cold weather, and the equipment (mostly) does work all right. While I did my time in the army our unit spent once more than a week in the forest while the temperature was below -40°C / -40°F. The only trouble I remember were milk and butter, which got frozen and had to be thawed out before eating. The frozen milk was quite sweet, which was at first a bit unpleasant. (You can try the taste by putting some milk in the freezer.)

Several years ago (in my teens) I took part in cross-country skiing competitions, which were arranged even when the temperature was at -30°C / -22°F. In fact, I used to do over 15 km (10 miles) training sessions almost every day, regardless of the weather.

On the other hand, last Summer was quite warm in Finland, much warmer than +15°C / 59°F, often over +25°C. And it rained so little that we now have shortage of water-powered electricity.