How cold will it get in winter?
Temperatures in the Oslo-region will normally be between +2 and -20 degrees celcius in wintertime, with large variations. The coldest time of the year is usually February, where temperatures can drop to -20 degrees celcius. That is, however, rare. Be prepared for somewhere between 0 and - 12 degrees on a day-tour between December and March. With proper clothing and equipment you will not get cold.