Norwegians flocked outdoors all over the country this weekend, soaking up the sunshine and temperatures as high as 15C (59F). Ferries to the Oslo Fjord's park-like islands were full on Sunday, while others spread out picnics, went bicycling or even sailing.

State meteoroligists warn, however, that the sunny days will soon wind down. Clouds are due to move in this week and by Friday, it will probably start raining.

It will continue to be cold at night, but mild during the day. After basking in warm sunshine Sunday afternoon, for example, overnight temps fell to as low as minus-3 at Oslo's main airport at Gardermoen early Monday. Temperatures in the city stood at a brisk 4C Monday morning.

It remains unclear how long the low-pressure system due to move in over southern Norway will last. NIghttime temperatures may rise when the rain starts falling.