The two or three days a year when the water temperatures peak above 10 degree centigrades, is called 'the Norwegianswimming window', or simply the 'swimming weekend' by Norwegians.
Bjørn: Wow, radio said the temperature in the river is 11 today, wanna go swimming?
Arne: Sure mate, who doesn't wanna go swim during the Norwegian swimming window?
Bjørn: You've got a point, let's call in Petter, Knut, Bjarne, Kjell and Fridtjof too.
Originating from the comedy show Brass Eye, 'as a window' is used to describe a characteristic in an individual that is obvious and others can see-through that person's best efforts to hide it.
"You described Steve as dangerously gay.", "Yes, he's totally gay. Steve is as gay asa window."