Most countries in Europe are having similar weather conditions right now, temperatures around 40 degrees. If anything, Qatar will be a bit cooler than Europe right now when the World Cup starts.
I don't think the weather will play a huge role in this World Cup, specially for the European countries.
It will probably be a pleasant and nice weather throughout the entire competition, maybe around 20s and 30s.
Europe is suffering from a heat wave, and that is why some of the cities there have temperature close to 40 degrees. That doesn't mean that Europeans are comfortable with that sort of weather. And from what I have seen from the previous editions of the world cup, European teams doesn't perform as per the expectations when the tournament is held outside the European continent. 2014 is an exception though. The tournament was held in South Africa, and still Germany managed to defeat Argentina in the final.