The reason, say scientists, is that cold air is still being brought in from the arctic by the so-called North Atlantic Oscillation. This weather phenomenon is in a 'negative' phase, just like it has been since December 2009.
Before that Sweden had 40 years of relatively mild winter, due to the oscillation being in a 'positive' phase.
Per Kållberg at SMHI says that this phenomenon has been known about for a long time, but scientists have no reason why it exists.
Already records are being broken - the lowest temperature in November since 1995 was recorded in Lappland, at minus 36.6 degrees celsius.