It may be white Christmas and so on, but take a look at the forecast temperatures above Finland high up in the stratosphere: +41°C on 23 Dec.

This phenomenon is called "Sudden Stratospheric Warming", and it can have implications for the weather in Europe during Jan-Feb period. pic.twitter.com/N2Rd01LF75

— Mika Rantanen (@mikarantane) December 18, 2018