There is a relationship between a small area filled with cold air in the stratosphere and troposphere over the Arctic and the beautiful phenomenon of nacreous clouds.
Currently, the stratospheric polar vortex has moved to Northern Europe. In its area, there is a very low temperature (down to -80). This is unrelated to surface weather, but contributes to the rare nacreous clouds.
Location of the polar vortex on January 28, 2020
These stratospheric clouds form at temperatures below -78. Such values occur inside the polar vortex at heights from 15 to 30 km. However, there is too little moisture at this altitude for ice to form. But there are tiny droplets of sulfuric acid that got there during volcanic eruptions. At temperatures below -78, they coagulate with water and nitric acid molecules. Nacreous clouds are formed from this mixture.
Temperature in the area of the polar vortex at an altitude of 30 km on January 28, 2020
Usually, nacreous clouds are observed in high latitudes - above 80 degrees latitude. But sometimes, when the polar vortex shifts from its usual location, they are observed in mid-latitudes, such as these January days.