Thread by @althecat

This freak weather event appears to be caused by two factors coinciding.
1. A burst in tropical moisture from the West African Monsoon moving North in five days time.
... colliding with...
2. Two cold northerly arctic blasts coming in from the North West.

This is the best visualisation I can find to show what is happening.

An animation 120-318 hours (days 5-13 from now) from @NOAA GFS showing the period when the monsoon boost takes place.

@NOAA Here's another view of the large scale dynamic, this time from Australia's Access G model. And here we can see that a warm wet Indian Ocean is contributing to the event. This shows 0-240 hours, the peak of the event which the simulations suggest will happen around NY Day.

@NOAA This 16-day Europe 850 HPA temperature animation shows a burst of cold air moving south west, at the end - you have to watch closely to see it.

This is the temperature anomaly picture at the hight of the monsoon burst when the ME is flooded with warm wet on New Years Day.

This animation (1500m alt temperature and wind lines 204-384 hours) starts on NYE. You see two low pressure systems heading south over the Sahara from the eastern Mediterranean. The cold air associated with these collides with the warm wet monsoon air producing the rain.