Century (flash)flood in Europe

We are all shocked about the extreme precipitation event which affected the Eifel region. I'm sure many in-depth analyses will follow in the next months.

Here I put some maps just to stimulate thought, not on the accuracy of the forecast itself, but on the synoptic situation which leads to this catastrophic event.

The approaching of a Rossby wave, later breaking in a cut-off low, generated heavy precip over central Europe, as often occurs in summer. However what is notable and usual here, is the stationarity of the low, the intensity of the precipitation and also the exceptional warm temperature anomaly of the air mass preceding the trough and then stagnating on the Baltic region.

As I tried to display in this EFI multiparameter map (left figure, below), there could be a direct connection between the intensity of precip on the Eifel region and the anomalously warm air mass still present to the northeast. The low-pressure area over central Europe is advecting low-level warm air from the northern side, generating the highest precipitation intensity on the western side of the cut-off low (this is quite unusual).  

The circulation of water vapour flux shows in fact a symmetric anomaly around the cut-off low (left figure, below), while usually, the largest positive anomalies are to the ascending branch. This, therefore, suggests an anomalous transport of water vapour over the western branch of the cut-off which could be linked to the temperature anomaly to the north. Cape was also anomalously high on the northern side of the low (right figure, below).

Although currently only speculative, it may be important to provide evidence of a direct and quantitative relationship between the temperature anomaly preceding this event and the intensity of precipitation in order also to show with concrete examples the increased likelihood of extreme events with global warming.

Finally, I include here for reference the observed precipitation maps produced by DWD.