The so-called ‘European Monsoon’ is not actually a monsoon at all. It is more an ill-defined phenomenon that generally applies to a return of westerly winds in June and July following a possible weakening in the late spring of the more typical westerly winds we see in the UK.
Meteorologists define a monsoon as a shift in the prevailing wind, caused by the heating differential between land and sea areas that brings a seasonal and often predictable period of significant rainfall. The Indian monsoon is the best known of these weather systems, and is critical for the inhabitants of the Indian subcontinent.
In Europe, and especially the UK, the predominant wind direction is westerly. These westerly winds are at their most frequent during winter but decrease in late spring. There is an ill-defined phenomenon that may see a return to more westerly winds once again, usually between late June and early July. The cause of the change of the general weather pattern is uncertain but may be linked to warming over continental Europe and it is this that has been coined as the ‘European Monsoon’ or perhaps more accurately the ‘Return of the Westerlies’.
There is no evidence to associate this with increased rainfall during June and July or indeed the rather unsettled conditions we are seeing in the UK right now. If this was the case rainfall totals ought to be influenced with increased rainfall during early summer. Generally speaking rainfall totals in the east of England vary little month by month but there is a marked increase in winter rainfall in the west.
So is the wet weather we are seeing right now down to this phenomena? Well, this spring saw the wettest April for 100 years and a May that was pretty unsettled too. Therefore it is quite difficult to say that the ‘westerly winds are returning’ this year as they never really left us to start with.
Official blog of the Met Office news team 