Since April this area has been very special if not historically significant. In fact, the first few days were exceptionally hot, with several months of heat records broken. A few days later, cold logs were broken by significant late frosts in France, which unfortunately had dramatic effects on agriculture. This large temperature difference is usually the type of phenomenon that does not show long-term trends. In fact, trends soften forecasts over several weeks. Therefore, being too hot and then too cold will eventually be more or less within the norms (cold and heat will cancel each other out).
It’s time to look at the seasonal patterns for May. Recall that the goal is to determine a signal that is extended throughout the month. It can cover the peak even within a month. When looking at seasonal patterns, a pretty clear trend emerges.
To simplify, the diagram above indicates the pressure irregularity at altitude. The more we move towards red, the more the trend is anticyclonic and conversely blue shows a continuum of low pressure. One can easily notice a low pressure irregularity near Portugal, which extends towards Spain. High pressure is pushing further north towards Iceland, Scandinavia and Eastern Europe.
If we know that a depression will change in the opposite direction in our hemisphere, we will usually be placed in a southwest flow. This flow can often be low pressure in the vicinity of low pressures in Portugal and Spain. This environment is ideal for stormy weather, especially in the south of France and Spain. It could start at the end of April.
The diagram below samples the rainfall irregularities from April 27 to May 4. We can clearly see the very wet signal over Portugal, Spain and a good part of southern France. This ensures that the recessions between the Mediterranean and Portugal are in circulation. In terms of temperature, they should be very hot overall with warmer temperatures from the southwest. Some cold spells are possible behind the scenes.
In the end, even if this seems paradoxical, we should have the same atmospheric circulation as the current one. For now, the cold drops bring us colder climates, but their employment will gradually give way to more stormy weather. The progress of the season is an important element. These cold winds, which are at higher altitudes when the change occurs from April to May, will face warmer winds on the ground. The heat variation will increase and be more favorable for stormy weather.