Europe boils in an unprecedented heatwave for a May month

BarcelonaEurope is experiencing an exceptional heat episode these days for a month of May, with values between 10 and 15 degrees above average. The temperatures, more typical of the summer heatwave, have sent thermometers soaring above 35 °C in several countries on the continent, from the Iberian Peninsula to Central Europe, as well as in southern countries, the United Kingdom, and the Balkans. Numerous regions are on alert for extraordinarily high temperatures. In fact, in recent hours, the government of Italy has activated the national climate alert system, raising it to the maximum risk level for highs of up to 35 °C in cities such as Rome, Bologna, Brescia, Florence, and Turin, and some regions have restricted outdoor work during the hours of maximum insolation to protect workers.

In France, the government still maintains many departments on yellow or orange alert for the worst premature heatwave in its history, especially in the west and south of the country, while Portugal maintains a yellow warning for high temperatures in fourteen districts. In the United Kingdom, temperatures have already started to fall, after reaching 35 °C for the first time in May in London on Tuesday, as well as the first tropical night in the country's history, with a minimum of 21.4 °C on Wednesday in Camborne, England. In fact, the record temperatures forced the issuance of public health warnings and special alerts due to the increase in heat-related incidents.

A historic and unprecedented heatwave at this time of year has left unusual images of tourists seeking shade and trying to cool off in the main European capitals. Records are spreading across many areas of Europe this week, with dire consequences, especially in countries not accustomed to such heat, even in summer. The extreme heat episode affecting part of the continent has already left fatalities and numerous consequences in several countries. France is, so far, the most affected territory: authorities have confirmed at least seven deaths directly or indirectly related to high temperatures, including several drownings while swimming in rivers and lakes to cool off in extreme heat.

This is not just a temporary heat episode, but a phenomenon of unusual intensity and extent for the end of May. The persistence of a strong mass of warm air over Western Europe is breaking temperature records and highlighting, once again, the trend towards increasingly frequent and earlier extreme episodes due to the climate crisis and global warming. Furthermore, it should be remembered that Europe is the continent that is warming the most on the planet.

In Catalonia, although the parameters to declare this episode a heatwave are not met, the situation is also unusual: thermometers have reached their peak in many regions this Thursday, with highs of over 35 °C throughout the interior, resulting in some heat records and premature tropical nights. For example, in Vinebre, temperatures reached 38.5 °C, equalling the heat record for a May in Catalonia set in 2022 in Castellbisbal and Anglès. The historic Ebre observatory reached 37.3 °C, the highest May maximum in its century-long series. And the Lleida station, with 86 years of data, also recorded 37.3 °C, a new May record.

Furthermore, this May has registered the record for nocturnal heat in our area, specifically in Portbou, where on Thursday morning the temperature did not drop below 28 °C. For the whole of Spain, Aemet maintains heat alerts until the weekend, especially in the southwest and the Ebro valley. In recent days, heat records have been broken in areas of the Cantabrian Sea.

What is happening?

The origin of this exceptional episode lies in the persistence of a powerful anticyclone over a large part of Western Europe. This high-pressure system acts as an atmospheric “tap” that blocks the arrival of Atlantic fronts and prevents air renewal. The result is a very stable situation, with clear skies, absence of rain, and temperatures that climb day after day. Furthermore, this blockage has lasted much longer than usual, allowing heat to gradually accumulate.

To this situation, a key factor is added: the strong solar radiation typical of late May. Although we are not yet in summer, the sun already has a very high incidence and the daylight hours are long, almost comparable to those in June. With the sky practically cloudless, the surface heats up very easily and temperatures quickly soar during the day. The nights, increasingly warm and short, also do not allow the atmosphere to cool down much.

And another factor must be taken into account: subsidence. That is, the descent of air from high layers of the atmosphere towards lower levels. When this air descends, it compresses and heats up even more, reinforcing the heat at the surface. All this has led to what is known as the “heat dome” effect, a kind of bubble of very hot air trapped over a region for days. This dome is affecting a large part of Europe and explains why the temperatures are so extreme and persistent for a month of May.

When will the temperatures drop?

Regarding the evolution of the situation, meteorological models indicate that it will still be very hot in many areas of Europe on Friday. But from the weekend onwards, the entry of slightly more Atlantic air could begin to wear down the anticyclone –which will move towards the Azores– and would allow a slight drop in temperatures, especially in the north and west of the continent. However, the decrease will be gradual and a clearly warm and summery atmosphere will still be maintained for the time of year, especially in the Mediterranean and in the south of the continent.

In Catalonia, the sensation of such intense heat will begin to ease, especially from the weekend onwards. Despite this respite, temperatures will remain above the usual average for late May and early June. Next week will not be so torrid, but forecasts indicate that this summer will again be much warmer than usual.