It's called trough and it arrives this Thursday to cool off, finally, in this suffocating summer, and to be able to enjoy more bearable nights, even cold ones, in some areas. After enduring the hottest month on Earth since there are records, August begins with a heat truce in half of Spain.

A truce that will be brief but intense thanks to the arrival of this meteorological phenomenon called trough that will plummet temperatures during Thursday and Friday in a large part of the country. In some places, like the northeast of the Peninsula, it will be an extraordinary drop, and they will be quite low for this time of year.. They really are rare,” he says.

The bad news, he adds, is that in the extreme south of the peninsula, in the south of Extremadura and especially in Andalusia, it will continue to be very hot and that thermal relief will hardly be noticed.. “It is likely that the maximum will not drop below 37 or 38 ºC in the Guadalquivir valley, nor 35 ºC in the province of Badajoz,” says Mar Gómez, a meteorologist for eltiempo.es. “In Córdoba they will go from 41 ºC on Wednesday to 40 ºC on Thursday and 39 ºC on Friday, so they will continue with a very warm environment,” says Del Campo.

But what is a trough and why are temperatures going to drop so drastically? “It is a region of the atmosphere in which the pressure is lower with respect to the nearby regions that are located at the same level, and normally appears in the middle and upper levels of the troposphere.. Why are they produced? We know that atmospheric circulation in these latitudes is governed by the polar jet stream, which is a current of very intense winds that circulate at high levels of the troposphere, from west to east.. At the crests of these waves, warm air remains that gives rise to ridges,” explains the Aemet spokesman.

Both the ridges and the troughs, he adds, “are completely normal meteorological situations, and they can appear at any time of the year. It is true that many times in summer the dorsals predominate, guaranteeing warm, stable, calm and rain-free weather, but almost no summer is exempt from the arrival of some trough, which usually causes a drop in temperatures, a refreshment and also many Sometimes they increase atmospheric instability due to the circulation of winds that are generated around the troughs and that give rise to storms”.

As Mar Gómez explains, “the troughs can have different sizes and shapes, depending on the air masses”. These phenomena that cause sudden drops in temperatures of 10 degrees from one day to the next, says the meteorologist, are not extraordinary, “although it is more common for them to occur on other dates and for temperatures to remain more homogeneous and high in summer “. “It is not rare, sometimes it happens, and this year it is happening with a little more frequency. But this drop is quite abrupt and there will be quite cool temperatures,” agrees Del Campo.

What awaits us in detail for these days? “We are going to experience a notable drop in temperatures on Thursday, especially in the northern half of the peninsula and in parts of the Mediterranean area.. The decrease will be notable but in some points, especially in areas of Navarra, Aragon and even in Catalonia and perhaps in the Valencian Community, it could be extraordinary, on Thursday the maximums could drop even 10 degrees or more compared to those of Wednesday. On Friday they will continue to drop compared to Thursday, especially in the south of Andalusia and the southeast, in Murcia and in the Pyrenees, and in this case they will be six or eight degrees less compared to Thursday,” details the Aemet spokesperson.

Therefore, he continues, “it will be a sharp drop, especially in the northeast, which can cause cities like Pamplona [33 ºC on Wednesday] to have 23 ºC on Thursday and 21 ºC on Friday, more typical of the end of May or June than at the beginning of August, in the heat of heat. Or in Zaragoza they will go from 38 on Wednesday to 29 on Thursday and Friday 27. In Madrid, where on Wednesday there was 37 ºC, the drop will be less noticeable: 33 ºC is expected for Thursday and about 29 ºC on Friday.

tropical and torrid nights

Unfortunately, the thermal relief will only last a couple of days: “In general, the downturn will be on Thursday and Friday and starting on Saturday they will begin to rise progressively and clearly throughout Spain, and it is possible that starting on Sunday and at the beginning of next week we are going to talk about a lot of heat”, says Del Campo.

“The decline will be widespread on Thursday, more notably in areas of the interior northeast of the peninsula and on Friday they will drop again in much of the eastern half and in the Balearic Islands. However, on Friday they will begin to rise in points in the west of the peninsula”, agrees Mar Gómez, who anticipates that “on Saturday we already expect a general ascent that will be repeated on Sunday”.

Regarding the drop in temperatures this week, Jaime Martínez-Urtaza, a researcher at the Department of Genetics and Microbiology at the Autonomous University of Barcelona (UAB) and one of the world experts participating in the global initiative The Lancet Countdown , believes that it is “something simply punctual, because the temperatures rise again on the weekend. These things must be seen in the long term, without looking too closely at a particular moment, because it is also just what the deniers use to find justifications for the current warming situation.”

At the moment, “this summer is being warm, but not as stifling as the previous one, with peaks of intense heat and heat waves but with lulls in between, at least in Spain. In other countries in Europe and the northern hemisphere, the temperatures have been record-breaking,” sums up Mar Gómez, but it is still an atypical year in terms of night heat.

In Spain, tropical nights were already frequent, which do not drop below 20 degrees, but the term that is beginning to be used more and more frequently is torrid or equatorial night, which is one in which the temperature is higher than 25 degrees. “This year there have been many tropical nights, especially in the cities bathed by the Mediterranean Sea, with temperatures that are really very high, and there have been night temperature records. For example, on July 18 in Malaga it was an extraordinarily warm night, with 31.7 degrees. And the city of Valencia has registered 18 torrid nights in July, that is to say, more than half of the nights did not drop below 25 degrees and this is something not seen in this city. And you also have to think that in the entire 1990s, in total, there were 12 torrid nights in Valencia. And in a month there have been 15. It's been tremendous,” says Del Campo.

In July 2023, the Madrid-Retiro station recorded 22 tropical and two equatorial nights, when the average for this month is 14-15 nights, says Mar Gómez.

Another example: the city of Teruel, broke its minimum temperature record on August 1, with 21.3 degrees, which is the hottest night since at least 1986.

After this drop in temperatures, it is most likely that the rest of August will be warmer than normal, “clearly it will be next week, and the second fortnight will also be warmer than normal”. And with little rain, according to Del Campo. Mar Gómez also predicts that “warm anomalies may continue this month of August throughout the country, although they are expected to be less prominent in the extreme north and the Canary Islands. As for rainfall, the weather in August could start slightly drier than normal in points of the western half such as Extremadura, southern Castilla y León, southern Galicia or inland southwestern Andalusia. In the rest, normal rains would be expected.