Wednesday, September 28

The AEMET explains how the “blowout” that caused the tragedy of the Cullera Medusa Festival took place

Tonight a meteorological phenomenon known as ‘warm blowout’ has occurred in different parts of the Valencian Community. One of them, in the town of Cullera, has caused a tragedy at the Medusa electronic music festival, which brought together thousands of people and has caused one death and 17 injuries of varying degrees who have had to be transferred to different hospitals. The events occurred after 4 in the morning when strong gusts of wind caused several structures to give way, falling on the people gathered there.

The State Meteorological Agency (AEMET) has explained that very strong gusts of wind and sudden rises in temperature have been recorded, “they have probably been convective blowouts (not caused by gravitational waves as we had initially said)”. At 2 in the morning, at the Alicante-Elche airport, temperatures exceeded 40 degrees and 80 kilometers per hour.

As detailed, the blowouts “have been generalized, in some cases there have been no strong gusts, because the investment is very high and the air reaches the ground very slowly, in others the investment has not broken but the temperature has risen due to compression of the lowest stratum”, and indicate how, “in the most adverse cases, strong gusts of wind and sudden rises in temperature have occurred locally in some localities due to those hot bursts”.

Thus, they relate how in the early hours there were storms in Albacete and the Region of Murcia moving east that first reached the coast of Alicante at around 2 in the morning and two hours later that of Valencia: “The storms brought precipitation and some lightning in the interior but, when approaching the coast, the rain was dissipating and there were hardly any lightning strikes. On the coast it has practically not rained or rather weak showers”.

But, “what causes these blowouts, why do the storms dissipate when they reach the coast, why do these strong gusts of wind occur, which have not been widespread, but where they have occurred they have exceeded 80 kilometers per hour?”. AEMET highlights that the atmospheric profiles that give rise to hot bursts “are all very similar. They are said to be onion-shaped boreholes, with moist and relatively cool air next to the ground (up to 700 meters) and a few hundred meters above an extremely dry and warm layer (between 900 and 5,000 meters)”. At about 5,000 meters high, where the base of the cloud would be, we find a “wet and unstable” layer.

Next to the ground we found temperatures below 29 degrees and less than 700 meters the temperature was already close to 33: “The coolest and most humid area next to the ground is maritime air coming from the breeze, the warm air above is very dry and warm of African origin”.

“The other wet layer, which would be the base of the cloud, was very high, at more than 5,000 meters of altitude, which was saturated between 5,800 and 6,500 meters of altitude”, they detail from the Agency, to add: “The base of the The cloud was therefore very high and below it was a very dry layer more than 4 kilometers thick. The precipitation that occurs at the base of the cloud, which is very high, evaporates in the lower dry stratum, as the air evaporates it cools and becomes denser than the surroundings, as it becomes denser it begins to descend and accelerate” .

“The strong downdraft is produced primarily by evaporation of rain and melting and sublimation of hail below the cloud base. You can almost always see virga (precipitation that does not reach the ground)”, they explain: “That is why it has not rained on the coast or it has been very weak, because the precipitation evaporated long before reaching the ground and that Evaporation cooled the air, which is what descends and causes the blowout”.

“What happens to the descending air? In its descent it is accelerating. If there is no thermal inversion, the air hits the ground causing strong gusts, but not a rise in temperature, it is what we call a dry blowout, which for example has occurred in Xàtiva, with gusts of 84 kilometers per hour”, they describe from the AEMET, and they continue: “But if there is inversion next to the ground (cool and humid air), on its way down the air can pass through the cool layer, causing the intrusion of warm air above it”.

“Crossing the humid layer is in fact a brake for the air that descends from more than 5 km of altitude, but if the inversion is very shallow, as it was today, the speed is sufficient to cross it and reach the ground with very strong speeds” .