Why are the nights in Medellín so warm? The phenomenon that explains the nighttime heat.

News: SIATA explains why cloud cover traps heat in the Aburrá Valley. Find out the rainfall forecast for May 13th and 14th. Hot days in Medellín. Photo: Metropolitan Area of the Aburrá Valley. JOURNALIST May 11, 2026, 17:59 Updated: May 11, 2026, 17:59 Residents of the Aburrá Valley have noticed an unusual change in the weather during the past week: the nights are no longer cooling down as much as before. According to the latest report from the Early Warning System (SIATA), during the first ten days of May, nighttime temperatures have remained between 20 and 22 °C, figures that exceed the usual historical values for this time of year. Daniel Ruiz Carrascal, General Coordinator of SIATA, explained that this phenomenon is not a coincidence. Although daytime temperatures remain within normal ranges (between 24 and 29 °C), the minimum temperatures are much higher than expected. The culprit is the cloudy sky: between May 6th and 10th, cloud cover exceeded 80% and 90% during the early morning hours. Hot days in Medellín. Photo: Metropolitan Area of the Aburrá Valley. The 'blanket' effect on the valley. The scientific explanation for this stifling feeling lies in the lack of radiative cooling. During the morning, the region receives high solar radiation that loads the surface with energy. Normally, this heat should escape into the upper atmosphere as the sun sets; however, the dense presence of low and mid-level clouds acts as a "layer" or thermal insulator, retaining heat on the surface and preventing the valley from cooling down. It is important to note that this nighttime heat is not related to global phenomena such as 'El Niño'. Currently, the Pacific Ocean is in a neutral ENSO phase, which is expected to continue with an 80% probability until July. However, experts warn that there is a 61% probability that the El Niño phenomenon will begin to manifest itself by the end of the May-June-July quarter, reaching its peak intensity at the end of 2026. Hot days in Medellín. Photo: Metropolitan Area of the Aburrá Valley. Forecast for the week: When will it rain? For the rest of the week, SIATA predicts a significant increase in atmospheric humidity. This condition will be the driving force for the formation of thunderstorm clouds, increasing the probability of precipitation, especially during the nights and early mornings of Wednesday, May 13th, and Thursday, May 14th. Conversely, for Tuesday, May 12th, and Friday, May 15th, a drier environment is expected. The decrease in humidity levels would reduce the probability of rain, which could translate into sunnier days, but, depending on nighttime cloud cover, also potentially warm nights if the accumulated energy is not released. Follow all the news from Colombia on Facebook and Twitter, or in our weekly newsletter. NEWSLETTERS FROM EL TIEMPO Register for our newsletters and receive news in your email according to your interests. Stay informed with what really matters to you. EL TIEMPO GOOGLE NEWS Follow us on GOOGLE NEWS. Stay always updated with the latest news, coverage, stories, and analysis directly on Google News. EL TIEMPO WHATSAPP Join the El Tiempo channel on WhatsApp to stay up-to-date with the most relevant news at the moment. EL TIEMPO APP Stay informed with the EL TIEMPO app. Receive the latest news, coverage, stories, and analysis directly on your device. SUBSCRIBE TO DIGITAL Reliable information for you. Subscribe to EL TIEMPO and access our journalistic content without limits.