With the permission of the Karlotta storm, this is being one of the warmest winters in memory. After weeks in which several Spanish cities have set new temperature records for the months of January and February, Aemet has announced a new episode of mud rain. But why does this happen? Although it may not seem like it, these weather patterns are more common than they seem and are due to a phenomenon called ridges.
A ridge is an axis of atmospheric pressure that is higher than that of its surroundings. According to Aemet, on isobar maps, it is represented as an anticyclone that moves between two 'U'-shaped depressions or troughs, oriented towards the highest pressures, which is why it is also called a barometric crest. The regions located under the epicenter of a ridge are characterized by meteorological stability, marked by the absence of precipitation and increased temperatures.
The ridges guarantee the permanence of anticyclones and, therefore, clear skies, absence of wind and dry weather. These are usually accompanied by other phenomena such as thermal inversion. High pressures up to 5,500 meters high (5,500 hPa) cause cold air to descend and be retained on the Earth's surface, while hot air rises in altitude. That is why in recent weeks there have been days and days of fog in the valleys in contrast to the sun and higher temperatures in the mountains.
The lack of air renewal leads to the accumulation of polluting elements and suspended dust particles that, when low pressures arrive, will end up falling in the form of precipitation. What comes after a high pressure axis is an atmospheric depression or trough, that is, fronts marked by winds, precipitation and low temperatures that will be harsher the lower the center of atmospheric pressure.
Ridges can last for days or weeks, depending on their extent in altitude through the atmosphere. If it coincides with a season like winter or autumn—when storms and instability are common—it can cause prolonged episodes of dry weather and unseasonable heat. The higher this barometric crest is, the longer the anticyclone will last. That is why we have experienced weeks of thermal anomalies, with temperatures 10 or more degrees above normal. Thank goodness that after the ridge, the valley always comes.
