Storm Barra was quite explosive and battered the Iberian Peninsula in December 2021. It was a powerful storm that caused widespread damage during the final stretch of the December long weekend. Given the questions surrounding why this storm occurred and why it was so intense, let's look for answers.
In this article we are going to tell you why the Barra storm occurred, what were its characteristics and the reason why it was so intense.
Squall Bar
Storm Barra, which triggered avalanches, caused significant damage in parts of the Iberian Peninsula. In fact, the Spanish Directorate General of Traffic (DGT) had to advise drivers to return home earlier than usual due to the likelihood of avalanches in the north of the country. The State Meteorological Agency (AEMET) warned of heavy rain, strong winds, cold temperatures, and heavy snowfall in the north, with snow levels expected to drop to 500 meters during the final stretch of the December long weekend.
According to the AEMET spokesman, Rubén del Campo, a cold front began to move across the peninsula from northwest to southeast, associated with a very deep storm called Barra, which was undergoing an explosive cyclonic process with its center.
In Spain, however, the impacts were not as severe, mainly causing the passage of weather fronts and generating strong marine storms in the Cantabrian Sea, with waves reaching heights of 6 to 8 meters. Storm Barra brought abundant and frequent rainfall to Galicia, the Cantabrian coast, and the Pyrenees, which also extended to the Iberian and Central mountain ranges and other areas of the Northwest, while in the South, mostly clear skies prevailed over the Iberian System and the Mediterranean coast. The snowpack was initially high, then dropped to around 1.000 or 1.200 meters throughout the day, and even fell to around 700 meters in the Cantabrian Mountains in the final hours.
Factors of the Barra squall
According to Del Campo, another factor to consider is the wind, which brought strong gusts to the coast and the mountains, especially in the northern half of the country. Cold northwesterly winds caused a sharp drop in temperatures, particularly in the far north, resulting in continued heavy rainfall. In addition, there was significant snowfall in the Pyrenees and the Cantabrian Mountains, as well as snowfall in the central and surrounding areas of the Iberian Peninsula. To better understand this meteorological process, you can consult our article on storm formation , which explains how a low-pressure system forms.
In this regard, these mountain ranges received more than 10 to 15 centimeters of snow in just 24 hours, and the snowfall was also low, around 500 to 700 meters in the far north and 600 to 800 meters in the rest of the north . Central parts of the peninsula also had snow, although light, in isolated spots on the plateau and in marshes in the central regions. Therefore, del Campo asked all citizens leaving the long weekend to be "extremely cautious" due to travel between the northern half and the central area.
Wednesday and Thursday of the storm
Compared to Wednesday, rainfall was less intense across the rest of the two plateaus and the mountainous interior of the peninsula. There were also showers in the Balearic Islands. On this day, people again needed to be vigilant about the wind, with occasional strong gusts exceeding 80 km/h in the Cantabrian Sea, the eastern coast of the peninsula, and the Balearic Islands. Storms at sea continued to play a significant role, with waves reaching up to 8 meters in the Cantabrian Sea and 4 meters in the Mediterranean.
Galicia, the Cantabrian region, and the Pyrenees will continue to receive heavy rain on Thursday and Friday, but warmer temperatures will cause snowpack to increase significantly, often exceeding 1.500 meters. Consequently, there was snowmelt during those days, a significant increase in river flow in these areas, and the soils became saturated due to the heavy rain and snowfall over approximately two weeks. You can read more about the intense rainfall that occurred in the region during those days in this article.
In fact, over 300 liters per square meter accumulated in the last 10 days in the towns of Asturias, Cantabria, the Basque Country, and northern Navarre, with the Urkiola reservoir in Biscay standing out, recording 10,378 liters per square meter per day. These rainfall amounts in the far north are typically more than three times the normal amount for this period over the last 10 days.
The rain on Thursday and Friday spread, though more weakly, to the north and center of the country and other parts of the Penibetic System, while the Mediterranean coast saw light showers in the Balearic Islands. Temperatures rose in these areas on Thursday, bringing milder conditions for this time of year, with little frost and daytime temperatures exceeding 20°C along the Mediterranean coast and near the Guadalquivir River.
Why did the Barra storm occur?
The Barra storm was formed as a result of a deepening of the process of generating explosive cyclones. Specifically, storms like Barra intensify rapidly when there is an effective interaction between these two precursors:
- Highly active higher order precursors formed by well-defined polar groove jets.
- Surface depression or low pressure precursor.
This phenomenon means that Storm Barra experienced an "anomalous intensification," with a pressure increase of nearly 50 hPa in 24 hours. This is known as a "weather bomb," the result of a low-pressure system or cyclone deepening in an extremely short period. For more information on this type of phenomenon, you can consult our article on explosive cyclogenesis.
Due to climate change, we are seeing a pattern of increasing both the frequency and intensity of the most severe storms. In other words, during the autumn season, which is when there is usually more atmospheric instability, these storms are more likely to occur. The air masses are moving with the alteration of the pressures that increase and drop sharply due to the alteration in the global average temperatures.
Completely changing the global average temperature scenario due to the excess production of greenhouse gases causes changes in storm formation patterns.
