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Why is the Iberian Peninsula experiencing a continuous string of storms?
In recent weeks, the Iberian Peninsula has experienced a drastic change in its weather pattern for this time of year, characterized by the incessant passage of fronts and storms. To understand why it keeps raining and why storms keep coming one after another, it's necessary to look to the upper atmosphere and analyze the behavior of the Jet Stream and atmospheric blocking patterns at high latitudes.
1. The Jet Stream
The direct cause of this situation is the Jet Stream. It's a river of strong winds that circulates at an altitude of about 10-12 km and acts as the "conductor" of the weather in mid-latitudes. This current separates the cold polar air from the warm subtropical air and guides the polar front, which is the area where storms originate and move. Storms typically circulate at higher latitudes. However, when the polar jet stream shifts south and points directly toward the Iberian Peninsula, it acts like a conveyor belt or "highway" that brings storms directly to us.
2. The culprit behind the detour: The Anticyclonic Blocking System in the North
The reason the polar jet stream has shifted southward and continues to point toward Spain lies in a phenomenon known as the North Atlantic Blocking System.
• The Wall in the North: Currently, a powerful blocking anticyclone has formed between Greenland and Scandinavia (high latitudes). This high-pressure system acts like a rock in a river, forcing the jet stream to deviate.
• The Open Path to the South: Unable to travel its usual route north, the jet stream is forced to shift southward. This opens a "corridor" or direct path from the Atlantic to the Iberian Peninsula, channeling a succession of very active storms toward our region.
3. The Negative North Atlantic Oscillation (NAO)
This atmospheric pattern coincides with a negative phase of the North Atlantic Oscillation (NAO).
• Positive NAO: Normally, the Azores High is strong and diverts storms towards northern Europe.
• Negative NAO: In the current situation, the Azores High is weakened or displaced. This allows storms to circulate further south than normal, directly impacting Spain and Portugal. Forecasts indicated that this index would turn negative, favoring the arrival of continuous rainfall.
4. Why is it so persistent? The connection with the Arctic
The duration of this episode is explained by the wavy and slow nature of the Jet Stream, influenced by Arctic warming.
• Wavy Jet Stream: When the temperature difference between the pole and the mid-latitudes decreases, according to several lines of research, the jet stream can tend to weaken and become more meandering, forming large meanders known as Rossby Waves.
• Stagnant Patterns: These large, slow waves cause weather patterns to become "stuck" or blocked. If the Iberian Peninsula is trapped on the flank of a trough (the lower part of the wave where low pressure systems are located) or under the influence of a "train of storms," the rainy situation can persist for weeks without significant changes.
5. The Intensity Factor: Atmospheric Rivers and Cyclogenesis
It's not just the frequency, but the intensity. These storms often arrive laden with moisture via atmospheric rivers, long, narrow bands that transport water vapor from the subtropics to our latitudes, acting as fuel for extreme precipitation. Furthermore, the interaction of these air masses with a strong jet stream can trigger explosive cyclogenesis, generating deep low-pressure systems and very strong winds in a short period.
Conclusion
The continuous succession of storms crossing the Iberian Peninsula is not a coincidence, but rather the result of a persistent anticyclonic blocking pattern at high latitudes (Greenland/Scandinavia) that has forced the jet stream to circulate further south than usual. This configuration, combined with a negative NAO (North Atlantic Oscillation) and a more wavy and slower jet stream, has left the Atlantic "door wide open."
As long as this blocking pattern persists, the Atlantic circulation will continue to act as a near-stationary system feeding storms over the Iberian Peninsula, prolonging periods of unsettled and rainy weather.
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