Upper-Level Trough Passage Triggers Severe Convection Warnings in Multiple Areas
According to the latest forecast from Spain’s State Meteorological Agency (AEMET), atmospheric conditions across Spain will change significantly starting Friday, August 21, due to the direct influence of a passing upper-level trough (vaguada). This system, bringing a cold upper-level jet stream into sharp contact with warm, moist surface air, will disrupt the stable circulation that has dominated the Iberian Peninsula, marking the end of the prolonged heatwave. However, this air mass convergence will also trigger intense convective activity. The Balearic Islands, the Cantabrian coast, the Catalan coast, and northern Castellón have been officially identified as primary risk areas for heavy rainfall and associated secondary hazards.
Severe Weather Begins at Dawn, Precipitation Focus Shifts Eastward
The onset of thunderstorms and showers will show a clear spatio-temporal progression. In the early hours of the 21st, the Balearic Islands will be the first to be hit by severe weather, with intense local convection and destructive wind gusts. Meteorological authorities are urging residents to be cautious of travel disruptions caused by strong winds. Simultaneously, localized, short-duration heavy rainfall will occur along the Cantabrian coast. Apart from potential morning fog and low clouds reducing road visibility in some inland parts of Cantabria, most of the peninsular interior will remain relatively calm in the morning.
As the trough continues to move eastward, the area of unstable weather will expand throughout the day. From the afternoon, the Iberian System mountain range in Aragon, as well as northeastern provinces like Barcelona and Girona, will begin to experience showers with thunder and lightning. By Friday evening, atmospheric instability along the Mediterranean coast will peak. The Catalan coast and northern Castellón province are at high risk for persistent heavy rainfall, where extreme short-term downpours could quickly lead to urban flooding and water accumulation in low-lying areas. In contrast, the rest of the Iberian Peninsula will largely maintain partly cloudy to clear skies.
Polarized Temperature Trend: Southern Regions Remain Hot
Another key feature of this weather shift is a widespread temperature drop across the country. Forecasts indicate that both minimum and maximum temperatures will fall to varying degrees in most of Spain on Friday. The most significant cooling is expected in the Iberian System, Castellón province, and the Balearic Islands. High temperatures in the northern plateau, the northeast, and along the Mediterranean coast will also ease.
Despite the cooling in most areas, the temperature distribution across the country will be highly uneven. In the southwest, temperatures will not only fail to drop but may even buck the trend and rise, with many areas remaining stable. Some coastal and southern capital cities will stay above the sweltering heat threshold. Murcia is forecast to lead the country with a high of 36°C, followed closely by Alicante at 34°C. Additionally, maximum temperatures in Albacete, Badajoz, Córdoba, Málaga, Sevilla, and Palma will hover around 33°C. Residents and tourists in these regions should continue to take precautions against the heat, in addition to being wary of thunderstorms and strong winds.
