Delhi woke up to cooler air and rain on Friday after days of punishing heat. The timing, however, raised a question: how did the national capital cool down just as the emergence of El Niño, a climate phenomenon historically linked to weaker monsoons and hotter weather over parts of India, was confirmed? To understand why Delhi’s weather has swung repeatedly between intense heat, dust storms and thunderstorms this pre-monsoon season, it is important to look at both the weather systems shaping conditions across north India and the broader climate signals emerging elsewhere. The immediate reason was a fast-moving squall line, a chain of intense thunderstorms, that developed over Punjab on Thursday evening and travelled eastwards across Haryana into Delhi-NCR overnight. The system brought light to moderate rainfall to many parts of Punjab and Haryana, accompanied by strong winds, including gusts reaching 111 kmph in Sangrur. “This squall line started over Punjab on Thursday evening and travelled across Haryana, causing light to moderate rainfall at many places in central and eastern Punjab and Haryana, along with …