Overview

• The UK experienced its warmest day of the year on March 20, 2025, with temperatures reaching 21.3°C in Northolt, west London, and Chertsey, Surrey.
• The warm spell coincided with the spring equinox, marking the start of astronomical spring, though it fell short of the 21.5°C record set in 1972.
• The 'Spanish plume,' a meteorological phenomenon bringing warm air from Spain, was identified as the primary driver of the high temperatures.
• London issued its first high air pollution alert of the year due to particulate matter from mainland Europe, prompting health warnings for individuals with respiratory conditions.
• The warm weather is expected to be brief, with rain and cooler temperatures forecast to return over the weekend, bringing more unsettled conditions.