Millions of Britons were forced to drink subpar cups of tea last November due to the record-breaking low pressure caused by Storm Ciarán. The low pressure caused the boiling point of water to drop below the 100C temperature some experts recommend to extract the full flavour from tea leaves. The study by meteorologists at the University of Reading, published in the journal Weather, reported that the water in Reading was boiling at 98C on the morning of the storm. For water to boil, the atmospheric pressure must match the vapour pressure of the liquid. It is normal for atmospheric pressures to drop during bad weather such as storms. On that date, the barometer fell to 956.0 millibars (corrected to mean sea level). That figure was the lowest pressure recorded since a reading of 952.1 millibars in February 1989, and before that the previous reading as low was more than 200 years ago, when a measurement of 946 millibars was taken in December 1821. On the morning of 2 November, Caleb Miller, a PhD student and co-author of the study, set up his equipment in the meteorology department’s laboratories to measure the boiling point. “As an experimentalist, I saw the opportunity to make some measurements of the properties of boiling water during low atmospheric pressure,” Miller said. By performing controlled experiments using temperature sensors and a standard electric kettle, Miller and his team were able to compare the results with previous boiling points observed under different air pressure conditions using the same apparatus. To determine the broader regional effect of the storm on boiling points, they also combined weather data from various resources, including roadside weather stations across southern England and pressure readings from the Reading University Atmospheric Observatory. This allowed them to monitor how the pressure minimum moved north-east across the region during the morning, coinciding with typical breakfast times. Such effects are rarely seen in densely populated areas. Alec Bennett, a co-author of the study, said: “The effect of pressure on boiling temperatures is long known to mountaineers, but Ciarán brought the effect to a wide region.”