This prediction market focuses on the total precipitation measured at London Heathrow Airport during March 2026. The market will resolve based on the official 'rain mm' figure published by the UK Met Office in its climate data archive for Heathrow. Participants are essentially betting on whether March 2026 will be unusually wet, dry, or near the historical average for London. The specific resolution source is the Met Office's text file containing station data, with the market rules specifying that if a reported value falls exactly between two defined brackets, it resolves to the higher range. This type of market attracts interest from meteorology enthusiasts, financial traders looking for uncorrelated assets, and individuals with weather-dependent business interests. The outcome depends on complex atmospheric patterns over the North Atlantic and Europe, making it a challenging forecast nearly two years in advance. Interest in such markets has grown as climate change increases variability in seasonal weather, and March precipitation in particular can significantly impact agriculture, water resources, and urban planning in southeast England.

Historical Context

Systematic rainfall measurement at the London Heathrow site began in January 1948, creating one of the longest continuous urban climate records in the world. This record shows that March precipitation in London is highly variable from year to year. The wettest March on record at Heathrow occurred in 1947, with 126.8 mm of rain, a period that coincided with severe post-war flooding. The driest March was in 1961, with just 3.1 mm recorded. A notable recent extreme was March 2018, which delivered 96.8 mm of rain, nearly double the monthly average, and contributed to significant transport disruption. The long-term average for March at Heathrow, calculated over the 1991-2020 climate normal period, is 41.6 mm. Historical analysis reveals no strong long-term trend in March rainfall totals for London over the past century, unlike increases observed in winter precipitation. However, climate models project a tendency toward wetter winters and springs for the UK under continued global warming, though with considerable year-to-year noise. The variability is largely driven by the position of the jet stream and the phase of the North Atlantic Oscillation; a negative NAO phase often brings colder, drier conditions from the east, while a positive phase typically results in milder, wetter westerly winds.

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