Trader consensus on Polymarket has locked in 100% implied probability for under 20mm of precipitation in London for April 2026, driven by provisional Met Office measurements at Heathrow Airport—the market's official resolution source—which record just 4.6mm total, tying for the third-driest April on record there over nearly 80 years of data. This extreme dryness followed early-month rain from Storm Dave (4–5 April), but high-pressure systems dominated afterward, yielding only 24% of average rainfall across England by mid-month and negligible accumulations thereafter, per Environment Agency summaries. Historical April norms hover around 40–45mm; final Met Office verification, expected soon, could theoretically revise totals upward via quality-controlled gauge data, though significant upward shifts are rare for provisionals this low.