Current ensemble forecasts from the Met Office and ECMWF converge on a London maximum of 14–16 °C for May 18, driven by scattered Atlantic showers and moderate westerly flow that restricts daytime heating. Mid-May climatology normally supports 16–17 °C, yet 2026’s cooler spring pattern has held readings 2–3 °C below average, tilting trader probabilities toward the closely matched 14 °C and 15 °C outcomes. Key differentiating factors include cloud-cover duration, which limits solar insolation, and wind speeds that enhance turbulent mixing in the boundary layer; clearer breaks could briefly reach 16 °C, while heavier showers would cap values near 13–14 °C. Updated model runs and satellite observations over the next 48 hours will determine whether the market’s narrow spread between these thresholds narrows further before resolution.